DYNAMICS OF ARTERIAL AND PORTAL VENOUS FLOW INTERACTIONS IN PERFUSED-RAT-LIVER - AN INTRAVITAL MICROSCOPIC STUDY

Intravital epifluorescent microscopy was used to quantitate microvascu lar parameters in the single-pass, dually perfused rat liver preparati on. Livers perfused via the hepatic artery (HA) and portal vein (PV) a t physiological pressures and perfusion rates responded to vasoactive agents and exhibited the HA buffer response. The distribution of arter ial blood was found to be highly heterogeneous, whereas PV flow was di stributed uniformly. The intrasinusoidal velocity of fluorescein isoth iocyanate (FITC)-labeled red blood cells (RBCs) arriving from the HA w as higher than that for RBCs arriving from the PV, indicating a shorte r transit time for the arterially delivered FITC-RBCs. Experiments on livers perfused simultaneously via the HA and retrogradely via the hep atic vein revealed the presence of arteriovenous shunts, with some of the arterially delivered FITC-RBCs reaching the terminal hepatic venul es via direct channels without traversing the sinusoidal bed. In liver s perfused portally only, changes in PV flow rate (from 8 to 20 ml/min ) produced small changes in perfusion pressure but large changes in va scular diameters, while portal pressure and transit time of portal blo od remained relatively constant. In experiments designed to identify t he location of hepatic vascular resistance, it was observed that hepat ic venular diameters measured in the preparation under identical press ure and flow conditions were greater during retrograde than during pro grade perfusion, suggesting that the site of hepatic vascular resistan ce is presinusoidal or sinusoidal.