Reduced vascular sensitivity to norepinephrine in portal-hypertensive rats.

The development of portal hypertension following chronic portal vein stenosis is accompanied by a significant increase in intestinal blood flow. The present study was designed to determine whether intestinal vascular sensitivity to norepinephrine (NE) is also affected by chronic portal vein stenosis. Using a blood-perfused, in situ rat small intestine preparation, we found that, when compared with control animals, a significantly greater molar concentration of NE was required to achieve the same proportional increase in intestinal vascular resistance in portal-hypertensive animals. The mean ED50 value (+/-SE) for the portal-hypertensive group (704.3 +/- 186.1 nM) was significantly greater (P less than 0.05) than the mean ED50 value for the control group (271.4 + 48.1 nM). This finding implies that sympathetic maintenance of intestinal vascular tone may be impaired following chronic portal vein stenosis, possibly accounting for part of the intestinal hyperemia associated with portal hypertension.