The hemodynamic effects of 1 hr intravenous infusions of vasopressin were evaluated in trained, unanesthetized dogs in the normal state and following sinoaortic baroreceptor denervation. Pressor sensitivity to vasopressin was greatly enhanced following baroreceptor denervation; threshold sensitivity was increased 11 fold and sensitivity at higher dose levels was increased 60 to 100 fold. Infusion of physiological levels of vasopressin caused an average increase in arterial blood pressure of 33 mm Hg in conscious, baroreceptor denervated dogs compared with an increase of 5 mm Hg in normal dogs. In contrast, similar intravenous infusions of norepinephrine at physiological levels resulted in a 3 fold increase in pressor sensitivity with no change in threshold dose. Hypophysectomy of baroreceptor denervated dogs did not significantly alter their pressor sensitivity to vasopressin in the conscious state. The arterial blood pressure response to intravenous vasopressin infusions was greatly depressed when a high background level of circulating vasopressin was present. Decapitated, spinal, anesthetized dogs maintained with a small continuous infusion of norepinephrine exhibited the greatest sensitivity to vasopressin; the threshold dose for a pressor response was similar to that in conscious baroreceptor denervated dogs, but pressor sensitivity at physiological dose levels was increased nearly 8,000 fold. The elevations in arterial blood pressure resulting from vasopressin infusions of less than 1.0 munits/kg min-1 were large enough to implicate the direct pressor effect of vasopressin in the normal control of arterial blood pressure.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine