Ethanol inhibits luteinizing hormone-releasing hormone release from the median eminence of prepubertal female rats in vitro: investigation of its actions on norepinephrine and prostaglandin-E2

Abstract

Recently, we have provided evidence that suggests that ethanol (ETOH) acts at the hypothalamic level to cause depressed serum LH levels and delay the onset of puberty in the female rat; however, the mechanism of this action is unknown. Thus, we evaluated the in vitro effects of ETOH on basal and stimulated LHRH and prostaglandin E2 (PGE2) secretion from the median eminence (ME) of prepubertal female rats. Brains were removed, and MEs dissected under a stereomicroscope, rinsed, and preincubated in Krebs-Ringer bicarbonate glucose buffer in an atmosphere of 95% O2-5% CO2 for 15 min. These media were discarded, and individual MEs were subjected to one of the following three experiments. In the first experiment, all MEs were incubated for 30 min in medium only. The media were collected and replaced in the control vials, again with medium only, or in the test vials with medium containing ETOH in doses from 15-70 mM. After this 60-min incubation, the media again were collected, then replaced with the respective control or test medium, each containing norepinephrine (NE; 60 microM). Another experiment was conducted as described above, except that the MEs were challenged with PGE2 (2.8 microM) in place of NE. In both experiments the amount of LHRH released into these media was measured by RIA. In a third experiment, NE was used for the challenge; however, this time the amount of PGE2 released was measured by RIA. Our results indicate that ETOH did not alter basal LHRH release but, compared with controls, significantly blocked NE-induced LHRH release in a dose-related manner. Conversely, ETOH had no effect on the PGE2-induced release of LHRH. Additionally, ETOH did not alter basal PGE2 release; however, it significantly blocked the NE-induced release of PGE2. We know that stimulation of LHRH release by NE is mediated by PGE2. Thus, these results suggest that the inhibitory effect of ETOH on LH release in the prepubertal female rat is due, at least in part, to the diminished secretion of LHRH resulting from altered PGE2 release from within the ME.