Metabolic clearance of immunoreactive vasopressin and immunoreactive [131I]iodo vasopressin in the hypophysectomized dog.

Fourteen acutely hypophysectomized, anesthetized dogs were given a constant infusion of arginine vasopressin (AVP) and 131I-labeled arginine vasopressin ([131I]AVP). After 90 min, 3 blood samples were collected at 15 min intervals for determination of total body clearances of immunoreactive AVP and immunoreactive [131I]AVP. Seven dogs were then nephrectomized. Ninety minutes later, a second set of 3 blood samples was collected at 15 min intervals for clearance measurements in these and the 7 time-control dogs. Prenephrectomy AVP clearance averaged 5.1+/-1.0 ml/min-kg (mean +/- SE, n=7), and the 210-240 min postnephrectomy AVP clearance average 4.9+/-0.8. The 90-120 min average clearance in the time-control dogs was 6.1+/-0.9 ml/min-kg (n=7) and AVP clearance in these dogs increased (P less than 0.01) with time to 7.3+/-0.9 ml/min-kg during the 210-240 min period of constant infusion. Although the postnephrectomy AVP clearance was not significantly changed from prenephrectomy levels, it was significantly lower (P less than 0.05) than the 210-240 min average clearance in the time-controls. Clearance of [131I]AVP was 3.3+/-0.2 ml/min-kg (n=7) before nephrectomy and 2.9+/-0.2 ml/min-kg after nephrectomy. This was a significant 12% reduction (P less than 0.01). [131I]AVP clearance in the time control dogs was 3.9+/-0.3 during 90-120 min of infusion and 3.9+/-0.4 during 210-240 min of infusion. [131I]AVP clearance before nephrectomy was 79+/-12% of AVP clearance (P less than 0.005) and afther nephrectomy was 74+/-16% of AVP clearance (P less than 0.05). Although these results might suggest that [131I]AVP clearance is at least a qualitative indicator of AVP clearance, there was no significant correlation (P less than 0.20) between AVP clearance and [131I]AVP clearance.