In order to elucidate the mechanism regulating the pulsatile secretion of the gonadotropins, LH and FSH, we have utilized a model in which endogenous gonadotropin affecting factors are selectively immunoneutralized and then replaced in a pulsatile manner using structurally modified agonists. Our results have demonstrated that pulsatile FSH secretion is independent of the gonadotropin releasing factor (GnRH) of the brain that controls LH secretion, and the involvement of, as of yet, unidentified, slow and fast acting FSH-affecting factors. Two candidates for these FSH regulating components, discovered by recombinant DNA methodology, are a peptide that may represent the non-GnRH portion of the GnRH prohormone (GAP) and a slow acting FSH inhibitor, inhibin. We have developed specific, high titer antisera and radioimmunoassays for these factors. Using our anti-GAP serum, we have demonstrated, by both immunocytochemistry and by radioimmunoassay quantitation, that the GAP peptide does indeed represent a portion of the GnRH prohormone. Screening of GAP fragments for biological activity, using cultured anterior pituitary cells, has revealed gonadotrophin releasing activity in the N-terminal region of the GAP sequence. We are not generation antiserum against this region for immunoneutralization studies. Using the anti-inhibin serum we have been able to demonstrate the presence of significant quantities of inhibin in human and porcine ovarian follicular fluid, rat plasma, and rat Sertoli cell cultures. In addition, we have initiated immunoneutralization studies in the rat and have demonstrated that FSH secretion is selectively increased following injection of the anti-inhibin serum. In related studies, we have also used a computer assisted perifusion system to reproduce in vitro the pulsatile gonadotropin patterns observed in vivo and are studying the intracellular messengers involved in pulsatile gonadotrophin secretion. These studies have already and will continue to greatly advance our understanding of the mechanisms regulating pulsatile gonadotropin secretion.
