Leumorphin is a potent inhibitor of vasopressin secretion

The effects of intracerebroventricular (i.c.v.) injection of leumorphin on the vasopressin secretion induced by angiotensin II or dehydration were studied in conscious unrestrained rats. The vasopressin secretion induced by angiotensin II (100 pmol) was significantly inhibited by the simultaneous injection of leumorphin (6 pmol-600 pmol) in a dose-dependent manner. In 72-hour water-deprived rats, the i.c.v. injection of leumorphin (60 pmol or 600 pmol) significantly suppressed the vasopressin secretion dose-dependently. These results suggest that leumorphin is involved in the regulation of the vasopressin secretion.