Nitric oxide synthase inibition and thermoregulatory control of local sweat rate in exercising humans

Abstract

The role of nitric oxide (NO) in modulating human thermoregulatory sweating was examined in 10 subjects (5 male/5 female). Three intradermal microdialysis probes were placed in the dorsal forearm. The control site was perfused with 0.9% saline while the two remaining sites were perfused with a nitric oxide inhibitor: 10 mM NG‐nitro‐L‐arginine (L‐NAME) or 10 mM NG‐monomethyl‐L‐arginine (L‐NMMA). Local sweat rate (SR) and skin blood flow (SkBF) were monitored directly over the path of the intradermal microdialysis probe while arterial blood pressure was measured in the opposite arm non‐invasively. Thermoregulatory sweating was induced by cycle ergometer exercise (60% VO2max) in a warm environment (30°C). Thermoregulatory control of SR was described by the following four parameters: resting sweat rate (SRREST), the increase in esophageal temperature required to initiate a significant rise in SR (ΔTesTHRESHOLD), the slope of the initial linear rate of rise in SR per unit rise in Tes (SR‐ΔTesSLOPE), and peak SR (SRPEAK). In general, NOS inhibition attenuated thermoregulatory sweating during dynamic exercise in a warm environment as shown in the Table below.L‐NMMA appeared to be more effective, than L‐NAME, in reducing the SR response. We conclude that NO has a subtle but physiologically active role in thermoregulatory control of sweating. (supported by NIH‐RO1‐HL039818)