Metabolic Clearance of Immunoreactive Vasopressin and Immunoreactive [131I]iodo Vasopressin in the Hypophysectomized Dog

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Abstract
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 2nd 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 .cntdot. 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 .cntdot. kg (n = 7) and AVP clearance in these dogs increased (P < 0.01) with time to 7.3 .+-. 0.9 ml/min .cntdot. 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 < 0.05) than the 210-240 min average clearance in the time-controls. Clearance of [131I]AVP was 3.3 .+-. 0.2 ml/min .cntdot. kg (n = 7) before nephrectomy and 2.9 .+-. 0.2 ml/min .cntdot. kg after nephrectomy. This was a significant 12% reduction (P < 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 < 0.005) and after nephrectomy was 74 .+-. 16% of AVP clearance (P < 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 < 0.20) between AVP clearance and [131I]AVP clearance.

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