Effect of arterial pulse pressure and hypoxia on myogenic responses in the gut

In intestine, raising venous pressure (PV) elicits a precapillary vasconstriction that has been ascribed to a myogenic mechanism through which passive stretch elicits active contraction of vascular smooth muscle. A previous report from this laboratory indicated that myogenic responses in the gut were largely dependent on control conditions. The purpose of the present study was to determine whether control blood flow rates or the arterial pulse pressure affects the magnitude of myogenic responses. In isolated perfused canine small bowel arterial hypoxia was used to increase blood flow. Myogenic responses to elevated PV were not significantly different in the normoxic and hypoxic periods, indicating that blood flow per se does not greatly alter myogenic responses. When gut loops were perfused with pulsatile arterial pressure, myogenic responses occurred more than twice as frequently as during nonpulsatile pefusion and they had a greater magnitude. The results are consistent with the observation that vascular smooth muscle is stimulated not only by steady stretch but also by the rate of stretch. The results also suggest that the arterial pressure pulse should be considered in the design and interpretation of future studies of local circulatory control.