HETEROGENEITY OF INTERSTITIAL FLUID SPACE DEMONSTRATED BY SIMULTANEOUS KINETIC-ANALYSIS OF THE DISTRIBUTION AND ELIMINATION OF INULIN AND GALLAMINE

  • 1 January 1982
    • journal article
    • research article
    • Vol. 222  (2) , 389-394
Abstract
The kinetics of inulin and gallamine were studied after simultaneous i.v. injection in anesthetized dogs. The distribution of both compounds in extracellular fluid space was characterized by a 3-compartment model in which the mean central compartment blood volume of 1.37 l was identical with the expected value. The 2 peripheral compartments of the model appear to represent rapid and slow equilibrating interstitial fluid compartments. A mammillary model structure was selected in which intercompartmental clearance corresponds to transcapillary exchange. Inulin and smaller hydrophillic molecules diffuse across capillary walls at rates proportional to their respective free water diffusion coefficients. For the ratio of the transcapillary permeability coefficients of inulin and gallamine to equal their free water diffusion coefficient ratio of 5.34 .+-. 0.02, it appears that the sum of blood flows to the fast and slow interstitial fluid compartments is less than cardiac output. When this assumption is made, blood flow to fast equilibrating interstitial fluid is estimated to be 39% of cardiac output, in agreement with previous measurements of splanchnic blood flow. Apparently, the fast equilibrating interstitial fluid space is supplied by porous splanchnic capillaries that lack a continuous investment of basement membrane.

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