Pituitary gonadotropin

The estrogens are secreted by the ovarian follicle and in smaller amounts by the adrenal cortex. Estrogens are important in the development and maintenance of the female reproductive system and the primary and secondary sex characteristics. At puberty, they promote growth and development of the vagina, uterus, fallopian tubes, and breasts. They also affect the release of pituitary gonadotropins (see Chap. 50). 

Progesterone is secreted by the corpus luteum, placenta, and in small amounts by the adrenal cortex. Progesterone and its derivatives (ie, the progestins) transform the proliferative endometrium into a secretory endometrium. Progestins are necessary for the development of the placenta and inhibit the secretion of pituitary gonadotropins, which in turn prevents maturation of the ovarian follicle and ovulation. The synthetic progestins are usually preferred for medical use because of the decreased effectiveness of progesterone when administered orally. 

Specifically, for women with PCOS, the use of depot and intermittent oral medroxyprogesterone acetate suppresses pituitary gonadotropins and circulating androgens.15 Further, the use of cyclic progesterone may benefit women over age 40 and in whom anovulatory bleeding occurs.11... 

The three recurrent theories proposed are the incessant-ovulation hypothesis, the pituitary gonadotropin hypothesis, and the chronic inflammatory processes hypothesis.2,31 The incessant-ovulation hypothesis proposes that the pathogenesis of ovarian... 

High-dose fish had 58% dead survivors had egg production reduced 77% and their livers had 33 mg total PCBs/kg DW. The two lower dose groups had 60 and 62% reduction in egg production and liver residues of 3 and 12 mg total PCBs/kg DW, respectively. Food consumption declined with increasing dose. Egg production was related to pituitary gonadotropin content and food consumption... 

Adashi EY, Hsueh AJ, Bambino TH, Yen SS (1981) Disparate effect of clomiphene and tamoxifen on pituitary gonadotropin release in vitro. Am J Physiol Endocrinol Metab 240 E125-130... 

Wersinger SR, Haisenleder DJ, Lubahn DB, Rissman EF (1999) Steroid feedback on gonadotropin release and pituitary gonadotropin subunit mRNA in mice lacking a functional estrogen receptor a. Endocrine 11 137-143... 

Pharmacology A synthetic androgen derived from ethisterone, danazol suppresses the pituitary-ovarian axis by inhibiting the output of pituitary gonadotropins. Danazol depresses the output of both follicle-stimulating hormone (FSH) and luteinizing... 

Clomiphene is a nonsteroidal agent with oestrogenic and anti-oestrogenic properties. The mechanism of action is not precisely clear, but it ultimately leads to the release of the pituitary gonadotropins FSH and LH. It stimulates ovulation in anovulatory or oligo-ovulatory women with adequate endogenous oestrogen activity and an intact hypothalamic-pituitary-ovarian axis. 

Mechanism of Action A testosterone derivative that suppresses the pituitary-ovarian axis by inhibiting the output of pituitary gonadotropins. Causes atrophy of both normal and ectopic endometrial tissue in endometriosis. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are depressed in fibrocystic breast disease. Inhibits steroid synthesis and binding of steroids to their receptors in breast tissues. Increases serum levels of esterase inhibitor. Therapeutic Effect Produces anovulation and amenorrhea, reduces the production of est rogen, corrects biochemical deficiency as seen in hereditary angioedema. 

Mechanism of Action A hormone that influences proliferative endometrium and transforms into secretory endometrium. Secretion of pituitary gonadotropins is inhibited which prevents follicular maturation and ovulation, TircrapeuticEffect Facilitates ureteral dilatation associated with hydronephrosis of pregnancy. 

Danazol is a weak androgen and also has a series of other hormonal and anti-hormonal properties. It inhibits pituitary gonadotropin and has been used in the treatment of endometriosis, fibrocystic disease of the breast, idiopathic thrombocytopenic purpura, and hereditary angioedema. Its hepatotoxic effects include reversible rises in serum transaminases and cholestatic hepatitis a few cases of hepatocellular tumors have been reported. 

Therefore, both pituitary gonadotropins are required for optimal androgen function. LH acts on the Leydig cells to stimulate testosterone synthesis,... 

Release of the pituitary gonadotropins (LH, FSH) is regulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus.21,144 A classic... 

DES is a synthetic estrogen that inhibits ovulation by affecting release of pituitary gonadotropins. Some of its uses include treatment for hypogonadism, primary ovarian... 

In the absence of pituitary gonadotropins, the gonads fail to develop properly and removal of the pituitary gland causes reproductive failure. 

Bookstaff RC, Kamel F, Moore RW, et al. 1990b. Altered regulation of pituitary gonadotropin-releasing hormone (GnRH) receptor number and pituitary responsiveness to GnRH in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated male rats. Toxicol Appl Pharmacol 105 78-92. 

These products effect a blockade of the pituitary gonadotropin secretion and a decrease in the LH-receptors in the Leydig cells of the testes, causing a reduction in the testosterone level (drug castration). 

It is well known that the pituitary gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), are indispensable for ovulation. FSH, in particular, is necessary for the stimulation of preovulatory ovarian estrogen production and the initiation of follicle maturation. This chapter will discuss the mechanisms underlying the FSH stimulation of ovarian cell differentiation and maturation. 

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