In animals subjected to hemorrhage, plasma arginine vasopressin concentrations increase to levels sufficient to cause vasoconstriction, thus attenuating the hypotensive response. The purpose of this study was to examine the contribution of vasopressin to blood pressure regulation during hypotension in humans. Hypotension was induced in twelve normal subjects by lower body negative pressure (LBNP) before and after intravenous administration of vasopressin V1 receptor antagonist. Before drug administration, LBNP reduced systolic blood pressure from 125 ± 4 to 78 ± 12 mmHg (P < 0.01) as vasopressin concentration increased from 2.9 ± 0.6 to 17 ± 6 pg/ml (P < 0.05). After administration of the vasopressin antagonist, LBNP reduced systolic blood pressure from 128 ± 3 to 89 ± 11 mmHg (P < 0.01). The hypotensive response to LBNP was not potentiated by inhibiting vasopressin's vasoconstrictive effects (P = NS). Thus hypotension causes marked increases in plasma vasopressin concentration. In contrast to findings in animal studies, however, vasopressin does not contribute to the maintenance of blood pressure during hypotension in humans.
- lower body negative pressure