Intestinal capillary filtration in acute and chronic portal hypertension.

The impact of acute and chronic portal hypertension on the dynamics of intestinal microvascular fluid exchange was examined in anesthetized, fasted, sham-operated control rats with normal portal pressures (CON), during acute elevations in portal pressure (APH) in control rats, and in rats in which chronic portal hypertension (CPH) was produced by calibrated stenosis of the portal vein 10 days prior to the experiments. Although intestinal blood flow and vascular resistance were not altered by APH in control rats, CPH was associated with an increased intestinal blood flow and reduced intestinal vascular resistance when compared with CON and APH. Intestinal capillary pressure and lymph flow were elevated in APH and CPH relative to control values. However, the increase in both variables was greater in CPH. The capillary filtration coefficient was elevated only in CPH. The transcapillary oncotic pressure gradient was not altered by APH or CPH. Interstitial fluid pressure was increased from -1.1 mmHg in CON to 3.9 mmHg during APH and to 5.0 mmHg in CPH. The results of this study indicate that chronic elevations in portal venous pressure produce larger increments in intestinal capillary pressure and filtration rate than do acute elevations in portal venous pressure of the same magnitude. However, the potential edemagenic effects of elevated capillary pressure in both acute and chronic portal hypertension are opposed by increases in lymph flow and interstitial fluid pressure.