Kinetics of Distribution of D₂O and Antipyrine in Isolated Perfused Rat Liver

¹ From the Department of Physiology, University of Minnesota Medical School, Minneapolis, Minnesota

Isolated rat livers were perfused via the portal vein with a blood-Ringer mixture containing a constant inflow concentration of D₂O and, in some cases, antipyrine. The rate of increase of outflow concentration was studied, comparisons being made between D₂O, antipyrine and a theoretical outflow curve based on completely flow-limited distribution. The effect of flow rate on the deviation of D₂O from theoretical was also studied. The results indicate that exchange of D₂O and antipyrine between blood and tissue in the perfused rat liver is extremely rapid relative to the rate of blood supply of these substances to the organ, even at flows several times that occurring in vivo. In the average experiment the average D₂O concentration in the liver during the early period of the perfusion was about 90% of the mixed venous concentration. The factors responsible for the failure of D₂O to distribute maximally, particularly tissue perfusion heterogeneity and diffusion limitation, are discussed. Although quantitation of the difference is difficult, antipyrine appears to distribute somewhat more rapidly than D₂O due to its greater solubility in cell membranes.

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