GnRH and Gonadotropins

The gonadotropins are peptides that have a close functional relaliunship U the esirtrgens. prugesleroiie. and teskrsterone. 

The hypothalamus rcleuites GnRH. a peptide that stimulates the anterior pituitary to secrete LH and FSH in males and females. This peptide controls and regulates both male and female reprixluction (Figs. 23-9 and 23-10). GnRH is a mod- 

The increased concentrations of estrogens and progesterone a gulate the hypothalamus and the anterior pituitary by a feedback inhibition process that decreases GnRH. LH.anil FSH production. The result is that further ovulation is inhibited. As described below in this chapter, this is the priniaty mechanism by which. steroid birth contnri products inhibit ovulation. 

If fertili/ation dites not occur by about day 25. thecorpih lutetim begins to degenerate, slowing down its privductionol 

The pharmacological actions of hCG are essentially the same as those of LH. In females during pregnancy, the hCG secreted by the placenta maintains the corpus luteum to continue secretion of estrogen and progesterone, thus inhibiting ovulation and menstruation. 

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Fig. 1. The major hypothalamic-pituitary-ovarian interactions mentioned in different parts of this review. Ovarian steroids exert effects on the secretion of GnRH and gonadotropins.

The present review will focus on the behavioral consequences of two peptidergic compounds, oxytocin and vasopressin. A variety of other peptides, such as corticotropin releasing hormone (CRH), gonadotropin-hormone releasing hormone (GNRH), and the endogenous opiates, such as beta-endorphin (to name only a few) also influence behavior. 

Melatonin affects reproduction in seasonally breeding animals. In humans, findings of increased endogenous melatonin in hypogonadism and low concentrations in precocious puberty imply an interaction between melatonin and gonadotropins however, data on the effects of exogenous melatonin are limited (1). In a randomized study in 16 women, melatonin enhanced LH and FSH responses to submaximal GnRH stimuli in the follicular but not the luteal phase of the menstrual cycle (24). 

Conn PM, Hazum E (1981) Luteinizing Hormone Release and Gonadotropin-Releasing Hormone (GnRH) Receptor Internalization Independent Actions of GnRH. Endocrinology 109 6 2040-2045... 

Gonadotropins (gonadorelin, GnRH, and analogues) [SED-15, 1536 SEDA-31, 703 SEDA-32, 789 SEDA-33, 909]... 

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