Effects of hematocrit on oxygenation of the isolated perfused rat liver

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Abstract
The isolated perfused rat liver is used ubiquitously for metabolic and endocrine studies of hepatic function, yet few data are available regarding the inadequacy of the oxygenation of such preparations. The isolated rat liver is usually deprived of its arterial supply and perfused via the hepatic portal vein with low-hematocrit or cell-free solutions. To investigate the efficacy of the O2 supply, the effect of hematocrit on the relation between O2 consumption and perfusate flow was determined. An attempt was made to define a hematocrit at which hepatic oxygenation was maximal. Livers of male rats anesthetized with pentobarbital sodium were perfused via the portal vein with fresh canine red blood cells suspended in Krebs-Ringer-bicarbonate buffer. Perfusions were carried out at various flow rates, and the relation between perfusate flow and O2 uptake was determined. At flow rates > 100 ml .cntdot. min-1 .cntdot. 100 g liver-1, O2 uptake was independent of flow but below that value was flow limited, regardless of whether the hematocrit was 10, 20 or 40%. To determine the optimal hematocrit for hepatic O2 uptake, hepatic portal venous and hepatic venous pressures were held at 10 and 0 mmHg, respectively. The hematocrit was lowered in steps from 80-10%. Blood flow increased exponentially as hematocrit fell while oxygen uptake increased to a maximum at .apprx. 20%. Evidently, a hematocrit of .apprx. 20% provides the optimal combination of blood flow and O2-carrying capacity while maintaining physiological perfusion pressures, e.g., 10 mmHg.