Apparent Volumes of Distribution of 125 l-lothalamate and Inulin in Chickens 1

Abstract

Summary

The suitability of utilizing ¹²⁵I-iothalamate to estimate the volume of extracellular fluid was assessed in ureterally ligated chickens. Subsequent to intravenous administration the movement of labeled iothalamate from the plasma compartment follows closed two-compartment kinetics and equilibration between vascular and ex-travascular phases is attained in about 20 minutes. The volume of distribution of ¹²⁵I-iothalamate prior to and following the infusion of 0.15 M NaCl (equal to 15% of the estimated ECFV) averaged 23.6 ± 0.61 and 28.4 ± 0.22% of the body weight, respectively. The observed postsaline labeled iothalamate space did not differ statistically from the expected value. When administered simultaneously inulin penetrates into an apparent volume that is 75 % of the labeled iothalamate space after 60 minutes. The content of ¹²⁵I-iothalamate is relatively high in liver and kidney tissue and suggests that these are major sites where removal of the indicator from plasma occur. It is suggested that ¹²⁵I-iothalamate, under appropriate conditions, could be used to measure the plasma volume and the extravascular fluid with which plasma is in rapid diffusion equilibrium. ¹²⁵I-Sodium Iothalamate for parts of this study was kindly provided by Abbott Laboratories of North Chicago, IL.