Effects of solute-coupled fluid absorption on blood flow and oxygen uptake in the dog colon.

In the resting colon (empty lumen) both metabolic and myogenic mechanisms contribute to the overall regulation of blood flow and oxygenation. In the present study, the effects of Tyrode's solution absorption on blood flow, vascular resistance, oxygen extraction, and oxygen uptake were analyzed in autoperfused segments of dog colon. Colonic oxygen uptake increased during Tyrode's solution absorption. The increased oxygen demand during absorption was met entirely by an increase in oxygen extraction. A linear relationship between oxygen uptake and absorption rate was obtained, indicating that the oxygen requirements of the absorbing colon are dependent on the rate of transport. In another series of experiments, the effects of Tyrode's solution absorption on the ability of the colon to autoregulate its blood flow and oxygen uptake during arterial and venous pressure alterations were assessed. In the empty colon, graded alterations in arterial perfusion pressure resulted in a moderate autoregulation of oxygen uptake but no autoregulation of blood flow. When the metabolic demands of the colon were enhanced (Tyrode's solution in the lumen), similar maneuvers resulted in almost perfect autoregulation of oxygen uptake and moderate autoregulation of blood flow. Elevation of venous pressure increased vascular resistance in the empty colon, but did not affect resistance when Tyrode's solution was present in the lumen. The results of this study indicate that the enhanced autoregulation of colonic blood flow and oxygenation during periods of elevated metabolic activity is a result of an increased sensitivity of the vasculature to metabolic factors.