Effects of ischemia and reperfusion on intrinsic vascular regulation in the postnatal intestinal circulation.

The purpose of these experiments was to determine the effect of 1 h of total ischemia followed by 2 h of reperfusion on intrinsic vascular regulation within intestine from 3- and 35-d-old swine. Intrinsic vascular regulation was defined as the ability of in vitro segments of small intestine to bring about adjustments of blood flow and the arteriovenous O2 content difference across the intestinal segment of sufficient magnitude to preserve tissue O2 uptake in response to a 35% reduction in arterial perfusion pressure. This response was elicited before (control conditions) and after ischemia-reperfusion (post-I/R). In older subjects, the efficacy of blood flow regulation was attenuated post-I/R, insofar as blood flow fell in response to pressure reduction. However, this group demonstrated a rise in arteriovenous content difference after pressure reduction under control and post-I/R conditions that were of sufficient magnitude to preserve tissue O2 uptake. In younger subjects, blood flow regulation was absent under control conditions and post-I/R. The arteriovenous O2 content difference increased in response to pressure reduction under control conditions but failed to do so post-I/R; consequently, tissue oxygenation decreased in response to arterial pressure reduction post-I/R in 3-d-old intestine. We conclude that ischemia-reperfusion affects intrinsic vascular regulation in postnatal intestine and that this effect is age-dependent. Intestine from older subjects maintains the intrinsic capacity to preserve tissue oxygenation in response to a hypotensive challenge despite the insult of ischemia-reperfusion, whereas intestine from younger subjects does not maintain this capacity.