Biol. Pharm. Bull. 30(7) 1329—1331 (2007)

mals, and they have various physiological roles. D-Aspartate is present in the central nervous system and various neuroendocrine cells, which include a subset of satellite and basket cells in the cerebellum, adrenal chromaffin cells, pituitary gland cells, Leydig cells and pinealocytes. D-Aspartate is believed to modulate neuroendocrine functions in either an intercellular or intracellular manner. In pinealocytes, D-aspartate is synthesized de novo, localized in the cytoplasm, and released through a Na -dependent glutamate/aspartate transporter at the plasma membrane. Then, D-aspartate may act as an intercellular messenger and inhibit melatonin synthesis in a receptor-mediated manner. Pheochromocytoma PC12 cells also synthesize D-aspartate de novo, store it in dopamine-containing secretory granules, and secrete it through exocytosis. In Leydig cells, D-aspartate is present in the cytoplasm and stimulates testosterone synthesis through modulation of steroidogenesis. In pituitary cells, D-aspartate is metabolically converted to N-methyl-D-aspartate (NMDA), which in turn stimulates the secretion of hypothalamic releasing hormones. Thus, the modes of action of D-aspartate in neuroendocrine cells seem to be diverse in nature but remain poorly understood. Recently, using immunohistochemical approaches with Daspartate specific antibodies, we found that the islet of Langerhans, a miniature endocrine organ for blood glucoseregulating hormones, also contains D-aspartate. More precisely, the highest amount of D-aspartate is present in glucagon-secreting a cells, there being a lower amount in insulin-secreting b cells. It would be interesting to determine whether islet cells secrete D-aspartate. In the present study, we investigated this issue using clonal islet b cells.