Effect of vasopressin blockade on blood pressure regulation during hemorrhage in conscious dogs.

The role of vasopressin in the regulation of blood pressure during nonhypotensive hemorrhage was assessed in conscious dogs. An antagonist of the vasoconstrictor activity of vasopressin was administered (10 microgram/kg) to four normal dogs five min prior to the commencement of a 15 min arterial hemorrhage (1 ml/kg/min). The withdrawn blood was reinfused 15 min after completion of the hemorrhage. In the absence of vasopressin blockade, blood pressure and heart rate did not change significantly, while plasma renin activity increased from 3.8 +/- 0.9 to 10.8 +/- 3.1 ng/ml/3h (P less than 0.005), and plasma corticosteroid concentration increased from 1.5 +/- 0.8 to 8.6 +/- 2.0 microgram/dl (P less than 0.001). Following vasopressin blockade, the same hemorrhage decreased mean arterial pressure from 96 +/- 264 +/- 7 mmHg (P less than 0.001), increased heart rate from 71 +/- 10 to 130 +/- 23 beats/min (P less than 0.05), increased plasma renin activity from 7.1 +/- 0.8 to 30.3 +/- 6.7 ng/ml/3h (P less than 0.005) and increased plasma corticosteroid concentration from 1.9 +/- 0.7 to 11.4 +/- 1.2 microgram/dl (P less than 0.001). These data indicate that vasopressin plays an important role in blood pressure regulation during mild hemorrhage in conscious dogs.