Cardiovascular, Sympathetic, and Renin-Angiotensin System Responses to Hemorrhage in Vasopressin-Deficient Rats

To determine if the subnormal blood pressure recovery after hemorrhage in Brattleboro rats is due to secondary abnormalities in the renin-angiotensin or sympathetic nervous systems, we measured the hemodynamic, catecholamine, and renin activity responses to moderate acute hemorrhage in anesthetized Brattleboro rats. Results were compared to responses in groups of animals matched for either age or weight. Blood pressure recovery was significantly blunted (P less than 0.01) in Brattleboro rats compared to that in either control group, but heart rate responses were similar. Basal plasma norepinephrine was significantly higher in Brattleboro rats than in controls (P less than 0.001), but the response to hemorrhage was not significantly different. Both plasma epinephrine levels and renin activity were significantly higher before hemorrhage and increased more after hemorrhage in vasopressin-deficient animals. Plasma vasopressin in controls increased approximately 10-fold, reaching levels of 790 +/- 140 pg/ml in age-matched controls and 425 +/- 60 pg/ml in weight-matched controls. Vasopressin levels in Brattleboro rats were undetectable both before and after hemorrhage. We conclude from these data that the subnormal blood pressure recovery observed in vasopressin-deficient rats is not due to secondary abnormalities of the renin-angiotensin or sympathetic nervous systems, but, instead, is related more directly to the vasopressin deficiency.