Contributions of pressure and flow sensitivity to autoregulation in mesenteric arterioles

The relative influence of presence and flow on dilation of arterioles with pressure reduction was examined in preparations of cat mesentery. Erythrocyte velocity and diameter were measured in individual arterioles during stepwise reduction in mesenteric arterial pressure. Volume flow was calculated from velocity and diameter data. Approximately half of the arterioles which dilated with pressure reduction also showed an increase in volume flow. In a second series of experiments, a graded reduction of flow in single arterioles was produced by local downstream occlusion. Graded occlusion caused dilation. In a third series, flow in single arterioles was completely stopped by downstream occlusion, and arterial pressure was then lowered. Most arterioles dilated with pressure reduction. In a fourth series, flow in the total preparation was completely stopped and static intravascular pressure set by a reservoir. Elevation of static pressure typically produced arteriolar constriction. We conclude from these studies that the mesenteric arteriole is sensitive both to intravascular pressure and flow, with the former probably more important than the latter in the phenomenon of autoregulation.