The Distribution of I131 Labeled Human Serum Albumin Introduced into Ascitic Fluid: Analysis of the Kinetics of a Three Compartment Catenary Transfer System in Man and Speculations on Possible sites of Degradation

Abstract

Following intraperit. admn. of I131 labeled human serum albumin, the kinetics of distr. were analyzed mathematically with reference to a 3-compartment schematic model composed of ascitic fluid, plasma, and extravascular fluid. Errors of the analysis arising from nonsteady state conditions and deficiencies in the schematic model are discussed. It was demonstrated that essentially complete distr. of intraperit. admn. I131 labeled albumin may require almost a mo. in the presence of marked ascites. The rate of albumin transfer from plasma to ascitic fluid was calculated to be approx. 24 g./day. During a 22-day period of observations the ascitic fluid showed a net increase in albumin content which averaged 4.4 g./day. Evidence is presented which indicates that this increase represented newly formed albumin rather than a depletion of exchangeable albumin stores in plasma and extravascular fluid. From considerations of relative available capillary surface areas it is concluded that the peritoneal capillary of the cirrhotic subject of the present study permitted a much greater albumin transfer out of plasma than the avg. capillary elsewhere in the body. From a comparison of the time course of renal excretion of radioactivity with the curves of I131 labeled albumin in ascitic fluid, plasma, and extravascular fluid following intraper. and intraven. admn. of the labeled albumin, the site of degradation of iodo-albumin was inferred to be the circulating plasma or some extravascular compartment equilibrating rapidly with plasma.