Immunoreactive arginine vasopressin in the rat thymus.

Immunoreactive arginine vasopressin (ir-AVP), coeluting with authentic nonapeptide on reverse phase HPLC, is present in the thymus of Sprague-Dawley, Long-Evans, and homozygous (di/di) Brattleboro rats, and BALB/c mice. By immunohistochemistry, ir-AVP positive cells are sparse, and do not appear to be lymphocytes. Adrenalectomy and dexamethasone administration to intact rats produces an identical response in terms of thymic ir-AVP, with a rise after 1-2 days followed by a fall to levels below baseline after 8 days. The rise 2 days after adrenalectomy, and the fall 8 days later, were both prevented by administration of aldosterone, but not by corticosterone or dexamethasone to adrenalectomized animals. The role(s) of thymic ir-AVP, and the physiological significance of its mineralocorticoid dependence, remain to be established.