NITRIC-OXIDE REGULATES LUTEINIZING-HORMONE-RELEASING HORMONE-SECRETION

We have analyzed the role of nitric oxide (NO), an unorthodox and novel neuromodulator, on luteinizing hormone-releasing hormone (LHRH) secretion. Sodium nitroprusside (SNP), an NO donor, was used to challenge LHRH neurons using both hypothalamic explants and an immortalized neuronal cell line (GTI cells) in vitro. In both paradigms, SNPwas able to stimulate LHRH release in a dose-dependent manner. This action of SNP was accompanied by an elevation in both extra- and intra-cellular cGMP levels. In addition, exposure of LHRH cells (GTI -7 cells) to increasing concentrations of a soluble analog of cGMP (8-Br-cGMP) enhanced LHRH release in a dose-dependent manner, indicating that LHRH neurons have the intrinsic ability to respond to the intracellular messenger elicited by NO,i.e.,cGMP. Furthermore, sodium nitroprusside-induced LHRH secretion from GTI-7 cells was blocked, in a dose-dependent manner, by Rp-8-Br-cGMPS, a cGMP analog which blocks cGMP-dependent protein kinase. These data clearly demonstrate that NO stimulates LHRH secretion by activating guanylate cyclase, and support a potential role of NO as a neuroactive agent involved in the control of LHRH secretion and, thereby, reproductive functions.