CROSS-CIRCULATION EXPERIMENTS ON UNANESTHETIZED RATS .3. CLEARANCE AND VOLUME OF DISTRIBUTION OF EXOGENOUS AND ENDOGENOUS ADH

1. In cross-circulation experiments with unanesthetized rats, the elimination characteristics of endogenous and exogenous antidiuretic hormone (ADH) are determined. With the described method the time course of elimination can be presented as a quantity-time curve as against the concentration-time data of conventional methods. 2. The half-life of arginine-vasopressin in the blood of rats is 3-3.8 min. The high clearance rates found in earlier work show, that the volume of distribution of ADH is far greater than plasma volume. Thus ADH leaves the intravascular space of rats. 3. The behaviour of endogenous ADH liberated in acute hemorrhage is in every aspect identical with that of exogenous arginine-vasopressin. Followingly, endogenous ADH is probably secreted as free peptide into the blood. © 1969 Springer-Verlag.