Regulation of Gonadotropin Gene Expression by Gonadotropin Releasing Hormone

Abstract

Pituitary luteinizing hormone and follicle stimulating hormone are composed of a common alpha and different beta subunits (1), which are coded for by 3 separate genes (2). Both hormones are secreted by the pituitary gonadotrope cells, and gonadotropin releasing hormone appears to be the major regulator of LH and FSH synthesis and secretion. GnRH is secreted by the hypothalamus in a pulsatile manner (3, 4), and this pattern of stimulus appears to be essential for maintaining gonadotropin production and secretion (5–7). GnRH secretion changes in different physiologic circumstances, and alterations in both the amplitude and frequency of GnRH pulses occur in normal physiology (8–15). These changes in GnRH stimulation are accompanied by differential release of LH and FSH, and it appears that a single gonadotropin releasing hormone is responsible for differential secretion of LH and FSH by the gonadotrope. The pattern of GnRH secretion and gonadotrope responses to GnRH can be modified by gonadal steroids and by peptides such as inhibin and activin. Thus, it appears that regulation of LH and FSH synthesis and secretion results from changes in the pattern of the GnRH pulse stimulus together with direct actions of gonadal steroids and of peptides on the gonadotrope cell.