Cutaneous vasodilation induced by local warming, sodium nitroprusside, andbretylium 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 b y vasodilation with alternate approaches to see if a greater vasodilation i s possible: blockade of the release of transmitters from the adrenergic ner ve endings with bretylium tosylate or direct pharmacological action on vasc ular smooth muscle using sodium nitroprusside. Nine healthy subjects partic ipated in two experiments in which SkBF was measured simultaneously by lase r Doppler flowmetry on the dorsal aspects of both hands. In the first proto col the vasodilator effects of 20 min of local warming at 44 degrees C were measured on one hand and the effects of iontophoresis of sodium nitropruss ide on the other. The second protocol was like the first except that iontop horesis 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 proto col 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, th e increase of SkBF attained during iontophoresis did not differ significant ly from the increase achieved by local warming. We conclude that the effect s of iontophoresis of sodium nitroprusside or of bretylium produce a cutane ous vasodilation as high as a local warming on the dorsal aspect of the han d. (C) 1998 Academic Press.