Vasopressin receptors in human adrenal medulla and pheochromocytoma

The nature of vasopressin (VP) receptors present in normal and tumoral huma n adrenal was investigated using various experimental approaches. Specific VP-binding sites were detected by autoradiography using [H-3]arginine VP as a radioligand in adrenal cortex and medulla. The V1a receptor subtype was expressed in the two parts of the gland, as shown by pharmacological studie s and RT-PCR experiments. By contrast, the V1b receptor subtype was only ex pressed in medullary chromaffin cells. This was confirmed by the characteri zation of V1b transcripts detected in adrenal medulla tissues. In pheochrom ocytoma, we also detected functional V1b receptors. These receptors trigger ed intracellular calcium mobilization from intracellular pools and were inv olved in catecholamine secretion. Binding experiments performed on pheochro mocytoma plasma membrane preparations also revealed V1a vasopressin-binding sites, whose roles and cellular localization have not yet been determined. RT-PCR experiments confirmed these data; 100% and 80% of the five tumors t ested exhibited V1a and V1b transcripts, respectively. Perifusion experimen ts also demonstrated that some pheochromocytomas may secrete large amounts of VP. Our findings imply that VP locally secreted by human adrenal medulla may regulate adrenal function by acting on V1a or V1b receptors. More inte restingly, we demonstrate that one pheochromocytoma oversecretes VP. In thi s particular case, this may contribute to the increase in blood pressure ob served.