HRT Drugs's use in Menopause

Literature Review


The proposed layout of the final dissertation is that it will be divided into three sections in order to answer the question stated. The question is: Are HRT Drugs such as Premarin containing Conjugated Oestrogens, safe for the use in women suffering from the menopause?

The three sections will be headed

1. The Menopause

2. The Drug

3. The Ethics

It is thought that by structuring the dissertation in this way, all the areas required will be covered fully, to provide an informative and relevant answer to the question.

The literature that has been reviewed is a follows:

1. The Menstrual Cycle

1.1 The Normal Function

In order to be able to understand and evaluate the events that occur within the menopause it is important that the normal menstruation cycle is reviewed first. This will aid in understanding the changes that then take place once the menopause begins.

Abernethy (2002: 3-4) describes the menstruation cycle in terms of the hormonal controls and changes that happen naturally in order for the process to occur. According to Abernethy (2002) ‘low levels of oestrogen and progesterone are released into the bloodstream. The hypothalamus controls the secretion of these hormones through the release of luteinizing hormone releasing hormone (LHRH), which then stimulates the pituitary gland to produce follicle stimulating hormone (FSH). FSH in turn stimulates the ovaries to produce oestradiol, which causes the endometrium to proliferate. As circulating levels of oestradiol increase, FSH and LH levels fall until around day 14 of the cycle. LH concentration then peaks and ovulation generally occurs. If fertilisation does not take place oestrogen and progesterone levels fall and the endometrium is shed- menstruation takes place. The falling levels of oestrogen and progesterone are detected by the hypothalamus and the cycle starts again'.

This sequence of the menstrual cycle is supported by Griffin and Ojeda (1996) who describe the cyclical process as a ‘series of functional interrelationships between the hypothalamus, the anterior pituitary, and the ovaries'. They continue to explain that this leads to a rupture of an ovarian follicle which happens monthly and the release of an ovum causing ovulation. The ovum then transported to the fallopian tubes where should fertilisation fail, menstruation will ensure within 14 days, where the events will then be repeated.

Both these descriptions are useful, as they provide a more complete view of the process, and help to raise the question, what happens within this cycle that leads to the onset of the menopause?

1.2 Duration

Griffin and Ojeda (1996) have also looked at the duration of the cycle, how it can be divided into four phases, and the duration of these phases. They state that the average duration of the cycle is 30 days, with a range from 25 to 35 days. The four phases that they have named are menstruation, follicular, ovulatory, and luteal. According to Griffin and Ojeda (1996), the menstruation phase lasts 4-5 days; the follicular phase lasts 10-16 days, the ovulatory phase last 36 hours, and the luteal phase that lasts 14 days. This then leads onto how the menopause begins the age group it is associated with and the effects it can have.

2. The Menopause

Through reading a variety of literature there is numerous research available on the menopause, its definition and how it effects today's women. However, there is more limited research on the exact cause of the changes that occur. This will require further investigation in order to provide more literature to include within the final dissertation.

Burger (1999) defines the menopause as the permanent cessation of menstruation resulting from the loss of ovarian follicular activity. He also states that ovarian primordial follicle numbers decrease with increasing age up to about age 38 following which there is a much steeper decline in the last 12 or so years of reproductive life. At the time of the menopause itself, few follicles remain within the ovary.

Norman (1987) suggest this begins in women between age 40 and 50 due to the utilisation of the fixed number of follicles that were established in the foetal ovary. Each month of ovulation several follicles disappear by the process of atresia and normally only one matures to contribute an ovum. Therefore he suggests that at some point by the age of forty, there are no more follicles to support this cyclical process.

More recent research by Burger (2006) that was concerned with the physiology and endocrinology of the menopause found that the major initial change underlying the cause of the menopause was in a selective, gradual decline in inhibin B, the major regulator of follicular phase follicle-stimulating hormone (FSH). He states that it is produced by the granulosa cells of antral follicles during the early follicular phase. The inhibin B decline leads to increased FSH, which can maintain and even increase oestradiol production for some years. This is an important finding, as it indicates that further research can be done within the area of inhibin B, to find out if any more changes have been looked into, or discovered in to the cause of the menopause. This is the author's intention, so that a more detailed picture can be illustrated in order to ascertain how the drugs prescribed for the menopause really target the cause.

2.1 Menopausal Transition

2.1.1 Hormones Associated

The onset of the menopausal transition is described by Burger (2006) as menstrual irregularity after previously regular cycles. Coope (2000) suggests that the premenopausal transition has a duration of over four years.

In order to investigate the changes that occur with this process further Sherman et al (1976) conducted a study analysing LH, FSH, oestradiol (E2), and progesterone (P) concentrations during menstrual cycles of older women. They compared the changes in serum concentrations of LH, FSH, oestradiol, and progesterone with those of young normal women. They found that in 8 women with an age range of 45-56 years old with regular cycles, cycle length was shorter and the mean E2 concentration was lower than in younger women. There was a striking increase in FSH concentration throughout the cycle while LH remained in the normal range. It was also noted that hormonal changes associated with follicular maturation and corpus luteum function occurred in the presence of high, menopausal levels of LH and FSH with a diminished secretion of E2 and P. Sherman et al (1976) concluded that their observation of elevated FSH concentrations and normal LH levels in perimenopausal women emphasises the complexity of the hypothalamic-pituitary-ovarian regulatory system and suggests that LH and FSH are modulated independently at the level of the pituitary.

This study allows some insight into the complexity of the hormonal control with the transition into the menopause. It is thought that this will be useful when combined with further research in producing a link that may be found between the more precise causes of this change, and therefore what treatments in terms of drugs would be the most beneficial.

Burger et al (1998) investigated serum inhibin A and B levels, as well as serum FSH levels. They suggest that FSH levels rise with increasing age in normal women, particularly as they enter the menopausal transition and progress to the postmenopausal state. The purpose of this particular study was to provide preliminary data between the dimeric inhibins, oestradiol (E2) and FSH in normal participants who had been defined with menopausal status.

They concluded that ‘the major significant endocrine event in women in the early perimenopausal phase of the menopausal transition is a substantial fall in the circulating levels of inhibin-B with no significant change in inhibin-A or oestradiol. Progression to late perimenopausal status is accompanied by a marked fall in inhibin-A and oestradiol and a rise in FSH without further change in inhibin-B. Inhibin-B, a marker of follicle number, is a significant factor in the endocrinology of the menopausal transition'.

It is argued that it is this previous study that lead to the more recent one mentioned earlier that was also conducted by Burger in 2006, who is re-affirming his findings of the significance of inhibin B and its role in the menopause.

Teede and Burger (1998) suggest that fluctuations in the levels of FSH and LH occur throughout the perimenopause, eventually peaking 2-3 years after periods stop and remaining high for the next 20 years. In support Abernethy (2002) states that FSH levels fluctuate widely during the menopausal transition.

Metcalf et al (2008) conducted a study into the pituitary-ovarian function in normal women during the menopausal transition. They measured the excretion of FSH, LH, oestrogens and pregnanediol in weekly urine samples collected from 14-87 weeks, from thirty-one perimenopausal women aged 36-55 years. They noted that the hormone patterns observed in the perimenopausal women varied widely, both between individuals and from time to time in the same individual. They ranged from ovulatory cycles with low premenopausal levels of FSH, to transient episodes indistinguishable from those found in postmenopausal women with high levels of FSH and LH.They concluded the study my suggesting that the appearance of high levels of FSH and LH is characteristic of the perimenopause and often precedes the sustained loss of sex hormone secretion by the ageing ovary.

It is becoming apparent from the literature regarding the menopausal transition that the roles of FSH, LH and oestrogen are particularly important, and that it is the changes that are occurring with these hormones, that are affecting the cessation of the normal menstrual cycle to begin the transition into the menopause.

A study by Langren et al (2004) on Menopause Transition: Annual Changes in Serum Hormonal Patterns over the Menstrual Cycle in Women during a Nine-Year Period Prior to Menopause is worth including in the final report but will require further reading on the author's part in order to gain a comprehensive understanding of the whole process. Oestradiol and Oestrone

Coope (2002) suggests that Oestradiol levels decline dramatically in the last year before the last menstrual cycle. Abernethy (2002) suggests that in premenopausal women, both oestradiol and oestrone are present, with oestradiol being the dominant hormone. Whilst both are secreted by the ovaries, oestrone on the other hand is available through the conversion in adipose tissue of the hormone androstenedione, which is secreted by the adrenal glands. Abernethy (2002) also suggest that oestrone is biologically less active than oestradiol, and after the menopause the ration of oestradiol to oestrone is changed with oestrone becoming the dominant hormone. Symptoms of the Menopause.

Martin (1985) reports that the hormonal changes of the menopause are usually accompanied with bodily changes. The most important being vasomotor instability. He suggests that the blood pressure can undergo wide fluctuations and that the majority of women will experience ‘hot flushes.' During these hot flushes there is marked vaso-dilation of the peripheral vessels supplying the face and upper parts of the body. He describes further symptoms as causing an uncomfortable sensation of warmth that is characteristically followed by sweating, the evaporation of which leads to feelings of cold or clamminess. (671)

Dennerstein et al (2000) conducted a study to identify the symptoms that change in prevalence and severity during midlife and evaluate their relationships to menopausal status, hormonal levels, and other factors.

They concluded that although middle-aged women are highly symptomatic, the symptoms that appear to be specifically related to hormonal changes of menopausal transition are vasomotor symptoms. They suggest that it is the midlife years of 45-55 that coincide with those of menopausal transition. They also note that a lot of research has gone into trying to identify which symptoms are related to hormonal changes underlying the menopause and which are caused by aging, other health states, psychosocial factors, or lifestyle.

This research is relevant as it is recognising that there are a variety of other factors other than hormonal changes that can contribute to the symptoms of the menopause. Whilst this dissertation is proposing to mainly focus on the hormonal factors, as it is predominately these that will be altered by drug treatment; it is still beneficial to consider the research of Dennerstein et al (2000) and their findings in order to recognise how all the variety of symptoms may be influenced and interact with each other.

3. The Drug

3.1 Metabolism

It is the author's opinion that in order to gain an understanding of how the drug Premarin may be working to alleviate the symptoms of the menopause it is important to first understand how drugs are metabolised by the body.

Thomas (2008) defines drug metabolism as chemical reactions responsible for the conversion of drugs into other products, or metabolites, within the body before and after they have reached their sites of action. He states that this can occur by more than route and these routes consist of a series of enzyme controlled reactions. The end compounds are usually more easily excreted than the original drug.

Thomas (2008) also comments on factors that can affect metabolism. An interesting one is that ability to metabolise drugs is lower in the very young and the elderly (over 60). Now whilst it has become apparent that the onset of the menopause can begin from approximately forty years of age, it is argued that the need to continue with drug treatment may take women beyond their sixties. So with the research from Thomas (2008) suggesting that the metabolism of drugs is affected beyond this age, this is worth further investigation. It could provide the evidence required to indicate as to the effectiveness, and possible safety of Premarin in older women.

Neal (2005) believes that drug metabolism has two important effects. The first one is that the drug is made more hydrophilllic; therefore hastening it's excretion by the kidneys. The second one is that similarly to Thomas (2008), the metabolites are usually less active than the parent drug. However, Neal (2005) does state that this is not always the case and that sometimes the metabolites can be as active, or more so, than the original drug.

3.1.1 Sites of Action

Thomas (2008) suggests that drug metabolism can occur in all tissues and most biological fluids. However the widest range of metabolic reactions occur in the liver. Also a more substrate-selective range of metabolic processes takes place in the kidney, lungs, brain, placenta and other tissues.

This is supported by Silverman (2004) who additionally suggests that the principal site of drug metabolism is the liver. He also states that the kidneys, lungs and GI Tract are also important metabolic sites.

Thomas (2008) looks at enzymatic activity on drug metabolism. He suggests that the body has both specific and non specific enzymes that aid in the metabolism of drugs.

Research by Krishna and Klotz (1994) supports the consideration of enzyme activity in the metabolism of drugs. They imply that depending on the particular drug and enzymes involved, the extra-hepatic organs, or tissues can contribute to the elimination of drugs and should be considered. In addition they state that with the use of relatively new techniques in molecular biology, the tissue distribution of these enzymes can also be determined. It is the author's opinion that further investigation into this area could offer indications into the effectiveness of drugs, in terms of how quickly they are able to produce their desired reaction within the body, to alleviate symptoms.

An interesting study by Wynne (2005) looked at drug metabolism and ageing. Process of Metabolism

Thomas (2005) suggests that the first region where a significant degree of metabolism takes place is the GI tract and within the intestinal wall. Once absorbed from the GI tract many potential and existing drugs are extensively metabolised by first-pass metabolism.

Pond and Tozer (1984) state that First-pass elimination takes place when a drug is metabolised between its site of administration and the site of sampling for measurement of drug concentration. This is further explained by Silverman (2004) who adds that this first pass effect may result in complete deactivation of the drug. Therefore if a large fraction of the drug is metabolised, then larger or multiple doses of the drug will be required to get the desired effect.

Further literature by Silverman (2004) explains that the function of drug metabolism is to convert a molecule that can cross biological membranes into one that is cleared, usually in the urine.

For this to happen, oxidation, reduction and hydrolysis need to take place. These are phase one reactions. Oxidation is the most important phase one reaction, and involves the enzyme monooxygenase. This is found on the smooth endoplasmic reticulum of the liver. Reduction is an important reaction for the metabolism of compounds that contain reducible groups, such as aldehydes, ketones, alkenes, and sulphoxides. Hydrolysis is an important metabolic reaction for those drugs whose structures contain ester and amide groups. All types of esters and amides can be metabolised by this route. Thomas (2005).

Phase two reactions or conjugation reactions also occur. Silverman (2004) explains how conjugating enzymes in general catalyze the attachment of small polar endogenous molecules such as glucuronic acid, sulphate and amino acids to drugs or, more often to metabolites arising from phase one metabolic processes. This modification further deactivates the drug, changes its physiochemical properties, and produces water soluble metabolites that are readily excreted in the urine.

With this information it will be possible to relate this specifically to the function of Premarin and how this is metabolised by the body. It is known that Premarin contains conjugated equine oestrogens, and so this indicates that further research should be directed in this area, as it may provide evidence that can be related back to the main question of this dissertation. Binding and Interacting with a Target

It is relevant to examine how a drugs binds with its proposed target, because without this knowledge it will not be possible to draw conclusions about how efficient the process is, and how crucial it is to the function of a drug.

According to Page et al (2002) Drugs that activate their molecular target are defined as agonists, whereas drugs that prevent or inhibit the actions, or deactivate a molecular target are defined as antagonists. They also explain that the target is a molecular entity which contains the binding site for the drug.

This target can include membrane proteins for recognition of hormones and neurotransmitters, and also ion channels, nucleic acids, carrier molecules or enzymes. Most drugs bind to a molecular target in order to produce their actions Page et al (2002).

Literature on receptors has been briefly examined, but it is acknowledged that further research will need to be done. The research found so far is from Page et al (2002) who propose that neurotransmitter or hormone receptors are generally large proteins that contain a site which ‘recognises' the drugs and binds to them. This binding site is usually linked to a transduction site. It has generally become apparent that many receptors are proteins. Such proteins have at least one distinct region to which drugs, both agonist and antagonists, bind. It may be possible to investigate into the specific receptor sites for Premarin and look at the interaction between the target and the receptor.

Drugs can theoretically bind to almost any three dimensional target, most drugs achieve their desired effects by interacting with target molecules that play important roles in normal physiologic functioning. Generally, drugs are molecules that interact with specific molecular components of an organism and drug receptors are macromolecules that, upon binding to a drug mediate biochemical and physiologic change within the organism Golan et al (2005). Premarin

Premarin is a widely distributed HRT drug, used to treat the symptoms of the menopause. Its main ingredient is conjugated oestrogens which are derived from the urine of pregnant mares. Premarin was introduced in 1942, and the pills are coated with pharmaceutical shellac, a substance derived from beetle husks Bonfield (2001).

There has been research into the effects of oestrogen on women when used in Hormone Replacement Therapy (HRT) to treat the symptoms of the menopause.

White and Grant (1998) conducted a study that looked at the possibility of developing an addiction to oestrogen and progesterone. In this study they state that exogenous oestrogens, progesterone and progestogens are prescribed for a variety of conditions in spite of lack of proof of efficacy.

The study continues to explain how brain function, amine metabolism and nutritional status can be altered by exposure to exogenous hormones. They found that direct and indirect mechanisms of psychoactivity may induce dependency, and that a doctor's severe 'menopausal type' withdrawal symptoms after exposure to oral conjugated oestrogens (Premarin 625 mu g/day) are reported.

Hargrove (1989) examined the safety and efficacy of a one daily dosage of micronized oestradiol and progesterone combined in a single capsule that was administered in a continuous (as opposed to cyclical) manner to

10 menopausal women with moderate-to-severe vasomotor symptoms. To compare 5 women in the study received Premarin daily and Provera daily, for the first ten days of each month. The results were that serum oestrone and oestradiol levels were increased significantly from baseline in both groups and remained increased for the 12 month study period. He also found that the combination of oestradiol and progesterone resulted in improvements in all women, whereas 3 of 5 women receiving Premarin and Provera continued to complain of hot flushes, and 3 of 4 who had reported experiencing nights sweats, continued to do so for the entire 12 month period.

Both of these studies are reporting negative effects when oestrogen is administered solely. This is something to be considered as there may be long term effects to women who are using Premarin and its varieties.

It is Conjugated Equine Oestrogens (CEE) that are used within the drug Premarin, but Lippert et al (2000) expresses concerns in the characterisation of them. They state that it is known that the preparation contains oestradiol metabolites, as well as equilin metabolites which are specific to horses. However there is scarce knowledge about the exact components of the urine extract. One interesting factor in this research is that they suggest that there have been indications that oestrogen metabolites can be involved in the development of hormone-dependent tumours, for example breast cancer.

In order to consider the main question this is an area that would be beneficial to research further, as this is a major concern if research indicates this suggestion to be valid.

It is proposed that the safety of Premarin as a HRT drug will be an area that is researched in further detail to include within the final dissertation.

4. The Ethics

4.1 Conditions of the Mares- PMU Farming

Houpt and Waran (2003) describe the conditions that the mares are kept in.

They foal and are rebred on pasture during the spring and summer. During the autumn and winter, the mares are housed in barns in tie stalls while straddling rubber harnesses suspended from the ceiling that are used to collect the urine.

Information from Duckworth (2003) also describes the conditions of the PMU mares. She gives details of the mares being confined indoors for at least six months of the year while their bodies produce high levels of oestrogen. The stalls that they are tethered in only measure 2.4 metres long by 1 to 1.5 metres wide. This small size leaves the mares unable to move more than a few steps in any direction, and have great difficulty in lying down.

Each horse has a Urine Collection device (UCD) fitted to collect the urine. The UCD is an unhygienic piece of equipment that often results in infected sores and also causes urine to soak the vulva, which can lead to other infections.

It is the author's opinion that the welfare implications here are very serious, and horses should not be kept in these conditions for the benefit of humans. Especially when research is providing evidence that the efficacy, and safety of the drug behind these dreadful conditions of the horses, is questionable.

Houpt and Waran (2003) also express concerns about the mare's access to water. They explain that the reasons given by the PMU industry is that the oestrogen production is higher within a more concentrated sample of urine.

However research by Freeman et al (1999) looked at behaviour as an indication of psychologic well-being of horses provided water continuously or through intermittent delivery systems. As a result this study they concluded that measures of behaviour did not differ significantly between horses provided continuous or intermittent access to drinking water. In addition, clinical assessments indicated clinically normal behaviour for all horses, without differences attributable to water delivery system. Analysis of these results indicated that the psychological well-being of horses was not affected by widely varying schedules and durations of access to water Freeman et al (1999).

It is argued that the conditions of this study may not have been truly representative of those experienced by the PMU mares. Due to the ethical implications it is unlikely that the horses used within this study would have been subject to restricted water access for months, as is the case with the PMU mares.

4.1.1 Patency Rights

It is the author's knowledge that the patency rights for Premarin belong to Wyeth-Ayerst Laboratories.

When the patent on Premarin expired the field was opened up to other pharmaceutical manufacturers interested in developing and marketing a generic version of Premarin. Several smaller companies, including Duramed Pharmaceuticals, were offering a generic version. However in 1990, Wyeth-Ayerst told the FDA that the generic products on the market released estrogens more quickly into the blood stream than Premarin. Relying on the Waxman-Hatch Act's requirement that a generic have the same rate (how fast the drug enters the blood) and extent (how much total drug enters the blood) of absorption as the listed drug product, Wyeth-Ayerst immediately used this discrepancy and began a campaign to take the generics off the market. The issue continued as Wyeth added that small differences in the absorption rate could lead to increased chances for endometrial or breast cancer and that a lower rate of absorption could leave women unprotected from osteoporosis. It argued that new research revealed that conjugated estrogens had a complex biochemistry which, if not exactly replicated, could make the drug toxic or ineffective Paige (1997). Delta 8, 9 Dehydroestrone

Wyeth Laboratories wanted to retain their hold over the marketing and production of Premarin. In order to do this they began analysing it to determine what additional oestrogens, if any, existed and whether they affect individual health. If one or more new components were found to provide a medical benefit, Wyeth would be able to petition the FDA to prevent a generic competitor from reaching the market until it contained that ingredient. Premarin's composition had been validated by a non-governmental panel called the United States Pharmacopoeia Convention (USPC). The USPC is the keeper of a chemical compendium that lists all the components of a drug, both active ingredients and impurities. In isolating delta 8, 9, Wyeth had developed a process of actually manufacturing the component, a process that, unlike Premarin itself, had a patent. If it could get the USPC to accept delta 8, 9 as an active ingredient and it held the patent, Wyeth could indefinitely prevent its competitors from adding delta 8, 9 Paige (1997). However Wyeth had not provided any scientific evidence that delta 8, 9 was active.

Baracat et al (1999) conducted a study that look at oestrogen activity and tissue selectivity of delta 8, 9 sulphate in postmenopausal women. Delta8, 9-DHES was given orally for 12 weeks in a group of 10 women. They found that there was a 95% suppression in all parameters of vasomotor symptoms, with administration which was sustained for the duration of the 12 weeks. They concluded that delta 8, 9 DHES is an active oestrogen with a distinct pharmacological profile that results in significant clinical activity in vasomotor, neuro-endocrine and bone preservation parameters.

Utian et al (2006) reported on the clinical significance of delta 8, 9 in treating the vasomotor symptoms of menopausal women. They also supported the findings of Baracat et al (1999) by stating that delta 8, 9 is a potent clinically active conjugated oestrogen that targets specific tissues and receptors.

It is the author's opinion that the reliability of these studies should be validated, because both the lead researchers are employed by Wyeth Laboratories. It is apparent that this was the research needed in order for Wyeth to prevent generics entering the market, and to hold a patent for delta 8, 9 to ensure this.

The literature that has been researched to date is enabling a picture to be given as to the complex nature of drugs and their uses for treatments. It is proposed that it is important to continue along this route and research the areas regarding Premarin and its effects on women further. It is also proposed that the ethical implications of the conditions of the horses, the patenting by Wyeth and the continued marketing of the drug despite questions over its safety and efficacy, requires more in depth research. Also it may be beneficial to consider the purity, quality and cost of the drug in order to compare that to its chemical synthesis, to enable conclusions to be drawn.


Abernethy, K., (2002) The Menopause and HRT. 2nd Edn, Harcourt Publishers Ltd.

Baracat, E.,Haidar, M.,Lopez, F.J.,Pickar, J.,Dey, M.,Negro-Vilar, A. (1999). Oestrogen activity and novel tissue selectivity of delta8,9-dehydroestrone sulfate in postmenopausal women. Journal of

Clinical Endocrinology and Metabolism. Vol 84,(6), June, pages 2020-2027.

Bolton J.L., Thatcher, G.R. Potential mechanisms of estrogen quinone carcinogenesis. Chemical Research in Toxicology. 2008 21(1):93-101.

Bonfield, T., (2001) New Hormone- Replacer called Better: Cincinnati -made drug said to have fewer side effects. The Cincinnati Enquirer.

Brinton, R.D., Proffitt, P.,Tran, J., Luu, R. (1997). Equilin, a Principal Component of the Estrogen Replacement Therapy Premarin, Increases the Growth of Cortical Neurons via an NMDA Receptor

Dependent Mechanism. Experimental Neurology. Vol 147, (2), October, Pages 211-220.

Burger, H.G.,Cahir, N.,Robertson, D.M.,Groome, N.P.,Dudley, E.,Green, A.,Dennerstein, L. Serum inhibins A and B fall differentially as FSH rises in perimenopausal women. Clinical Endocrinology.1998, 48, (6), pages 809-813.

Burger, H.G. The Endocrinology of the Menopause. (1999) The Journal of Steroid Biochemistry and Molecular Biology. Vol 69(1-6), pages 31-35.

Burger, H.G., Dudley, E.C., Robertson, D.M., and Dennerstein. L. (2002). Hormonal Changes in theMenopauseTransition. Recent Progress in Hormone Research. Vol 57, pages 257-275.

Burger, H.G. Physiology and Endocrinolgy of the Menopause. (2006) Medicine., Vol 34,(1), Pages 27-30

Coope, J., (2000) Strategies for Managing the Menopause. 2nd Edn, Publishing Initiatives Ltd, Great Britain.

Colacurci, N., Manzella, D., Fornaro, F., Carbonella, M., and Paolisso, G. (2003) Endothelial Function and Menopause: Effects of Raloxifene Administration

The Journal of Clinical Endocrinology & Metabolism. Vol 88, (5), pages 2135-2140.

Dennerstein, L., Dudley, E.c., Hopper, J.L., Guthrie, J.R., Burger H.G. (2000). A Prospective Population-Based Study of Menopausal Symptoms. Obstetrics & Gynecology. Vol 96, (3), September, pages 351-358.

Duckworth, J., (2003) Hormone Hell: The inhuman practice of Pregnant Mares' Urine (PMU) farming. (Online)Available at (accessed on 1.12.09)

Golan, D.E., Tashjian, A.H., Armstrong, E.J., Galanter, J.M., Armstrong, A.W., Arnaout, R.A., Rose, H.S., (2005) Principles of Pharmacology: The Pathophysiologic Basis of Drug Therapy. Lippincott Williams, USA.

Griffin, J.E., & Ojeda, S.R. (1996) Textbook of Endocrine Physiology. 3rd Edn, Oxford University Press, Oxford.

Hale, G.E. (2009) Hormonal changes and biomarkers in late reproductive age, menopausal transition and menopause. Clinical Obstetrics and Gynaecology. Vol 23, (1), Pages 7-23

Houpt, K.A., Waran, N., (2003) Horse Welfare since 1950. (Online) Available at (accessed on 1.12.09)

Iqbal, J., and Zaidi, M (2009). Understanding Estrogen Action duringMenopause. Endocrinology. Vol 150, (8), pages 3443-3445.

Krishna, D.R.,Klotz, U (1994). Extrahepatic metabolism of drugs in humans. Clinical Pharmacokinetics. Vol 26, (2), February, pages 144-160.

Landgren, B.M., Collins, A., Csemiczky, G., Burger, H.G., Baksheev, L, and Robertson, D.M (2004). Menopause Transition: Annual Changes in Serum Hormonal Patterns over the Menstrual Cycle in Women during a Nine-Year Period Prior to Menopause. The Journal of Clinical Endocrinology and Metabolism. Vol 89, (6), pages 2763-2769.

Lippert, T.H., Alfred, M.O., Seeger, H. (2000). Is the use of equine oestrogens in hormone replacement therapy still appropriate? British journal of Clinical Pharmocology. 49 (5), 489-490.

Martin C.R., (1985) Endocrine Physiology. Oxford University Press, New York.

McDonnell, S.M.,Freeman, D.A.,Cymbaluk, N.F.,Schott, H.C., Hinchcliff, K.,Kyle B. (1999). Behaviour of stabled horses provided continuous or intermittent access to drinking water. American Journal of Veterinary Research. Vol 60, (11), November, pages 1451-6.

Metcalf, M.G., Donald, R.A., Livesey, J.H (2008). Pituitary-Ovarian Function in Normal Women During the Menopausal Transition. Clinical Endocrinology. Vol 14, (3),March, Pages245-255.

Neal, M.J., (2005) Medical Pharmacology at a Glance. 5th Edn, Blackwell Publishing Ltd, Oxford.

Norman, A.W & Litwack, G., (1987) Hormones. Academic Press Inc, London.

Page, C., Curtis, M., Sutter, M., Walker, M., Hoffman, B., (2002) Integrated Pharmacology. 2nd Edn, Harcourt Publishers Limited, Edinburgh

Paige, L.K (1997) Premarin, Politics, and the Public Health: An Expose Revealing How Politics Trumped Science at the FDA. (Online) Available at (accessed on 1.12.09)

Pfeilschifter, J.,Köditz, R., Pfohl, M.,and Schatz, H (2002). Changes in Proinflammatory Cytokine Activity after Menopause. Endocrine Reviews. Vol 23,(1), pages 90-119.

Pond, S.M.,Tozer, T.N (1984). First-pass elimination. Basic concepts and clinical consequences. Clinical Pharmacokinetics. Vol 9, (1), January-February, pages 1-25.

Rick, N.G (2009) Drugs from discovery to Approval. 2nd edn, John Wiley and Sons Inc, New Jersey.

Silverman, R.B., (2004) The Organic chemistry of drug design and drug action. 2nd Edn, Elsevier Academic Press, London.

Sherman, B.M.,West, J.H.,Korenman, S.G. (1976) The menopausal transition: analysis of LH, FSH, estradiol, and progesterone concentrations during menstrual cycles of older women. Journal of Clinical Endocrinology and Metabolism. Vol 42,(4), pages 629-36.

Tabibzadeh, S. The Signals and Molecular Pathways Involved in Human Menstruation, a Unique Process of Tissue Destruction and Remodelling. (1996). MolecularHuman Reproduction. Vol. 2, (2), pages 77-92.

Teede, H., Burger, H.G. The Menopausal Transition. In: Studd JW (ed.) The Management of the Menopause, Annual Review, pages 1-12. Parthenon, London.

Thomas, G., (2008) Medicinal Chemistry: An introduction. 2nd edn, John Wiley and Sons Ltd, England

White, M., Grant, E.C.G. (1998) Addiciton to oestrogen and Progesterone. Journal of Nutritional and Environmental Medicine. Vol. 8,(2), Pages 117-120

Utian, W., Ravnikar, V.A., Sarrel, P and Simon, J.A (2006) The Clinical Significance of Delta 8,9 Dehyrdoesterone Sulfate in Treating Menopausal Vasomotor Symptoms. (Online). Available at (accessed on 1.12.09).

Zhang, F., Yao, D., Hua, Y., van Breemen, R. B., and Bolton, J. L. Synthesis and reactivity of the catechol metabolites from the equine estrogen, 8,9-dehydroestrone. Chem. Res. Toxicol. 2001, 14, 754-763

Please be aware that the free essay that you were just reading was not written by us. This essay, and all of the others available to view on the website, were provided to us by students in exchange for services that we offer. This relationship helps our students to get an even better deal while also contributing to the biggest free essay resource in the UK!