It has been known that pinealocytes contain the highest level of D- aspartate among various neuroendocrine cells in the rat. Here, we report that exogenous D-aspartate strongly inhibited norepinephrine-dependent melatonin synthesis in the rat pineal gland, the concentration required for 50% inhibition being 75 μM. This inhibition was due at least partly to decreased norepinephrine-dependent serotonin N-acetyltransferase activity. Upon incubation, D-aspartate was gradually released from pinealocytes and accumulated in the incubation medium as determined by high-performance liquid chromatography on a Pirkle-type chiral column. These results suggest that D- aspartate acts as a negative regulator for melatonin synthesis in the pineal gland.
- Cyclic AMP
- Serotonin N- acetyltransferase
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