scholarly journals Geldanamycin attenuates NO-mediated dilation in human skin

2002 ◽  
Vol 282 (1) ◽  
pp. H232-H236 ◽  
Author(s):  
Shubha Shastry ◽  
Michael J. Joyner
Keyword(s):  
Human Skin ◽  
Potential Role ◽  
Local Heating ◽  
Specific Inhibitor ◽  
Heat Shock Protein 90 ◽  
No Synthase ◽  
Vascular Conductance ◽  
Endothelial Nitric Oxide ◽  
Cutaneous Vascular Conductance ◽  
Cutaneous Blood

The binding of heat shock protein 90 (HSP90) to endothelial nitric oxide (NO) synthase (eNOS) can enhance eNOS activation. Studies have shown that the HSP90-specific inhibitor geldanamycin (GA) can cause attenuation of NO-mediated processes. Twenty subjects participated in one of two protocols. In each protocol, one forearm of each subject was instrumented with two intradermal microdialysis probes for drug delivery. Laser Doppler flowmeters were used to measure cutaneous blood flow. Skin sites were either treated with the endothelial agonist acetylcholine or locally heated to 42°C, a maneuver that evokes NO-mediated dilation. Interventions were performed with and without GA. In the presence of GA, maximal cutaneous vascular conductance (CVC) to ACh was 20 ± 3% lower than with ACh alone ( P < 0.001). During local heating, maximal CVC in the presence of GA was 22 ± 6% lower than during heating alone ( P < 0.01). The results show that GA can attenuate NO-mediated dilation in human skin, suggesting a potential role for HSP90 in activation of eNOS in the microcirculation.

Acetylcholine-induced vasodilation is mediated by nitric oxide and prostaglandins in human skin

2005 ◽  
Vol 98 (2) ◽  
pp. 629-632 ◽  
Author(s):  
D. L. Kellogg ◽  
J. L. Zhao ◽  
U. Coey ◽  
J. V. Green
Keyword(s):  
Nitric Oxide ◽  
Human Skin ◽  
Control Site ◽  
Relative Increase ◽  
No Synthase ◽  
Vascular Conductance ◽  
Doppler Flowmetry ◽  
Endothelial Nitric Oxide ◽  
Cutaneous Vascular Conductance ◽  
Cutaneous Blood

Acetylcholine (ACh) can effect vasodilation by several mechanisms, including activation of endothelial nitric oxide (NO) synthase and prostaglandin (PG) production. In human skin, exogenous ACh increases both skin blood flow (SkBF) and bioavailable NO levels, but the relative increase is much greater in SkBF than NO. This led us to speculate ACh may dilate cutaneous blood vessels through PGs, as well as NO. To test this hypothesis, we performed a study in 11 healthy people. We measured SkBF by laser-Doppler flowmetry (LDF) at four skin sites instrumented for intradermal microdialysis. One site was treated with ketorolac (Keto), a nonselective cyclooxygenase antagonist. A second site was treated with NG-nitro-l-arginine methyl ester (l-NAME) to inhibit NO synthase. A third site was treated with a combination of Keto and l-NAME. The fourth site was an untreated control site. After the three treated sites received the different inhibiting agents, ACh was administered to all four sites by intradermal microdialysis. Finally, sodium nitroprusside (SNP) was administered to all four sites. Mean arterial pressure (MAP) was monitored by Finapres, and cutaneous vascular conductance (CVC) was calculated (CVC = LDF/MAP). For data analysis, CVC values for each site were normalized to their respective maxima as effected by SNP. The results showed that both Keto and l-NAME each attenuated the vasodilation induced by exogenous ACh (ACh control = 79 ± 4% maximal CVC, Keto = 55 ± 7% maximal CVC, l-NAME = 46 ± 6% maximal CVC; P < 0.05, ACh vs. Keto or l-NAME). The combination of the two agents produced an even greater attenuation of ACh-induced vasodilation (31 ± 5% maximal CVC; P < 0.05 vs. all other sites). We conclude that a portion of the vasodilation effected by exogenous ACh in skin is due to NO; however, a significant portion is also mediated by PGs.

scholarly journals Tetrahydrobiopterin increases NO-dependent vasodilation in hypercholesterolemic human skin through eNOS-coupling mechanisms

2013 ◽  
Vol 304 (2) ◽  
pp. R164-R169 ◽  
Author(s):  
Lacy M. Alexander ◽  
Jessica L. Kutz ◽  
W. Larry Kenney
Keyword(s):  
Human Skin ◽  
Local Heating ◽  
Antioxidant Properties ◽  
Local Heat ◽  
Control Site ◽  
No Synthase ◽  
Endothelial Nitric Oxide ◽  
Coupling Mechanisms ◽  
Cutaneous Vascular Conductance ◽  
Antioxidant Effects

Localized exogenous R-tetrahydrobiopterin (R-BH4) corrects the deficit in local heat-induced vasodilation (VD) in hypercholesterolemic (HC) human skin through one of two plausible mechanisms: by serving as an essential cofactor to stabilizing endothelial nitric oxide (NO) synthase (eNOS) or through generalized antioxidant effects. We used the stereoisomer S-BH4, which has the same antioxidant properties but does not function as an essential NOS cofactor, to elucidate the mechanism by which R-BH4 restores cutaneous VD in HC humans. Intradermal microdialysis fibers were placed in 20 normocholesterolemic (NC), 13 midrange cholesterolemic (MC), and 18 HC (LDL: 94 ± 3, 124 ± 3 and 179 ± 6 mg/dl, respectively) men and women to perfuse Ringer (control site) and R-BH4. In 10 NC, 13 MC, and 9 HC subjects (LDL: 94 ± 3, 124 ± 3, 180 ± 10 mg/dl), S-BH4 was perfused at a third microdialysis site. Skin blood flow was measured during a standardized local heating protocol to elicit eNOS-dependent VD. After cutaneous vascular conductance (CVC = LDF/MAP) plateaued, NO-dependent VD was quantified by perfusing NG-nitro-l-arginine methyl ester (l-NAME). Data were normalized as %CVCmax. Fully expressed VD (NC: 97.9 ± 2.3 vs. MC: 85.4 ± 5.4, HC: 79.9 ± 4.2%CVCmax) and the NO-dependent portion (NC: 62.1 ± 3 vs. MC: 45.8 ± 3.9, HC: 35.7 ± 2.8%CVCmax) were reduced in HC (both P < 0.01 vs. NC), but only the fully expressed VD was reduced in MC ( P < 0.01 vs. NC). R-BH4 increased the fully expressed (93.9 ± 3.4%CVCmax; P < 0.01) and NO-dependent VD (52.1 ± 5.1%CVCmax; P < 0.01) in HC but not in NC or MC. S-BH4 increased full-expressed VD in HC ( P < 0.01) but did not affect NO-dependent VD in HC or MC. In contrast S-BH4 attenuated NO-dependent VD in NC (control: 62.1 ± 3 vs. S-BH4: 41.6 ± 7%CVCmax; P < 0.001). Exogenous R-BH4 restores NO-dependent VD in HC human skin predominantly through NOS coupling mechanisms but increases full expression of the local heating response through generalized antioxidant properties.

scholarly journals New approach to measure cutaneous microvascular function: an improved test of NO-mediated vasodilation by thermal hyperemia

2014 ◽  
Vol 117 (3) ◽  
pp. 277-283 ◽  
Author(s):  
Patricia J. Choi ◽  
Vienna E. Brunt ◽  
Naoto Fujii ◽  
Christopher T. Minson
Keyword(s):  
Healthy Subjects ◽  
Rapid Heating ◽  
Local Heating ◽  
Ringer Solution ◽  
No Synthase ◽  
Microvascular Function ◽  
Vascular Conductance ◽  
New Approach ◽  
Cutaneous Vascular Conductance

Cutaneous hyperemia in response to rapid skin local heating to 42°C has been used extensively to assess microvascular function. However, the response is dependent on both nitric oxide (NO) and endothelial-derived hyperpolarizing factors (EDHFs), and increases cutaneous vascular conductance (CVC) to ∼90–95% maximum in healthy subjects, preventing the study of potential means to improve cutaneous function. We sought to identify an improved protocol for isolating NO-dependent dilation. We compared nine heating protocols (combinations of three target temperatures: 36°C, 39°C, and 42°C, and three rates of heating: 0.1°C/s, 0.1°C/10 s, 0.1°C/min) in order to select two protocols to study in more depth ( protocol 1; N = 6). Then, CVC was measured at four microdialysis sites receiving: 1) lactated Ringer solution (Control), 2) 50-mM tetraethylammonium (TEA) to inhibit EDHFs, 3) 20-mM nitro-L-arginine methyl ester (L-NAME) to inhibit NO synthase, and 4) TEA+L-NAME, in response to local heating either to 39°C at 0.1°C/s ( protocol 2; N = 10) or 42°C at 0.1°C/min ( protocol 3; N = 8). Rapid heating to 39°C increased CVC to 43.1 ± 5.2%CVCmax (Control), which was attenuated by L-NAME (11.4 ± 2.8%CVCmax; P < 0.001) such that 82.8 ± 4.2% of the plateau was attributable to NO. During gradual heating, 81.5 ± 3.3% of vasodilation was attributable to NO at 40°C, but at 42°C only 32.7 ± 7.8% of vasodilation was attributable to NO. TEA+L-NAME attenuated CVC beyond L-NAME at temperatures >40°C (43.4 ± 4.5%CVCmax at 42°C, P < 0.001 vs. L-NAME), suggesting a role of EDHFs at higher temperatures. Our findings suggest local heating to 39°C offers an improved approach for isolating NO-dependent dilation and/or assessing perturbations that may improve microvascular function.

Effects of nitric oxide synthase inhibition on cutaneous vasodilation during body heating in humans

1998 ◽  
Vol 85 (3) ◽  
pp. 830-834 ◽  
Author(s):  
Shubha Shastry ◽  
Niki M. Dietz ◽  
John R. Halliwill ◽  
Ann S. Reed ◽  
Michael J. Joyner
Keyword(s):  
Nitric Oxide ◽  
Potential Role ◽  
Contralateral Side ◽  
Laser Doppler ◽  
Cutaneous Vasodilation ◽  
Synthase Inhibitor ◽  
Oxide Synthase ◽  
Cutaneous Vascular Conductance ◽  
Cutaneous Blood

We sought to examine further the potential role of nitric oxide (NO) in the neurally mediated cutaneous vasodilation in nonacral skin during body heating in humans. Six subjects were heated with a water-perfused suit while cutaneous blood flow was measured by using laser-Doppler flowmeters placed on both forearms. The NO synthase inhibitor N G-monomethyl-l-arginine (l-NMMA) was given selectively to one forearm via a brachial artery catheter after marked cutaneous vasodilation had been established. During body heating, oral temperature increased by 1.1 ± 0.1°C while heart rate increased by 30 ± 6 beats/min. Mean arterial pressure stayed constant at 84 ± 2 mmHg. In the experimental forearm, cutaneous vascular conductance (CVC; laser-Doppler) decreased to 86 ± 5% of the peak response to heating ( P < 0.05 vs. pre-l-NMMA values) afterl-NMMA infusion. In some subjects, l-NMMA caused CVC to fall by ∼30%; in others, it had little impact on the cutaneous circulation. CVC in the control arm showed a similar increase with heating, then stayed constant whilel-NMMA was given to the contralateral side. These results demonstrate that NO contributes modestly, but not consistently, to cutaneous vasodilation during body heating in humans. They also indicate that NO is not the only factor responsible for the dilation.

Effects of chronic sympathectomy on locally mediated cutaneous vasodilation in humans

2002 ◽  
Vol 92 (2) ◽  
pp. 685-690 ◽  
Author(s):  
Nisha Charkoudian ◽  
John H. Eisenach ◽  
John L. D. Atkinson ◽  
Robert D. Fealey ◽  
Michael J. Joyner
Keyword(s):  
Nitric Oxide ◽  
Human Skin ◽  
Lower Body Negative Pressure ◽  
Local Heating ◽  
Sympathetic Innervation ◽  
Sensory Nerve ◽  
Laser Doppler ◽  
Sympathetic Denervation ◽  
Vascular Conductance ◽  
Local Warming

In human skin, the vasodilator response to local heating includes a sensory nerve-dependent peak followed by a nadir and then a slower, nitric oxide-mediated, endothelium-dependent vasodilation. To investigate whether chronic sympathectomy diminishes this endothelium-dependent vasodilation, we studied individuals who had previously undergone surgical T2 sympathectomy ( n = 9) and a group of healthy controls ( n = 8). We assessed the cutaneous vascular response (laser-Doppler) to 30 min of local warming to 42.5°C on the ventral forearm (no sympathetic innervation) and the lower legs (sympathetic nerves intact). Lower body negative pressure (LBNP) was measured to confirm sympathetic denervation. During local warming in sympathectomized individuals, vascular conductance reached an initial peak at both sites [achieving 1.73 ± 0.22 laser-Doppler units (LDU)/mmHg in the forearm and 1.92 ± 0.21 LDU/mmHg in the leg]. It then decreased to a nadir in the innervated leg [to 1.77 ± 0.23 LDU/mmHg ( P < 0.05)] but not in the sympathectomized arm (1.69 ± 0.21 LDU/mmHg; P > 0.10). The maximal vasodilation seen during the slower phase was not different between limbs or between groups. Furthermore, LBNP caused a 44% reduction in forearm vascular conductance (FVC) in control subjects, but FVC did not decrease significantly in sympathectomized individuals, confirming sympathetic denervation. These data indicate that endothelial function in human skin is largely preserved after sympathectomy. The altered pattern of the response suggests that the nitric oxide-dependent portion may be accelerated in sympathectomized limbs.

Local ascorbate administration augments NO- and non-NO-dependent reflex cutaneous vasodilation in hypertensive humans

2007 ◽  
Vol 293 (2) ◽  
pp. H1090-H1096 ◽  
Author(s):  
Lacy A. Holowatz ◽  
W. Larry Kenney
Keyword(s):  
Local Heating ◽  
Oxidant Stress ◽  
Control Site ◽  
No Synthase ◽  
Oral Temperature ◽  
Antioxidant Supplementation ◽  
Doppler Flowmetry ◽  
Cutaneous Vasodilation ◽  
Reflex Cutaneous Vasodilation ◽  
Cutaneous Vascular Conductance

Full expression of reflex cutaneous vasodilation (VD) is dependent on nitric oxide (NO) and is attenuated with essential hypertension. Decreased NO-dependent VD may be due to 1) increased oxidant stress and/or 2) decreased l-arginine availability through upregulated arginase activity, potentially leading to increased superoxide production through uncoupled NO synthase (NOS). The purpose of this study was to determine the effect of antioxidant supplementation (alone and combined with arginase inhibition) on attenuated NO-dependent reflex cutaneous VD in hypertensive subjects. Nine unmedicated hypertensive [HT; mean arterial pressure (MAP) = 112 ± 1 mmHg] and nine age-matched normotensive (NT; MAP = 81 ± 10 mmHg) men and women were instrumented with four intradermal microdialysis (MD) fibers: control (Ringer), NOS inhibited (NOS-I; 10 mM NG-nitro-l-arginine), l-ascorbate supplemented (Asc; 10 mM l-ascorbate), and Asc + arginase inhibited [Asc+A-I; 10 mM l-ascorbate + 5 mM ( S)-(2-boronoethyl)-l-cysteine-HCl + 5 mM Nω-hydroxy- nor-l-arginine]. Oral temperature was increased by 0.8°C via a water-perfused suit. NG-nitro-l-arginine was then ultimately perfused through all MD sites to quantify the change in VD due to NO. Red blood cell flux was measured by laser-Doppler flowmetry over each skin MD site, and cutaneous vascular conductance (CVC) was calculated (CVC = flux/MAP) and normalized to maximal CVC (%CVCmax; 28 mM sodium nitroprusside + local heating to 43°C). During the plateau in skin blood flow (ΔTor = 0.8°C), cutaneous VD was attenuated in HT skin (NT: 42 ± 4, HT: 35 ± 3 %CVCmax; P < 0.05). Asc and Asc+A-I augmented cutaneous VD in HT (Asc: 57 ± 5, Asc+A-I: 53 ± 6 %CVCmax; P < 0.05 vs. control) but not in NT. %CVCmax after NOS-I in the Asc- and Asc+A-I-treated sites was increased in HT (Asc: 41 ± 4, Asc+A-I: 40 ± 4, control: 29 ± 4; P < 0.05). Compared with the control site, the change in %CVCmax within each site after NOS-I was greater in HT (Asc: −19 ± 4, Asc+A-I: −17 ± 4, control: −9 ± 2; P < 0.05) than in NT. Antioxidant supplementation alone or combined with arginase inhibition augments attenuated reflex cutaneous VD in hypertensive skin through NO- and non-NO-dependent mechanisms.

scholarly journals Nitric oxide and cutaneous active vasodilation during heat stress in humans

1998 ◽  
Vol 85 (3) ◽  
pp. 824-829 ◽  
Author(s):  
D. L. Kellogg ◽  
C. G. Crandall ◽  
Y. Liu ◽  
N. Charkoudian ◽  
J. M. Johnson
Keyword(s):  
Nitric Oxide ◽  
Heat Stress ◽  
Laser Doppler Flowmetry ◽  
Sweat Rate ◽  
Ringer Solution ◽  
No Synthase ◽  
Laser Doppler ◽  
Vascular Conductance ◽  
Doppler Flowmetry ◽  
Cutaneous Vascular Conductance

Whether nitric oxide (NO) is involved in cutaneous active vasodilation during hyperthermia in humans is unclear. We tested for a role of NO in this process during heat stress (water-perfused suits) in seven healthy subjects. Two forearm sites were instrumented with intradermal microdialysis probes. One site was perfused with the NO synthase inhibitor N G-nitro-l-arginine methyl ester (l-NAME) dissolved in Ringer solution to abolish NO production. The other site was perfused with Ringer solution only. At those sites, skin blood flow (laser-Doppler flowmetry) and sweat rate were simultaneously and continuously monitored. Cutaneous vascular conductance, calculated from laser-Doppler flowmetry and mean arterial pressure, was normalized to maximal levels as achieved by perfusion with the NO donor nitroprusside through the microdialysis probes. Under normothermic conditions,l-NAME did not significantly reduce cutaneous vascular conductance. During hyperthermia, with skin temperature held at 38–38.5°C, internal temperature rose from 36.66 ± 0.10 to 37.34 ± 0.06°C ( P < 0.01). Cutaneous vascular conductance at untreated sites increased from 12 ± 2 to 44 ± 5% of maximum, but only rose from 13 ± 2 to 30 ± 5% of maximum at l-NAME-treated sites ( P < 0.05 between sites) during heat stress. l-NAME had no effect on sweat rate ( P > 0.05). Thus cutaneous active vasodilation requires functional NO synthase to achieve full expression.

scholarly journals Sex differences in the mechanisms mediating blunted cutaneous microvascular function in young black men and women

2018 ◽  
Vol 315 (4) ◽  
pp. H1063-H1071 ◽  
Author(s):  
Jordan C. Patik ◽  
Bryon M. Curtis ◽  
Aida Nasirian ◽  
Jennifer R. Vranish ◽  
Paul J. Fadel ◽  
...  
Keyword(s):  
Sex Differences ◽  
Black Women ◽  
Black Men ◽  
Local Heating ◽  
Black Population ◽  
Control Site ◽  
Microvascular Function ◽  
Vascular Conductance ◽  
Men And Women ◽  
Cutaneous Vascular Conductance

The black population exhibits attenuated vasodilatory function across their lifespan, yet little is known regarding the mechanisms of this impairment. Recent evidence suggests a potential role for oxidative stress. Therefore, we tested the hypothesis that NADPH oxidase (NOX) and/or xanthine oxidase (XO) contribute to blunted nitric oxide (NO)-mediated cutaneous microvascular function in young black adults. In 30 white and black subjects (8 men and 7 women in each group), local heating was performed while NOX and XO were inhibited by apocynin and allopurinol, respectively, via intradermal microdialysis. The plateau in cutaneous vascular conductance (red blood cell flux/mean arterial pressure) during 39°C local heating at each site was compared with a control site perfused with lactated Ringer solution. Subsequent inhibition of NO synthase via Nω-nitro-l-arginine methyl ester allowed for quantification of the NO contribution to vasodilation during heating. Black individuals, relative to white individuals, had a blunted cutaneous vascular conductance plateau at the control site (45 ± 9 vs. 68 ± 13%max, P < 0.001) that was increased by both apocynin (61 ± 15%max, P < 0.001) and allopurinol (58 ± 17%max, P = 0.005). Black men and black women had similar responses to heating at the control site ( P = 0.99), yet apocynin and allopurinol increased this response only in black men (both P < 0.001 vs. control). The NO contribution was also increased via apocynin and allopurinol exclusively in black men. These findings suggest that cutaneous microvascular function is reduced because of NOX and XO activity in black men but not black women, identifying a novel sex difference in the mechanisms that contribute to blunted vascular responses in the black population. NEW & NOTEWORTHY We demonstrate that cutaneous microvascular responses to local heating are consistently reduced in otherwise healthy young black men and women relative to their white counterparts. Inhibition of NADPH oxidase and xanthine oxidase via apocynin and allopurinol, respectively, augments microvascular function in black men but not black women. These data reveal clear sex differences in the mechanisms underlying the racial disparity in cutaneous microvascular function.

Oral vitamin C enhances the adrenergic vasoconstrictor response to local cooling in human skin

2012 ◽  
Vol 112 (10) ◽  
pp. 1689-1697 ◽  
Author(s):  
Fumio Yamazaki
Keyword(s):  
Human Skin ◽  
Local Administration ◽  
Adrenergic System ◽  
Local Cooling ◽  
Oral Vitamin ◽  
Vascular Conductance ◽  
Doppler Flowmetry ◽  
Vasoconstrictor Response ◽  
Forearm Skin ◽  
Cutaneous Vascular Conductance

Local administration of ascorbic acid (Asc) at a supraphysiological concentration inhibits the cutaneous vasoconstrictor response to local cooling (LC). However, whether orally ingesting Asc inhibits the LC-induced vasoconstrictor response remains unknown. The purpose of the present study was to examine the acute influence of oral Asc on the adrenergic vasoconstrictor response to LC in human skin. In experiment 1, skin blood flow (SkBF) was measured by laser-Doppler flowmetry at three sites (forearm, calf, palm). The three skin sites were locally cooled from 34 to 24°C at −1°C/min and maintained at 24°C for 20 min before (Pre) and 1.5 h after (Post) oral Asc (2-g single dose) or placebo supplementation. Cutaneous vascular conductance (CVC) was calculated as the ratio of SkBF to blood pressure and expressed relative to the baseline value before LC. Oral Asc enhanced ( P < 0.05) the reductions in CVC in the forearm (Pre, −50.3 ± 3.3%; Post, −57.8 ± 2.2%), calf (Pre, −52.6 ± 3.7%; Post, −66.1 ± 4.3%), and palm (Pre, −46.2 ± 6.2%; Post, −60.4 ± 5.6%) during LC. The placebo did not change the responses at any site. In experiment 2, to examine whether the increased vasoconstrictor response caused by oral Asc is due to the adrenergic system, the release of neurotransmitters from adrenergic nerves in forearm skin was blocked locally by iontophoresis of bretylium tosylate (BT). Oral Asc enhanced ( P < 0.05) the reductions in CVC at untreated control sites but did not change the responses at BT-treated sites during LC. In experiment 3, to further examine whether adrenergically mediated vasoconstriction is enhanced by oral Asc, 0.1 mM tyramine was administered using intradermal microdialysis in the forearm skin at 34°C in the Pre and Post periods. Oral Asc increased ( P < 0.05) the tyramine-induced reduction in CVC. These findings suggest that oral Asc acutely enhances the cutaneous vasoconstrictor responses to LC through the modification of adrenergic sympathetic mechanisms.

scholarly journals Effects of atropine and l-NAME on cutaneous blood flow during body heating in humans

2000 ◽  
Vol 88 (2) ◽  
pp. 467-472 ◽  
Author(s):  
Shubha Shastry ◽  
Christopher T. Minson ◽  
Shurea A. Wilson ◽  
Niki M. Dietz ◽  
Michael J. Joyner
Keyword(s):  
Blood Flow ◽  
Receptor Activation ◽  
No Synthase ◽  
Cutaneous Blood Flow ◽  
Cutaneous Vasodilation ◽  
Forearm Skin ◽  
Synthase Inhibitor ◽  
Cutaneous Vascular Conductance ◽  
Cutaneous Blood ◽  
Doppler Flowmeter

We sought to investigate further the roles of sweating, ACh spillover, and nitric oxide (NO) in the neurally mediated cutaneous vasodilation during body heating in humans. Six subjects were heated with a water-perfused suit while cutaneous blood flow was measured with a laser-Doppler flowmeter. After a rise in core temperature (1.0 ± 0.1°C) and the establishment of cutaneous vasodilation, atropine and subsequently the NO synthase inhibitor N G-nitro-l-arginine methyl ester (l-NAME) were given to the forearm via a brachial artery catheter. After atropine infusion, cutaneous vascular conductance (CVC) remained constant in five of six subjects, whereasl-NAME administration blunted the rise in CVC in three of six subjects. A subsequent set of studies using intradermal microdialysis probes to selectively deliver drugs into forearm skin confirmed that atropine did not affect CVC. However, perfusion ofl-NAME resulted in a significant decrease in CVC (37 ± 4%, P < 0.05). The results indicate that neither sweating nor NO release via muscarinic receptor activation is essential to sustain cutaneous dilation during heating in humans.

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