Cutaneous vasodilation induced by local warming, sodium nitroprusside, and bretylium iontophoresis on the hand.

Local warming alone induces a cutaneous vasodilation considered as maximal. The argument that local warming generates a maximum flow is being tested by vasodilation with alternate approaches to see if a greater vasodilation is possible: blockade of the release of transmitters from the adrenergic nerve endings with bretylium tosylate or direct pharmacological action on vascular smooth muscle using sodium nitroprusside. Nine healthy subjects participated in two experiments in which SkBF was measured simultaneously by laser Doppler flowmetry on the dorsal aspects of both hands. In the first protocol the vasodilator effects of 20 min of local warming at 44 degreesC were measured on one hand and the effects of iontophoresis of sodium nitroprusside on the other. The second protocol was like the first except that iontophoresis of bretylium tosylate instead of sodium nitroprusside was performed. Local warming induced an increase of SkBF from 17.6 +/- 4.4 to 140.2 +/- 33.2 AU (P < 0.01) while it rose from 16.7 +/- 4.0 to 114.7 +/- 11.0 AU (P < 0.001) during sodium nitroprusside iontophoresis. During the second protocol local warming induced an increase of SkBF from 14.9 +/- 2.1 to 117.7 +/- 25.4 AU (P < 0.01) while it rose from 19.6 +/- 2.6 to 120.5 +/- 11.3 AU (P < 0.001) during bretylium iontophoresis. However, in both experiments, the increase of SkBF attained during iontophoresis did not differ significantly from the increase achieved by local warming. We conclude that the effects of iontophoresis of sodium nitroprusside or of bretylium produce a cutaneous vasodilation as high as a local warming on the dorsal aspect of the hand.