Importance Of Androgens In Male Sex Characteristics example essay topic

Androgens are hormones that effect both male sexual behaviour and male characteristics (Sutherland, 1995). In order to discuss the importance of androgens in male sex characteristics, organizational affects in prenatal hormonal gender and the development of the male internal and external sex organs will be discussed using androgen insensitivity syndrome to explain the importance of androgens. The role of androgens in sexual maturation and the effects of deficient androgen production in Klinefelters syndrome will also be discussed to show the importance of androgens in male sex characteristics. To explain the importance of androgens in producing male sexual behaviour, activation al effects of androgens in both castrated rodents and human will be discussed, and other hormones which play a role in male sexual activity will also be considered. The effect of androgens on sexual behaviour in terms of masculinization and defeminization will also be discussed. Homosexuality will also be discussed and suggestions for the role of androgens in producing homosexual males will be suggested.

During prenatal development hormones have organizational effects which influence the development of a person!'s sex organs. In males once the testes have formed they produce a set of steroid hormones called androgens which stimulate the development of the Wolffian system. Testosterone is one of the androgens that are produced, and an enzyme called 5|'A reductase converts some of the testosterone into another androgen called dihydrotestosterone. The presence of these hormones along with the anti-M"^1 llerine hormone (which prevents the M"^1 llerine system from developing), forms the prenatal hormonal gender male. This is evidence that androgens are important in the production of male sex characteristics due to the fact that if testosterone and dihydrotestosterone are not present then the prenatal hormonal gender would be female and the M"^1 llerine system would develop instead of the Wolffian system. When molecules of androgens bind with androgen receptors in the precursor of the male internal sex organs, the epididymis, vas deferens, and seminal vesicles develop and grow, and in the presence of dihydrotestosterone the external genitalia will be male.

However some people are insensitive to androgens and have androgen insensitivity syndrome (MacLean et al, 1995). It is caused by a genetic mutation which prevents the formation of functioning androgen receptors. The primitive gonads of a genetic male foetus with androgen insensitivity syndrome become testes and secrete anti-M"^1 llerine hormone and androgens. Because there are no androgen receptors, the androgens do not have a masculinizing effect and therefore the epididymis, vas deferens, seminal vesicles, and prostate fail to develop. The lack of androgen receptors means that the cells can not respond to the androgens that are being produced, resulting in female external genitalia, and breasts developing at puberty. This is strong evidence that androgens are important in the development of the Wolffian system and the development of the external genitalia of males.

Androgens are also important at sexual maturation in terms of secondary sex characteristics. At puberty cells in the hypothalamus secrete gonadotropin-releasing hormones (GnRH), which stimulate the production and release of two gonadotropic hormones by the anterior pituitary gland. In males the gonadotropic hormones stimulate the testes to produce testosterone. Testosterone is ultimately responsible for sexual maturation.

Dietrich et al (2002) showed the importance of androgens in producing secondary male sex characteristics. The authors exposed fish to methyl testosterone (a potential model androgen) using a flow through system. The results showed that after 13 days of exposure 100% of the fish showed typical male secondary sex characteristics. This is strong evidence that suggests that androgens are important in the development of male secondary sex characteristics. However it is important to remember that the research that was conducted by Dietrich et al (2002) was conducted on non-human animals and that the findings can not be generalised to the human population. Klinefelters syndrome shows how important androgens are in terms of male sexual characteristics and what happens when there is deficient androgen production.

The gonads are testes, however due to the lower levels of androgen production they do not develop at puberty and are called pea-sized testes. Am individual with Klinefelters syndrome will be unable to produce sperm and therefore be sterile, and at the on-set of puberty may also develop breasts. The deficient androgen production means that the individual will not develop the sex characteristics associated with a male, and so suggests support for the view that androgens are important in producing male sex characteristics. Sexual behaviour of male rodents depends on the androgen testosterone. Davidson (1974) showed this when they castrated male rats and found that their sexual activity stops altogether, due to the fact that they did not have any testes to produce testosterone. However the author found that when injections of testosterone were given to the rats then their sexual activity was reinstated, giving evidence for the view that androgens are important in terms of sexual activity.

However this is not true of human males. Money and Ehrhardt (1972) showed that that the decline of sexual activity of human males after castration is quite variable. They found that some men lose potency immediately, whereas others show a slow gradual decline over several years. This may be due to the fact that practise and experience of sexual activity slows down the decrease in sexual activity. There is no direct evidence to suggest this is what happens in humans; however Rosenblatt and Aronson (1958) found that male cats that engaged in higher amounts of sexual activity remained a lot more potent for a longer period of time after castration. Another reason for the high variability of sexual activity after castration in human males may also be due to the fact that the adrenal glands, the prostate gland, and even fat tissue are sources for androgen production and so can maintain low levels of sexual activity in males.

Androgens are not the only hormones that are responsible for male sexual behaviour. Other hormones play vital roles in male sexual behaviour. Oxytoxin is a hormone that is produced by the poster ia pituitary gland. It is released at the time of orgasm in males (and females) and appears to contribute to the contractions of the smooth muscle in the male ejaculatory (Carmichael et al, 1987). Like Oxytoxin, Prolactin (a hormone secreted by the anterior pituitary gland) is also released by males after ejaculation (Oaknin et el, 1989). Prolactin has also been found to have an inhibitory effect on male sexual desire.

Over secretion of prolactin causes hyperprolactinemia in which one of the symptoms is loss of sexual desire (Foster et el, 1990). The two organizational effects of androgens on the brain; behavioural masculinization and behavioural defeminization; are stimulated by testosterone, and appear to involve androgen receptors. This is because an enzyme called aromatase converts testosterone into estradiol which stimulates oestrogen receptors located in the nucleus of some of the cells. There is strong evidence in the research of rodents that suggests that exposure of androgens to the brain is important in behavioural masculinization and behavioural defeminization. Brand et al (1991) found that if they treated male rats early in life with drugs that block aromatization, then the male rats are less likely to show male sexual behaviour and more likely to show female sexual behaviour and prefer the company of males than females. These results suggest that behavioural defeminization and masculinization is largely due to the indirect effects of aromatized testosterone on oestrogen receptors.

Although many animals occasionally engage in sexual activity with a member of the opposite sex, exclusive homosexuality appears to occur only in humans (Ehrhardt and Meyer-Bahlburg, 1981). Some people believe that homosexuality is a result of childhood experience, more so interactions between the child and their parents. However there is research that does not support this point of view. Bell et al (1981) conducted a large scale study of several hundred homosexuals and found no evidence that the relationship between a child and their parents is related to homosexuality. A more likely biological cause of homosexuality is a subtle difference in brain structure which is caused by differences in the amount of prenatal exposure to androgens.

Lower levels of androgens in a male during prenatal development might mean that the brain of a male does not become either masculinized or defeminized and so they want to spend time with members of the same sex and do not show the same sexual behaviour as a heterosexual male. However this is just speculation, there is not as yet any research into this area and there is no human data to support this. It therefore can be concluded that androgens are very important in terms of male sexual characteristics. They are responsible for both the development of the Wolffian system into the internal sex organs, and the development of external genitalia of males. Klinefelters syndrome shows that androgen deficiency produces genetic males that do not have male sexual characteristics, which is also strong evidence for the fact that androgens are very important in producing male sex characteristics. Dietrich et al (2002) found that androgens were also important in producing secondary male characteristics at sexual maturation.

In humans, after castration the level of sexual activity is variable, which could be due to previous experience or the fact that there are other sources that produce low levels of androgens that maintain sexual activity. In terms of sexual behaviour androgens are not the only important hormone. There are also other important hormones that play a role in male sexual behaviour such as oxytoxin and prolactin, which are associated with contraction of the male ejaculatory system and male sexual desire respectively. It can also be concluded that aromatized testosterone indirectly effect oestrogen receptors which effects masculinization and defeminization. It is also suggested that lower levels of androgens result in the brain not being masculinized or defeminized resulting in a male not showing male sexual behaviour and being homosexual homosexual. However this is just speculation and is an avenue for future research.

Bibliography

Bell, A.P., Weinberg, M.S., & Hammersmith, S.K. (1981).
Sexual preference: its development in men and women. Bloomington: Indiana University Press. Brand, T., Kroon en, J., Mos, J., & Slob, A.K. (1991).
Adult partner preference and sexual behaviour of male rats affected by prenatal endocrine manipulation. Hormones and behaviour, 25,323-341. Carmichael, M.S., Humbert, R., Dixon, J., Palmisano, G., Greenleaf, W., & Davidson, J.M. (1987).
Plasma oxytoxin increases in the human sexual response. Journal of Clinical Endocrinology and Metabolism, 64, 27-31. Davidson, G.C., and Neale, J.M. (1974).
Abnormal psychology: An experimental Clinical Approach. New York: John Wiley & sons. Dietrich, D.R., Hutchinson, T., Lange, R., Painter, G., Steger-Hartmann, T., & Zerulla, M. (2002) [Abstract of Morphological sex reversal upon short-term exposure to endocrine modulators in juvenile fathead minnow: Journal of Toxicology Letters, 131, 1-2, 51-63, ] [Electronic].
Available: Web of Science [2002, May 10th].
Ehrhardt, A.A., & Meyer-Bahlburg, H.F.L. (1981).
Effects of prenatal sex hormones on gender-related behaviour. Science, 211, 1312-1318. Foster, R.S., Mulcahy, J.J., Callaghan, J.T., Crabtree, R., & Brashear, D. (1990).
Role of serum prolactin determination in evaluation of impotent patient. Urology, 36,499-501. Maclean, H.E., Warne, G.L., & Za jac, J.D. (1995).
Defects of androgen receptor functions: From sex reversal to motor-neuron disease. Molecular and cellular Endocrinology, 112,133-141. Money, J., & Ehrhardt, (1972).
A. Man and woman, boy and girl. Baltimore: John Hopkins University Press. Oaknin, S., Rodriguez del Castillo, A., Guerra, M., Battaner, E., & Mas, M. (1989).
Change in forebrain Na, K-ATPase activity and serum hormone levels during sexual behaviour in male rats. Physiology and Behaviour, 407-410. Rosenblatt, J.S., & Aronson, L.R. (1958).
The influence of experience on the behavioural effects of androgen in prepuberally castrated male cats. Animal Behaviour, 6,171-182. Sutherland, S. (1995).