Urinary clearance of arginine vasotocin in Pekin ducks

To quantify the renal excretion of arginine vasotocin (AVT) in birds, synthetic AVT was infused into conscious Pekin ducks at rates of 0.03, 0.10, and 0.30 ng/kg/min for 30 min and the relationships between plasma and urine AVT concentrations were monitored by radioimmunoassay. As plasma AVT concentrations increased (from a basal value of 7.8 +/- 1.1 pg/ml to levels of 11.5 +/- 1.9, 17.6 +/- 2.2, and 24.2 +/- 2.5 pg/ml, respectively) the urinary concentrations and excretion rates increased linearly from basal levels of 26.0 +/- 3.1 pg/ml and 14.9 +/- 1.8 pg/min to 215.6 +/- 36.6 pg/ml and 39.2 +/- 3.7 pg/min, respectively. The metabolic clearance rate of AVT (approximately 23 ml/min/kg) and urinary clearance (approximately 0.91 ml/min/kg) remained constant at each infusion dose and were therefore independent of plasma AVT levels. Over the range of plasma AVT concentrations tested, a constant fraction of about 5% of the AVT cleared from the blood was excreted intact in the urine.