L-ASPARTATE-EVOKED INHIBITION OF MELATONIN PRODUCTION IN RAT PINEAL GLANDS

Our previous studies in rat indicated that pinealocytes secrete L-glut amate through microvesicle-mediated exocytosis to regulate negatively melatonin production. Recently, we further found that pinealocytes sec rete L-aspartate through microvesicle-mediated exocytosis. In the pres ent study, we investigated the role of L-aspartate in the melatonin pr oduction in isolated rat pineal glands. It was found that L-aspartate inhibits norepinephrine-stimulated melatonin production as well as ser otonin N-acetyltransferase activity reversibly and dose dependently, t he concentrations required for 50% inhibition being 150 and 175 mu M, respectively. L-Asparagine and oxaloacetate, metabolites of L-aspartat e, had no effect on the melatonin production. These results suggest th at pinealocytes use L-aspartate, as well as L-glutamate, as a negative regulator for melatonin production. (C) 1997 Elsevier Science Ireland Ltd.