Cutaneous interstitial nitric oxide concentration does not increase duringheat stress in humans

Inhibition of cutaneous nitric oxide (NO) synthase reduces the magnitude of cutaneous vasodilation during whole body heating in humans. However, this observation is insufficient to conclude that NO concentration increases in the skin during a heat stress. This study was designed to test the hypothes is that whole body heating increases cutaneous interstitial NO concentratio n. This was accomplished by placing 2 microdialysis membranes in the forear m dermal space of 12 subjects. Both membranes were perfused with lactated R inger solutions at a rate of 2 mul/min. In both normothermia and during who le body heating via a water perfused suit, dialysate from these membranes w ere obtained and analyzed for NO using the chemiluminescence technique. In six of these subjects, after the heat stress, the membranes; were perfused with a 1 M solution of acetylcholine to stimulate NO release. Dialysate fro m these trials was also assayed to quantify cutaneous interstitial NO conce ntration. Whole body heating increased skin temperature from 34.6 +/- 0.2 t o 38.8 +/- 0.2 degreesC (P < 0.05), which increased sublingual temperature (36.4 +/- 0.1 to 37.6 +/- 0.1<degrees>C; P < 0.05), heart rate (63 +/- 5 to 93 +/- 5 beats/min; P < 0.05), and skin blood flow over the membranes (21 +/- 4 to 88 +/- 10 perfusion units; P < 0.05). NO concentration in the dial ysate did not increase significantly during of the heat stress (7.6 +/- 0.7 to 8.6 +/- 0.8 <mu>M; P > 0.05). After the heat stress, administration of acetylcholine in the perfusate significantly increased skin blood flow (128 +/- 6 perfusion units) relative to both normothermic and heat stress value s and significantly increased NO concentration in the dialysate (15.8 +/- 2 .4 muM). These data suggest that whole body heating does not increase cutan eous interstitial NO concentration in forearm skin. Rather, NO may serve in a permissive role in facilitating the effects of:an unknown neurotransmitt er, leading to cutaneous vasodilation during a heat stress.