Nitric oxide mediates the stimulation of luteinizing-hormone releasing hormone release induced by glutamic acid in vitro

Previous experiments from our laboratory have indicated that LHRH release is controlled in vivo and in vitro by NO. Since glutamic acid, the major excitatory transmitter in the brain, has been shown to release LHRH, we wished to determine whether or not this LHRH release was mediated by NO. Consequently, arcuate-median eminence explants from normal male rats were incubated in vitro in Krebs-Ringer bicarbonate glucose (KRBG) media in a Dubnoff metabolic shaker for a preincubation period of 30 min. Fresh media were added containing the substances to be tested and incubation was continued for 30 min. Sodium nitroprusside (NP, 500 μM), which releases NO spontaneously, stimulated the release of LHRH, which indicates that NO can release LHRH. Glutamic acid (10 mM) also produced a robust release of LHRH, and this release was blocked by the inhibitor of NO synthase, N^G-monomethyl-L-arginine (NMMA). Furthermore, the release of LHRH induced by glutamic acid was prevented by the addition of hemoglobin (20 βg/ml), a scavenger of NO, which would remove the NO released by the action of glutamic acid. The results indicate that glutamic acid stimulated LHRH release is induced by NO.