Acetylcholine released from cholinergic nerves is involved in heat loss responses of cutaneous vasodilation and sweating. K(+) channels are thought to play a role in regulating cholinergic cutaneous vasodilation and sweating, though which K(+) channels are involved in their regulation remains unclear. We evaluated the hypotheses that 1) Ca(2+)-activated K(+) (KCa), ATP-sensitive K(+) (KATP), and voltage-gated K(+) (KV) channels all contribute to cholinergic cutaneous vasodilation; and 2) KV channels, but not KCa and KATP channels, contribute to cholinergic sweating. In 13 young adults (24 ± 5 years), cutaneous vascular conductance (CVC) and sweat rate were evaluated at intradermal microdialysis sites that were continuously perfused with: 1) lactated Ringer (Control), 2) 50 mM tetraethylammonium (KCa channel blocker), 3) 5 mM glybenclamide (KATP channel blocker), and 4) 10 mM 4-aminopyridine (KV channel blocker). At all sites, cholinergic cutaneous vasodilation and sweating were induced by coadministration of methacholine (0.0125, 0.25, 5, 100, and 2,000 mM, each for 25 min). The methacholine-induced increase in CVC was lower with the KCa channel blocker relative to Control at 0.0125 (1 ± 1 vs. 9 ± 6%max) and 5 (2 ± 5 vs. 17 ± 14%max) mM methacholine, whereas it was lower in the presence of KATP (69 ± 7%max) and KV (57 ± 14%max) channel blocker compared with Control (79 ± 6%max) at 100 mM methacholine. Furthermore, methacholine-induced sweating was lower at the KV channel blocker site (0.42 ± 0.17 mg·min(-1)·cm(-2)) compared with Control (0.58 ± 0.15 mg·min(-1)·cm(-2)) at 2,000 mM methacholine. In conclusion, we show that KCa, KATP, and KV channels play a role in cholinergic cutaneous vasodilation, whereas only KV channels contribute to cholinergic sweating in normothermic resting humans.

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While the mechanisms underlying the control of cutaneous vasodilation have been extensively studied, there remains a lack of understanding of the different factors that may modulate cutaneous perfusion during an exercise-induced heat stress. We evaluated the hypothesis that heat shock protein 90 (HSP90) contributes to the heat loss response of cutaneous vasodilation via the activation of nitric oxide synthase (NOS) during exercise in the heat. In 11 young males (25 ± 5 yr), cutaneous vascular conductance (CVC) was measured at four forearm skin sites that were continuously treated with ) lactated Ringer solution (control),) NOS inhibition with 10 mM -nitro-l-arginine methyl ester (l-NAME),) HSP90 inhibition with 178 μM geldanamycin, or ) a combination of 10 mM l-NAME and 178 μM geldanamycin. Participants rested in a moderate heat stress (35°C) condition for 70 min. Thereafter, they performed a 50-min bout of moderate-intensity cycling (~52% V̇o) followed by a 30-min recovery period. We showed that NOS inhibition attenuated CVC (~40-50%) relative to the control site during pre- and postexercise rest in the heat ( ≤ 0.05); however, no effect of HSP90 inhibition was observed ( > 0.05). During exercise, we observed an attenuation of CVC with the separate inhibition of NOS (~40-50%) and HSP90 (~15-20%) compared with control (both ≤ 0.05). However, the effect of HSP90 inhibition was absent in the presence of the coinhibition of NOS ( > 0.05). We show that HSP90 contributes to cutaneous vasodilation in young men exposed to the heat albeit during exercise only. We also show that the HSP90 contribution is due to NOS-dependent mechanisms. We show that heat shock protein 90 functionally contributes to the heat loss response of cutaneous vasodilation during exercise in the heat, and this response is mediated through the activation of nitric oxide synthase. Therefore, interventions that may activate heat shock protein 90 may facilitate an increase in heat dissipation through an augmentation of cutaneous perfusion. In turn, this may attenuate or reduce the increase in core temperature and therefore the level of heat strain.

Key pointsr β-Adrenergic receptor agonists such as isoproterenol induce cutaneous vasodilatation and sweating in humans, but the mechanisms underpinning this response remain unresolved.r Using intradermal microdialysis, we evaluated the roles of nitric oxide synthase (NOS) and cyclooxygenase (COX) in β-adrenergic cutaneous vasodilatation and sweating elicited by administration of isoproterenol.r We show that while NOS contributes to β-adrenergic cutaneous vasodilatation, COX restricts cutaneous vasodilatation.r We also show that combined inhibition of NOS and COX augments β-adrenergic sweating r These new findings advance our basic knowledge regarding the physiological control of cutaneous blood flow and sweating, and provide important and new information to better understand the physiological significance of β-adrenergic receptors in the skin.Abstract β-Adrenergic receptor agonists such as isoproterenol can induce cutaneous vasodilatation and sweating in humans, but the mechanisms underpinning this response remain unresolved. We evaluated the hypotheses that (1) nitric oxide synthase (NOS) contributes to β-adrenergic cutaneous vasodilatation, whereas cyclooxygenase (COX) limits the vasodilatation, and (2) COX contributes to β-adrenergic sweating. In 10 young males (25 ± 5 years), cutaneous vascular conductance (CVC) and sweat rate were evaluated at four intradermal forearm skin sites infused with (1) lactated Ringer solution (control), (2) 10 mM N ω -nitro-L-arginine (L-NNA), a non-specific NOS inhibitor, (3) 10 mM ketorolac, a non-specific COX inhibitor, or (4) a combination of L-NNA and ketorolac. All sites were co-administered with a high dose of isoproterenol (100 μM) for 3 min to maximally induce β-adrenergic sweating (β-adrenergic sweating is significantly blunted by subsequent activations). Approximately 60 min after the washout period, three incremental doses of isoproterenol were co-administered (1, 10 and 100 μM each for 25 min). Increases in CVC induced by the first and second 100 μM isoproterenol were attenuated by L-NNA alone, and those in response to all doses of isoproterenol were reduced by L-NNA with co-infusion of ketorolac (all P ࣘ 0.05). Ketorolac alone augmented increases in CVC induced by 10 μM and by the second 100 μM isoproterenol (both P ࣘ 0.05). While isoproterenol-induced sweating was not affected by the separate administration of L-NNA or ketorolac (all P > 0.05), their combined administration augmented sweating elicited by the first 3 min of 100 μM isoproterenol (P = 0.05). We show that while NOS contributes to β-adrenergic cutaneous vasodilatation, COX restrains the vasodilatation. Finally, combined inhibition of NOS and COX augments β-adrenergic sweating.

We recently showed the varying roles of Ca-activated (K), ATP-sensitive (K), and voltage-gated (K) K channels in regulating cholinergic cutaneous vasodilation and sweating in normothermic conditions. However, it is unclear whether the respective contributions of these K channels remain intact during dynamic exercise in the heat. Eleven young (23 ± 4 yr) men completed a 30-min exercise bout at a fixed rate of metabolic heat production (400 W) followed by a 40-min recovery period in the heat (35°C, 20% relative humidity). Cutaneous vascular conductance (CVC) and local sweat rate were assessed at four forearm skin sites perfused via intradermal microdialysis with: ) lactated Ringer solution (control);) 50 mM tetraethylammonium (nonspecific K channel blocker); ) 5 mM glybenclamide (selective K channel blocker); or ) 10 mM 4-aminopyridine (nonspecific K channel blocker). Responses were compared at baseline and at 10-min intervals during and following exercise. K channel inhibition resulted in greater CVC versus control at end exercise ( = 0.04) and 10 and 20 min into recovery (both < 0.01). K channel blockade attenuated CVC compared with control during baseline ( = 0.04), exercise (all ≤ 0.04), and 10 min into recovery ( = 0.02). No differences in CVC were observed with K channel inhibition during baseline ( = 0.15), exercise (all ≥ 0.06), or recovery (all ≥ 0.14). With the exception of K channel inhibition augmenting sweating during baseline ( = 0.04), responses were similar to control with all K channel blockers during each time period (all ≥ 0.07). We demonstrated that K and K channels contribute to the regulation of cutaneous vasodilation during rest and/or exercise and recovery in the heat.

Edited by: Philip Atherton New Findings r What is the central question of this study?Acetylcholine released from cholinergic nerves can activate both muscarinic and nicotinic receptors. Although each receptor can independently induce cutaneous vasodilatation and eccrine sweating, it remains to be elucidated whether the two receptors interact in order to mediate these responses. r What is the main finding and its importance?We show that although nicotinic receptor activation does not modulate muscarinic cutaneous vasodilatation, it lowers the muscarinic receptor agonist threshold at which onset for eccrine sweating (augmentation of muscarinic eccrine sweating) occurs in young men in normothermic resting conditions. These results provide new insights into the physiological significance of nicotinic receptors in the regulation of cutaneous perfusion and eccrine sweating.Acetylcholine released from cholinergic nerves can activate both muscarinic and nicotinic receptors; each is known independently to induce cutaneous vasodilatation and eccrine sweating in humans. However, it is not known whether the two receptors interact in order to mediate cutaneous vasodilatation and eccrine sweating. In 10 young men (27 ± 6 years old), cutaneous vascular conductance and sweat rate were evaluated at intradermal microdialysis sites that were continuously perfused with either lactated Ringer's solution (control) or three different concentrations of nicotine (0.1, 1 and 10 mm), a nicotinic receptor agonist. Co-administration of methacholine, a muscarinic receptor agonist, was performed at all skin sites in a dose-proportional fashion (0.0125, 0.25, 5, 100 and 2000 mm, each for 25 min). Administration of nicotine alone caused dose-dependent transient increases in cutaneous vascular conductance and sweat rate (all P ࣘ 0.05), which thereafter returned to pre-nicotine levels, except that a portion of transient responses remained with continuous administration of 10 mm nicotine (both P ࣘ 0.05). Cutaneous vascular conductance was increased by administration of ࣙ0.25 mm methacholine at the control site, and this response was likewise observed in the presence of co-administration of all doses of nicotine used (all P ࣘ 0.05). Sweat rate at the control site was increased by administration of ࣙ0.25 mm methacholine, but the lowest dose of methacholine (0.0125 mm) was able to increase sweat rate in the presence of 10 mm nicotine (P ࣘ 0.05). We conclude that nicotinic receptor activation lowers the muscarinic

What is the central question of this study? Protease-activated receptor 2 (PAR2) is located in the endothelial cells of skin vessels and eccrine sweat glands. However, a functional role of PAR2 in the control of cutaneous blood flow and sweating remains to be assessed in humans in vivo. What is the main finding and its importance? Our results demonstrate that in normothermic resting humans in vivo, activation of PAR2 elicits cutaneous vasodilatation partly through nitric oxide synthase-dependent mechanisms, but does not mediate sweating. These results provide important new insights into the physiological significance of PAR2 in human skin. Protease-activated receptor 2 (PAR2) is present in human skin, including keratinocytes, endothelial cells of skin microvessels and eccrine sweat glands. However, whether PAR2 contributes functionally to the regulation of cutaneous blood flow and sweating remains entirely unclear in humans in vivo. We hypothesized that activation of PAR2 directly stimulates cutaneous vasodilatation and sweating via actions of nitric oxide synthase (NOS) and cyclo-oxygenase (COX). In 12 physically active young men (29 ± 5 years old), cutaneous vascular conductance (CVC) and sweat rate were measured at four intradermal microdialysis forearm skin sites that were treated with the following: (i) lactated Ringer's solution (control); (ii) 10 mm N -nitro-l-arginine (NOS inhibitor); (iii) 10 mm ketorolac (COX inhibitor); or (iv) a combination of both inhibitors. At all sites, a PAR2 agonist (SLIGKV-NH ) was co-administered in a dose-dependent fashion (0.06, 0.18, 0.55, 1.66 and 5 mm, each for 25 min). The highest dose of SLIGKV-NH (5 mm) increased CVC from baseline at the control site (P ≤ 0.05). This increase in CVC associated with PAR2 activation was attenuated by NOS inhibition regardless of the presence or absence of simultaneous COX inhibition (both P ≤ 0.05). However, COX inhibition alone did not affect the PAR2-mediated increase in CVC (P > 0.05). No increase in sweat rate was measured at any administered dose of SLIGKV-NH (all P > 0.05). We show that in normothermic resting humans in vivo, PAR2 activation does not increase sweat rate, whereas it does modulate cutaneous vasodilatation through NOS-dependent mechanisms.

The present study evaluated whether type 2 diabetes (T2D) attenuates muscarinic and/or nicotinic cutaneous vasodilatation and sweating as well as purinergic cutaneous vasodilatation. Cutaneous vascular conductance and sweat rate were evaluated in 12 healthy non-diabetic older adults (Control, 60 ± 8 years) and 13 older adults with T2D (62 ± 10 years) at three intradermal forearm skin sites perfused with the following: (i) methacholine (muscarinic receptor agonist, five doses: 0.0125, 0.25, 5, 100 and 2000 mm); (ii) nicotine (nicotinic receptor agonist, five doses: 1.2, 3.6, 11, 33 and 100 mm); or (iii) ATP (purinergic receptor agonist, five doses: 0.03, 0.3, 3, 30 and 300 mm). Each agonist was administered for 25 min per dose. At the end of the protocol, 50 mm sodium nitroprusside was administered to all skin sites to elicit maximal cutaneous vasodilatation. Cutaneous vascular conductance during methacholine and nicotine administration did not differ between groups (all P > 0.05). In contrast, cutaneous vascular conductance during administration of 30 mm (42 ± 28 versus 63 ± 26% maximum, P ≤ 0.05) and 300 mm ATP (56 ± 24 versus 71 ± 20% maximum, P ≤ 0.05) was attenuated in individuals with T2D in comparison to the Control participants. Furthermore, cutaneous vascular conductance during administration of 50 mm sodium nitroprusside was lower in individuals with T2D relative to Control subjects (P = 0.04). Methacholine- and nicotine-induced sweating was similar between groups (all P > 0.05). Thus, T2D attenuates purinergic cutaneous vasodilatation without affecting muscarinic and nicotinic cutaneous vascular and sweating responses.