Clearance and urinary excretion of vasopressin in conscious dogs

The purpose of this study was to determine the relationship between plasma arginine vasopressin (PAVP) levels and the urinary clearance rate, the nonurinary plasma clearance rate, and the urinary excretion rate of AVP. Female conscious dogs were given an intravenous infusion of p-aminohippuric acid and inulin, and, after a 90-min control period, the infusion was either continued or AVP was added to the infusate to produce doses of 0, 40, 100, and 200 microU.kg-1.min-1 for the last 90 min of the experiment. The resulting PAVP levels were 1.2, 8.2, 11.4, and 21.6 microU/ml, respectively. The urinary clearance rate of AVP nearly doubled between the infusion rates of 0 and 100 microU.kg-1.min-1. Likewise, the nonurinary plasma clearance rate of AVP also nearly doubled between the infusion rates of 40 and 100 microU.kg-1.min-1. However, at the rate of infusion of 200 microU.kg-1.min-1, both the urinary and nonurinary clearance rates were unchanged compared with the 100-microU.kg-1.min-1 rate. The largest incremental rise in PAVP was observed between the doses of 100 and 200 microU.kg-1.min-1, when the clearance rates were apparently plateaued. The urinary excretion rate of AVP was linearly correlated with PAVP (R = 0.91) under the conditions of this study. The results suggest that the measurement of the urinary excretion rate of AVP is a reliable method of assessing PAVP and that the clearance of AVP increases when PAVP is elevated.