Continuous monitoring of portal vein and hepatic artery hemodynamics in unrestrained rats

Abstract

Continuous measurement of portal vein and hepatic artery blood flows during physiological experimental conditions, even in large animals, poses difficult problems. We report the successful use of miniaturized flow probes and pulsed Doppler flowmetry for chronic monitoring of hepatic artery and portal vein flows in intact unrestrained rats and describe the probe construction and implantation. Proportionality between portal vein velocity and portal flow was made possible by a technique for stabilizing the diameter of the venous segment from which velocity is recorded. The accuracy of the method in detecting changes in portal vein flow was established by the high statistically significant correlation between changes in velocity recorded simultaneously from portal vein and superior mesenteric artery in a series of rats with ligated celiac and inferior mesenteric arteries. In these preparations all portal vein flow is derived from the superior mesenteric artery. Complex dynamic changes in the hepatic circulation of conscious unrestrained rats were recorded in response to systemic injections of glucagon and angiotensin II. In the resting state several characteristic velocity patterns were recorded from the portal vein. Oscillations linked to respiration were not observed while the animals rested quietly but were noted during sleep and anesthesia. Two hitherto unrecognized patterns produced respectively by the pulsations of the superior mesenteric artery and by spontaneous contractions of the portal vein were also observed. The method described here provides the first opportunity to study hepatic circulation in chronically instrumented rats during physiological experimental conditions.