Nitric oxide inhibits cutaneous vasoconstriction to exogenous norepinephrine

Facial fanning reduces heart rate but not tolerance to a simulated hemorrhagic challenge following exercise heat stress in young healthy humans

We investigated whether reducing face skin temperature alters arterial blood pressure control and lower body negative pressure (LBNP) tolerance after exercise heat stress. Eight subjects (1 female; age, 27 ± 9 yr) exercised at ∼63% V̇o2max until core temperature had increased ∼1.5°C before undergoing LBNP to presyncope either with fanning to return face skin temperature to baseline (Δ-5°C, Fan trial) or without (No Fan trial). LBNP tolerance was quantified as cumulative stress index (CSI; mmHg·min). Before LBNP, whole body and face skin temperatures were elevated from baseline in both trials (38.0 ± 0.5°C and 36.3 ± 0.5°C, respectively, both P < 0.001). During LBNP, face skin temperature decreased in the Fan trial (30.9 ± 1.0°C) but was unchanged in the No Fan trial (36.1 ± 0.6°C, between trials P < 0.001). Mean arterial pressure was not different between trials (P = 0.237) and was similarly reduced at presyncope in both trials (from 82 ± 7 to 67 ± 8 mmHg, P < 0.001). During LBNP, heart rate was attenuated in the Fan trial at Mid LBNP (146 ± 16 vs. 158 ± 12 beats/min, P = 0.036) and at peak heart rate (158 ± 15 vs. 170 ± 15 beats/min; P < 0.001). LBNP tolerance was not different between trials (321 ± 248 vs. 328 ± 115 mmHg·min, P = 0.851). In exercise heat-stressed individuals, lowering face skin temperature to normothermic values suppressed heart rate thereby altering cardiovascular control during a simulated hemorrhagic challenge without reducing tolerance.

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.

Combination of Electrochemistry and Mass Spectrometry to Study Nitric Oxide Metabolism and Its Modulation by Compound K in Breast Cancer Cells

The levels of l-arginine and asymmetric dimethylarginine (ADMA) and the amount of the nitric oxide (NO) production have recently been linked to breast cancer and pharmaceutical effect evaluation. Herein, a method combining electrochemistry and high-resolution mass spectrometry (HRMS) was established and used to study NO metabolism and its modulation by ginsenoside compound K (CK) in breast cancer cells. Platinum nanoparticles-decorated fluorine tin oxide was employed as an electrochemical sensor for in situ detection of NO release, while HRMS was used for the analysis of the NO-related metabolites. Through the combination of the electrochemical and HRMS results, decreases in arginine and NO and increases in ADMA and ornithine were observed after modulation by CK, and two highly correlated metabolic pathways including arginine and proline metabolism and vascular smooth muscle contraction were found. This method offers a new strategy for fast evaluation of pharmaceutical efficacy based on NO metabolism.

Sex differences in blood pressure regulation during the isometric exercise under heated environment

In the absence of heat stress, females increase blood pressure (BP) during isometric handgrip exercise due to cardiac output more than total peripheral resistance (TPR) compared to men. Although heat stress seems to blunt BP responses at rest and during handgrip, possible sex differences remained unknown. We hypothesized that BP responses during handgrip under a heated environment (HOT) will be different between men and women. Eight healthy men (29 ± 6 years) and eight women (26 ± 4 years) participated in this study. The experimental protocol was separated into two environmental conditions: HOT (~ 36 °C) and thermoneutral (TC; ~ 24 °C). In both conditions, participants rested for 30 min and performed the handgrip for 3 min. BP, heart rate (HR) stroke volume and cardiac output were continuously recorded, and TPR was calculated (TPR = mean blood pressure (MBP)/cardiac output). HOT reduced BP and TPR at baseline and during handgrip in females as compared to TC, while males showed similar responses in both thermal conditions. HR was higher under HOT in both groups. Cardiac output and stroke volume were not different under HOT compared to TC for females. In males, cardiac output increased at the last minute of handgrip under HOT through augmented HR, because stroke volume was unchanged. In conclusion, the main effect of HOT was to shift downwards BP and total peripheral resistance at rest and during isometric exercise in females. In males, the combination of handgrip and HOT increased cardiac output by augmented HR, whereas BP presented similar responses between thermal conditions during handgrip.

Independent and combined impact of hypoxia and acute inorganic nitrate ingestion on thermoregulatory responses to the cold

Purpose

This study assessed the impact of normobaric hypoxia and acute nitrate ingestion on shivering thermogenesis, cutaneous vascular control, and thermometrics in response to cold stress.

Method

Eleven male volunteers underwent passive cooling at 10 °C air temperature across four conditions: (1) normoxia with placebo ingestion, (2) hypoxia (0.130 F_iO₂) with placebo ingestion, (3) normoxia with 13 mmol nitrate ingestion, and (4) hypoxia with nitrate ingestion. Physiological metrics were assessed as a rate of change over 45 min to determine heat loss, and at the point of shivering onset to determine the thermogenic thermoeffector threshold.

Result

Independently, hypoxia expedited shivering onset time (p = 0.05) due to a faster cooling rate as opposed to a change in central thermoeffector thresholds. Specifically, compared to normoxia, hypoxia increased skin blood flow (p = 0.02), leading to an increased core-cooling rate (p = 0.04) and delta change in rectal temperature (p = 0.03) over 45 min, yet the same rectal temperature at shivering onset (p = 0.9). Independently, nitrate ingestion delayed shivering onset time (p = 0.01), mediated by a change in central thermoeffector thresholds, independent of changes in peripheral heat exchange. Specifically, compared to placebo ingestion, no difference was observed in skin blood flow (p = 0.5), core-cooling rate (p = 0.5), or delta change in rectal temperature (p = 0.7) over 45 min, while nitrate reduced rectal temperature at shivering onset (p = 0.04). No interaction was observed between hypoxia and nitrate ingestion.

Conclusion

These data improve our understanding of how hypoxia and nitric oxide modulate cold thermoregulation.

The nitric oxide dependence of cutaneous microvascular function to independent and combined hypoxic cold exposure

When separated from local cooling, whole body cooling elicited cutaneous reflex vasoconstriction via mechanisms independent of nitric oxide removal. Hypoxia elicited cutaneous vasodilatation via mechanisms mediated primarily by nitric oxide synthase, rather than xanthine oxidase-mediated nitrite reduction. Cold-induced vasoconstriction was blunted by the opposing effect of hypoxic vasodilatation, whereas the underpinning mechanisms did not interrelate in the absence of local cooling. Full vasoconstriction was restored with nitric oxide synthase inhibition.

Visualization of skin capillaries with moving red blood cells in arbitrary area of the body

Evaluation of skin microcirculation allows for the assessment of functional states for neuroendocrine and endothelial regulation. We present a novel method to visualize skin microvessels in any area of the body, which is in contrast to classical capillaroscopy, in which the application areas are limited to the nailfold and retina capillaries. The technique is based on microscopic video-image analysis. It exploits a specific feature of irregularity of red-blood-cells motion. Feasibility of the method is demonstrated by mapping the skin capillaries in the forearm and face of 11 healthy volunteers. The proposed method is promising for the quantitative assessment of cutaneous microcirculation in a wide range of diseases and functional states.

A new approach to the analysis of skin blood flow oscillations in human

It is considered that there are six non-overlapping frequency intervals with constant boundaries. These intervals correspond to different mechanisms of skin blood flow regulation. The boundaries do not depend on functional conditions but this statement should be verified. Also it remains unclear how the oscillatory components of skin blood flow are related. Thus the study is aimed to verify statistically the boundaries of frequency intervals, to test the hypothesis that the boundaries depend on age and to search for relationships between spectral components of skin blood flow. The study involved 105 healthy volunteers aged from 20 to 65 years, which were divided into two age groups. Skin blood flow was registered with laser Doppler flowmeter (LDF). Assessments of frequency interval boundaries and relationship between the frequency oscillatory components of blood flow were conducted with histogram approach, bootstrap method and correlation analysis. New frequency interval boundaries were found. They were different in two groups. A linear correlation and frequency areas with moderate (0.5-0.7) and high (>0.7) correlation coefficients were found between spectral components of blood flow. The dependence of these correlations on the age was shown. Thus we proposed a conceptually new approach to analysis of spectral components of skin microhemodynamics and interpretation of results obtained by laser Doppler techniques. This approach is the result of the development of modern understanding of relationships between skin blood flow regulation mechanisms and spectral components of LDF signals. It allows one to have a new look at these relationships as well as demonstrates their dependence on the functional state of the organism as a whole.

Impact of environmental stressors on tolerance to hemorrhage in humans

Hemorrhage is a leading cause of death in military and civilian settings, and ~85% of potentially survivable battlefield deaths are hemorrhage-related. Soldiers and civilians are exposed to a number of environmental and physiological conditions that have the potential to alter tolerance to a hemorrhagic insult. The objective of this review is to summarize the known impact of commonly encountered environmental and physiological conditions on tolerance to hemorrhagic insult, primarily in humans. The majority of the studies used lower body negative pressure (LBNP) to simulate a hemorrhagic insult, although some studies employed incremental blood withdrawal. This review addresses, first, the use of LBNP as a model of hemorrhage-induced central hypovolemia and, then, the effects of the following conditions on tolerance to LBNP: passive and exercise-induced heat stress with and without hypohydration/dehydration, exposure to hypothermia, and exposure to altitude/hypoxia. An understanding of the effects of these environmental and physiological conditions on responses to a hemorrhagic challenge, including tolerance, can enable development and implementation of targeted strategies and interventions to reduce the impact of such conditions on tolerance to a hemorrhagic insult and, ultimately, improve survival from blood loss injuries.

Small reductions in skin temperature after onset of a simulated hemorrhagic challenge improve tolerance in exercise heat-stressed individuals

We investigated whether small reductions in skin temperature 60 s after the onset of a simulated hemorrhagic challenge would improve tolerance to lower body negative pressure (LBNP) after exercise heat stress. Eleven healthy subjects completed two trials (High and Reduced). Subjects cycled at ~55% maximal oxygen uptake wearing a warm water-perfused suit until core temperatures increased by ~1.2°C before lying supine and undergoing LBNP to presyncope. LBNP tolerance was quantified as cumulative stress index (CSI; product of each LBNP level multiplied by time; mmHg·min). Skin temperature was similarly elevated from baseline before LBNP and remained elevated 60 s after the onset of LBNP in both High (37.72 ± 0.52°C) and Reduced (37.95 ± 0.54°C) trials (both P < 0.0001). At 60%CSI skin temperature remained elevated in the High trial (37.51 ± 0.56°C) but was reduced to 34.97 ± 0.72°C by the water-perfused suit in the Reduced trial ( P < 0.0001 between trials). Cutaneous vascular conductance was not different between trials [High: 1.57 ± 0.43 vs. Reduced: 1.39 ± 0.38 arbitrary units (AU)/mmHg; P = 0.367] before LBNP but decreased to 0.67 ± 0.19 AU/mmHg at 60%CSI in the Reduced trial while remaining unchanged in the High trial ( P = 0.002 between trials). CSI was higher in the Reduced (695 ± 386 mmHg·min) relative to the High (441 ± 290 mmHg·min; P = 0.023) trial. Mean arterial pressure was not different between trials at presyncope (High: 62 ± 10 vs. Reduced: 62 ± 9 mmHg; P = 0.958). Small reductions in skin temperature after the onset of a simulated hemorrhagic challenge improve LBNP tolerance after exercise heat stress. This may have important implications regarding treatment of an exercise heat-stressed individual (e.g., soldier) who has experienced a hemorrhagic injury.

Anti-oxidative treatment with vitamin E improves peripheral vascular function in patients with diabetes mellitus and Haptoglobin 2-2 genotype: A double-blinded cross-over study

Vascular dysfunction in both conduit arteries and small vessels is a major contributor to the development of cardiovascular disease (CVD) in diabetes mellitus (DM). In diabetes there is a process of systemic chronic inflammation accompanied by high oxidative stress causing a subsequent decrease in vascular reactivity and negatively affect the metabolic processes responsible for functioning of the microvasculature. Vitamin E is classified as an antioxidant due to its ability to scavenge lipid radicals and terminate oxidative chain reactions. We conducted a double-blinded cross-over study with vitamin E versus placebo in individuals with type 2DM and the Hp2-2 genotype and assessed different aspects of peripheral vascular function in these patients. Twenty patients completed the study with 10 individuals in each study cohort. We were able to show significant improvement of indirect indices of vascular function following 8weeks of treatment with vitamin E. This improvement was consistent for weeks even after stopping the vitamin E treatment. We concluded that a pharmacogenomic rationale utilizing the Hp genotype might potentially provide cardiovascular benefit with vitamin E.

Application of shortwave diathermy to lower limb increases arterial blood flow velocity and skin temperature in women: a randomized controlled trial

•

The velocity of popliteal artery flow remained unchanged with MWD and increased with SWD, remaining above baseline even 20 min after application.

•

Despite changes in blood flow velocity, no correlation was found between the temperature variation and arterial blood flow.

•

SWD and MWD both increase skin temperature, but only SWD increased it for over 20 min after the end of application.

•

The temperature was greater in the areas under the MWD and SWD electrodes.

•

The position of the knee interfered with the skin temperature of the hamstring only after 10 min of SWD application.

Background

Shortwave diathermy (SWD) and microwave diathermy (MWD) are frequently used by physical therapists to treat musculoskeletal conditions. The therapeutic benefits are usually associated with an increase in tissue temperature; however, there is no consensus on the changes in blood flow.

Objectives

1) To evaluate the behavior of temperature and arterial blood flow after the application of SWD and MWD to the lower limb of healthy women aged 18–30 and 2) to assess whether changes in limb positioning can influence SWD response.

Method

Among the subjects analyzed, 40 women were eligible to participate in the trial and were randomly allocated to the SWD group or the MWD group. Each group received 20 min of diathermy. After receiving the interventions, all patients crossed over to the other group, but the devices were detuned (sham). SWD was applied to the posterior compartment of the thigh and leg, with the knee in 0° and 90° of flexion, and the MWD applied to the posterior thigh. Skin temperature evaluation (digital infrared thermography) and assessment of blood flow velocity (Doppler ultrasound) were performed immediately before and 10 and 20 min after the application.

Results

Arterial blood flow increased after SWD diathermy (vs. Sham), but not after MWD diathermy. SWD promoted skin heating at the end of therapy in all areas analyzed, remaining above baseline even 20 min after the end of the application. MWD diathermy promoted skin heating in the posterior thigh, reflecting a rise in the temperature of the popliteal fossa area that remained for 10 min after the end of the application.

Conclusion

The increase in arterial blood flow velocity depends on the size of the heating area, since it was only observed in the application of the SWD. However, after 20 min of application, the position of the lower leg did not affect the heating.

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.

Mechanisms of orthostatic intolerance during heat stress

Heat stress profoundly and unanimously reduces orthostatic tolerance. This review aims to provide an overview of the numerous and multifactorial mechanisms by which this occurs in humans. Potential causal factors include changes in arterial and venous vascular resistance and blood distribution, and the modulation of cardiac output, all of which contribute to the inability to maintain cerebral perfusion during heat and orthostatic stress. A number of countermeasures have been established to improve orthostatic tolerance during heat stress, which alleviate heat stress induced central hypovolemia (e.g., volume expansion) and/or increase peripheral vascular resistance (e.g., skin cooling). Unfortunately, these countermeasures can often be cumbersome to use with populations prone to syncopal episodes. Identifying the mechanisms of inter-individual differences in orthostatic intolerance during heat stress has proven elusive, but could provide greater insights into the development of novel and personalized countermeasures for maintaining or improving orthostatic tolerance during heat stress. This development will be especially impactful in occuational settings and clinical situations that present with orthostatic intolerance and/or central hypovolemia. Such investigations should be considered of vital importance given the impending increased incidence of heat events, and associated cardiovascular challenges that are predicted to occur with the ensuing changes in climate.

Human cardiovascular responses to passive heat stress

Heat stress increases human morbidity and mortality compared to normothermic conditions. Many occupations, disease states, as well as stages of life are especially vulnerable to the stress imposed on the cardiovascular system during exposure to hot ambient conditions. This review focuses on the cardiovascular responses to heat stress that are necessary for heat dissipation. To accomplish this regulatory feat requires complex autonomic nervous system control of the heart and various vascular beds. For example, during heat stress cardiac output increases up to twofold, by increases in heart rate and an active maintenance of stroke volume via increases in inotropy in the presence of decreases in cardiac preload. Baroreflexes retain the ability to regulate blood pressure in many, but not all, heat stress conditions. Central hypovolemia is another cardiovascular challenge brought about by heat stress, which if added to a subsequent central volumetric stress, such as hemorrhage, can be problematic and potentially dangerous, as syncope and cardiovascular collapse may ensue. These combined stresses can compromise blood flow and oxygenation to important tissues such as the brain. It is notable that this compromised condition can occur at cardiac outputs that are adequate during normothermic conditions but are inadequate in heat because of the increased systemic vascular conductance associated with cutaneous vasodilation. Understanding the mechanisms within this complex regulatory system will allow for the development of treatment recommendations and countermeasures to reduce risks during the ever-increasing frequency of severe heat events that are predicted to occur.

Active and passive heat stress similarly compromise tolerance to a simulated hemorrhagic challenge

Passive heat stress increases core and skin temperatures and reduces tolerance to simulated hemorrhage (lower body negative pressure; LBNP). We tested whether exercise-induced heat stress reduces LBNP tolerance to a greater extent relative to passive heat stress, when skin and core temperatures are similar. Eight participants (6 males, 32 ± 7 yr, 176 ± 8 cm, 77.0 ± 9.8 kg) underwent LBNP to presyncope on three separate and randomized occasions: 1) passive heat stress, 2) exercise in a hot environment (40°C) where skin temperature was moderate (36°C, active 36), and 3) exercise in a hot environment (40°C) where skin temperature was matched relative to that achieved during passive heat stress (∼38°C, active 38). LBNP tolerance was quantified using the cumulative stress index (CSI). Before LBNP, increases in core temperature from baseline were not different between trials (1.18 ± 0.20°C; P > 0.05). Also before LBNP, mean skin temperature was similar between passive heat stress (38.2 ± 0.5°C) and active 38 (38.2 ± 0.8°C; P = 0.90) trials, whereas it was reduced in the active 36 trial (36.6 ± 0.5°C; P ≤ 0.05 compared with passive heat stress and active 38). LBNP tolerance was not different between passive heat stress and active 38 trials (383 ± 223 and 322 ± 178 CSI, respectively; P = 0.12), but both were similarly reduced relative to active 36 (516 ± 147 CSI, both P ≤ 0.05). LBNP tolerance is not different between heat stresses induced either passively or by exercise in a hot environment when skin temperatures are similarly elevated. However, LBNP tolerance is influenced by the magnitude of the elevation in skin temperature following exercise induced heat stress.

Nail fold capillary diameter changes in acute systemic hypoxia

The present study was undertaken to determine the effect of arterial blood hypoxemia induced by acute systemic hypoxia (pO2=12%) on capillary recruitment and diameter, and red blood cell (RBC) velocity in human nail fold capillaries during rest, arterial post-occlusive reactive hyperemia (PRH), and venous occlusion (VO) using intravital video-capillaroscopy. Capillary recruitment was unchanged in acute systemic hypoxia (H) versus normoxia (N). There was no difference in RBC velocity measurements between normoxia and hypoxia (P<0.63). However, a statistically significant increase in nail fold capillary total width (N, 39.9±9.1 vs. H, 42.7±10.3 μm; P<0.05), apical diameter (N, 15.5±4.3 vs. H, 16.8±4.3 μm; P<0.05), arterial diameter (N, 11.9±3.5 vs. H, 13.9±4.1 μm; P<0.05), and venous diameter (N, 15.5±4.3 vs. H, 17.2±4.8 μm; P<0.05) was observed and continued to be significant most often during post-occlusive reactive hyperemia (PRH) and venous congestion (VO). These data suggest that acute systemic hypoxia does not increase capillary recruitment, but instead increases capillary diameter, resulting in increased capillary blood flow.

Oral sapropterin augments reflex vasoconstriction in aged human skin through noradrenergic mechanisms

Reflex vasoconstriction is attenuated in aged skin due to a functional loss of adrenergic vasoconstriction. Bioavailability of tetrahydrobiopterin (BH4), an essential cofactor for catecholamine synthesis, is reduced with aging. Locally administered BH4 increases vasoconstriction through adrenergic mechanisms in aged human skin. We hypothesized that oral sapropterin (Kuvan, a pharmaceutical BH4) would augment vasoconstriction elicited by whole-body cooling and tyramine perfusion in aged skin. Ten healthy subjects (age 75 ± 2 yr) ingested sapropterin (10 mg/kg) or placebo in a randomized, double-blind crossover design. Venous blood samples were collected prior to, and 3 h following ingestion. Three intradermal microdialysis fibers were placed in the forearm skin for local delivery of 1) lactated Ringer, 2) 5 mM BH4, and 3) 5 mM yohimbine + 1 mM propranolol (Y+P; to inhibit adrenergic vasoconstriction). Red cell flux was measured at each site by laser-Doppler flowmetry (LDF) as reflex vasoconstriction was induced by lowering and then clamping whole-body skin temperature (Tsk) using a water-perfused suit. Following whole-body cooling, subjects were rewarmed and 1 mM tyramine was perfused at each site to elicit endogenous norepinephrine release from the perivascular nerve terminal. Cutaneous vascular conductance was calculated as CVC = LDF/mean arterial pressure and expressed as change from baseline (ΔCVC). Plasma BH4 was elevated 3 h after ingestion of sapropterin (43.8 ± 3 vs. 19.1 ± 2 pmol/ml; P < 0.001). Sapropterin increased reflex vasoconstriction at the Ringer site at Tsk ≤ 32.5°C (P < 0.05). Local BH4 perfusion augmented reflex vasoconstriction at Tsk ≤ 31.5°C with placebo treatment only (P < 0.05). There was no treatment effect on reflex vasoconstriction at the BH4-perfused or Y+P-perfused sites. Sapropterin increased pharmacologically induced vasoconstriction at the Ringer site (-0.19 ± 0.03 vs. -0.08 ± 0.02 ΔCVC; P = 0.01). There was no difference in pharmacologically induced vasoconstriction between treatments at the BH4-perfused site (-0.16 ± 0.04 vs. -0.14 ± 0.03 ΔCVC; P = 0.60) or the Y+P-perfused site (-0.05 ± 0.02 vs.-0.06 ± 0.02 ΔCVC; P = 0.79). Sapropterin increases both reflex (cold-induced) and pharmacologically induced vasoconstriction through adrenergic mechanisms and may be a viable intervention to improve reflex vasoconstriction in aged humans.

Blood pressure regulation III: what happens when one system must serve two masters: temperature and pressure regulation?

When prolonged intense exercise is performed at high ambient temperatures, cardiac output must meet dual demands for increased blood flow to contracting muscle and to the skin. The literature has commonly painted this scenario as a fierce competition, wherein one circulation preserves perfusion at the expense of the other, with the regulated maintenance of blood pressure as the ultimate goal. This review redefines this scenario as commensalism, an integrated balance of regulatory control where one circulation benefits with little functional effect on the other. In young, healthy subjects, arterial pressure rarely falls to any great extent during either extreme passive heating or prolonged dynamic exercise in the heat, nor does body temperature rise disproportionately due to a compromised skin blood flow. Rather, it often takes the superimposition of additional stressors--e.g., dehydration or simulated hemorrhage--upon heat stress to substantially impact blood pressure regulation.

Heat and α1-adrenergic responsiveness in human skeletal muscle feed arteries: the role of nitric oxide

Increased local temperature exerts a sympatholytic effect on human skeletal muscle feed arteries. We hypothesized that this attenuated α(1)-adrenergic receptor responsiveness may be due to a temperature-induced increase in nitric oxide (NO) bioavailability, thereby reducing the impact of the α(1)-adrenergic receptor agonist phenylephrine (PE). Thirteen human skeletal muscle feed arteries were harvested, and wire myography was used to generate PE concentration-response curves at 37 °C and 39 °C, with and without the NO synthase (NOS) inhibitor N(G)-monomethyl-L-arginine (L-NMMA). A subset of arteries (n = 4) were exposed to 37 °C or 39 °C, and the protein content of endothelial NOS (eNOS) and α(1)-adrenergic receptors was determined by Western blot analysis. Additionally, cultured bovine endothelial cells were exposed to static or shear stress conditions at 37 °C and 39 °C and assayed for eNOS activation (phosphorylation at Ser(1177)), eNOS expression, and NO metabolites [nitrate + nitrite (NOx)]. Maximal PE-induced vasocontraction (PE(max)) was lower at 39 °C than at 37 °C [39 ± 10 vs. 84 ± 30% maximal response to 100 mM KCl (KCl(max))]. NO blockade restored vasocontraction at 39 °C to that achieved at 37 °C (80 ± 26% KCl(max)). Western blot analysis of the feed arteries revealed that heating increased eNOS protein, but not α(1)-adrenergic receptors. Heating of bovine endothelial cells resulted in greater shear stress-induced eNOS activation and NOx production. Together, these data reveal for the first time that, in human skeletal muscle feed arteries, NO blockade can restore the heat-attenuated α(1)-adrenergic receptor-mediated vasocontraction and implicate endothelium-derived NO bioavailability as a major contributor to heat-induced sympatholysis. Consequently, these findings highlight the important role of vasodilators in modulating the vascular response to vasoconstrictors.

Telangiectasia macularis multiplex acquisita: a new entity in Chinese populations and an analysis of associated factors

BACKGROUND

  Telangiectasia macularis multiplex acquisita (TMMA) is a rarely documented entity with distinctive clinical manifestation. Most patients are middle-aged adults. It may be associated with other diseases such as hepatitis, diabetes, or cardiovascular diseases.

OBJECTIVES

  To assess the clinical presentation of TMMA and its association to other systemic diseases, especially the correlation to liver disease, in Taiwan.

METHODS

  We identified and retrospectively analyzed clinical criteria-matched and skin biopsy-proven patients from 2002 to 2010 at a single medical center. The clinical criteria for diagnosis of TMMA included: (i) crops of telangiectasia superimposed on erythematous macules symmetrically on bilateral upper arms, possibly extending to the forearms, shoulders, V-shaped area of the anterior chest, back or thighs; (ii) no mucosal or systemic involvement; (iii) not associated with autoimmune diseases, such as lupus erythematosus, dermatomyositis or systemic scleroderma that may induce cutaneous telangiectasia; and (iv) no ataxia or unsteady gait.

RESULTS

  Twenty-five patients were enrolled in this study. The male-to-female ratio was 19:6. The age of onset was variable, mostly between the third to sixth decades. The V-shaped area of the anterior chest was commonly involved (68%), in addition to the arms (100%). Viral hepatitis was diagnosed in 56.5% of the patients (13/23); 38.9% (7/18) and 50% (9/18) of the patients had diabetes and hypertension, respectively. In addition, 64.7% of the patients (11/17) had dyslipidemia. The pathological reports of most cases showed only mild perivascular lymphocytic infiltration with or without telangiectasia.

CONCLUSIONS

  TMMA should be assigned to a distinct entity with unique clinical manifestation. It has not been well recognized and mostly misdiagnosed as other diseases with telangiectasia. It is important to evaluate the complete liver function tests when TMMA is suspected.

Elevated local skin temperature impairs cutaneous vasoconstrictor responses to a simulated haemorrhagic challenge while heat stressed

During a simulated haemorrhagic challenge, syncopal symptoms develop sooner when individuals are hyperthermic relative to normothermic. This is due, in part, to a large displacement of blood to the cutaneous circulation during hyperthermia, coupled with inadequate cutaneous vasoconstriction during the hypotensive challenge. The influence of local skin temperature on these cutaneous vasoconstrictor responses is unclear. This project tested the hypothesis that local skin temperature modulates cutaneous vasoconstriction during simulated haemorrhage in hyperthermic humans. Eight healthy participants (four men and four women; 32 ± 7 years old; 75.2 ± 10.8 kg) underwent lower-body negative pressure to presyncope while heat stressed via a water-perfused suit sufficiently to increase core temperature by 1.2 ± 0.2 °C. At forearm skin sites distal to the water-perfused suit, local skin temperature was either 35.2 ± 0.6 (mild heating) or 38.2 ± 0.2 °C (moderate heating) throughout heat stress and lower-body negative pressure, and remained at these temperatures until presyncope. The reduction in cutaneous vascular conductance during the final 90 s of lower-body negative pressure, relative to heat-stress baseline, was greatest at the mildly heated site (-10 ± 15% reduction) relative to the moderately heated site (-2 ± 12%; P = 0.05 for the magnitude of the reduction in cutaneous vascular conductance between sites), because vasoconstriction at the moderately heated site was either absent or negligible. In hyperthermic individuals, the extent of cutaneous vasoconstriction during a simulated haemorrhage can be modulated by local skin temperature. In situations where skin temperature is at least 38 °C, as is the case in soldiers operating in warm climatic conditions, a haemorrhagic insult is unlikely to be accompanied by cutaneous vasoconstriction.

Pharmacological curve fitting to analyze cutaneous adrenergic responses

Although dose-response curves are commonly used to describe in vivo cutaneous α-adrenergic responses, modeling parameters and analyses methods are not consistent across studies. The goal of the present investigation was to compare three analysis methods for in vivo cutaneous vasoconstriction studies using one reference data set. Eight women (22 ± 1 yr, 24 ± 1 kg/m(2)) were instrumented with three cutaneous microdialysis probes for progressive norepinephrine (NE) infusions (1 × 10(-8), 1 × 10(-6), 1 × 10(-5), 1 × 10(-4), and 1 × 10(-3) logM). NE was infused alone, co-infused with NG-monomethyl-l-arginine (l-NMMA, 10 mM) or Ketorolac tromethamine (KETO, 10 mM). For each probe, dose-response curves were generated using three commonly reported analyses methods: 1) nonlinear modeling without data manipulation, 2) nonlinear modeling with data normalization and constraints, and 3) percent change from baseline without modeling. Not all data conformed to sigmoidal dose-response curves using analysis 1, whereas all subjects' curves were modeled using analysis 2. When analyzing only curves that fit the sigmoidal model, NE + KETO induced a leftward shift in ED(50) compared with NE alone with analyses 1 and 2 (F test, P < 0.05) but only tended to shift the response leftward with analysis 3 (repeated-measures ANOVA, P = 0.08). Neither maximal vasoconstrictor capacity (E(max)) in analysis 1 nor %change CVC change from baseline in analysis 3 were altered by blocking agents. In conclusion, although the overall detection of curve shifts and interpretation was similar between the two modeling methods of curve fitting, analysis 2 produced more sigmoidal curves.

Progesterone enhances adrenergic control of skin blood flow in women with high but not low orthostatic tolerance

Women are more susceptible to orthostatic intolerance. Peripheral α-adrenergic responsiveness is important in orthostasis and is lower in women compared to men, and is modulated by female sex hormones. We tested the hypothesis that oestradiol attenuates peripheral cutaneous adrenergic responses in women with low orthostatic tolerance (LT), whereas progesterone enhances adrenergic responses in women with high orthostatic tolerance (HT). After completing a maximal lower body negative pressure test to determine level of orthostatic tolerance (cumulative stress index, CSI), women self administered a gonadotropin releasing hormone (GnRH) antagonist for 16 days to suppress endogenous sex hormone production. Oestradiol (E2, 0.2 mg day−1, patch; days 4–16), and progesterone (P4, 200 mg day−1, oral; days 12–16) were administered. Skin blood flow responses to graded intradermal microdialysis infusions of noradrenaline (NA) were measured during GnRH antagonist, E2, and E2+P4, in eight HT (s.e.m. = 22 ± 1 years, CSI −871 ± 86 mmHg min) and eight LT (21 ± 1 years, CSI −397 ± 65 mmHg min) women. In separate probes, NA was infused alone, and co-infused with the nitric oxide synthase inhibitor NG-monomethyl-l-arginine (l-NMMA, 10 mm), the non-selective cyclooxygenase inhibitor ketorolac tromethamine (Keto, 10 mm), and combined l-NMMA + Keto (10 mm each). Progesterone administration enhanced adrenergic responses in HT women (logEC50 GnRH −4.02 ± 0.39, E2+P4 −5.18 ± 0.31, P < 0.05); this response was reversed with Keto (E2+P4 logEC50 NA+Keto −3.82 ± 0.35, P < 0.05). In contrast, no change in adrenergic responsiveness occurred in LT women during any hormone condition. These data indicate differential regulation of cutaneous adrenergic responses by progesterone via the cyclooxygenase pathway in women with high and low orthostatic tolerance.

Tetrahydrobiopterin does not affect end-organ responsiveness to norepinephrine-mediated vasoconstriction in aged skin

We have recently demonstrated that tetrahydrobiopterin (BH(4)) augments reflex vasoconstriction (VC) in aged skin. Although this appears to occur through its role in norepinephrine (NE) biosynthesis, the extent with which vascular mechanisms are affected are unknown. We hypothesized that localized BH(4) supplementation would not affect the VC response to exogenous NE when sympathetic nerves were blocked. Two microdialysis fibers were placed in bretylium tosylate pretreated (presynaptically blocks neurotransmitter release from sympathetic adrenergic nerve terminals; iontophoresis, 200 μA for 20 min) 3-cm(2) forearm skin of 10 young (Y) and 10 older (O) subjects for perfusion of 1) Ringer (control) and 2) 5 mM BH(4). While local skin temperature was clamped at 34°C, six concentrations of NE (10(-12), 10(-10), 10(-8), 10(-6), 10(-4), 10(-2) M) were infused at each drug-treated site. Cutaneous vascular conductance (CVC) was calculated (CVC = laser Doppler flux/mean arterial pressure) and normalized to baseline (%ΔCVC(base)). Despite prejunctional adrenergic blockade, NE-mediated VC was blunted in aged skin at each NE dose (10(-12): -12 ± 2 vs. -21 ± 2; 10(-10): -15 ± 2 vs. -27 ± 1; 10(-8): -22 ± 2 vs. -32 ± 2; 10(-6): -27 ± 2 vs. -38 ± 1; 10(-4): -52 ± 3 vs. -66 ± 5; 10(-2): -62 ± 3 vs. -75 ± 4%ΔCVC(base); P < 0.01), and this response was not affected by pretreatment with BH(4) (P > 0.05). Localized BH(4) did not affect end-organ responsiveness to exogenous NE, suggesting that the effects of BH(4) on cutaneous VC are primarily isolated to the NE biosynthetic pathway.

Insufficient cutaneous vasoconstriction leading up to and during syncopal symptoms in the heat stressed human

As much as 50% of cardiac output can be distributed to the skin in the hyperthermic human, and therefore the control of cutaneous vascular conductance (CVC) becomes critical for the maintenance of blood pressure. Little is known regarding the magnitude of cutaneous vasoconstriction in profoundly hypotensive individuals while heat stressed. This project investigated the hypothesis that leading up to and during syncopal symptoms associated with combined heat and orthostatic stress, reductions in CVC are inadequate to prevent syncope. Using a retrospective study design, we evaluated data from subjects who experienced syncopal symptoms during lower body negative pressure (N = 41) and head-up tilt (N = 5). Subjects were instrumented for measures of internal temperature, forearm skin blood flow, arterial pressure, and heart rate. CVC was calculated as skin blood flow/mean arterial pressure × 100. Data were obtained while subjects were normothermic, immediately before an orthostatic challenge while heat stressed, and at 5-s averages for the 2 min preceding the cessation of the orthostatic challenge due to syncopal symptoms. Whole body heat stress increased internal temperature (1.25 ± 0.3°C; P < 0.001) and CVC (29 ± 20 to 160 ± 58 CVC units; P < 0.001) without altering mean arterial pressure (83 ± 7 to 82 ± 6 mmHg). Mean arterial pressure was reduced to 57 ± 9 mmHg (P < 0.001) immediately before the termination of the orthostatic challenge. At test termination, CVC decreased to 138 ± 61 CVC units (P < 0.001) relative to before the orthostatic challenge but remained approximately fourfold greater than when subjects were normothermic. This negligible reduction in CVC during pronounced hypotension likely contributes to reduced orthostatic tolerance in heat-stressed humans. Given that lower body negative pressure and head-up tilt are models of acute hemorrhage, these findings have important implications with respect to mechanisms of compromised blood pressure control in the hemorrhagic individual who is also hyperthermic (e.g., military personnel, firefighters, etc.).

Local thermal control of the human cutaneous circulation

The level of skin blood flow is subject to both reflex thermoregulatory control and influences from the direct effects of warming and cooling the skin. The effects of local changes in temperature are capable of maximally vasoconstricting or vasodilating the skin. They are brought about by a combination of mechanisms involving endothelial, adrenergic, and sensory systems. Local warming initiates a transient vasodilation through an axon reflex, succeeded by a plateau phase due largely to nitric oxide. Both phases are supported by sympathetic transmitters. The plateau phase is followed by the die-away phenomenon, a slow reversal of the vasodilation that is dependent on intact sympathetic vasoconstrictor nerves. The vasoconstriction with local skin cooling is brought about, in part, by a postsynaptic upregulation of α(2c)-adrenoceptors and, in part, by inhibition of the nitric oxide system at at least two points. There is also an early vasodilator response to local cooling, dependent on the rate of cooling. The mechanism for that transient vasodilation is not known, but it is inhibited by intact sympathetic vasoconstrictor nerve function and by intact sensory nerve function.

Intradermal administration of ATP does not mitigate tyramine-stimulated vasoconstriction in human skin

Cutaneous vasodilation associated with whole-body heat stress occurs via withdrawal of adrenergic vasoconstriction and engagement of cholinergic "active" vasodilation, the latter of which attenuates cutaneous vasoconstrictor responsiveness. However, the precise neurotransmitter(s) responsible for this sympatholytic-like effect remain unknown. In skeletal muscle, ATP inhibits adrenergically mediated vasoconstriction. ATP also may be responsible for attenuating cutaneous vasoconstriction since it is co-released from cholinergic neurons. The effect of ATP on cutaneous vasoconstrictor responsiveness, however, has not been investigated. Accordingly, this study tested the hypothesis that ATP inhibits adrenergically mediated cutaneous vasoconstriction. To accomplish this objective, four microdialysis probes were inserted in dorsal forearm skin of 11 healthy individuals (mean +/- SD; 35 +/- 11 years). Local temperature at each site was clamped at 34 degrees C throughout the protocol. Skin blood flow was indexed by laser-Doppler flowmetry and was used to calculate cutaneous vascular conductance (CVC; laser-Doppler-derived flux/mean arterial pressure), which was normalized to peak CVC achieved with sodium nitroprusside infusion combined with local skin heating to approximately 42 degrees C. Two membranes were perfused with 30 mM ATP, while the other two membranes were flow matched via administration of 2.8 mM adenosine to serve as control sites. After achieving stable baselines, 1 x 10(-4) M tyramine was administered at all sites, while ATP and adenosine continued to be infused at their respective sites. ATP and adenosine infusion increased CVC from baseline by 35 +/- 26% CVC(peak) units and by 36 +/- 15% CVC(peak) units, respectively (P = 0.75). Tyramine decreased CVC similarly (by about one-third) at all sites (P < 0.001 for main effect and P = 0.32 for interaction). These findings indicate that unlike in skeletal muscle, ATP does not attenuate tyramine-stimulated vasoconstriction in human skin.

Adrenergic control of the human cutaneous circulation

The cutaneous circulation is influenced by a variety of thermoregulatory (skin and internal temperature-driven) and nonthermoregulatory (e.g., baroreflex, exercise-associated reflexes) challenges. The responses to these stimuli are brought about through vasoconstrictor nerves, vasodilator nerves, and changes in the local temperature of the vessels themselves. In this review, we examine how thermoregulatory influences mediate changes in skin blood flow through the sympathetic nervous system. We discuss cutaneous vascular responses to both local and whole-body heating and cooling and the mechanisms underlying these responses, with the overarching conclusion that sympathetic function plays significant roles in reflex vasoconstriction and vasodilatation and in the responses to both local cooling and local heating of the skin.

Reflex vasoconstriction in aged human skin increasingly relies on Rho kinase-dependent mechanisms during whole body cooling

Primary human aging may be associated with augmented Rho kinase (ROCK)-mediated contraction of vascular smooth muscle and ROCK-mediated inhibition of nitric oxide synthase (NOS). We hypothesized that the contribution of ROCK to reflex vasoconstriction (VC) is greater in aged skin. Cutaneous VC was elicited by 1) whole body cooling [mean skin temperature (T(sk)) = 30.5 degrees C] and 2) local norepinephrine (NE) infusion (1 x 10(-6) M). Four microdialysis fibers were placed in the forearm skin of eight young (Y) and eight older (O) subjects for infusion of 1) Ringer solution (control), 2) 3 mM fasudil (ROCK inhibition), 3) 20 mM N(G)-nitro-l-arginine methyl ester (NOS inhibition), and 4) both ROCK + NOS inhibitors. Red cell flux was measured by laser-Doppler flowmetry over each site. Cutaneous vascular conductance (CVC) was calculated as flux/mean arterial pressure and normalized to baseline CVC (%DeltaCVC(baseline)). VC was reduced at the control site in O during cooling (Y, -34 + or - 3; and O, -18 + or - 3%DeltaCVC(baseline); P < 0.001) and NE infusion (Y, -53 + or - 4, and O, -41 + or - 9%DeltaCVC(baseline); P = 0.006). Fasudil attenuated VC in both age groups during mild cooling; however, this reduction remained only in O but not in Y skin during moderate cooling (Y, -30 + or - 5; and O, -7 + or - 1%DeltaCVC(baseline); P = 0.016) and was not altered by NOS inhibition. Fasudil blunted NE-mediated VC in both age groups (Y, -23 + or - 4; and O, -7 + or - 3%DeltaCVC(baseline); P < 0.01). Cumulatively, these data indicate that reflex VC is more reliant on ROCK in aged skin such that approximately half of the total VC response to whole body cooling is ROCK dependent.

Local tetrahydrobiopterin administration augments cutaneous vasoconstriction in aged humans

Reflex vasoconstriction (VC) is attenuated in aged skin resulting in greater skin blood flow and heat loss during cold exposure. We hypothesized that adrenergic function is compromised due to depletion of tetrahydrobiopterin (BH(4)), an essential cofactor required for catecholamine synthesis, and therefore local BH(4) supplementation would functionally augment reflex and pharmacologically induced VC elicited by gradual whole-body cooling (skin temperature (T(sk)) = 30.5 degrees C) and tyramine infusion, respectively. Four microdialysis (MD) fibres were placed in the forearm skin of 11 young (Y) and 11 older (O) human subjects for infusion of (1) Ringer solution (control), (2) 5 mM BH(4), (3) 5 mM BH(4) + 10 mM ascorbate, and (4) 5 mM BH(4) + adrenoreceptor blockade (5 mM yohimbine + 1 mM propranolol). Laser Doppler flux (LDF) was measured over each MD site and cutaneous vascular conductance was calculated as CVC = LDF/MAP and expressed as per cent change from baseline (% DeltaCVC(base)). The VC response was lower at the control site in O during cooling (Y: -34 +/- 2% DeltaCVC(base), O: -17 +/- 2% DeltaCVC(base); P < 0.001) and tyramine infusion (Y: - 33 +/- 4% DeltaCVC(base), O: -15 +/- 3% DeltaCVC(base); P < 0.001). BH(4) infusion normalized O to Y values during both cooling (Y: -34 +/- 4% DeltaCVC(base), O: -34 +/- 2% DeltaCVC(base); P < 0.001) and tyramine (Y: -38 +/- 4% DeltaCVC(base), O: -35 +/- 3% DeltaCVC(base); P < 0.001), however, adding adrenoreceptor blockade abolished VC in aged skin indicating that BH(4) acts through adrenergic, not cotransmitter, mechanisms. Local BH(4) supplementation augments reflex and tyramine-induced VC in aged skin, suggesting that reduced BH(4) bioavailability may contribute to attenuated VC during whole-body cooling.

Neural and non-neural control of skin blood flow during isometric handgrip exercise in the heat stressed human

During heat stress, isometric handgrip (IHG) exercise causes cutaneous vasoconstriction, but it remains controversial whether neural mechanisms are responsible for this observation. The objective of this study was to test the hypothesis that cutaneous vasoconstriction during IHG exercise in heat stressed individuals occurs via a neural mechanism. An axillary nerve blockade was performed to block efferent nerve traffic to the left forearm in seven healthy subjects. Two intradermal microdialysis probes were placed within forearm skin of the blocked area. Forearm skin blood flow was measured by laser-Doppler flowmetry over the microdialysis probes as well as from skin of the contralateral (unblocked) forearm. Cutaneous vascular conductance (CVC) was calculated from the ratio of skin blood flow to mean arterial pressure. Effectiveness of nerve blockade was verified by the absence of tactile sensation, as well as an absence of sweating and cutaneous vasodilatation during a whole-body heat stress. Upon this confirmation, adenosine was perfused through one of the microdialysis probes to increase skin blood flow similar to that of the unblocked site. After internal temperature increased approximately 0.7 degrees C, subjects performed 2 min of IHG exercise at 35% of maximal voluntary contraction using the non-blocked arm. IHG exercise significantly decreased CVC at the unblocked site (82.3 +/- 5.7 to 70.9 +/- 5.4%max, P = 0.005, means +/- S.E.M.) and the adenosine treated site of the blocked arm (75.2 +/- 7.2 to 68.3 +/- 6.6%max, P = 0.005), whereas CVC was unchanged at the blocked site that did not receive adenosine (15.7 +/- 2.8 to 13.7 +/- 2.0%max, P = 0.10). Importantly, the reduction in CVC was greater at the unblocked site than at the adenosine treated site (11.4 +/- 2.6 vs. 6.9 +/- 1.6%max, respectively, P = 0.01). These findings suggest that neural and non-neural mechanisms contribute to the reduction in forearm CVC during IHG exercise in heat stressed humans.

Effect of elevated local temperature on cutaneous vasoconstrictor responsiveness in humans

Cutaneous vascular conductance (CVC) increases in response to local skin heating. Although attenuation of vasoconstrictor responsiveness due to local heating has been demonstrated, the mechanism(s) responsible for this attenuation remains unclear. Nitric oxide has been shown to at least partially contribute to this response, but other mechanisms also may be involved. The purpose of this study was to test the hypothesis that local heating diminishes cutaneous vasoconstrictor responsiveness through a nitric oxide-independent mechanism by altering postsynaptic reactivity to norepinephrine. A follow-up protocol tested the hypothesis that local heating attenuates the presynaptic release of neurotransmitters that cause vasoconstriction, also via non-nitric oxide mechanisms. In protocol I, CVC was assessed in eight subjects during administration of increasing doses of norepinephrine (via intradermal microdialysis) at adjacent sites separately heated to 34 degrees C and 40 degrees C. In protocol II, which was identical to, but separate from, protocol I, CVC was assessed in seven subjects during administration of increasing doses of tyramine, which causes release of neurotransmitters from adrenergic nerves. At each site for both protocols, nitric oxide synthesis was inhibited (via microdialysis administration of N(G)-nitro-l-arginine methyl ester) and flow was matched (via microdialysis administration of adenosine); therefore, temperature was the only variable that differed between the sites. For both protocols, nonlinear regression analysis revealed no difference (P > 0.05) in the effective drug concentration causing 50% of the vasoconstrictor response. Minimum CVC [6.3 +/- 2.0 and 9.0 +/- 4.0% of peak CVC (mean +/- SD) for protocol I and 19.3 +/- 9.3 and 20.5 +/- 11.9% of peak CVC for protocol II at 34 degrees C and 40 degrees C sites, respectively] was not different between sites. Independent of nitric oxide, local skin heating to 40 degrees C does not attenuate adrenergically mediated cutaneous vasoconstriction through pre- or postsynaptic mechanisms.