Secretion of Pressor Amounts of Vasopressin in Experimentally Hypertensive Rats

Vasopressin secretion in pressor amounts was studied in one-clip, two-kidney and one-clip, one-kidney renovascular hypertensive rats as well as DOCA-salt hypertensive rats in various conditions in the conscious state. The characteristic, almost step-wise lowering of arterial pressure induced by intravenous injection of vasopressin antagonist was considered to indicate the presence of secretion of vasopressin in pressor amounts. Without any premedication and pretreatment, vasopressin antagonist was without effect on arterial pressure in any of the three kinds of hypertensive rats. After ganglion blockade with he:xamethonium bromide, injection of vasopressin antagonist lowered arterial pressure only in DOCA-salt hypertensive rats. One hr after spinal cord transection at C8 performed under ether anesthesia, when the rats had recovered consciousness and arterial pressure had recovered partially from the spinal shock, injection of vasopressin antagonist lowered arterial pressure in all the three kinds of hypertensive rats. Since injection of vasopressin antagonist after spinal transection is without effect on arterial pressure in normotensive control rats but has a depressor effect in sponstaneously hypertensive rats (SHR), it may be said that vasopressin secretion in pressor amounts is facilitated in the three kinds of hypertensive rats as in SHR.