Effects of Changes in Steady State Plasma Vasopressin Levels on Renal and Urinary Vasopressin Clearances in the Dog*

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Abstract
A study was made of the effects of changes in the plasma vasopressin concentration on the extraction ratio and the renal organ and urinary clearances of vasopressin. Plasma vasopressin levels were increased in a stepwise fashion in anesthetized dogs by the iv infusion of vasopressin at rates of 100, 400, and 800 μU/min-kg. A steady state was achieved by infusing vasopressin for 60 min at each dose. Before the infusion of vasopressin, the extraction ratio and the renal and urinary clearances of vasopressin (one kidney) were 0.30 ± 0.04, 1.8 Plusmn; 0.2, and 1.4 ± 0.1 ml/min kg, respectively. The urinary clearance of vasopressin did not differ significantly from the inulin clearance (1.5 ± 0.1 ml/min-kg). The infusion of vasopressin, which increased the plasma vasopressin concentration from an initial value of 4.3 ± 1.3 to 54.6 ± 2.4 μU/ml at the highest rate of infusion, was without effect on the vasopressin extraction ratio and the renal and urinary clearances of vasopressin. The MCR of vasopressin was estimated to be approximately 16 ml/min kg. The renal clearance of vasopressin, calculated for both kidneys in all periods of all experiments, accounted for approximately 27% of the total clearance of vasopressin from the plasma. Thus, over a broad range of plasma vasopressin concentrations, a constant fraction of the vasopressin delivered to the kidney was removed from the blood perfusing the kidney, and the mechanisms for the renal extraction of vasopressin were not saturated.