The interactive contributions of Na ⁺ /K ⁺ ‐ATPase and nitric oxide synthase to sweating and cutaneous vasodilatation during exercise in the heat

KEY POINTS: Nitric oxide synthase (NOS) contributes to sweating and cutaneous vasodilatation during exercise in the heat. Similarly, reports show that Na(+) /K(+) -ATPase activation can modulate sweating and microvascular circulation. In light of the fact that NO can activate Na(+) /K(+) -ATPase, we evaluated whether there is an interaction between Na(+) /K(+) -ATPase and NOS in the regulation of heat loss responses during an exercise-induced heat stress. We demonstrate that Na(+) /K(+) -ATPase and NOS do not synergistically influence local forearm sweating during moderate intensity (fixed rate of metabolic heat production of 500 W) exercise in the heat (35°C). Conversely, we show an interactive role between NOS and Na(+) /K(+) -ATPase in the modulation of cutaneous vasodilatation. These findings provide novel insight regarding the mechanisms underpinning the control of sweating and cutaneous vasodilatation during exercise in the heat. Given that ouabain may be prescribed as a cardiac glycoside in clinical settings, potential heat loss impairments with ouabain administration should be explored. ABSTRACT: Nitric oxide (NO) synthase (NOS) contributes to the heat loss responses of sweating and cutaneous vasodilatation. Given that NO can activate Na(+) /K(+) -ATPase, which also contributes to sweating and microvasculature regulation, we evaluated the separate and combined influence of Na(+) /K(+) -ATPase and NOS on sweating and cutaneous vasodilatation. Thirteen young (23±3 years) males performed two 30 min semi-recumbent cycling bouts in the heat (35°C) at a fixed rate of metabolic heat production (500 W) followed by 20 and 40 min recoveries, respectively. Local sweat rate (LSR) and cutaneous vascular conductance (CVC) were measured at four forearm skin sites continuously perfused via intradermal microdialysis with either: (1) lactated Ringer solution (Control); (2) 6 mᴍ ouabain (Ouabain), a Na(+) /K(+) -ATPase inhibitor; (3) 10 mᴍ l-N(G) -nitroarginine methyl ester (l-NAME), a NOS inhibitor; or (4) 6 mᴍ ouabain and 10 mᴍ l-NAME (Ouabain+l-NAME). At the end of both exercise bouts relative to Control, LSR was attenuated with Ouabain (54-60%), l-NAME (12-13%) and Ouabain+l-NAME (68-74%; all P < 0.05). Moreover, the sum of attenuations from Control induced by independent administration of Ouabain and l-NAME was similar to the combined infusion of Ouabain+l-NAME (both P ≥ 0.74). Compared to Control, CVC at the end of both exercise bouts was similar with Ouabain (both P ≥ 0.30), but attenuated with l-NAME (%CVCmax reduction from Control, 24-25%). Furthermore, CVC at the Ouabain+l-NAME site (38-39%; all P < 0.01) was attenuated compared to Control and did not differ from baseline resting values (both P ≥ 0.81). We show that Na(+) /K(+) -ATPase and NOS do not synergistically mediate sweating, whereas they influence cutaneous blood flow in an interactive manner during exercise in the heat.

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