TYROSINE-HYDROXYLASE INDICATES CELL-DIFFERENTIATION OF CATECHOLAMINE BIOSYNTHESIS IN NEUROENDOCRINE TUMORS

The intracellular localization of tyrosine hydroxylase (TH), which is the rate limiting enzyme in catecholamine (CA) biosynthesis, and its a ctivity in various adrenal and other neuroendocrine tumors was studied . TH was strongly localized in adrenal medulla, pheochromocytoma, and paraganglioma, but was scatteredly expressed in neuroblastoma. TH was not detected in adrenocortical tumors, ganglioneuroma, and other neuro endocrine tumors. Neuron specific enolase (NSE) was found in all neuro endocrine tumors, but Grimelius staining showed only the secreting gra nules of the tumor cells. TH activity was significantly high in pheoch romocytoma and paraganglioma as compared with that in normal adrenal g land, whereas TH activity was low in a neuroblastoma and was undetecta ble in other tumors. These findings indicate that TH correlates well w ith the biosynthetic function of CA in the tumor cell and, thus, both the immunostaining of TH and the measurement of its activity in adreno -medullary and related tumors may provide some information about the p rocess of cell differentiation in these tumors.