Cumulative conducted vasodilation within a single arteriole and the maximum conducted response

The vascular network functions to distribute blood flow to the tissues that require it, and conducted vasodilation may facilitate this function. Experiments on arterioles in anesthetized hamster cheek pouch modeled the conducted responses that may come from a series of neighboring capillary modules and determined whether cumulative conducted responses could thereby maximally dilate upstream arterioles. Methacholine (10(-5) M) was simultaneously microapplied on an arteriole (resting diameter, approximately 22 microns; maximum diameter, approximately 47 microns) from one to four micropipettes spaced 100 microns apart, and with each added pipette the conducted dilation increased (up to a maximum dilation of approximately 5 microns). Increasing the methacholine 10-fold (10(-4) M) did not further increase the conducted response. The conducted response could also not be increased by lengthening the duration of microapplication. Yet, dilations that were not cumulative along a single arteriole became cumulative when initiated instead on adjacent arterioles. Therefore, these data demonstrate that conducted dilation along a single arteriole is limited and, if this model is correct, suggest that neighboring capillary modules may communicate only a limited conducted response to the network.