RESUMO
The antidiuretic and possibly natriuretic effects of small doses of vasopressin (AVP) were investigated in conscious dogs. Plasma composition and renal excretion of water, Na+, and K+ were measured after overhydration by 20 ml/kg performed during infusion of AVP at rates of 50, 100, 150, 200, or 400 pg X min-1 X kg body wt-1 or of 1-desamino-8-D-arginine vasopressin (DDAVP) 50 pg X min-1 X kg body wt-1. Hydration lowered plasma osmolality and sodium concentration by 4.2 +/- 0.3 and 3.8 +/- 0.2%, respectively; plasma protein showed a larger decrease, 8.5 +/- 0.4% (P less than 0.01). Urine osmolality during hydration was 52 +/- 3 mosmol/kg H2O. AVP infusion at 100 pg X min-1 X kg-1 elevated plasma vasopressin by 1.7 +/- 0.3 pg/ml and urine osmolality by 1,049 +/- 152 mosmol/kg H2O and elicited marked natriuresis and kaliuresis but no change in osmolar clearance. During DDAVP infusion urine osmolality was 1,365 +/- 134 mosmol/kg H2O, but electrolyte excretion was indistinguishable from control. It is concluded that 1) AVP is associated with marked natriuresis and kaliuresis even in doses required to prevent water diuresis, 2) DDAVP--although strongly antidiuretic--does not affect electrolyte excretion, and 3) the water load causes disproportionate dilution of plasma protein and osmolality, probably due to protein redistribution.
