Role of humoral factors in the intestinal hyperemia associated with chronic portal hypertension.

The role of neural, metabolic, physical, and humoral factors in the intestinal hyperemia associated with chronic portal hypertension was examined by use of the rat portal vein stenosis model. Intestinal blood flow and splenic pulp pressure were increased, while systemic arterial pressure and total vascular resistance were reduced in portal vein-stenosed rats as compared with controls. The reduction in total vascular resistance was entirely due to a fall in precapillary resistance and was accompanied by an increase in intestinal capillary pressure, which exceeded that produced by acute portal pressure elevation to the same level. Arteriovenous shunting of 15-micron microspheres was four times higher in portal-hypertensive rats. Cross-perfusion of control intestinal preparations with arterial blood from portal-hypertensive rats produced a 30% increase in blood flow. Plasma glucagon levels in portal-hypertensive rats were three times higher than in controls. Intra-arterial infusion of glucagon (at a rate that achieved the concentration measured in portal-hypertensive animals) produced a 20% reduction in intestinal vascular resistance. The results of these studies indicate that humoral factors, including glucagon, are primarily responsible for the hyperemia associated with portal hypertension.