MATURATIONAL DIFFERENCES IN HEPATIC MICROHEMODYNAMICS IN RATS

Age-related changes in the hepatic microcirculation may contribute to the increased susceptibility of the immature liver to microvascular injury. We quantified sinusoidal and acinar diameters, sinusoidal red cell velocities (VRBC), and sinusoidal volume flows to characterize microhemodynamics of weanling and adult rat livers with and without hepatic artery (HA) ligation using intravital fluorescence videomicroscopy. Despite a 20% faster heart rate and a nearly 20% lower mean arterial and portal vein pressure in weanling rats relative to those in the adults, weanling periportal and pericentral sinusoidal velocities were ∼30 and 25% faster, respectively, than those in adults. Furthermore, the HA was found to contribute more to maintenance of sinusoidal VRBC in the immature liver as demonstrated by a significant decrease in both periportal and pericentral VRBC following HA ligation. HA ligation had no effect on VRBC of either zone in adults. Zonal volume flow (HA intact), however, was maintained independent of age. These results suggest a lower extrasinusoidal resistance in the weanling. The 25% shorter acinar diameter that we found in weanling livers likely contributes to a lower extrasinusoidal resistance by allowing a higher ratio of inflow vessels to volume of tissue. Shorter sinusoidal pathways in weanling livers also decreases sinusoidal resistance 1.3-fold relative to that in the adult, countering the ∼1.5 times increase in resistance due to the smaller caliber of sinusoidal vessels so that overall sinusoidal resistance is not age-dependent. The apparent susceptibility of the pediatric liver to vascular injury under conditions such as reperfusion following ischemia may, hence, reflect an underlying immaturity of hepatic presinusoidal, sinusoidal, and postsinusoidal microvascular anatomy and of vasoregulatory mechanisms. © 1993 Academic Press. All rights reserved.