Hormonal Regulation of Pituitary Gonadotropin Gene Expression

Abstract

It is well known that the endocrine regulation of the reproductive system is complex, involving multiple hypothalamic, pituitary, and gonadal factors in the coordination of gonadal function. The pituitary gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), play pivotal roles in this regulatory network. They act directly on gonadal tissue to stimulate the production and release of gonadal sex-steroid hormones and to regulate gametogenesis. Hence, appropriate levels of LH and FSH determine oocyte maturation and ovulation in female animals and spermatocyte development in male animals. As a result, the regulation of LH and FSH synthesis and secretion must be a critical element involved in normal reproductive function (Fig. 19.1). Much has been learned over the last few decades concerning the factors that modulate LH and FSH production and secretion. It has been long known that the gonadal sex-steroid hormones, including estrogen, testosterone, and progesterone, regulate the pituitary gonadotropins either directly at the pituitary or indirectly at the hypothalamic levels. In addition, a hypothalamic factor, gonadotropin-releasing hormone (GnRH), has been shown to be the major positive controller of LH and FSH release. Recent data indicate that GnRH is released by neurons in the median eminence of the hypothalamus in a pulsatile fashion that varies in amplitude and frequency, both of which influence the amount of LH and FSH produced and secreted (16).