L-Aspartate-evoked inhibition of melatonin production in rat pineal glands

Our previous studies in rat indicated that pinealocytes secrete L glutamate through microvesicle-mediated exocytosis to regulate negatively melatonin production. Recently, we further found that pinealocytes secrete L- aspartate through microvesicle-mediated exocytosis. In the present study, we investigated the role of L-aspartate in the melatonin production in isolated rat pineal glands. It was found that L-aspartate inhibits norepinephrine- stimulated melatonin production as well as serotonin N-acetyltransferase activity reversibly and dose dependently, the concentrations required for 50% inhibition being 150 and 175 μM, respectively, L-Asparagine and oxaloacetate, metabolites of L-aspartate, had no effect on the melatonin production. These results suggest that pinealocytes use L-aspartate, as well as M glutamate, as a negative regulator for melatonin production.