In vitro LH release and cAMP accumulation induced by synthetic GnRH derivatives

Oxytocin augmentation of gonadotropin-releasing hormone-stimulated luteinizing hormone release is modulated by cyclic AMP

Oxytocin has been previously shown to augment GnRH-stimulated LH release. However it is currently unknown which intracellular mediators participate in the process. In this study, after preincubation with oxytocin for 3 hours, quartered pituitaries were stimulated for 15 minutes with GnRH. The effects of diBucAMP, a cell permeable analog of cAMP, and DDA, an adenyl cyclase inhibitor, on the augmentation by oxytocin were investigated. Although addition of diBucAMP increased GnRH-stimulated LH release, it inhibited the augmentation by oxytocin of the response to GnRH. On the other hand addition of DDA induced an increased augmentation by oxytocin. These results indicate that intracellular cAMP inhibits the augmentory activity of oxytocin, and suggest that oxytocin modulation of GnRH action in vivo would be optimal when the hormonal milieu results in reduced levels of cAMP.

Blockade of LHRH-induced lordosis by alpha- and beta-adrenergic antagonists in ovariectomized, estrogen primed rats

The participation of a noradrenergic mechanism in the facilitation of lordosis by luteinizing hormone-releasing hormone (LHRH) was studied in two groups of ovariectomized estrogen primed rats, with or without sexual experience. The administration of 5 micrograms estradiol benzoate (EB) alone to sexually inexperienced subjects (Ss) induced weak lordosis behavior in some of them (mean lordosis quotient, LQ = 12 +/- 19). The SC injection of 5 micrograms LHRH significantly increased this response four hours later (LQ = 38 +/- 41), though great variability was observed (59% of Ss showing LQs below 30). The systemic administration of either prazosin, an alpha-adrenergic antagonist (0.2 or 1 mg/kg), or propranolol, a beta-adrenergic antagonist (20 mg/kg), totally suppressed LHRH-induced lordosis in sexually inexperienced Ss (mean LQs = 8 +/- 11; 5 +/- 10; 18 +/- 31, respectively). In sexually experienced Ss (tested on two previous occasions with EB and LHRH) the administration of EB alone on a third test induced significant levels of lordosis (mean LQ = 51 +/- 41). The administration of 5 micrograms LHRH to sexually experienced, estrogen primed Ss induced near maximal levels of lordosis (LQ = 94 +/- 18). In these Ss, prazosin (0.2 and 1 mg/kg) and, to a lesser extent, propranolol (20 mg/kg) significantly depressed lordosis to values that were not significantly different from those obtained after EB alone (mean LQs = 59 +/- 38; 63 +/- 20; 74 +/- 32, respectively). These results indicate that blockade of noradrenergic transmission by either alpha- or beta-antagonists counteracts the stimulatory effect of LHRH on lordosis in ovariectomized estrogen primed rats with or without sexual experience.(ABSTRACT TRUNCATED AT 250 WORDS)