A MODULATORY ROLE FOR SUBSTANCE-P ON THE REGULATION OF LUTEINIZING-HORMONE SECRETION BY CULTURED PORCINE GONADOTROPHS

Substance P (SP) has been suggested to regulate gonadotroph function b oth directly and indirectly in different species, In pigs, the possibl e role of hypothalamic and pituitary SP in the control of LM release h as not been examined. Here, we investigated SP effects on basal and Gn RH-stimulated LH secretion by porcine gonadotrophs in vitro, in both s tatic and dynamic culture systems. SP concentrations of 100 nM or abov e stimulated LH release from monolayer cultures without affecting intr acellular LH content. In the same cultures, SP potentiated GnRH (10 nM )-stimulated LH release and reversed the GnRH-induced decrease of gona dotroph LH stores, The GnRH, but not the SP, effect was completely blo cked by the potent GnRH-receptor antagonist antide. In superfused pitu itary fragments, three successive pulses of SP or GnRH also stimulated LH release, yet the combined administration of both factors did not r esult in a synergistic stimulation. These results demonstrate that SP acts directly on porcine gonadotrophs to stimulate LH release, and to maintain the levels of hormonal stores, through a GnRH receptor-indepe ndent mechanism. Furthermore, our findings suggest that continuous exp osure of gonadotrophs to SP would potentiate GnRH-stimulated LH secret ion, thus supporting a possible role of SP as modulator of porcine gon adotroph function.