Chapter 5
Progestogens, Androgens and Oestrogens

This chapter has been written to give a functional account of progestogens, androgens and oestrogens, rather than a biochemical script to compare their structural similarities and differences. Understanding their metabolic and morphological effects and their interactions with each other and with other endocrine glands forms the final objectives behind writing this chapter.

Progestogens, androgens and oestrogens are steroidal compounds made of 4 interconnected cyclic hydrocarbons rings designated as A, B, C and D rings respectively. They can be natural or synthetic. All steroidal hormones attach to intracytoplasmic receptors, before being carried into the nuclei to exert their specific effects. Different hormones have different potency, depending on the duration of time a single dose of steroid- receptor complex occupies the nucleus of the target cell. In their natural forms, they are produced by the adrenal glands and ovaries in non pregnant women. Peripheral conversions also play an important role in the synthesis and degradation of oestrogens and androgens. The placenta is a major source during pregnancy


Progesterone was discovered in 1934. It is a natural 21-carbon molecule formed from pregnenolone by the microsomal enzyme 3β- hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase. Pregnenolone itself is made from cholesterol through a reaction catalysed by cytochrome P450scc, as described in Chapter 4. In a way, progesterone is a mother molecule of androgens and oestrogens, as shown by the following chart:

                        Progesterone → 17α-hydroxyprogesterone 


                                                       Androstenedione Oestrone 


                                                                       Testosterone Oestradiol 

The importance of this interrelationship has been discussed in Chapter 4, where failure of conversion of progesterone to 17α- hydroxyprogesterone can lead to failure of androgens and oestrogens production.

The three molecules shown in Figures 12 - 14 represent progesterone, testosterone and oestradiol respectively. Note the small differences in the basic two dimensional structures of the three molecules.

Natural progesterone is produced by the corpus luteum, adrenal glands and the placenta. Synthetic progestogens, on the other hand, are mainly the derivatives of:

  • 17α-hydroxyprogesterone which are non-androgenic;
  • 19-norprogesterone derivatives which are also non-androgenic;
  • 19-nortestosterone derivatives which are androgenic.

Natural progesterone is >95% bound to plasma proteins, mainly albumen and transcortin. Once in the blood, it has a short half-life of 5- 20 minutes. Accordingly, the efficacy of exogenous progesterone depends more on the route of administration and its absorption half- life, rather than its elimination rate. It is metabolised in the liver successively into pregnanedione, pregnolone, and finally pregnandiol. The effects of natural progesterone can be divided into the following categories:

1. Endocrine or chemical effects

Following ovulation, progesterone produced by the corpus luteum modulates the function of the hypothalamo-pituitary units. It affects GnRH pulse generation leading to slower LH pulse pattern with high amplitude during the luteal phase. The central effect of progesterone is affected at the level of the hypothalamus itself (1). Patients with reduced hypothalamic sensitivity to progesterone will have rapid GnRH and LH pulses, as seen in patients with polycystic ovary syndrome (2). It depletes oestrogen receptors as well as its own. This is important at the endometrial level, as prolonged endometrium exposure to progesterone can lead to endometrial atrophy, and possibly dysfunctional uterine bleeding. It also affects oestradiol metabolism by increasing its conversion to oestrone. This is affected through activation of the enzyme 17-hydroxysteroid dehydrogenase. It competes weakly with testosterone at its receptors level.It has a thermogenic effect by increasing the core body temperature during the luteal phase.

2. Morphological effects 

  • The immediate morphological effect of progesterone after ovulation is to increase cervical mucous viscosity, which reduces migration of bacteria and sperm into the cervical canal.

  • It converts the oestrogen primed endometrium into a secretory one. This is one of the most commonly used indications for progesterone medication. It can be given by deep intramuscular injections, or vaginally during fertility treatment, especially with assisted reproduction. Cyclogest pessaries and crinone gel are just two examples in common use. A meta-analysis published by Zarutskiea and Phillips in 2007 (3) showed that transvaginal progesterone medication in the right daily dosage is equally effective as the intramuscular route in this respect. Micronization of progesterone increased its surface area, and improved its absorption through the stomach. It has been licensed by the American Food and Drug Administration (FDA) for the management of secondary amenorrhoea and for hormone replacement therapy since 1998.

  • It has an effect on tubal peristaltic activity, and reduces the number of cilia and mucous production by the fallopian tubes.

  • The antioestrogenic effect of progesterone has a direct effect in reducing myometrial sensitivity and contractility.

It augments the effect of prolactin in preparing the breasts for lactation, but also inhibits lactation during pregnancy. The dramatic decline in the blood level of progesterone following childbirth triggers milk production.

3. Metabolic and immunological effects

Progesterone has an immunosuppressant effect which is not mediated through progesterone or glucocorticoid receptors. This effect was thought to be secondary to non-receptor mediated activity, conversion of progesterone to another steroid within the microenvironment of the immune cell, and interaction of progesterone with other members of the steroid and thyroid hormone receptor superfamily (4).

  • It has a catabolic effect, as shown by a rapid decline in the plasma concentration of many amino acids after progesterone administration (5). There is also increased total urinary nitrogen excretion without aminoaciduria.
  • It may induce hyperinsulinaemia by acting directly on the pancreas and promotes hepatic storage of glycogen. 
  • Its also antagonises the effect of insulin on glucose metabolism in adipose tissues and muscles (6). This is coupled by increased deposition of fat in the breasts and adipose tissue. 
  • It also reduces the hypertriglyceridaemic effect of oestrogen.
  • It has an anti aldosterone effect, and increases sodium loss.
  • It increases the respiratory minute tidal volume, hence reduces the alveolar and blood CO2.

Synthetic progestogens

Synthetic progesterone analogues have been produced, as progesterone is poorly absorbed from the gastrointestinal tract unless it is micronised  Such progestogens have different structures and characteristics, but they all share the common ability to induce secretory changes in an oestrogen primed endometrium. Unlike natural progesterone, many of them can be taken orally. Like natural progesterone, they modify oestrogen effects but have different characteristics otherwise:Progestogens derived from 19-nortestosterone have different degrees of androgenicity. The sequence of ascending androgenicity is: ethynodiol diacetate, norethindrone, norethindrone acetate, norgestimate and desogestrel in thatorder, with levonorgestrel and gestodene having the highest androgenicity. Derivatives of 19-norprogesterone are referred to as pure progestational molecules, as they have no androgenic, oestrogenic or glucocorticoid activity. They bind almost exclusively to progesterone receptors. This group includes nestorone, trimegestone and nomegestrol (7).Mild corticoid effect has been attributed to cyproterone acetate (8), but it also competes with cortisol at its receptor sites (9). Furthermore, it has mild inhibitory effect on the enzyme 21- hydroxylase and to a lesser extent 3βol-dehydrogenase (10). Accordingly, it can inhibit the production of both cortisol and aldosterone at the same time. The degree of inhibition is dependent on the metabolic clearance rate of the drug, and the degree of the genetic mutations of the two enzymes in the individual concerned. Because of adrenal glands suppression and their reduced response to ACTH, cyproterone acetate should be withdrawn slowly to prevent adrenal failure, especially if it has been used in a high dose for a long period of time. The new progestogen drospirenone is a derivative of spironolactone, and has an anti mineralocorticoid effect. Accordingly, it decreases salt and water retention with a potential for lowering blood pressure (6). It also has a mild antiandrogenic effect. Progestogens have anti gonadotrophin effect when given in a high dose. Most progestogens suppress the production of endogenous progesterone by affecting the corpus luteum enzymatic activity, if used during the luteal phase. There is no actual luteolytic activity, as suppression can be reversed by human chorionic gonadotrophin injections. The lowest total dose necessary to produce such an effect was 30 mg for northisterone, 12 mg for norgestrel, 300 mg for chlormadinone acetate and 360 mg for medroxyprogesterone acetate (11).

Most synthetic progestogens are derived from testosterone, especially those used in oral contraceptives. More information about their biochemical subgrouping will be found in Chapter 13. They have different effects on lipids and lipoproteins, depending on their androgenicity and the dosage used (12). They increase LDL production, but increase its clearance rate as well. Accordingly, they have no significant effect in this respect when used with oestrogen. Androgenic progestogens, such as levonorgestrel, decrease triglyceride levels by reducing secretion of very- low density lipoprotein (VLDL). On the downside, they can also counteract the beneficial effect of oestrogen on HDL (13). Conversely, non-androgenic progestogens have variable effects on oestrogen induced increase in HDL level. Dydrogesterone, as an example, has little negative effect (14), whereas medroxyprogesterone acetate reduces this effect. In general, C-21 progestogens do not prevent the increase in triglycerides induced by oral oestrogens.

The derivatives of 17α-hydroxyprogesterone and 19-norprogesterone are antioestrogenic and antigonadotrophic. They have no androgenic effect, which makes them favourable to use in patients with hyperandrogenic tendency. They can be given orally or by injection. The two main subgroups of 17α hydroxyprogesterone are:

  • 17α-hydroxyprogesterone caproate which is given intramuscularly;
  • 6α-methyl-hydroxyprogesterone acetate which is also known as medroxyprogesterone acetate or provera can be used orally. It can also be used intramuscularly in a depo form which increases its duration of action (depo-medroxyprogesterone acetate).Depo-medroxyprogesterone acetate is used mainly as a long acting injectable contraceptive, and for ovulation suppression in cases of endometriosis. The term medroxy is an abbreviation for methyl- hydroxy. Deep intramuscular injections can be repeated every 3 months in doses of 150 mg. More frequent injections do not improve the efficacy of the drug, but may result in more side effects. The main side effects even when the drug is used in the recommended doses include:Prolonged amenorrhoea may occur even after suspending medication. The average period for the return of normal fertility has been quoted as 9 months (15), but it may take even longer time after prolonged use of the drug.
  • Risk of abnormal uterine bleeding is also an issue. Prolonged periods of bleeding both heavy and light may be encountered.
  • There is a risk of developing ovarian cysts.
  • The prolonged anti oestrogenic effect on the brain may lead to lower mood spells, and occasionally depression.
  • Other anti oestrogenic side effects may be a problem, mainly osteoporosis.There is also a risk of weight gain after prolonged use of the drug.

Other long acting 17-hydroxyprogestogen derivatives have been used for:

  • Supplementing pregnancy following repeated miscarriages and premature labour has been one indication for using 17- hydroxyprogesterone caproate. The brand mostly used was Delalutin, which has been withdrawn in 1999. In 2008, the American FDA regarded 17-hydroxyprogesterone caproate as a category D drug, which indicated evidence of fetal harm, when this drug was used during pregnancy. Nonetheless, many articles have defended the safety of 17- hydroxyprogesterone during pregnancy on theoretical basis, as it is produced in large amounts by the placenta, and according to the results of animal and clinical studies. Most of these publications dated back to the 60s, 70s and 80s.

  • A well known member of this subgroup is cyproterone acetate. It has a very potent anti androgenic effect by competing with testosterone and dihydrotestosterone at their receptors. It also has a strong antigonadotrophic effect. It is most commonly used for treatment of female hyperandrogenisation in a reversed sequential therapy in severe cases. Because of its depo effect, it may lead to menstrual irregularities or dysfunctional uterine bleeding, unless it is combined with an oestrogen. It can be used in a dose of 10-50 mg every day plus 30 μg of ethinyl oestradiol for 10 days, to be followed by unopposed ethinyl oestradiol for 15 days. In milder cases, it can be used in a small dose of 2 mg combined with 35 μg ethinyl oestradiol in a designated contraceptive pill called Dianette (Bayer plc). Cyproterone acetate can cause breast tenderness, lethargy, depression, loss of libido and adrenal suppression. An important side effect is dysfunctional uterine bleeding. Accordingly, it should not be used in the second half of the cycle. The objective of using oestrogen is to regulate the monthly withdrawal bleeding. Cyproterone acetate is contraindicated in cases of liver disease, severe depression, history of deep vein thrombosis and during pregnancy.

In most cases, further progestogen medication will not stop progestogen induced abnormal uterine bleeding, and may even make it worse. This is especially so after using long acting progestogens. During mild to moderate bleeding episodes, oral oestrogen helps in building up the endometrium and gives it some structural integrity, before bleeding stops. In severe cases, only intravenous oestrogen may be effective. Premarin can be used in a dose of 25 mg every 4 hours for 24 hours, followed by oral oestrogen for further 10 – 14 days. A progestogen is needed during the last 5-7 days of therapy to induce secretory endometrial changes, before suspending treatment to provoke a medically controlled withdrawal bleeding. Blood loss usually eases off substantially, or even stops after the 3rd or 4th premarin intravenous dose. Progestogens are also useful for treating patients with anovulatory irregular or abnormal uterine bleeding. However, luteal progestogens medication is not useful for controlling ovulatory abnormal uterine periods. They may even be detrimental, and cause more menstrual blood loss (16; 17). In contrast, longer regimens from days 5-25 of the cycle are equally effective as levonorgestrel intrauterine devices, but only have 30% acceptability by patients for repeated prescriptions (18). Transvaginal ultrasound scan examination can be very useful in setting the management plan. Patients presenting with abnormal uterine bleeding and a thin endometrium should have oestrogen to build up the endometrium, and to benefit from its local haemostatic effect. The indiscriminate use of progestogens for all patients should be avoided.

Androgenic progestogens are mainly testosterone derivatives, after removal of the C19 methyl group (19-nortestosterone). The most commonly used one outside the contraception field is norethisterone (primolut N) which is a 17α-ethinyl derivative of 19-nortestosterone. It is mainly used for inducing withdrawal bleeding after periods of amenorrhoea, and for treatment of anovulatory menorrhagia. The other commonly used derivative is 13 ethinyl-17α-ethinyl-19 nortestosterone (norgestrel). This and other androgenic progestogens are mainly used in minute amounts either as progestogen only pills, or as part of combined contraceptive pills. The mirena system is a levonorgestrel loaded intrauterine contraceptive device which is used for contraception, control of excessive uterine bleeding, and in cases of endometriosis for pain control. It is impregnated with 52 mg of levonorgestrel, and releases 20 μg of the hormone into the uterine cavity every day. Only a small fraction reaches the general circulation, though it has been detectable in significant amounts in the peritoneal fluid in the pelvis. It has also been shown to have anti-inflammatory and immunomodulatory effects (19). Furthermore, levonorgestrel decreases and then blocks DNA synthesis and mitotic activity (20). In addition, it increases endometrial apoptotic activity by reducing expression of the Bcl-2 gene which has an anti-apoptotic effect (21).

It is advisable to avoid androgenic progestogens use in hyperandrogenic women, as they may worsen this condition. This is especially so for norgestrel and levonorgestrel as they can suppress the production of sex hormone binding globulin by the liver, and increases the level of free testosterone. High doses of norethisterone acetate for long periods of time in repeated cycles, to control abnormal uterine bleeding, are better replaced with medroxyprogesterone acetate which is equally effective when used in the right dose. Furthermore, many 19-nortestosterone derivatives are capable of reducing HDL cholesterol level, and inducing insulin resistance. This is also valid for gestational diabetes mellitus (GDM), as shown by Hedderson et al in 2007 (22). Their results suggested 43% increased risk of GDM associated with pre-pregnancy use of high androgen hormonal contraceptives.

Human testing of progestogens

Progestogens potency was measured in different ways including:

  • The progestational dose is the one capable of converting an oestrogen primed endometrium into a secretory one. Secondary amenorrhoeic women were prescribed unopposed oestrogen for two weeks, followed by combined oestrogen and progestogen medication for 10 days. The endometrium by the end of this period was assessed for different grades of secretory changes. The limitations of this test were discussed by Swyer in 1984 (23), who argued that no data satisfied the standards of acceptability, on his opinion, by the time his paper was published. 
  • The cycle delaying dose was documented first by Greenblatt et al in 1958 (24). It is the progestogen dose capable of delaying menstruation when started 7 days after ovulation, and continued for 3 or more weeks. Bleeding should only start 2-3 days after stopping the effective progestogen therapy, and not during medication.
  • Other parameters used to test progestogens potency included depression of the vaginal karyopyknotic index, inhibition of oestrogen induced cervical mucous changes, inhibition of ovulation, and withdrawal bleeding after 5-days courses in women with secondary amenorrhoea and oestrogen primed endometrium. These tests were utilised as a guide for selecting the right doses of progestogens to be used in new contraceptives, with standardized doses of ethinyl oestradiol. They are also helpful in selecting the effective dosage to control abnormal uterine bleeding. They should not be used for delaying menstruation for social or religious occasions. Such practice may lead to abnormal uterine bleeding, especially if the correct cycle delaying dose is not used.

Table 1: shows the total progestational dose (TPD), and the daily cycle delaying dose (CDD) of tested progestogens




Pure progesterone im

200 mg

1000 mg


100-150 mg

15 mg

Medroxyprogesterone acetate

60 mg

20 mg

Cyproterone acetate

20 mg

Not tested


7 mg

5 mg


Androgens are C19 steroidal hormones which are capable of initiating and maintaining secondary male sexual characteristics. They may be natural or synthetic in origin. They are also capable of inducing nitrogen retention, and have high affinity to certain cytoplasmic prostate cell receptors. They are produced in women by the ovaries, adrenal glands, and by peripheral conversion in the skin, fat, and by the liver. The two main circulating androgens are testosterone and androstenedione (Δ4- A). However, in a decreasing order of production in adult women, the major androgens are dehydroepiandrostenedione sulphate (DHEAS), dehydroepiandrostenedione (DHEA), androstenedione, androstandiol (Δ5A-diol), testosterone and dihydrotestosterone (DHT) (25). At skin level, dihydrotestosterone is the main functional androgen molecule, and is made by peripheral conversion from androstenedione (70%) and testosterone (20%), as well as other precursors by the enzyme 5α- reductase. Such conversion is not required at other tissues including the brain or muscles, as testosterone is the main active molecule in these sites. Only a small amount of dihydrotestosterone is actively produced by the ovaries.

Normally, the ovaries and adrenals produce 20-25% of circulating testosterone each, with the remaining 50% produced by peripheral conversion of androstenedione. On the other hand 35% of circulating androstenedione is produced by the ovaries and 25% by the adrenals, with the rest through peripheral conversion. Almost 80% of circulating testosterone is bound to SHBG, 19% to albumen and 1% is free as an active fraction. The blood level of androgens depends on the production rate, available SHBG receptor sites and the metabolic clearance rate by the liver, skin, peripheral fat and other tissues.

Many routes are available for androgens metabolism. Peripheral fat and muscles are two main tissues involved with aromatisation of androgens to oestradiol and oestrone. Testosterone is also metabolised to androsterone and aetiocholanolone in peripheral tissues, before being conjugated in the liver to glucuronide and sulphate by-products. These are water soluble and excreted in urine. Such conjugation occurs mainly at C-17 and C-3 sites in the androgen molecules. In general hepatic extraction of androgens is inversely related to their SHBG binding. About 40-60 % of testosterone and 30-40% DHT are extracted by the liver (26; 27). Generally androgens have the following functions in the human female:

  • Classical teaching attributed the initiation of puberty and growth in linear height to adrenal androgens. This concept has been challenged recently, and both phenomena were related instead to increased levels of oestrogen and growth hormone, as discussed in Chapter 2.
  • They are responsible for the growth of ambisexual axillary and pubic hair, which needs only small amount of androgens.
  • They act as substrate for oestrogens production.They are involved in maintaining female fertility, mainly through regulation of the hypothalamo-pituitary axis in a dose dependantmanner (28);
  • They play a role in regulating follicles development and ovulation at the level of the ovaries. This is partly affected through down regulation of FSH receptors in the small follicles to promote monofollicular ovulation.
  • They can help in increasing libido at the time of ovulation.The biological activity of androgens is controlled mainly by their free fraction in circulation which is controlled by their production rate, metabolic clearance rate, and interaction with other hormones. In normal circumstance, this is mainly affected by the level of SHBG which is produced by the liver. SHBG production is increased by oestrogens, thyroxine and reduced by obesity, hypothyroidism and high androgens production. It protects androgens against rapid degradation, and accordingly controls their metabolic clearance rate. It also has a role in controlling interconversions between androgens, and the peripheral conversion of testosterone to oestradiol. In this respect, measurement of total testosterone does not reflect the free and effective fraction during investigations of female hyperandrogenicity. Accordingly, the testosterone / SHBG ratio, usually known as the free androgen index, is a better measure of clinically relevant androgenicity than the total testosterone level.
  • Certain androgens have higher affinity to SHBG sites than others, and displace testosterone from its binding sites, leading to high levels of the biologically active free testosterone. Norgestrel is one example with higher tendency in smaller doses than northisterone. Small doses of 300 μg of northisterone may not affect SHBG level, but daily doses of 5 mg, which are usually used to control abnormal uterine bleeding, can do so. On the other hand, cyproterone acetate does not affect SHBG.
Timing the blood test for androgens level assessment is important in relation to the time of the day, and relative to the menstrual cycle. Androgens are produced in circadian pattern, especially the adrenal ones, and are higher in morning blood samples. Afternoon samples may give erroneously low values. Furthermore, blood samples should be timed to the early or mid follicular phase, as testosterone level can be high in the middle of the cycle. An example of such a scenario is thathigh LH and testosterone blood levels on days 5-7 of the cycle can represent PCOS. In contrast, even higher LH and testosterone levels at the middle of the cycle will be a normal physiological finding at the time of the LH surge.

Excessive androgens may affect a female patient during the different stages of her life differently, as follows:Excessive exposure of a female fetus to androgens during intrauterine life can lead to ambiguous genitalia at birth. Similar exposure of the fetal brain may adversely affect gender identity during childhood and adulthood life. It can also impinge on the heterosexuality of the adult woman.

Excessive androgens exposure during childhood can lead to precocious heterosexual puberty as discussed in Chapter 2. It may also cause primary or secondary amenorrhea and skin hyperandrogenic signs.
During adult life excessive androgens exposure leads to general hyperandrogenic symptoms and signs including weight gain, acne, hirsutism, androgenic alopecia, and other masculinization signs. Severe cases will show virilization signs including cliteromegaly, frontal hair recession and coarse voice. Occasionally, excessive sexual hair growth and acne may occur despite normal levels of circulating androgens. In such cases increased production of DHT can follow high tissues 5α-reductase activity. This is reflected by increased production of 5α-androstandiol-3α, 17β-diol glucoronide which is a byproduct of DHT (29).

Excessive androgens can also affect the HPO axis and uterus, and cause luteal phase defects, polymenorrhoea, menorrhagia, dysfunctional uterine bleeding, oligomenorrhoea and amenorrhoea. Detrimental direct effects at the level of the oocytes and endometrium have also been confirmed. Androgens can reduce oocytes maturation capacity, reduce granulosa cells mitotic activity, and FSH induced aromatase activity.

Management of hyperandrogenaemic states

The most important steps in the management of hyperandrogenaemia are:

  • Stop any medication which can lead to hyperandrogenism.

  • Exclude adrenal or ovarian tumours as a cause, especially in women with adults’ onset conditions, rapid progressive signs, and very high blood levels of androgens.

  • Stop or reduce the production of the androgens, being ovarian or adrenal in origin. Different drugs are available for this purpose. Adrenal enzymatic deficiencies are treated with glucocorticoids and ovarian sources are managed with oral contraceptive pills, or gonadotrophin releasing hormone analogues

  • Increase the level of blood SHBG which reduces the level of free testosterone. This can be affected through the oestrogen fraction of an oral contraceptive pill. It has been shown that 30 μg ethinyl oestradiol did not increase SHBG level beyond levels seen in normal ovulating women. The effect was more dramatic with 50 μg doses.

  • Antiandrogens should be used to counteract the effects of the androgens on peripheral tissues. The most widely used drugs are spironolactone and cyproterone acetate. They compete with androgens at their receptor sites.

  • Patients with polycystic ovary syndrome may benefit from metformin which can reduce ovarian production of excessive androgens.

  • Skin care and proper use of cosmetic aids are important parts of the management plan, to support the antiandrogenic treatment.

Assess the psychological impact of the problem and the basis for presentation. Counselling may help as well.

Clinical use of androgens in female reproductive medicine is limited by their side effects, which can be disfiguring and not acceptable. Danazol, which is an isoxazole derivative of 17α-ethinyl testosterone, used to be popular for the treatment of endometriosis. It has also been used for the treatment of mastalgia in a daily dose of 50-100 mg during the luteal phase. Testosterone implants were also used to supplement oestrogen HRT in women with low libido, but are not popular now. Recently, the transdermal route has been tested as well. Intrinsa patches (Procter and Gamble) provide 300 μg of testosterone every day, and each patch can be used for 3-4 days. They are licensed for women with hypoactive sexual disorder on concomitant oestrogen therapy, after bilateral oophorectomy. Beside acne, excessive hair growth and weight gain, androgens can cause migraine, insomnia, breast pain, and dyslipidaemia with low HDL cholesterol and high LDL cholesterol.


Oestrogens are biologically defined as chemicals which promote sexual heat or oestrous in ovariectomised premature rats. They are also defined as substances that promote vaginal cornification or uterotropic effects in the oophorectomised rat or mouse. In a clinical context, oestrogens are known as chemicals that stimulate and maintain growth of female secondary sexual characteristics. As for progestogens, they are also classified as naturally occurring, and synthetic. It has been shown earlier in this chapter that oestradiol and oestrone are steroidal compounds produced from androgens, both in the ovaries and adrenal glands in non pregnant women. Peripheral conversion of androgens in the skin and fat also contributes to the level of these two hormones. The placenta is a major source of oestriol during pregnancy.

Structurally oestrone, oestradiol and oestriol have 18 carbon atoms each, but differ in the number of the hydroxyl groups within the molecule.

Figures 15 - 17 show oestrone, oestradiol and oestriol molecules showing one, two and three hydroxyl groups respectively. Note the ketone group (=O) attached to the D ring instead of a hydroxyl group in oestrone.

Oestrogen production and clearance are affected by the stage of the menstrual cycle in premenopausal women. Furthermore, more than 95% of the circulating oestradiol is produced by the ovary containing the dominant follicle or corpus luteum (30). After the menopause, ovarian oestrogen production and clearance decline substantially. Most of the circulating oestradiol and oestrone production result from extra glandular aromatisation of testosterone and androstenedione. Increased body fat will increase such aromatisation, resulting in higher circulating levels of oestradiol and oestrone (31).

Oestradiol is the main biologically active oestrogen in premenopausal women. It circulates in the blood in 3 forms, bound to proteins, conjugated in bile salts, and 2% as a free active fraction. About 60% of oestradiol in circulation is bound to albumen, and 38% to SHBG. On the other hand, oestrone is not strongly bound to plasma proteins, with a higher metabolic clearance rate than oestradiol. At the same time, oestrone forms the first step in the biological inactivation of oestradiol. This is followed by its conversion to oestrone sulphate, catechol oestrogens, as well as oestriol and epioestriol (32). Catechol oestrogens are so named because of their structural similarity to catecholamines of having two hydroxyl groups on the aromatic A ring (33). The main compounds in this subgroup are 2-hydroxyoestrone and its metabolite 2-methyloestrone. The oestrogenic effects of catechol oestrogens are limited to the central nervous system, but have antioestrogenic effect in other oestrogen sensitive organs. All metabolites are biologically less active than oestradiol itself (34).

Oestrogens function through genomic or non-genomic effects. The genomic effect is imposed through their nuclear receptors, leading to specific changes in gene transcription. As for progestogens and androgens, the effects of oestrogens will be studied under 3 headings:

1. Chemical and endocrine; 
2. Morphological;
3. Metabolic.

Chemical and endocrine effects of oestrogens

Oestradiol is the main oestrogen in the non-pregnant young female. It is mainly produced by the granulosa cells during the follicular phase and the corpus luteum during the luteal phase. The rising levels of oestrogen during the middle of the follicular phase reduce FSH production by the pituitary gland through the negative feedback mechanism. This allows mono-follicular growth, as the dominant follicle continues growing in response to lower levels of FSH, unlike the smaller ones which stop growing and become atretic. This is because the dominant follicle has more FSH receptors, and higher aromatase enzyme activity which allow easy conversion of androgens to oestradiol. It also has more LH receptors and a rich micro vascular capillary network. Accumulation of androgens in the smaller follicles is an important factor leading to their demise. The ability of the dominant follicle to produce enough oestradiol to initiate the negative feedback mechanism is important for mono-follicular ovulation. This may not be the case in older women in their late 30s or early 40s, due to the age related change in hypothalamic sensitivity. Accordingly, the pituitary gland continues producing more FSH till 2 or 3 follicles are capable of producing enough oestradiol to initiate the negative feedback mechanism, and reduce FSH production. This is the scientific reason why women in their late reproductive years are more likely to have spontaneous multiple pregnancies.

Metabolic effects

Oestradiol is responsible for inducing hepatic production of SHBG, thyroxine binding globulin and transcortin which are carrier molecules for androgens and oestrogen, thyroxine, and cortisol respectively. Accordingly, it has an important role to play in regulating the free fractions of these hormones, and their metabolic clearance rate. Other non-genomic effects of oestrogens include protein anabolic activity, though to a lesser extent than that of androgens. They also have anti osteoporotic effect as they promote bone deposition and reduce its resorption. Oestrogen receptors have been isolated in bone. Oestradiol is also known to cause vasodilatation, due to its direct activation of the potassium channels in the plasma membranes. This leads to potassium exit and relaxation of the vascular smooth muscle fibres. High doses of oestradiol can cause excessive sodium and water retention, and lead to high blood pressure.

Morphological effects of oestrogens

The main effects of oestradiol in this respect are:

  • Oestrogens in general have no direct or indirect role in the development of female organs during intrauterine fetal life. Nonetheless, maternal use of exogenous synthetic oestrogens may lead to abnormality of the vagina and shape of the uterus, as shown by the diethylstilbestrol effect. Offsprings of these mothers developed vaginal polyposis, as well as T-shaped uterine configuration;

  • Initiation of breasts development and its growth to adult size with the help of other hormones including progesterone and prolactin;

  • Linear acceleration in height at puberty and final closure of the epiphyseal plates;

  • Cornification of the vaginal skin, and increase in total vaginal size;

  • Increasing the size of the cervix, uterus and tubes in preparation to reproductive function;

  • Deposition of fat in certain areas of the body which is a female physical characteristic;

  • Oestradiol increases endometrial cells hyperplasia and proliferation during the follicular phase. Together with progesterone they sustain endometrial secretory changes and activity in preparation for implantation during the luteal phase;

  • Oestradiol induces midcycle changes in the quantity and quality of the cervical mucus to facilitate sperm migration into the upper uterine cavity. The cervix also acts as sperm reservoir to facilitate continuous sperm availability for many hours after intercourse.

Natural non-human oestrogens

The most commonly used oestrogen in this group is premarin which is a conjugated equine product. It is isolated from mares’ urine. The composition of this product is made of:

    • 48% oestrone sulphate;
    • 26% equilin sulphate which is the major circulating oestrogen in women using conjugated equine oestrogens. It is 4 times more potent than the oestrone part, and is stored in the adipose tissues;
    • 15% 17α-dihydroequilin sulphate.

Premarin has been used extensively orally as hormone replacement therapy mainly for vasomotor symptoms, and as vaginal cream for postmenopausal vulvovaginal atrophic changes. Injectable forms are also available, and the use of intravenous premarin in acute cases of severe uterine bleeding has been mentioned before in this chapter.

Synthetic oestrogens

These chemicals are divided into steroidal and non-steroidal compounds, and have different functional characteristics in comparison to natural oestrogens. The most commonly used steroidal ones are ethinyl oestradiol and mestranol which is 3-methyl ether of ethinyl oestradiol. Examples of the non-steroidal group include diethylstilbestrol, chlorotrianisene, clomiphene citrate and tamoxifen. Few of these synthetic oestrogens have very long nuclear retention. They act accordingly as oestrogens in a single dose, but as oestrogen receptor modulators in repeated doses. This is secondary to downregulation of the cytosol receptors, and inhibition of messenger RNA transcription, due to prolonged nuclear occupation.

This effect can also be tissue specific, as these drugs act as anti oestrogens in one tissue, and as oestrogens in others. A good example is tamoxifen which has a very potent antioestrogenic effect on the breast tissues, through its metabolite hydroxyl tamoxifen. A similar antioestrogenic effect at the level of the hypothalamus is utilised for induction of ovulation, by stimulating gonadotrophins secretion. Conversely, it has an oestrogenic effect on the myometrium and the endometrium, through different metabolites. This explains the endometrial hyperplasia, polyps and carcinoma risks reported with prolonged use of tamoxifen by patients who had breast cancer.

Many drugs inhibit oestrogens synthesis directly by interfering with the aromatase enzyme activity, without any direct effect on the cytoplasmic receptors. The most commonly known ones in this group are letrozole and anastrozole which are non-steroidal drugs. They can be used as anti oestrogens for different purposes including induction of ovulation, and for the treatment of endometriosis.

Oestrogens potency

Oestrogens potency depends on the time the oestrogen-receptor complex occupies the nucleus of the target organ, after a single dose. Oestrone and oestriol occupy the same receptors as oestradiol, but have shorter nucleus retention time. Accordingly, they have weaker biological effects than oestradiol, but repeated doses of either hormone may have equivalent effects as a single oestradiol dose (35). The nuclear retention time of oestradiol was found to be 1-4 hours. Diethylstilbestrol had a longer time of 6-24 hours, and tamoxifen retention time was 24-48 hours. Oestrogens potency has been tested against the following parameters in postmenopausal women:

• The ability to build up a proliferative endometrium; 
• The ability to induce cornification of the vagina;
• The ability to reduce FSH and LH levels.

For these tests to be of any value in comparing different oestrogens, many factors should be taken into consideration:

  • The type and dose of the oestrogen used;

  • The route of administration is very important. Conversion of oestradiol to oestrone takes place after oral administration by the enzyme 17-keto reductase, which is available in the gastrointestinal tract, but not in the vagina. Accordingly, vaginal administration is more likely to increase oestradiol rather than oestrone blood level. Similarly transdermal administration has a similar effect, as oestradiol escapes the first pass through the gastrointestinal tract and the liver, and its conversion to oestrone;

  • The absorption rate and whether it is affected by other factors;

  • The metabolic clearance rate which depends on the blood level of the carrier molecules, and hence the free fraction of the hormone;

  • The particular system under evaluation.

Use and side effects of oestrogen therapy

The most common uses for oestrogens in female patients in chronological age order are:

  • To initiate pubertal development in cases of delayed puberty;
  • In different contraceptives in combination with progestogens;
  • For the treatment of dysfunctional uterine bleeding;
  • In preparation of the endometrium during ovum donation cycles;
  • Hormone replacement therapy in cases of surgical or natural menopause, and in cases of gonadal dysgenesis.

Side effects of synthetic oestrogens cover a wide range of organs and effects. The most publicised risks following unopposed oestrogen use are endometrial hyperplasia and carcinoma of the endometrium. Accordingly, a progestogen should be used for a minimum duration of 12- 13 days with oestrogen HRT. This is not necessary in patients who already had a hysterectomy. Further discussions about the relationship between HRT and breast cancer, or cardiovascular disease will be found in Chapter 9. Other side effects of synthetic oestrogens include:

  1. Hypertension is a risk in susceptible patients, due to increased plasma renin activity and renin substrate. There is also increased aldosterone production and sodium retention.

  2. There is a two-foldincreasedthromboembolictendency,causedby increased production of factors II, VII, X and fibrinogen. This is coupled with decreased antithrombin III activity. The final outcome is a hypercoagulable state. This risk is especially high in heavy smokers, diabetics, and with previous history of thrombosis. Certain conditions may also increase this risk including immobilisation, trauma or surgical procedures, sepsis and obesity. The route of administration also has an important effect. There is more thrombosis risk with the oral route than the transdermal or vaginal routes, because of the first hepatic pass of oestrogens, and increased production of coagulation factors with the oral route.

  3. Ischaemic heart disease risk is also increased because of the increase in triglycerides level, despite the favourable effects of oestrogens on HDL cholesterol and LDL cholesterol.

  4. Cholelithiasis is also a side effect of synthetic oestrogens. The relative risk in postmenopausal women is 2.5, compared to those who are not using HRT. This effect may follow:

    a. Alteration in lipid balance;
    b. Alteration in bile salts content; 
    c. Alteration in HDL cholesterol.

Contraindication to oestrogen use

Taking into account all the metabolic, endocrine and anatomical points mentioned before, oestrogens should not be used in the following conditions:

• During pregnancy;
• With undiagnosed genital bleeding;
• In case of acute liver disease;
• Present or past history of oestrogen dependent cancer; 
• History of thromboembolism.

Few conditions should be taken into consideration in a risk / benefit assessment, before prescribing oestrogens. These conditions include:

• History of liver disease; 
• Diabetes mellitus;
• Hypertension;
• Uterine fibroids;
• Familial porphyria cutanea tarda.


Antioestrogens are substances that compete with oestrogens at their binding receptor sites. This effect can be universal, or specific to few but not all tissues. Clomiphene citrate and tamoxifen are the classical examples in this group. Tamoxifen acts as an antioestrogen at the breasts, but stimulates oestrogen receptors in the uterus, which may result in hyperplasia and polyps, or even endometrial carcinoma. The role of catechol oestrogens as antioestrogens outside the central nervous system (CNS) has been mentioned before. Within the CNS, they compete with catecholamines for the enzyme catechol- methyltransferase, which results in reduced degradation of CNS catecholamines. This will prolong the effects of catecholamines within the brain, with consequent modulation of catecholamines sensitive hypothalamic releasing and inhibiting factors (32). Though progestogens are usually considered to have an antioestrogenic effect, they tend to exhaust rather than occupy oestrogen receptors. So strictly speaking progestogens modify oestrogen effects, but do not compete with them for their receptor sites.


It is evident that progestogens, androgens, and oestrogens have similar basic steroidal rings, yet subtle changes in those molecules gave them different endocrine, morphological and metabolic characteristics. Such features may even be different within the different subgroups of each hormone. This depends on the chemical structure, half-life and bioavailability, affinity to receptors, potency and metabolic clearance rate. More clinical information will be provided in Chapters, 9, 10, 12 and 13. It is also important to take the information provided in this chapter into consideration, when reading the chapters dealing with hormone replacement therapy and contraception.


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