Chronic effects of vasopressin on fluid volume distribution in conscious dogs

Previous studies have suggested that acute elevations of arginine vasopressin (AVP) may result in an extravascular to intravascular shift of fluid independent of any change in total body H2O (TBW). The present studies examined the chronic influence of elevated AVP on fluid volume distribution in five splenectomized, sodium-deprived conscious dogs (avg body wt = 18.9 +/- 0.7 kg). During 4 days of continuous intravenous AVP infusion (0.36 ng X kg-1 X min-1), the computerized average 24-h total body weight was maintained within 110 g of the control value by means of a sensitive servo-controlled scale device. Urine flow and urine osmolality averaged 335 +/- 52 ml/day and 637 +/- 36 mosmol/kg during the preinfusion period and changed to levels averaging 151 +/- 14 and 1,377 +/- 121 with elevated AVP (P less than 0.05). Chromium-51-labeled red cell volume (51Cr RBC), plasma volume (Evans blue), TBW (3H2O), calculated total blood volume (using 51Cr RBC and Hct), and mean arterial pressure averaged 22 +/- 1 ml/kg, 54 +/- 7 ml/kg, 0.62 +/- 0.04 l/kg, 68 +/- 3 ml/kg, and 99 +/- 3 mmHg, respectively, during the control period and remained unchanged during the AVP infusion period. Plasma protein, sodium, and osmolality averaged 6.4 +/- 0.1 g/dl, 145.7 +/- 0.8 meq/l, and 295.0 +/- 1.5 mosmol/kg during the preinfusion period and also remained unchanged with elevated AVP. We conclude from the present studies that AVP has minimal or no chronic influence on internal volume redistribution.