INCREASED HEPATOCYTE PERMEABILITY SURFACE-AREA PRODUCT FOR RB-86 WITHINCREASE IN BLOOD-FLOW

Liver cell recruitment (the equivalent of capillary recruitment in oth er organs) was explored by carrying out multiple indicator dilution ex periments with labeled rubidium across the liver of the anesthetized d og under basal conditions and after bleeding with saline replacement i nfusion, which increases liver blood flow. A mixture of Cr-51-labeled red blood cells (a vascular reference), Na-22 (which immediately equil ibrates in the extracellular space, the sum of the sinusoidal plasma a nd Disse or interstitial spaces, the expected distribution space for l abeled rubidium in the absence of cellular entry), and Rb-86 was injec ted into the portal vein, and normalized outflow patterns, expressed a s outflowing fractions of each injected tracer per milliliter versus t ime, were obtained. In relation to the labeled red blood cell curve, t he labeled sodium curve is displaced by flow-limited distribution into the Disse or interstitial space; it is lower on the upslope, reaches a lower and delayed peak, and decays more slowly. The early part of th e labeled rubidium curve lies within the labeled sodium curve; it reac hes a much reduced peak, and the later return of tracer entering cells is so slow that it is obscured by recirculation. Modeling of the conc entrative cellular uptake of rubidium from the Disse space provided an influx permeability surface area product for labeled rubidium. This i ncreases with flow over the observed flow range, demonstrating that si nusoidal recruitment occurs with increase in hepatic blood flow.