To test for an active vasodilator system in human hand and finger skin, seven subjects had a small area of dorsal hand, palm, or dorsal finger pretreated with bretylium (BT) to block adrenergic vasoconstriction. Skin blood flow was monitored at a BT-treated site, a comparable untreated site, and the forearm by laser-Doppler flowmetry. Cutaneous vascular conductance (CVC) was evaluated from the ratio of blood flow to arterial pressure. Body cooling, to evaluate vasoconstrictor system blockade, caused CVC at untreated sites of forearm, palm, dorsal hand, and dorsal finger to fall by 45 +/- 4, 85 +/- 5, 51 +/- 9, and 63 +/- 7%, respectively (all P < 0.05). At BT-treated sites of palm, dorsal hand, and dorsal finger, reductions in CVC were only 13 +/- 3, 2 +/- 18, and 13 +/- 4%, respectively (dorsal hand not significant, others P < 0.05). With body heating, increases in CVC at untreated sites of forearm, palm, dorsal hand, and dorsal finger were 881 +/- 165, 779 +/- 368, 423 +/- 115, and 1,430 +/- 716%, respectively (all P < 0.05). At BT-treated sites of palm, dorsal hand, and dorsal finger, increases were 35 +/- 15, 342 +/- 107, and 343 +/- 34%, respectively (palm not significant, others P < 0.05). Increased CVC at the palm began after 1.2 +/- 0.2 min of heating, significantly earlier than forearm (11.8 +/- 2.5 min), dorsal hand (16.4 +/- 3.4 min), or dorsal finger (15.6 +/- 3.6 min), which did not differ significantly from one another.(ABSTRACT TRUNCATED AT 250 WORDS)