IN-VIVO AND IN-VITRO RESPONSES OF THE BOVINE CORPUS-LUTEUM AFTER EXPOSURE TO EXOGENOUS GONADOTROPIN-RELEASING-HORMONE AND PROSTAGLANDIN-F2-ALPHA

Administration of gonadotropin-releasing hormone (GnRH) early in the e strous cycle has been shown to cause subsequent altered luteal functio n. To determine whether membrane-related events may be involved in GnR H-attenuated luteal function, corpora lutea (CL) were removed from bee f heifers on day seven of the estrous cycle after iv injection of GnRH or saline on day two of the cycle (n = 5/group). Luteal slices were i ncubated with saline (control), luteinizing hormone (LH), or 8-bromo-c AMP for 2 h. In vivo administration of GnRH reduced LH and cAMP-stimul ated progesterone production by tissue (p < 0.01), but basal progester one production was not affected (p > 0.05). Luteal adenylyl cyclase ac tivity did not differ between saline and GnRH-treated animals (p > 0.0 5). Then, to examine if early administration of GnRH alters response o f the CL to prostaglandin (PG) F-2 alpha, beef heifers were injected w ith GnRH as described above (n = 4/group), and then injected with PGF( 2 alpha) on day eight and the CL removed 60 min later. Blood samples w ere collected for oxytocin (OT) analysis at frequent intervals after P GF(2 alpha) injection and for progesterone at 0 and 60 min. Induction of the early response gene c-jun or release of OT by PGF(2 alpha) was not altered by Gn RH injection (p > 0.05). Injection of PGF,, decrease d serum progesterone by 60 min postinjection (p < 0.05), but concentra tions of this steroid were unaffected by GnRH (p > 0.05). Collectively , these data suggest that GnRH-induced alteration of bovine luteal fun ction may be owing to events distal to cAMP synthesis that do not inte rfere with PGF(2 alpha)-induced expression of c-jun or OT release, cel lular phenomena involved in luteolysis.