Vasopressin release by histamine in the conscious goat

The vasopressin releasing activity of histamine was studied in conscious goats. Histamine was infused into the brain ventricles or intravenously and serial blood samples were taken from the jugular vein. Plasma vasopressin was assayed by a radioimmunoassay for arginine vasopressin (AVP). After i.v. infusions of 300 micrograms and 1 mg of histamine, a pronounced increase in plasma AVP up to greater than 100 pg/ml occurred. This was considered secondary to hypotension, since it only occurred with doses that markedly decreased arterial blood pressure. When given i.c.v. even smaller doses of histamine increased plasma AVP without any concomitant decrease in blood pressure. There was a simultaneous decrease in renal free water clearance in hydrated animals. Up to the dose of 300 microgramshistamine, the increase in AVP was modest. Histamine 1 mg i.c.v., given to either hydrated or non-hydrated animals, increased plasma AVP about tenfold, up to 38.3 +/- 23.3 pg/ml and 56.7 +/- 19.0 pg/ml, respectively. In individual experiments the correlation between the AVP level and the degree of antidiuresis was less apparent, since the kidney seemed to be very sensitive even to small changes in plasma AVP. It is concluded that histamine releases vasopressin through a central mechanism and it is reasonable to suppose that histamine may act as a neurotransmitter in the vasopressin releasing system.