Immunoreactive oxytocin and arginine vasopressin (AVP) were measured in the adrenal
medulla of both rat and man as well as in tissue from two pheochromocytomas using
highly specific RIAs. In all instances, oxytocin predominated over AVP. The concentrations
of oxytocin ranged from 19.9-162.7 pg/g tissue, whereas those for AVP were 9.8-102
pg/g. These values are far greater than those found in plasma. The oxytocin- and AVP-related
neurophysins were also present in large quantities in human adrenal medulla and pheochromocytoma.
Identity of the peptides was confirmed by demonstrating parallel immunoreactivity
with standard compounds and by the high performance liquid chromatographic profiles.
In experiments carried out in rats, the source of the adrenal medullary AVP and oxytocin
did not appear to be the paraventricular nucleus. It is postulated that the neurohypophysial
peptides may have a regulatory function in the secretion of catecholamines.