Intestinal microvascular adaptation to chronic portal hypertension in the rat.

Microvascular pressures, diameters, and flow velocities were measured in the small intestine of rats with chronic stenosis of the portal vein. Ten days after portal vein stenosis, portal venous pressure increased (13.8 +/- 0.4 mmHg vs, 7.3 +/- 0.5 mmHg; p less than 0.05) whereas systemic arterial pressure decreased (94.2 +/- 2.0 mmHg vs. 106.5 +/- 1.6 mmHg; p less than 0.05). Red blood cell centerline velocity, measured in first-order arterioles, was significantly higher in portal hypertensive rats (24.3 +/- 1.2 mm/s vs. 19.6 +/- 1.3 mm/s), yet there was no significant change in the diameters of these vessels. Microvascular pressures and diameters of first- and second-order arterioles were not different between control and portal hypertensive rats. However, both pressure (34.3 +/- 2.7 mmHg vs. 28.0 +/- 1.8 mmHg) and diameter (30.4 +/- 0.6 microns vs. 21.4 +/- 2.1 microns) were significantly increased in the third-order arterioles of portal hypertensive rats. A consistent elevation in pressure was observed throughout the distal segments (capillaries to first-order venules) of the intestinal microcirculation of portal hypertensive rats. The results of these studies indicate that the increased intestinal vascular pressures associated with chronic portal hypertension result from a combination of reduced arteriolar resistance and venous congestion.