Transcapillary exchange and distribution of carbon-11 labelled ethanol in the isolated perfused rat liver

The distribution kinetics of ethanol in the isolated perfused rat liver at various flow rates and ethanol concentrations were studied by the indicator diffusion technique using 11C-labelled ethanol. A double tracer solution with 99mTc-labelled red blood cells as the vascular reference and 11C-ethanol as the test substance was injected into the catheter connected to the portal vein. Time-activity curves were monitored by a NaI(Tl) scintillation detector above the outflow catheter. The following values were obtained: 0.95 +/- 0.01 for the maximal extraction (Emax), 3.0 +/- 0.1 x flow (r = 0.98) for the capillary permeability surface area product (PScap), 18.7 +/- 2.5% for the vascular volume (V1) and 56.2 +/- 9.0% for the ethanol distribution volume (V2). The volumes were calculated from the products of mean transit time (MTT) and flow (f), and PScap was calculated from the equation PScap = -f x ln(1-Emax). The results show that the ethanol distribution in the liver is flow limited since Emax was constant at various flow rates (0.67-2.55 ml/g x min-1). The distribution volumes obtained agree well with the values for liver vascular volume and water distribution volume reported in the literature.