Antidiuretic effect of subnormal levels of arginine vasopressin in normal humans

Abstract
The renal responses to 120-min infusions of arginine vasopressin (AVP) were investigated in healthy volunteers undergoing water diuresis induced by an oral water load of 20 ml/kg body wt. AVP at 1 pg .cntdot. min-1 .cntdot. kg-1 (.apprx.10-15 mol .cntdot. min-1 .cntdot. kg-1) decreased urine flow (12.2 .+-. 1.7 to 7.4 .+-. 1.5 ml/min) and free water clearance (9.7 .+-. 1.5 to 4.8 .+-. 1.4 ml/min) and increased urine osmolality (Uosmol,; 71 .+-. 6 to 115 .+-. 15 mosmol/kgH2O); 5 pg .cntdot. min-1 .cntdot. kg-1 elicited pronounced antidiuresis (14.4 .+-. 0.9 to 0.9 .+-. 0.3 ml/min) with maximal Uosmol of 621 .+-. 95 mosmol/kg. In response to 25 pg .cntdot. min-1 .cntdot. kg-1, maximal Uosmol was 869 .+-. 38 mosmol/kg. Response developed gradually and stabilized within the 2nd h of infusion. AVP at 1 and 5 pg .cntdot. min-1 .cntdot. kg-1 was without effect for at least 20 min. Only 25 pg .cntdot. min-1 .cntdot. kg-1 caused a significant rise in plasma AVP (1.2 .+-. 0.2-2.0 .+-. 0.1 pg/ml), and with this dose sodium excretion decreased. The rates of K+ excretion, as well as plasma aldosterone and atrial natriuretic peptide concentrations, were unaffected by AVP. It is concluded that the human kidney is sensitive to changes in the rate of secretion of AVP of <1 pg .cntdot. min-1 .cntdot. kg-1 and that the maximal changes occurs after 1-2 h of constant infusion. It is estimated that the rate of infusion of AVP required to produce isomolar urine during overhydration is .apprx. 3 pg .cntdot. min-1 .cntdot. kg-1.