Pressure-flow relationships in isolated dog colon

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Abstract
Data are given on the vascular resistance in 32 dogs colon preparations. Segments of colon weighing 50-100 g were surgically isolated and perfused with blood from the femoral artery by way of cannulae to the arteries supplying the segment (caudal mesenteric and middle colic). Outflow was by way of a cannula to the left colic veto. Evidence of autoregulation was seen to only 20% of the 25 experiments in which arterial pressure-flow studies were done over the range of arterial pressure from 120 down to 20 mg Hg. In 80% of the colon preparations resistance increased as arterial pressure was reduced to a stepwise fashion over the entire range. By contrast, resistance to-creased consistently to all 32 colon preparations with stepwise elevation of venous pressure from 0 to 20 mm Hg. At a venous pressure to 20 mm Hg, the average increase to resistance of 31% was accompanied by a 35% decrease to flow. Venous pressure elevations were reported to 10 preparations while papavarine was infused tatra-arterially at a dose of approximately 0.6 mg/min. In this group elevation of venous pressure from 0 to 20 mm Hg resulted to a 23% decrease to flow, whereas the resistance increase was abolished. The results are compared with those from similar experiments on the small intestine and hepatic arterial system.

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