Small intestinal transit in the portal hypertensive rat. The purpose of this study was to determine the effects of portal hypertension on gastrointestinal transit. Portal hypertension was induced in a group of 15 rats by the staged portal vein ligation technique. A control group of 15 rats underwent a sham operation. Ten days later, a 51Cr-labeled Krebs' buffer solution was instilled into the duodenum and the distribution or radioactivity along the length of the small intestine was determined after 15, 30, and 60 minutes. Portal hypertension was consistently established in the study group; splenic pulp pressure (mm Hg, mean +/- SD, portal hypertensive vs. control) was 20.0 +/- 3.9 vs. 12.7 +/- 3.9, P less than 0.002. Various measures of intestinal transit revealed delayed transit in the portal hypertensive group. Retention of radioactivity in the most proximal quartile of the intestine was greater [percentage retained (portal hypertensive vs. control) was 57.9 +/- 17.3 vs. 31.2 +/- 15.3, P less than 0.02, 49.1 +/- 15.5 vs. 28.3 +/- 4.8, P = 0.03, and 42.4 +/- 17.6 vs. 29.0 +/- 8.8, P = 0.08, at 15, 30, and 60 minutes, respectively] and the geometric mean of transit was located more proximally (P less than 0.02) at each study interval in the portal hypertension group. It was concluded that portal hypertension is associated with delayed intestinal transit. This abnormality could predispose to bacterial overgrowth and contribute to altered digestion and absorption. 