Catecholamine-synthesizing enzymes and chromogranin proteins in drug-induced proliferative lesions of the rat adrenal medulla.

Both epinephrine (E) and norepinephrine (NE) cells in the rat adrenal medulla are able to proliferate in response to pharmacologic stimulation. However, previous biochemical studies have suggested that drug-induced or spontaneous pheochromocytomas in rats are almost invariably NE-producing. To resolve these apparently conflicting data, immunocytochemical techniques were utilized to establish functional profiles of adrenal medullary lesions classified as pheochromocytoma or nodular hyperplasia in rats treated chronically with a phosphodiesterase inhibitor which induced pheochromocytomas. Sixteen of 17 pheochromocytomas and all hyperplastic nodules stained positively for tyrosine hydroxylase and dopamine beta-hydroxylase, consistent with an ability to produce NE. No lesion of either type stained for phenylethanolamine N-methyltransferase, consistent with an inability to produce epinephrine. Lesions of both types showed variable staining for chromogranin proteins. The findings indicate that qualitative functional differences cannot be used to discriminate hyperplastic nodules from small pheochromocytomas in rats. Some lesions currently classified as hyperplastic nodules might in fact be small pheochromocytomas. Others might represent diffuse hyperplasia within pre-existing islands of NE-cells in a background of hyperplastic epinephrine-cells.