Regional differences in microvascular response in rat intestine during acute elevation of portal pressure.

The effect of acute elevation of portal pressure on the blood flow of rat intestinal microvessels was studied using a laser Doppler velocimeter and in vivo microscopy. The total intestinal blood flow decreased when portal pressure increased more than +15 cmH2O above the basal value. Blood flow in villus capillaries did not change at portal pressures of +5 to +15 cmH2O, but did decrease at +20 cmH2O. Blood flow in muscle capillaries decreased at all steps of portal hypertension. Red blood cell velocity was decreased by portal hypertension in large venules, but not in small venules of the submucosa. Large venules, but not small venules, dilated in acute portal hypertension. Large arterioles in the submucosa constricted, while small arterioles dilated at portal pressures of +10 to +15 cmH2O. In conclusion, the intestinal microvascular flow response differs according to the degree of portal hypertension and the location on the microvascular tree. Blood flow in villus capillaries and in small submucosal venules is maintained at a small degree of portal hypertension.