CUTANEOUS VASCULAR AND SUDOMOTOR RESPONSES TO ISOMETRIC-EXERCISE IN HUMANS

To identify whether isometric handgrip exercise (IHG) affects cutaneou s vasoconstrictor and/or active vasodilator activities, seven subjects (6 men and 1 woman) performed 30% maximal voluntary contraction of a forearm under normothermic (1 bout) and hyperthermic (2 bouts) conditi ons. Skin blood flow was indexed by laser-Doppler flowmetry at a contr alateral forearm site at which adrenergic vasoconstrictor function was blocked by iontophoresis of bretylium tosylate (BT) and therefore onl y has active vasodilation as a mechanism for reflex control. Skin bloo d flow was also monitored at an adjacent untreated site. Cutaneous vas cular conductance (CVC) was calculated from the flow signal and noninv asive blood pressure. CVC was normalized to the value obtained from ma ximal vasodilation at that site. Sweat rate (SR) was measured at the s ame locations. During normothermia, IHG did not affect CVC at the cont rol or BT-treated sites, nor did IHG affect SR (P > 0.05). The second bout of IHG in hyperthermia evoked significant reductions in CVC at th e untreated(69.4 +/- 3.4 to 58.9 +/- 2.5% of maximum, P < 0.05) and BT -treated sites (75.4 +/- 6.1 to 64.4 +/- 6.2% of maximum, P < 0.05), w hereas SR significantly increased (0.62 +/- 0.16 to 0.70 +/- 0.17 mg . cm(-2). min(-1), P < 0.05). These findings uniquely show that, in hyp erthermia, IHG reduces active vasodilator activity while at the same t ime sudomotor activity is increasing. This suggests independent contro l of these effecters.