Evidence for cyclooxygenase-dependent sweating in young males during intermittent exercise in the heat

Abstract

Our recent work implicated nitric oxide (NO) in the control of sweating during intermittent exercise; however, it is unclear if cyclooxygenase (COX) is also involved. On separate days, ten healthy young (24 ± 4 years) males cycled in the heat (35°C). Two 30 min exercise bouts were performed at either a moderate (400 W, moderate heat load) or high (700 W, high heat load) rate of metabolic heat production and were followed by 20 and 40 min of recovery, respectively. Forearm sweating (ventilated capsule) was evaluated at four skin sites that were continuously perfused via intradermal microdialysis with: (1) lactated Ringer solution (Control), (2) 10 mm ketorolac (a non-selective COX inhibitor), (3) 10 mm N^G-nitro-l-arginine methyl ester (l-NAME; a non-selective NO synthase inhibitor) or (4) a combination of 10 mm ketorolac + 10 mml-NAME. During the last 5 min of the first exercise at moderate heat load, forearm sweating (mg min⁻¹ cm⁻²) was equivalently reduced with ketorolac (0.54 ± 0.08), l-NAME (0.55 ± 0.07) and ketorolac+l-NAME (0.56 ± 0.08) compared to Control (0.67 ± 0.06) (all P < 0.05). Similar results were obtained for the second exercise at moderate heat load (all P < 0.05). However, forearm sweating was similar between the four sites during exercise at high heat load and during recovery regardless of exercise intensity (all P > 0.05). We show that (1) although both COX and NO modulate forearm sweating during intermittent exercise bouts in the heat at a moderate heat load, the effects are not additive, and (2) the contribution of both enzymes to forearm sweating is less evident during intermittent exercise when the heat load is high and during recovery.