LEAD (PB) ALTERS THE NOREPINEPHRINE-INDUCED SECRETION OF LUTEINIZING-HORMONE-RELEASING HORMONE FROM THE MEDIAN-EMINENCE OF ADULT MALE-RATS IN-VITRO

In the present study, we evaluated the in vitro effects of lead (Pb) o n basal and stimulated luteinizing hormone releasing hormone (LHRH) an d Prostaglandin E(2) (PGE(2)) secretion. Median eminences (ME) were re moved from brains of adult male rats and preincubated for 15 minutes i n Krebs-Ringer bicarbonate glucose buffer in an atmosphere of 95% O-2- 5% CO2. These media were discarded and all MEs were subjected to one o f the following experiments. In Experiment 1, all MEs were incubated f or 30 minutes in medium only. These media were collected and replaced with medium only (controls) or with medium containing Pb doses ranging from 5 to 20 mu M. After this 60-minute incubation, media were collec ted, then replaced with new medium containing 60 mu M norepinephrine ( NE), or NE plus each dose of Pb, then incubated for a final 30-minute period. Experiment 2 was conducted as above, except PGE(2) (2.8 mu M) replaced the NE. In both experiments, the amounts of LHRH released was measured by RIA. In experiment 3, NE was again used for the challenge ; however, this time, the amount of PGE(2) released was measured by RI A. Results indicate that Pb did not alter basal LHRH release, but comp ared with controls, significantly blocked NE-induced LHRH release in a dose-related manner. Conversely, Pb had no effect on the PGE(2)-induc ed release of LHRH. Additionally, Pb did not alter basal PGE(2) releas e; however, it significantly blocked the NE-induced release of PGE(2). Since NE-induced LHRH release is mediated by PGE(2), these results su pport the hypothesis that Pb is capable of altering the hypothalamus a nd suggest that this effect is due, at least in part, to the diminishe d PGE(2) synthesis/release within the ME, resulting in diminished LHRH secretion.