Gonadotrophin secretion

Bronson F., Singer A. and Macrides F. (1988). Chemical properties of a female mouse pheromone that stimulates gonadotrophin secretion in males. Biol Reprod 38, 193-199. 

McCann, S.M., Karanth, S., Mastronardi, C.A., Dees, W.L., Childs, G., Miller, B., Sower, S., and Yu, W.H. 2001. Control of gonadotrophin secretion by follicle stimulating hormone-releasing factor, luteinizing hormonereleasing hormone and leptin. Archives of Medical Research 32(6), 476-485. 

These combined contraceptives seem to function by inducing feedback inhibition of gonadotrophin secretion which, in turn, inhibits the process of ovulation (Chapter 8). They also induce alterations in the endometrial tissue that may prevent implantation. Furthermore, the progestogen promotes thickening of the cervical mucus, which renders it less hospitable to sperm cells. This combination of effects is quite effective in preventing pregnancy. 

Danazol is an isoxazole derivative of 17alpha-ethinyl testosterone. It has weak androgenic activity. It inhibits gonadotrophin secretion and is used to suppress ovarian function. It induces endometrial atrophy and has found its major use in the management of endometriosis. Gestrinon has the same indication and acts via a similar mechanism. Danazol has also been used in the management of benign breast disorders such as fibrocystic disease. 

So far no simple equivalent of the oral contraceptive pill has been developed for men. Relatively large doses of testosterone do inhibit gonadotrophin secretion and hence spermatogenesis, and different schedules are under clinical trial at present. 

What is known about the neural circuitry for mammalian maternal behavior has been delineated using animal models, predominantly the rat. The medial preoptic area (MPOA) of the hypothalamus is important in reproductive function—i.e., in sexual behavior, gonadotrophin secretion, and the expression of normal maternal behavior (Numan, 1974). Maternal behaviors... 

Gonadotrophin secretion is under the control of hypothalamus and sex hormones. The hypothalamic nuclei secrete a specific releasing factor for the release of both FSH LH. 

Due to its probable direct effect on ovaries, it may increase the gonadotrophin secretion. It also exerts a weak estrogenic action on endometrium. 

It inhibits gonadotrophin secretion from pituitary in both men and women thus inhibiting both testicular/ovarian function. 

Howland BE. The influence of feed restriction and subsequent re-feeding on gonadotrophin secretion and serum testosterone levels in male rats. J Reprod Fertil 1975 44 429-436. 

However, chronic administration (e.g. as a depot injection) evokes an initial agonist phase of several days to weeks, followed by a suppression of gonadotrophin secretion. The precise molecular site of action of this process is unclear, but it is thought to involve an initial loss of receptors, followed by an uncoupling of receptors from their effector systems. Chronic administration is used clinically in the treatment of sex-hormone responsive tumors such as prostate and breast cancer. 

Mesterolone provides oral therapy its molecular structure is such that its hypothalamic feedback inhibition of pituitary gonadotrophin secretion is less and it does not cause liver injury (see below). 

Some agonist progestogenic activity on hypothalamic receptors, inhibiting gonadotrophin secretion, which also inhibits testicular androgen production. 

Combined oestrogen-progestogen oral contraceptives have been extensively used since 1956. The principal mechanism is inhibition of ovulation (4, above) through inhibition of gonadotrophin secretion from the h3 othalamus. In addition the endometrium is altered, so that implantation is less likely (7, above) and cervical mucus becomes more viscous and impedes the passage of the spermatozoa (5, above). 

Fernandez-Ruiz JJ, Munoz RM, Romero J, Villanua MA, Makryannis A, Ramos JA (1997) Time course of the effects of different cannabimimetics on prolactin and gonadotrophin secretion evidence for the presence of CBl receptors in hypothalamic structures and their involvement in the effects of cannabimimetics. Biochem Pharmacol 53 1919-1927... 

Barnea ER, Shurtz-Swirski R. 1992. Modification of pulsatile human chorionic gonadotrophin secretion in first trimester placental explants induced by polycyclic aromatic hydrocarbons. Hum Reprod 7(3) 305-310. 

In normal adults. GnRH elicits a marked release of l.H and a smaller relea.se of FSH. This test is frequently used to investigate possible damage to pituitary gonadotrophin secreting cells. 

The hypothalamic factors which control anterior pituitary hormone secretion are shown in Figure I. Tumours secreting each of the anterior pituitary hormones have been identified. T.SH and gonadotrophin secreting tumours are rare. Gil and ACTH secreting tumours arc more common. Prolactin secreting adenomas (prolactinomas) arc the most common. 

A single injection of chlorpromazine in infant male rats interfered with the gonadotrophin secretion (Ladosky et al. 1970). In the Indian wall lizard, Hemidactylus flaviviridis (Ruppell), after a daily injection of 15 ng chlorpromazine for two days the neurones of the paraventricular nucleus showed a slight depletion of aldehyde fuchsin-stained neurosecretory material (Haider 1974). In the supraoptic nucleus, neurones were enlarged and many of them showed vacuolisation of their cytoplasm, while the quantity of their neurosecretory material was not reduced as compared with the controls. 

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