Components of methacholine-initiated conducted vasodilation are unaffected by arteriolar pressure.

Conducted vasodilation occurs remotely from a site of microapplication of a drug. Intravascular pressure is required for a conducted response in vivo, yet in vitro studies in unpressurized arterioles show pressure is not essential. To determine how pressure affects conducted vasodilation, intra-arteriolar pressure was controlled within an in situ isolated segment (average length 950 +/- 96 microns, average baseline diameter 28 +/- 2.1 microns) of arterioles in the hamster cheek pouch. Methacholine (10(-4) M, 5 s) was microapplied either onto the isolated segment or remotely, with local and conducted vasodilation measured at both locations. Increasing pressure in the lumen of the segment (0-80 cmH2O) increased the segment local dilation to methacholine, and the segment-conducted dilation plateaued (at 4.1 +/- 0.8 micron) when segment pressure reached 20 cmH2O. Any local (16 +/- 1.5 microns) and conducted (4.4 +/- 1.3 microns) dilations viewed outside the segment were unaffected by segment pressure and persisted in its absence. Thus segment pressure affected only electromechanical transduction of the conducted response. Thus vasomotor signals move throughout the vasculature regardless of tone, but tone is essential to transduce the response.