Hypothalamic knife cuts alter vasopressin induced recovery of blood pressure following hemorrhage.

Effects of knife cuts posterior to the paraventricular nucleus (PVN) alone or to both the PVN and the supraoptic nucleus (SON) on vasopressin dependent restoration and maintenance of blood pressure following hemorrhage were tested in the rat. Conscious, unrestrained animals were hemorrhaged a volume equivalent to 1.8% of body weight from a femoral arterial catheter. Blood pressure was monitored for 30 min with no treatment, 30 min following iv injection of a specific antagonist to the pressor action of vasopressin, and 15 min during iv infusion of the competitive blocker of angiotensin II, saralasin. Restoration of blood pressure and the decrease in blood pressure with vasopressin blockade in rats with knife cuts posterior to the PVN alone were similar to that of control-operated animals. However, if knife cuts extended to the level of the SON, blood pressure was not restored, and vasopressin blockade did not result in a reduction of blood pressure. Saralasin infusion produced a similar decrease in blood pressure in all groups of animals. These data show that when knife cuts are confined to the area posterior to the PVN, vasopressin contributes to the restoration of blood pressure following hemorrhage. However, when cuts extend into the ventral hypothalamus, the contribution of vasopressin is eliminated.