Deloris C. Rogers

Evidence for calcium mediation of gonadotropin releasing hormone action in the pituitary

Abstract Despite the relatively long time since the isolation, characterization, and complete chemical synthesis of the gonadotropin releasing hormone (GnRH), very little information has become available which has elucidated the manner by which this hormone evokes gonadotropin release from the pituitary. Recently, a line of evidence has developed which suggests that calcium (Ca 2+ ) may play a central role in GnRH stimulation of gonadotropin release from cultured rat pituitary cells.

Restoration of responsiveness to gonadotropin releasing hormone (GnRH) in calcium-depleted rat pituitary cells

Abstract GnRH-stimulated, but not basal, luteinizing hormone (LH) release from cultured pituitary cells requires extra-cellular calcium. The present studies were designed to show whether cells which had lost responsiveness to GnRH in the absence of extracellular calcium (“Ca 2+ -depleted cells”) could regain responsiveness by readdition of calcium to the media. The addition of calcium-containing medium to cells which were preincubated (75 min) in calcium-free medium resulted in elevated basal LH release. Addition of GnRH to the media in the presence of calcium did not cause additional stimulation of LH release above the elevated basal level. Incubation of Ca 2+ -depleted cells in calcium-containing media for 2 h before measuring responsiveness depressed the basal level to near that seen in control cells and GnRH was able to stimulate LH release, but not to as high a level as in control cells (which were preincubated in 1 mM Ca 2+ -containing media). After incubation of calcium depleted cells in calcium-containing media for 3 h or 5 h, the basal and stimulated levels of LH response were statistically indistinguishable from those seen in control cells.

GnRH Receptor Microaggregation: Regulation of Gonadotropin Release, GnRH Receptors, and Gonadotrope Responsiveness

Gonadotropin releasing hormone (GnRH) stimulates luteinizing hormone (LH) and follicle stimulating hormone (FSH) release from pituitary gonadotropes. Additional receptor-mediated actions of the releasing hormone include regulation of both the GnRH receptor and of cell responsiveness. While it is apparent that the release mechanism is Ca2+ mediated, it remains unclear how this receptor-mediated action is integrated with regulation of the receptor and of cell responsiveness. It is the purpose of this presentation to describe the requirements of gonadotropin release as well as receptor and response regulation in order to prepare an integrated model for these actions of the releasing hormone.