Regional tissue uptake of D2O in perfused organs: rat liver, dog heart and gastrocnemius

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Abstract
Regional tissue D2O concentrations were measured in the isolated dog heart, dog gastrocnemius and rat liver following relatively brief perfusions with D2O-labeled fluid. Results indicate heterogeneity of tissue concentrations in all three organs. A venous outflow concentration curve for the liver was reconstructed on the assumptions that each regional tissue sample represented an equally probable portion of a composite organ and that in each region D2O transport was flow-limited. The agreement between this curve and the observed outflow curve was sufficiently good to suggest that the discrepancies between the observed venous curve and that for the theoretical case of a completely flow-limited organ can be largely explained for the liver by macroscopic regional perfusion heterogeneity without invoking microscopic tissue transport limitation. In the case of the heart and the gastrocnemius, the observed macroscopic tissue heterogeneity was insufficient to account for the discrepancies between the respective venous outflow concentration curves and the theoretical case. However, in the heart, regions of low tissue concentration were apparently systematically missed in the sampling procedure. The actual heterogeneity in both organs was probably underestimated.

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