Renal hypersensitivity to vasopressin in congestive heart failure

Plasma vasopressin (AVP) levels are often elevated in congestive heart failure (CHF). To determine the significance of AVP in CHF, we performed clearance studies on the UM-X7.1 strain of cardiomyopathic (CM) hamsters with moderate heart failure and age-matched healthy controls. Exogenous AVP or a selective V2 agonist (0.3 ng.kg-1. min-1) reduced the fractional excretion of sodium (FENa) and water (FEH2O) by 40-46% in the control group. Although the CM hamsters exhibited a blunted physiological response to the V2 agonist, their urinary cAMP levels were fivefold that of normal and reflect an altered regulation of V2 receptor signalling during CHF. Additional studies also showed that infusion of a V2 antagonist (0.3 ng.kg-1. min-1) produced natriuresis and diuresis in CM hamsters (FENa: 7.9 +/- 1.1 vs. 4.8 +/- 0.6%, p < 0.05; FEH2O: 2.2 +/- 3 vs. 1.5 +/- 0. 2%, p < 0.05) but did not decrease fluid reabsorption in the normal hamsters. In conclusion, the attenuated renal response to exogenous AVP in CM hamsters may be attributed to an enhanced endogenous AVP response during CHF.