Mechanism and Extent of Distribution of Inulin and Sucrose in Chloride Space of Tissues

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Abstract
Analysis of muscle and subcut. tissue removed from rats after varying periods of in vivo equilibration of inulin or sucrose with maintenance of a constant plasma level being by constant infusion showed a biphasic distr. After 2 hrs. the saccharide vol. of distr. reached 80-85% of the vol. of distr. of Cl naturally present (rapid phase, with halftime under 20 min.); after 15-45 hrs., it reached 93-103% (slow phase, with half-time of 120-300 min.). The distr. in tendon of rabbits and dogs in vivo was slow; the half-time for inulin was 225 min., for sucrose 21-120 min., and similar data in the literature for these and smaller substances showed a positive correlation of half-time with molecular wt. Diffusion coefficients detd. in rabbit tendon in vitro at 30[degree] and 37[degree] C of inulin, sucrose, and C136 were about 25% of the respective free diffusion coefficients. Avg. inter-capillary distances in rat tissues were 25[mu] in muscle, 150[mu] in fascia, and 300[mu] in tendon. An approx. descr. of the data is provided by the mathematical formulation by Schmidt of the exchange of lipid-insoluble substances. The principal factors delaying equilibration are long intercapillary distance, retarded diffusion through capillary wall and interstitial matrix, small free diffusion coefficient, and low blood flow relative to the tissue vol. supplied. The distr. of inulin appears to be diffusion limited and of sucrose at least partly diffusion limited. The implications of the findings in interpretation of exchange rates and distr. vols. of substances in normal and pathological conditions are discussed.