Intestinal villus microcirculatory response to hemorrhage in adult and immature rats

The response of the villus microcirculation to moderate hemorrhage was compared in adult and immature rats. As an estimate of villus blood flow, flux of red blood cells through the terminal arteriole loop at the villus tip was quantified in vivo using fluorescence epilumination videomicroscopy. Baseline red blood cell flux and mean arterial pressure (MAP) of immature rats (973 cells/s, 84 mm Hg) were significantly less than that of adults (1,435 cells/s, 131 mm Hg). Following hemorrhage of 30% of estimated blood volume, MAP of immature rats was still 24% less than that of adults; however, villus flux was not significantly different (578 cells/s immature, 640 cells/s adult; P = .63). Thus, as indicated by changes in villus flux, immature rats do not appear to be more susceptible to acute intestinal blood flow reduction induced by a single moderate hemorrhage. Immaturity of villus microvascular anatomy and of intestinal vasoregulatory mechanisms may account for the differential response.