Clearance of exogenous vasopressin from plasma of dogs

Abstract

Bovine Pitressin was infused intravenously into five pentobarbital-anesthetized dogs (13–24 kg) at constant rates (33.3–382 mu/min.) for 121–198 minutes in 10 experiments. Arterial plasma, obtained just before the end of the infusion, was assayed for antidiuretic hormone concentration in conscious, hydrated female dogs. Total plasma clearance was calculated as the quotient, Pitressin infusion rate/Pitressin concentration in arterial plasma. Pitressin clearance was equivalent to 16.1% of the plasma volume per minute (range 10.2–25.7%/min.). The Pitressin clearance averaged 2.2 times as large as concurrent glomerular filtration rate (creatinine clearance) and 0.63 as large as effective renal plasma flow (p-aminohippurate clearance). In five of the experiments, arterial plasma, obtained 15 minutes after cessation of the infusion, had an average Pitressin concentration of 14% of the steady-state concentration. On the assumption, as a crude first approximation, that the disappearance was semilogarithmic, the averaged data indicate, for this first 15-minute interval, that 12.9% of the ‘apparent’ volume of Pitressin distribution was cleared per minute, that the half-life was 5.4 minutes, and that the ‘apparent’ volume of distribution of Pitressin was only about 14% larger than the plasma volume.