Effect of O2 availability on intrinsic vascular response to venous pressure elevation in postnatal swine intestine.

The goal of these experiments was to determine whether the intrinsic vascular response of postnatal intestine to acute venous pressure elevation was dependent on the preexisting level of oxygen availability. To this end, acute venous hypertension was applied to denervated loops of small intestine from 3- and 35-day-old swine anesthetized with pentobarbital during free-flow and controlled-flow perfusion. During controlled-flow perfusion, the base-line blood flow rate was set slightly above (+5%; high flow) or significantly below (-50%; low flow) the rate noted during free-flow perfusion so as to directly alter intestinal oxygen availability. The vascular response to venous hypertension noted under controlled high-flow perfusion was similar in both age groups and generally consistent with that noted under free-flow perfusion. In contrast, the response noted during low-flow perfusion was clearly age dependent. In the older group, vascular resistance decreased (27%), while arteriovenous oxygen content difference [(a-v)O2] and tissue oxygen uptake remained unchanged. In the younger group, vascular resistance remained unchanged, whereas (a-v)O2 and oxygen uptake decreased (14%). We conclude that the intrinsic vascular response to venous pressure elevation is dependent on the preexisting level of oxygen availability in intestine from 35- but not from 3-day-old swine. We speculate that the local metabolic vascular response to venous hypertension is more effective in intestine from older than from younger swine.