Antagonism of soluble guanylyl cyclase attenuates cutaneous vasodilation during whole body heat stress and local warming in humans

A natural heme deficiency exists in biology that allows nitric oxide to control heme protein functions by regulating cellular heme distribution

A natural heme deficiency that exists in cells outside of the circulation broadly compromises the heme contents and functions of heme proteins in cells and tissues. Recently, we found that the signaling molecule, nitric oxide (NO), can trigger or repress the deployment of intracellular heme in a concentration-dependent hormetic manner. This uncovers a new role for NO and sets the stage for it to shape numerous biological processes by controlling heme deployment and consequent heme protein functions in biology.

Skin Microhemodynamics and Mechanisms of Its Regulation in Type 2 Diabetes Mellitus

The review presents modern ideas about peripheral microhemodynamics, approaches to the ana-lysis of skin blood flow oscillations and their diagnostic significance. Disorders of skin microhemodynamics in type 2 diabetes mellitus (DM) and the possibility of their interpretation from the standpoint of external and internal interactions between systems of skin blood flow regulation, based on a comparison of couplings in normal and pathological conditions, including models of pathologies on animals, are considered. The factors and mechanisms of vasomotor regulation, among them receptors and signaling events in endothelial and smooth muscle cells considered as models of microvessels are discussed. Attention was drawn to the disturbance of Ca2+-dependent regulation of coupling between vascular cells and NO-dependent regulation of vasodilation in diabetes mellitus. The main mechanisms of insulin resistance in type 2 DM are considered to be a defect in the number of insulin receptors and impaired signal transduction from the receptor to phosphatidylinositol-3-kinase and downstream targets. Reactive oxygen species plays an important role in vascular dysfunction in hyperglycemia. It is assumed that the considered molecular and cellular mechanisms of microhemodynamics regulation are involved in the formation of skin blood flow oscillations. Parameters of skin blood microcirculation can be used as diagnostic and prognostic markers for assessing the state of the body.

TRPA1 channel activation with cinnamaldehyde induces cutaneous vasodilation through NOS, but not COX and KCa channel, mechanisms in humans

ABSTRACT

Transient receptor potential ankyrin 1 (TRPA1) channel activation induces cutaneous vasodilation in humans in vivo. However, the mechanisms underlying this response remains equivocal. We hypothesized that nitric oxide (NO) synthase (NOS) and Ca2+ activated K+ (KCa) channels contribute to the TRPA1 channel-induced cutaneous vasodilation with no involvement of cyclooxygenase (COX). Cutaneous vascular conductance (CVC) in 9 healthy young adults was assessed at four dorsal forearm skin sites treated by intradermal microdialysis with either: 1) vehicle control (98% propylene glycol + 1.985% dimethyl sulfoxide + 0.015% lactated Ringer solution), 2) 10 mM L-NAME, a non-selective NOS inhibitor, 3) 10 mM ketorolac, a non-selective COX inhibitor, or 4) 50 mM tetraethylammonium, a non-selective KCa channel blocker. Cinnamaldehyde, a TRPA1 channel activator, was administered to each skin site in a dose-dependent manner (2.9, 8.8, 26 and 80 %, each lasting ≥30min). Administration of ≥8.8% cinnamaldehyde increased CVC from baseline at the vehicle control site by as much as 27.4% [95 % confidence interval of 5.3] (P<0.001). NOS inhibitor attenuated the cinnamaldehyde induced-increases in CVC at the 8.8, 26.0, and 80.0% concentrations relative to the vehicle control site (all P≤0.05). In contrast, both the COX inhibitor and KCa channel blockers did not attenuate the cinnamaldehyde induced-increases in CVC relative to the vehicle control site for all concentrations (all P≥0.130). We conclude that in human skin in vivo, NOS plays a role in modulating the regulation of cutaneous vasodilation in response to TRPA1 channel activation with no detectable contributions of COX and KCa channels.

Inhibition of iNOS augments cutaneous endothelial NO-dependent vasodilation in prehypertensive non-Hispanic Whites and in non-Hispanic Blacks

We tested the hypothesis that inducible nitric oxide synthase (iNOS) contributes to reduced nitric oxide (NO)-dependent vasodilation in non-Hispanic Blacks and prehypertensive non-Hispanic Whites. Twenty Black and twenty White participants (10 normotensive, 10 prehypertensive per group; n = 40 total) participated in this study. Participants were instrumented with two microdialysis fibers, and each site was randomized as control (lactated Ringer) or iNOS inhibition (0.1 mM 1400W). Laser-Doppler flow probes and local heaters were used to measure skin blood flow and heat the skin to induce vasodilation, respectively. Each site was heated from 33°C to 39°C (rate: 0.1°C/s). Once a plateau was established, 20 mM nitro-l-arginine methyl ester (l-NAME), a nonspecific NOS inhibitor, was infused at each site to quantify NO-dependent vasodilation. At control sites, %NO-dependent vasodilation was reduced in prehypertensive Whites (47 ± 10%NO) and in both normotensive and prehypertensive Blacks (39 ± 9%NO and 28 ± 5%NO, respectively) relative to normotensive Whites (73 ± 8%NO; P < 0.0001 for all comparisons). Compared with respective control sites, iNOS inhibition increased NO-dependent vasodilation in prehypertensive Whites (68 ± 8%NO) and in both normotensive and prehypertensive Blacks (78 ± 8%NO and 55 ± 6%NO, respectively; P < 0.0001 for all comparisons). We failed to find an effect for normotensive Whites (77 ± 7%NO). After iNOS inhibition, %NO-dependent vasodilation was similar between normotensive Whites, prehypertensive Whites, and normotensive Blacks. Inhibition of iNOS increased NO-dependent vasodilation to a lesser extent in prehypertensive Blacks. These data suggest that iNOS contributes to reduced NO-dependent vasodilation in prehypertension and in Black participants.NEW & NOTEWORTHY Inducible nitric oxide synthase (iNOS) is typically upregulated in conditions of increased oxidative stress and may have detrimental effects on the vasculature. Endothelial nitric oxide (NO), which is cardioprotective, is reduced in prehypertensive non-Hispanic Whites and in non-Hispanic Blacks. We found that inhibition of iNOS can increase endothelial NO-dependent vasodilation in prehypertensive White participants and in both normotensive and prehypertensive Black participants.Inducible nitric oxide (NO) synthase (iNOS) can be upregulated under conditions of increased oxidative stress and may have detrimental effects on the vasculature. Endothelial NO, which is cardioprotective, is reduced in prehypertensive non-Hispanic Whites and in non-Hispanic Blacks. We found that inhibition of iNOS can increase endothelial NO-dependent vasodilation in prehypertensive White participants and in both normotensive and prehypertensive Black participants.

Sensory nerve-mediated and nitric oxide-dependent cutaneous vasodilation in normotensive and prehypertensive non-Hispanic blacks and whites

The purpose of this study was to investigate the effect of race and subclinical elevations in blood pressure (i.e., prehypertension) on cutaneous sensory nerve-mediated and nitric oxide (NO)-dependent vasodilation. We recruited participants who self-identified as either non-Hispanic black (n = 16) or non-Hispanic white (n = 16). Within each group, participants were subdivided as either normotensive (n = 8 per group) or prehypertensive (n = 8 per group). Each participant was instrumented with four intradermal microdialysis fibers: 1) control (lactated Ringer's), 2) 5% lidocaine (sensory nerve inhibition), 3) 20 mM N^ω-nitro-l-arginine methyl ester (l-NAME) (NO synthase inhibition), and 4) lidocaine + l-NAME. Skin blood flow was assessed via laser-Doppler flowmetry, and each site underwent local heating from 33°C to 39°C. At the plateau, 20 mM l-NAME were infused at control and lidocaine sites to quantify NO-dependent vasodilation. Maximal vasodilation was induced via 54 mM sodium nitroprusside and local heating to 43°C. Data are means ± SD. Sensory nerve-mediated cutaneous vasodilation was reduced in prehypertensive non-Hispanic white (34 ± 7%) and both non-Hispanic black groups (normotensive, 20 ± 9%, prehypertensive, 24 ± 15%) relative to normotensive non-Hispanic whites (54 ± 12%). NO-dependent vasodilation was also reduced in prehypertensive non-Hispanic white (41 ± 7%) and both non-Hispanic black groups (normotensive, 44 ± 7%, prehypertensive, 19 ± 7%) relative to normotensive non-Hispanic whites (60 ± 11%). The decrease in NO-dependent vasodilation in prehypertensive non-Hispanic blacks was further reduced relative to all other groups. These data suggest subclinical increases in blood pressure adversely affect sensory-mediated and NO-dependent vasodilation in both non-Hispanic blacks and whites.NEW & NOTEWORTHY Overt hypertension is known to reduce cutaneous sensory nerve-mediated and nitric oxide (NO)-dependent vasodilation, but the effect of subclinical increases in blood pressure (i.e., prehypertension) is unknown. The combined effect of race and prehypertension is also unknown. In this study, we found that prehypertension reduces cutaneous sensory nerve-mediated and NO-dependent vasodilation in both non-Hispanic white and black populations, with the greatest reductions observed in prehypertensive non-Hispanic blacks.

Intradermal Administration of Atrial Natriuretic Peptide Attenuates Cutaneous Vasodilation but Not Sweating in Young Men during Exercise in the Heat

INTRODUCTION

Prolonged exercise in the heat stimulates plasma release of atrial natriuretic peptide (ANP) in association with dehydration-induced reductions in blood volume. Elevated plasma ANP levels under these conditions may indirectly attenuate cutaneous blood flow and sweating responses due to the effects of this hormone on central blood volume and plasma osmolality and the resulting stimulation of nonthermal reflexes. However, it remains unclear whether cutaneous blood flow and sweating are directly modulated by ANP at the level of the cutaneous end organs (cutaneous microvessels and eccrine sweat glands) during prolonged exercise in the heat.

OBJECTIVE

Therefore, we evaluated the effects of local ANP administration on forearm cutaneous vascular conductance (CVC) and local sweat rate (LSR) during rest and exercise in the heat.

METHODS

In 9 habitually active young men (26 ± 6 years) CVC and LSR were evaluated at 3 intradermal microdialysis sites continuously perfused with lactated Ringer solution (control) or ANP (0.1 or 1.0 μM). Participants rested in a non-heat-stress condition (25°C) for approximately 60 min followed by 70 min in the heat (35°C). They then performed 50 min of moderate-intensity cycling (approx. 55% VO2 peak), with a 30-min recovery. Thereafter, 50 mM sodium nitroprusside was administered at all sites to elicit maximum CVC, which was subsequently used to normalize all values (CVC%max).

RESULTS

No effects of ANP on CVC%max were observed in the non-heat-stress resting condition compared to the untreated control site (both p > 0.05). Conversely during rest in the heat there was an 11% (5-17%) reduction in CVC%max at the 1.0 μM ANP site relative to the untreated control site (p < 0.05). At the end of exercise CVC%max was attenuated by 12% (1-23%) at the 0.1 μM ANP site and by 21% (7-35%) at the 1.0 μM ANP site relative to the untreated control site (all p < 0.05). Conversely, neither concentration of ANP influenced sweating at any time point (all p > 0.05).

CONCLUSION

Intradermal ANP administration directly attenuated cutaneous blood flow, but not sweating, in habitually active young men during rest and exercise in the heat.

Effects of vehicle microdialysis solutions on cutaneous vascular responses to local heating

Microdialysis is a minimally invasive technique often paired with laser Doppler flowmetry to examine cutaneous microvascular function, yet presents with several challenges, including incompatibility with perfusion of highly lipophilic compounds. The present study addresses this methodological concern, with an emphasis on the independent effects of commonly used vehicle dialysis solutions to improve solubility of pharmacological agents with otherwise low aqueous solubility. Four microdialysis fibers were placed in the ventral forearm of eight subjects (4 men, 4 women; 25 ± 1 yr) with sites randomized to serve as 1) control (lactated Ringer's), 2) Sodium carbonate-bicarbonate buffer administered at physiological pH [SCB-HCl; pH 7.4, achieved via addition of hydrochloric acid (HCl)], 3) 0.02% ethanol, and 4) 2% dimethyl sulfoxide (DMSO). After baseline (34°C), vehicle solutions were administered throughout a standardized local heating protocol to 42°C. Laser Doppler flowmetry provided an index of blood flow. Cutaneous vascular conductance was calculated and normalized to maximum (%CVC_max, sodium nitroprusside and 43°C local heat). The SCB-HCl solution increased baseline %CVC_max (control: 9.7 ± 0.8; SCB-HCl: 21.5 ± 3.5%CVC_max; P = 0.03), but no effects were observed during heating or maximal vasodilation. There were no differences with perfusion of ethanol or DMSO at any stage of the protocol ( P > 0.05). These data demonstrate the potential confounding effects of some vehicle dialysis solutions on cutaneous vascular function. Notably, this study provides evidence that 2% DMSO and 0.02% ethanol are acceptable vehicles with no confounding local vascular effects to a standardized local heating protocol at the concentrations presented. NEW & NOTEWORTHY This study examined the independent effects of common vehicle solutions on cutaneous vascular responses. A basic buffer (SCB-HCl) caused baseline vasodilation; 2% DMSO and 0.02% ethanol had no effects. This highlights the need for considering potential confounding effects of solubilizing solutions when combined with low aqueous soluble pharmacological agents. Importantly, DMSO and ethanol do not appear to influence cutaneous vascular function during baseline or local heating at the concentrations studied, allowing their use without confounding effects.

Nitric oxide synthase and cyclooxygenase modulate β-adrenergic cutaneous vasodilatation and sweating in young men

KEY POINTS

β-Adrenergic receptor agonists such as isoproterenol induce cutaneous vasodilatation and sweating in humans, but the mechanisms underpinning this response remain unresolved. 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. We show that while NOS contributes to β-adrenergic cutaneous vasodilatation, COX restricts cutaneous vasodilatation. We also show that combined inhibition of NOS and COX augments β-adrenergic sweating 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.

The association between diabetes and dermal microvascular dysfunction non-invasively assessed by laser Doppler with local thermal hyperemia: a systematic review with meta-analysis

Background/Introduction

Diabetes and cardiovascular disease develop in concert with metabolic abnormalities mirroring and causing changes in the vasculature, particularly the microcirculation. The microcirculation can be affected in different parts of the body of which the skin is the most easily accessible tissue.

Purpose

The association between diabetes and dermal microvascular dysfunction has been investigated in observational studies. However, the strength of the association is unknown. Therefore we conducted a systematic review with meta-analysis on the association between diabetes and dermal microvascular dysfunction as assessed by laser Doppler/laser speckle contrast imaging with local thermal hyperaemia as non-invasive indicator of microvascular functionality.

Methods

PubMed and Ovid were  systematically searched for eligible studies through March 2015. During the first selection, studies were included if they were performed in humans and were related to diabetes or glucose metabolism disorders and to dermal microcirculation. During the second step we selected studies based on the measurement technique, measurement location (arm or leg) and the inclusion of a healthy control group. A random effects model was used with the standardised mean difference as outcome measure. Calculations and imputation of data were done according to the Cochrane Handbook.

Results

Of the 1445 studies found in the first search, thirteen cross-sectional studies were included in the meta-analysis, comprising a total of 857 subjects. Resting blood flow was similar between healthy control subjects and diabetes patients. In contrast, the microvascular response to local skin heating was reduced in diabetic patients compared to healthy control subjects [pooled effect of −0.78 standardised mean difference (95% CI −1.06, −0.51)]. This effect is considered large according to Cohen’s effect size definition. The variability in effect size was high (heterogeneity 69%, p < 0.0001). However, subgroup analysis revealed no difference between the type and duration of diabetes and other health related factors, indicating that diabetes per se causes the microvascular dysfunction.

Conclusion

Our meta-analysis shows that diabetes is associated with a large reduction of dermal microvascular function in diabetic patients. The local thermal hyperaemia methodology may become a valuable non-invasive tool for diagnosis and assessing progress of diabetes-related microvascular complications, but standardisation of the technique and quality of study conduct is urgently required.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-016-0487-1) contains supplementary material, which is available to authorized users.

Intradermal administration of endothelin-1 attenuates endothelium-dependent and -independent cutaneous vasodilation via Rho kinase in young adults

We recently showed that intradermal administration of endothelin-1 diminished endothelium-dependent and -independent cutaneous vasodilation. We evaluated the hypothesis that Rho kinase may be a mediator of this response. We also sought to evaluate if endothelin-1 increases sweating. In 12 adults (25 ± 6 yr), we measured cutaneous vascular conductance (CVC) and sweating during 1) endothelium-dependent vasodilation induced via administration of incremental doses of methacholine (0.25, 5, 100, and 2,000 mM each for 25 min) and 2) endothelium-independent vasodilation induced via administration of 50 mM sodium nitroprusside (20-25 min). Responses were evaluated at four skin sites treated with either 1) lactated Ringer solution (Control), 2) 400 nM endothelin-1, 3) 3 mM HA-1077 (Rho kinase inhibitor), or 4) endothelin-1+HA-1077. Pharmacological agents were intradermally administered via microdialysis. Relative to the Control site, endothelin-1 attenuated endothelium-dependent vasodilation (CVC at 2,000 mM methacholine, 80 ± 10 vs. 56 ± 15%max, P < 0.01); however, this response was not detected when the Rho kinase inhibitor was simultaneously administered (CVC at 2,000 mM methacholine for Rho kinase inhibitor vs. endothelin-1 + Rho kinase inhibitor sites: 73 ± 9 vs. 72 ± 11%max, P > 0.05). Endothelium-independent vasodilation was attenuated by endothelin-1 compared with the Control site (CVC, 92 ± 13 vs. 70 ± 14%max, P < 0.01). However, in the presence of Rho kinase inhibition, endothelin-1 did not affect endothelium-independent vasodilation (CVC at Rho kinase inhibitor vs. endothelin-1+Rho kinase inhibitor sites: 81 ± 9 vs. 86 ± 10%max, P > 0.05). There was no between-site difference in sweating throughout (P > 0.05). We show that in young adults, Rho kinase is an important mediator of the endothelin-1-mediated attenuation of endothelium-dependent and -independent cutaneous vasodilation, and that endothelin-1 does not increase sweating.

Current concepts of active vasodilation in human skin

In humans, an increase in internal core temperature elicits large increases in skin blood flow and sweating. The increase in skin blood flow serves to transfer heat via convection from the body core to the skin surface while sweating results in evaporative cooling of the skin. Cutaneous vasodilation and sudomotor activity are controlled by a sympathetic cholinergic active vasodilator system that is hypothesized to operate through a co-transmission mechanism. To date, mechanisms of cutaneous active vasodilation remain equivocal despite many years of research by several productive laboratory groups. The purpose of this review is to highlight recent advancements in the field of cutaneous active vasodilation framed in the context of some of the historical findings that laid the groundwork for our current understanding of cutaneous active vasodilation.

Cutaneous blood flow during intradermal NO administration in young and older adults: roles for calcium-activated potassium channels and cyclooxygenase?

Nitric oxide (NO) increases cutaneous blood flow; however, the underpinning mechanism(s) remains to be elucidated. We hypothesized that the cutaneous blood flow response during intradermal administration of sodium nitroprusside (SNP, a NO donor) is regulated by calcium-activated potassium (KCa) channels and cyclooxygenase (COX) in young adults. We also hypothesized that these contributions are diminished in older adults given that aging can downregulate KCa channels and reduce COX-derived vasodilator prostanoids. In 10 young (23 ± 5 yr) and 10 older (54 ± 4 yr) adults, cutaneous vascular conductance (CVC) was measured at four forearm skin sites infused with 1) Ringer (Control), 2) 50 mM tetraethylammonium (TEA), a nonspecific KCa channel blocker, 3) 10 mM ketorolac, a nonspecific COX inhibitor, or 4) 50 mM TEA + 10 mM ketorolac via intradermal microdialysis. All skin sites were coinfused with incremental doses of SNP (0.005, 0.05, 0.5, 5, and 50 mM each for 25 min). During SNP administration, CVC was similar at the ketorolac site (0.005-50 mM, all P > 0.05) relative to Control, but lower at the TEA and TEA + ketorolac sites (0.005-0.05 mM, all P < 0.05) in young adults. In older adults, ketorolac increased CVC relative to Control during 0.005-0.05 mM SNP administration (all P < 0.05), but this increase was not observed when TEA was coadministered (all P > 0.05). Furthermore, TEA alone did not modulate CVC during any concentration of SNP administration in older adults (all P > 0.05). We show that during low-dose NO administration (e.g., 0.005-0.05 mM), KCa channels contribute to cutaneous blood flow regulation in young adults; however, in older adults, COX inhibition increases cutaneous blood flow through a KCa channel-dependent mechanism.

Cutaneous vasodilator and vasoconstrictor mechanisms in temperature regulation

In this review, we focus on significant developments in our understanding of the mechanisms that control the cutaneous vasculature in humans, with emphasis on the literature of the last half-century. To provide a background for subsequent sections, we review methods of measurement and techniques of importance in elucidating control mechanisms for studying skin blood flow. In addition, the anatomy of the skin relevant to its thermoregulatory function is outlined. The mechanisms by which sympathetic nerves mediate cutaneous active vasodilation during whole body heating and cutaneous vasoconstriction during whole body cooling are reviewed, including discussions of mechanisms involving cotransmission, NO, and other effectors. Current concepts for the mechanisms that effect local cutaneous vascular responses to local skin warming and cooling are examined, including the roles of temperature sensitive afferent neurons as well as NO and other mediators. Factors that can modulate control mechanisms of the cutaneous vasculature, such as gender, aging, and clinical conditions, are discussed, as are nonthermoregulatory reflex modifiers of thermoregulatory cutaneous vascular responses.

Hemodynamic responses elicited by systemic injections of isotonic and hypertonic saline in hemorrhaged rats

PURPOSE

The objectives of this study were (i) to characterize the hemodynamic responses caused by controlled hemorrhage (HEM) in pentobarbital-anesthetized rats, and (ii) to determine the responses elicited by systemic bolus injections of isotonic saline (0.15M) or hypertonic saline (3M) given 5min after completion of HEM.

RESULTS

Controlled HEM (4.3±0.2ml/rat at 1.5ml/min) resulted in a pronounced and sustained fall in mean arterial blood pressure (MAP) to about 40mmHg. The fall in MAP was associated with a reduction in hindquarter vascular resistance (HQR) but no changes in renal (RR) or mesenteric (MR) vascular resistances. Systemic injections of isotonic saline (96-212μmol/kg i.v., in 250-550μl) did not produce immediate responses but promoted the recovery of MAP to levels below pre-HEM values. Systemic injections of hypertonic saline (750-3000μmol/kg, i.v., in 250-550μl) produced immediate and pronounced falls in MAP, RR, MR and especially HQR of 30-120s in duration. However, hypertonic saline prompted a full recovery of MAP, HQR and RR to pre-HEM levels and an increase in MR to levels above pre-HEM values.

CONCLUSIONS

This study demonstrates that (i) HEM induced a pronounced fall in MAP which likely involved a fall in cardiac output and HQR, (ii) isotonic saline did not fully normalize MAP, and (iii) hypertonic saline produced dramatic initial responses, and promoted normalization of MAP probably by restoring blood volume and cardiac output through sequestration of fluid from intracellular compartments.

Noradrenaline and neuropeptide Y contribute to initial, but not sustained, vasodilatation in response to local skin warming in humans

NEW FINDINGS

What is the central question of this study? Previous work has produced the counterintuitive finding that the vasoconstrictor neurotransmitters noradrenaline and neuropeptide Y are involved in vasodilatation. We aimed to discover whether sympathetic neurotransmitters are required for the sustained vasodilatation in response to local skin warming, as has been previously suggested, and to determine whether noradrenaline and neuropeptide Y are 'mediating' the sustained vasodilator response directly or acting to 'prime' (or kick-start) it. What is the main finding and its importance? We have found that noradrenaline and neuropeptide Y are required at the initiation of vasodilatation in response to local skin warming, if a complete vasodilator response is to be achieved; however, they are not required once vasodilatation has begun. In a three-part study, we examined whether noradrenaline, neuropeptide Y (NPY) and endothelial nitric oxide synthase (eNOS) were involved in the sustained vasodilatation in response to local skin warming. Forearm skin sites were instrumented with intradermal microdialysis fibres, local skin heaters and laser-Doppler flow probes. Local skin temperature (T(loc)) was increased from 34 to 42°C at a rate of 0.5°C (10 s)(-1). Laser-Doppler flow was expressed as cutaneous vascular conductance (CVC; laser-Doppler flow/mean arterial pressure). In part 1, three skin sites were prepared; two were treated with the study vehicle (lactated Ringer solution), while the third site was treated with yohimbine and propranolol to antagonize α- and β-receptors, and 10 min of baseline data were record at a T(loc) of 34°C. Receptor antagonism was confirmed via infusion of clonidine. The T(loc) was increased to 42°C at all sites. Once CVC had stabilized, site 2 was treated with yohimbine and propranolol to examine the effect of adrenergic receptor blockade on sustained vasodilatation of the skin. Receptor antagonism was again confirmed via infusion of clonidine. All sites were treated with sodium nitroprusside, and T(loc) was increased to 43°C to elicit maximal vasodilatation. In parts 2 and 3, the general protocol was the same, except that BIBP-3226 was used to antagonize Y(1)-receptors, NPY to test the efficacy of the antagonism, N(G)-amino-l-arginine to inhibit eNOS and ACh to test the adequacy of inhibition. Compared with control conditions, antagonism of α- and β-receptors, Y(1)-receptors and eNOS before local skin warming reduced the initial and sustained vasodilatation in response to increased T(loc). However, treatment with yohimbine and propranolol or BIBP-3226 after local skin warming did not affect the sustained vasodilatation [CVC, 90 ± 3 versus 89 ± 3%max (control vs. yohimbine and propranolol) and 88 ± 5 versus 87 ± 4%max (control vs. BIBP-3226); P > 0.05]. N(G)-Amino-l-arginine perfusion caused a large reduction in CVC during this phase (89 ± 5 versus 35 ± 4%max; P < 0.05). These data indicate that if their actions are antagonized after local warming and cutaneous vasodilatation has occurred, noradrenaline and NPY play little, if any, role in the sustained vasodilatation in response to local skin warming. However, eNOS contributes markedly to the sustained vasodilatation regardless of when it is inhibited.

L-NAME iontophoresis: a tool to assess NO-mediated vasoreactivity during thermal hyperemic vasodilation in humans

BACKGROUND

Decreased endothelial Nitric oxide (NO) bioavailability is one of the earliest events of endothelial dysfunction. Assessment of microvascular blood flow using a Laser Doppler Imager during local noninvasive administration of L-N-Arginine-Methyl-Ester (L-NAME) by skin iontophoresis may help discriminate the relative contributions of NO and non-NO pathways during a skin thermal hyperemic test.

METHODS

In healthy nonsmokers, the effects of thermal vasodilation and sodium nitroprusside-mediated vasodilation were tested on skin pretreated with 0.9% saline solution, 2% L-NAME iontophoresis (n = 12), or intradermal injection of 25 nmol L-NAME (n = 10). The effects of L-NAME iontophoresis were also measured in a group of smokers (n = 10).

RESULTS

L-NAME iontophoresis and intradermal injection of L-NAME decreased the skin response to local heating to a similar degree (-41% ± 4% vs. -44% ± 6%). L-NAME iontophoresis site-to-site and day-to-day coefficients of correlation were 0.83 and 0.76, respectively (P < 0.01). The site-to-site and day-to-day coefficients of correlation of L-NAME injection were lower than those of iontophoresis at 0.66 (P < 0.05) and 0.12, respectively (P = not significant). Sodium nitroprusside-induced skin hyperemia was not affected by L-NAME administration. L-NAME iontophoresis-mediated inhibition of skin thermal hyperemia was greater in smokers than in nonsmokers (P < 0.05).

CONCLUSIONS

Laser Doppler Imager assessment of skin thermal hyperemia after L-NAME iontophoresis provides a reproducible and selective bedside method of qualitatively analyzing the contribution of the NO pathway to microvascular vasomotor function.

Contributions of endothelial nitric oxide synthase, noradrenaline, and neuropeptide Y to local warming-induced cutaneous vasodilatation in men

We performed a two-part study to determine the roles of endothelial nitric oxide synthase (eNOS) and the vasoconstrictor nerves neurotransmitters noradrenaline (NA) and neuropeptide Y (NPY) in the cutaneous vasodilator response to local skin warming. Forearm skin sites were instrumented with intradermal microdialysis fibres, local heaters, and laser-Doppler flow (LDF) probes. Sites were locally heated from 34 to 42°C. LDF was expressed as cutaneous vascular conductance (CVC; LDF/mean arterial pressure). In Part I, we tested whether sympathetic noradrenergic nerves acted via eNOS. In 8 male participants, treatments were as follows: 1) untreated; 2) bretylium tosylate (BT), preventing sympathetic neurotransmitter release; 3) l-NAA to inhibit eNOS; and 4) combined BT+l-NAA. At treated sites, the initial peak response was markedly reduced, and the plateau phase response to 35min of local warming was also reduced (P<0.05), which was not different among those sites (P>0.05). In Part II, we tested whether NA and NPY were involved in the vasodilator response to local warming. In Part IIa, treatments were: 1) untreated; 2) propranolol and yohimbine to antagonize α- and β-receptors; 3) l-NAA; and 4) combined propranolol, yohimbine, and l-NAA. In Part IIb, conditions were: 1) untreated; 2) BIBP to antagonize Y1-receptors; 3) l-NAA; and 4) combined BIBP and l-NAA. All treatments caused a reduction in the initial peak and plateau responses to local skin warming (P<0.05). The results of Part II indicate that both NA and NPY play roles in the cutaneous vasodilator response and their actions are achieved via eNOS. These data indicate that NA and NPY are involved in the initial, rapid rise in skin blood flow at the onset of local skin warming. However, their vasodilator actions in response to local skin warming appears to be manifested through eNOS.

Age-associated induction of cell membrane CD47 limits basal and temperature-induced changes in cutaneous blood flow

OBJECTIVE

We tested the hypothesis that the matricellular protein thrombospondin-1 (TSP1), through binding to and activation of the cell receptor CD47, inhibits basal and thermal-mediated cutaneous blood flow.

BACKGROUND

Abnormal and decreased cutaneous blood flow in response to temperature changes or vasoactive agents is a feature of cardiovascular disease and aging. The reasons for decreased cutaneous blood flow remain incompletely understood. Furthermore, a role for matricellular proteins in the regulation skin blood flow has never been proposed.

METHODS

C57BL/6 wild type, TSP1-null, and CD47-null 12- and 72-week-old male mice underwent analysis of skin blood flow (SkBF) via laser Doppler in response to thermal stress and vasoactive challenge.

RESULTS

Young and aged TSP1- and CD47-null mice displayed enhanced basal and thermal sensitive SkBF changes compared with age-matched wild type controls. Nitric oxide-mediated increases in SkBF were also greater in null mice. TSP1 and CD47 were expressed in skin from young wild type mice, and both were significantly upregulated in aged animals. Tissue 3',5'-cyclic guanosine monophosphate, a potent vasodilator, was greater in skin samples from null mice compared with wild type regardless of age. Finally, treating wild type animals with a CD47 monoclonal antibody that inhibits TSP1 activation of CD47 enhanced SkBF in both young and aged animals.

CONCLUSIONS

These results suggest that secreted TSP1, via its cognate receptor CD47, acutely modulates SkBF. These data further support therapeutically targeting CD47 to mitigate age-associated loss of SkBF and maximize wound healing.

Regional relation between skin blood flow and sweating to passive heating and local administration of acetylcholine in young, healthy humans

Regional variation in sweating over the human body is widely recognized yet variation in vasomotor responses and mechanisms causing this variation remain unclear. This study aimed to explore the relation between regional sweating rates (RSR) and skin blood flow (SkBF) responses to thermal and pharmacological stimuli in young, healthy subjects. In nine subjects (23 ± 3 yr), intradermal microdialysis (MD) probes were inserted into the ventral forearm, abdomen, thigh, and lower back and perfused with lactated Ringer solution. RSR over each MD membrane were measured using ventilated capsules with a laser Doppler probe housed in each capsule for measurement of red cell flux (laser Doppler flux, LDF) as an index of SkBF. Subjects completed a whole body heating protocol to 1°C rise in oral temperature and an acetylcholine dose response (ACh 1 × 10(-7)-0.1 M; mean skin temperature 34°C). Maximal LDF were obtained at the end of both protocols (50 mM sodium nitroprusside).During heating RSR varied among sites (P < 0.0001) and was greater on the back versus other sites (P < 0.05), but LDF was similar between sites (P = 0.343). RSR and SkBF showed a strong relation during initial (arm: r = 0.77 ± 0.09, thigh: r = 0.81 ± 0.08, abdomen: r = 0.89 ± 0.04, back: r = 0.86 ± 0.04) but not latter stages of heating. No differences in RSR (P = 0.160) or SkBF (LDF, P = 0.841) were observed between sites during ACh perfusion. Taken together, these data suggest that increases in SkBF are necessary to initiate and increase sweating, but further rises in RSR are not fully dependent on SkBF in a dose-response manner. Furthermore, RSR cannot be explained by cholinergic sensitivity or variation in SkBF.

Nitric oxide and receptors for VIP and PACAP in cutaneous active vasodilation during heat stress in humans

VPAC2 receptors sensitive to vasoactive intestinal polypeptide (VIP) and pituitary adenylyl cyclase activating polypeptide (PACAP), PAC1 receptors sensitive to PACAP, and nitric oxide (NO) generation by NO synthase (NOS) are all implicated in cutaneous active vasodilation (AVD) through incompletely defined mechanisms. We hypothesized that VPAC2/PAC1 receptor activation and NO are synergistic and interdependent in AVD and tested our hypothesis by examining the effects of VPAC2/PAC1 receptor blockade with and without NOS inhibition during heat stress. The VPAC2/PAC1 antagonist, pituitary adenylate cyclase activating peptide 6-38 (PACAP6-38) and the NOS inhibitor, N(G)-nitro-l-arginine methyl ester (l-NAME) were administered by intradermal microdialysis. PACAP6-38, l-NAME, a combination of PACAP6-38 and l-NAME, or Ringer's solution alone were perfused at four separate sites. Skin blood flow was monitored by laser-Doppler flowmetry at each site. Body temperature was controlled with water-perfused suits. Blood pressure was monitored by Finapres, and cutaneous vascular conductance (CVC) calculated (CVC = laser-Doppler flowmetry/mean arterial pressure). The protocol began with a 5- to 10-min baseline period without antagonist perfusion, followed by perfusion of PACAP6-38, l-NAME, or combined PACAP6-38 and l-NAME at the different sites in normothermia (45 min), followed by 3 min of whole body cooling. Whole body heating was then performed to induce heat stress and activate AVD. Finally, 58 mM sodium nitroprusside were perfused at all sites to effect maximal vasodilation for normalization of blood flow data. No significant differences in CVC (normalized to maximum) were found among Ringer's PACAP6-38, l-NAME, or combined antagonist sites during normothermia (P > 0.05 among sites) or cold stress (P > 0.05 among sites). CVC responses at all treated sites were attenuated during AVD (P < 0.05 vs. Ringer's). Attenuation was greater at l-NAME and combined PACAP6-38- and l-NAME-treated sites than at PACAP6-38 sites (P > 0.05). Because responses did not differ between l-NAME and combined treatment sites (P > 0.05), we conclude that VPAC2/PAC1 receptors require NO in series to effect AVD.

Transient receptor potential vanilloid type 1 channels contribute to reflex cutaneous vasodilation in humans

Mechanisms underlying the cutaneous vasodilation in response to an increase in core temperature remain unresolved. The purpose of this study was to determine a potential contribution of transient receptor potential vanilloid type 1 (TRPV-1) channels to reflex cutaneous vasodilation. Twelve subjects were equipped with four microdialysis fibers on the ventral forearm, and each site randomly received 1) 90% propylene glycol + 10% lactated Ringer (vehicle control); 2) 10 mM l-NAME; 3) 20 mM capsazepine to inhibit TRPV-1 channels; 4) combined 10 mM l-NAME + 20 mM capsazepine. Whole body heating was achieved via water-perfused suits sufficient to raise oral temperature at least 0.8°C above baseline. Maximal skin blood flow was achieved by local heating to 43°C and infusion of 28 mM nitroprusside. Systemic arterial pressure (SAP) was measured, and skin blood flow was monitored via laser-Doppler flowmetry (LDF). Cutaneous vascular conductance (CVC) was calculated as LDF/SAP and normalized to maximal vasodilation (%CVC(max)). Capsazepine sites were significantly reduced compared with control (50 ± 4%CVC(max) vs. 67 ± 5%CVC(max), respectively; P < 0.05). l-NAME (33 ± 3%CVC(max)) and l-NAME + capsazepine (30 ± 4%CVC(max)) sites were attenuated compared with control (P < 0.01) and capsazepine (P < 0.05); however, there was no difference between l-NAME and combined l-NAME + capsazepine. These data suggest TRPV-1 channels participate in reflex cutaneous vasodilation and TRPV-1 channels may account for a portion of the NO component. TRPV-1 channels may have a direct neural contribution or have an indirect effect via increased arterial blood temperature. Whether the TRPV-1 channels directly or indirectly contribute to reflex cutaneous vasodilation remains uncertain.

Sensory and sympathetic nerve contributions to the cutaneous vasodilator response from a noxious heat stimulus

We investigated the roles of sensory and noradrenergic sympathetic nerves on the cutaneous vasodilator response to a localized noxious heating stimulus. In two separate studies, four forearm skin sites were instrumented with microdialysis fibres, local heaters and laser-Doppler probes. Skin sites were locally heated from 33 to 42 °C or rapidly to 44 °C (noxious). In the first study, we tested sensory nerve involvement using EMLA cream. Treatments were as follows: (1) control 42 °C; (2) EMLA 42 °C; (3) control 44°C; and (4) EMLA 44 °C. At the EMLA-treated sites, the axon reflex was reduced compared with the control sites during heating to 42 °C (P < 0.05). There were no differences during the plateau phase (P > 0.05). At both the sites heated to 44 °C, the initial peak and nadir became indistinguishable, and the EMLA-treated sites were lower compared with the control sites during the plateau phase (P < 0.05). In the second study, we tested the involvement of noradrenergic sympathetic nerves in response to the noxious heating using bretylium tosylate (BT). Treatments were as follows: (1) control 42 °C; (2) BT 42 °C; (3) control 44 °C; and (4) BT 44 °C. Treatment with BT at the 42 °C sites resulted in a marked reduction in both the axon reflex and the secondary plateau (P < 0.05). At the 44 °C sites, there was no apparent initial peak or nadir, but the plateau phase was reduced at the BT-treated sites (P < 0.05). These data suggest that both sympathetic nerves and sensory nerves are involved during the vasodilator response to a noxious heat stimulus.