Kinetics of Inulin Distribution and Excretion Following a Constant Infusion

Abstract

After terminating a 2-hr. constant infusion of inulin, the concn. of inulin in the plasma decreases more rapidly than that in the interstitial compartment, with the result that the computed inulin space progressively increases. The rate of inulin excretion by the kidneys is asymptotic to complete elimination from the body. When plotted semilogarithmically against time, the relationship is curvilinear, being convex to the coordinate axes. The graph relating the logarithm of excretion to time is virtually linear during the last 2.5 hrs. of a 5-hr. collection period. Using the slope of this last 2.5-hr. period, it is possible to approx. the quantity of inulin which could theoretically be recovered until infinity. By adding this to the amt. recovered during the 5-hr. collection period, the volume of inulin distr. may be computed by dividing this sum by the plasma inulin concn. at equilibrium.