Exogenous nitric oxide inhibits sympathetically mediated vasoconstriction in human skin

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.

Physiological and Metabolic Adaptation to Heat Stress at Different Altitudes in Yaks

Yaks have strong adaptability to extremely cold and hypoxic conditions but are susceptible to high ambient temperature when yaks are raised in low-altitude areas during the high-temperature season. Twenty-four adult male yaks with similar weights and ages were randomly divided into TN (Thermoneutral, altitude = 3464 m), LHS (Light heat stress, altitude = 1960 m), and MHS (Medium heat stress, altitude = 906 m) groups to evaluate adaptation strategies to HS. Non-targeted and targeted metabolomics were applied to investigate the effects of different extents of HS on yaks. LHS- and MHS-yaks showed higher rectal temperatures and respiratory rates than TN-yaks. MHS-yaks had higher levels of red blood cells (RBCs), hemoglobin (Hb), whole blood relative index of middle shear at a shear rate of 5 S-1 (WMS), whole blood relative index of high shear at a shear rate of 200 S-1 (WHS), Casson viscosity (CV), middle shear flow resistance at a shear rate of 5 S-1 (MSFR), and high shear flow resistance at a shear rate of 200 S-1 (HSFR) as compared to TN- and LHS-yaks. Differential metabolites and metabolic pathways, including fatty acid metabolism, lipid metabolism, glucose metabolism, and amino acid metabolism, were altered by HS. Metabolites in the glucose metabolism pathway in LHS- and MHS-yaks were lower than those in TN-yaks. However, LHS-yaks showed higher levels of metabolites in the HIF-1 signaling pathway compared to TN- and MHS-yaks. Most of the tricarboxylic acid cycle (TCA) intermediates and fatty acids were significantly decreased in MHS-yaks compared to the other two groups. As a whole, yaks raised at a low altitude (25.6 °C) suffered from severe HS, but they adapted to HS with vasodilatation for dissipating heat and the increased antioxidants and metabolite levels of energy substrates.

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.

Impaired l-arginine-nitric oxide pathway contributes to the pathogenesis of resistant hypertension

The precise mechanisms underlying resistant hypertension remain elusive. Reduced nitric oxide (NO) bioavailability is frequently documented in chronic kidney disease, obesity, diabetes and advanced age, all of which are risk factors for resistant hypertension. Sympathetic overactivity and chronic activation of the renin-angiotensin system are salient features of resistant hypertension. Interestingly, recent data indicate that renal sympathetic overactivity can reduce the expression of neuronal nitric oxide synthase in the paraventricular nucleus. Reduced NO levels in the paraventricular nucleus can increase sympathetic outflow and this can create a vicious cycle contributing to resistant hypertension. Angiotensin II can reduce l-arginine transport and hence NO production. Reduced NO levels may reduce the formation of angiotensin 1-7 dampening the cardio-protective effects of the renin-angiotensin system contributing to resistant hypertension. In addition, interleukin-6 (IL-6) is demonstrated to be independently associated with resistant hypertension, and IL-6 can reduce NO synthesis. Despite this, NO levels have not been quantified in resistant hypertension. Findings from a small proof of concept study indicate that NO donors can reduce blood pressure in patients with resistant hypertension but more studies are required to validate these preliminary findings. In the present paper, we put forward the hypothesis that reduced NO bioavailability contributes substantially to the development of resistant hypertension.

Comparison of the effect of Elaeagnus angustifolia flower capsule and sildenafil citrate tablet female sexual interest/arousal disorder in clinical trial study

Background and Aims:

Sexual desire is one of the main issues affecting people's individual and social life. The present study aimed to compare the effects of Elaeagnus angustifolia extract and sildenafil citrate tablet on female sexual interest/arousal disorder (FSIAD) among the women referring to health centers in 2013.

Methods:

In this randomized clinical trial, 125 women between 18 and 40 years old who suffered from FSIAD were divided into Elaeagnus angustifolia, sildenafil citrate, and control groups. The study data were gathered using Female Sexual Function Index (FSFI) and through measurement of TSH and prolactin. The first intervention group had to consume 4.5 g Elaeagnus angustifolia in two divided doses for 35 days and the second one had to use 50 mg sildenafil citrate tablets for 4 weeks one hour before their sexual relationships. On the other hand, the control group was required to consume the placebo. The data were analyzed using the SPSS statistical software (v. 18) and P < 0.05 was considered as statistically significant.

Results:

The frequency of sexual interest/arousal before the intervention was 53.7%, 50. %, and 66.7% in the Elaeagnus angustifolia, sildenafil citrate, and control groups, respectively (P = 0.269). However, these measures were respectively obtained as 19.5%, 33.3%, and 52.4% after the intervention (P = 0.007).

Conclusion:

Both interventions were effective in improvement of sexual interest/arousal. Yet, further studies are required to be conducted on the issue. Therefore, direct examination of health care providers, identifying and diagnosing sexual problems are the most important primary care.

Influences the process of couples’ sexual problems.

Docosahexaenoic acid reduces resting blood pressure but increases muscle sympathetic outflow compared with eicosapentaenoic acid in healthy men and women

Supplementation with monounsaturated or ω-3 polyunsaturated fatty acids ( n-3 PUFA) can lower resting blood pressure (BP) and reduce the risk of cardiovascular events. The independent contributions of the n-3 PUFAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on BP, and the mechanisms responsible, are unclear. We tested whether EPA, DHA, and olive oil (OO), a source of monounsaturated fat, differentially affect resting hemodynamics and muscle sympathetic nerve activity (MSNA). Eighty-six healthy young men and women were recruited to participate in a 12-wk, randomized, double-blind trial examining the effects of orally supplementing ~3 g/day of EPA ( n = 28), DHA ( n = 28), or OO ( n = 30) on resting hemodynamics; MSNA was examined in a subset of participants ( n = 31). Both EPA and DHA supplements increased the ω-3 index ( P < 0.01). Reductions in systolic BP were greater [adjusted intergroup mean difference (95% confidence interval)] after DHA [−3.4 mmHg (−0.9, −5.9), P = 0.008] and OO [−3.0 mmHg (−0.5, −5.4), P = 0.01] compared with EPA, with no difference between DHA and OO ( P = 0.74). Reductions in diastolic BP were greater following DHA [−3.4 mmHg (−1.3,−5.6), P = 0.002] and OO [−2.2 mmHg (0.08,−4.3), P = 0.04] compared with EPA. EPA increased heart rate compared with DHA [4.2 beats/min (−0.009, 8.4), P = 0.05] and OO [4.2 beats/min, (0.08, 8.3), P = 0.04]. MSNA burst frequency was higher after DHA [4 bursts/min (0.5, 8.3), P = 0.02] but not OO [−3 bursts/min (−6, 0.6), P = 0.2] compared with EPA. Overall, DHA and OO evoked similar responses in resting BP; however, DHA, but not OO, increased peripheral vasoconstrictor outflow. These findings may have implications for fatty acid supplementation in clinical populations characterized by chronic high BP and sympathetic overactivation.

NEW & NOTEWORTHY We studied the effects of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and olive oil supplementation on blood pressure (BP) and muscle sympathetic nerve activity (MSNA). After 12 wk of 3 g/day supplementation, DHA and olive oil were associated with lower resting systolic and diastolic BPs than EPA. However, DHA increased MSNA compared with EPA. The reductions in BP with DHA likely occur via a vascular mechanism and evoke a baroreflex-mediated increase in sympathetic activity.

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.

Skin vasoconstriction as a heat conservation thermoeffector

Cold exposure stimulates heat production and conservation to protect internal temperature. Heat conservation is brought about via reductions in skin blood flow. The focus, here, is an exploration of the mechanisms, particularly in humans, leading to that cutaneous vasoconstriction. Local skin cooling has several effects: (1) reduction of tonic nitric oxide formation by inhibiting nitric oxide synthase and element(s) downstream of the enzyme, which removes tonic vasodilator effects, yielding a relative vasoconstriction; (2) translocation of intracellular alpha-2c adrenoceptors to the vascular smooth-muscle cell membrane, enhancing adrenergic vasoconstriction; (3) increased norepinephrine release from vasoconstrictor nerves; and (4) cold-induced vasodilation, seen more clearly in anastomoses-rich glabrous skin. Cold-induced vasodilation occurs in nonglabrous skin when nitric oxide synthase or sympathetic function is blocked. Reflex responses to general body cooling complement these local effects. Sympathetic excitation leads to the increased release of norepinephrine and its cotransmitter neuropeptide Y, each of which contributes significantly to the vasoconstriction. The contributions of these two transmitters vary with aging, disease and, in women, reproductive hormone status. Interaction between local and reflex mechanisms is in part through effects on baseline and in part through removal of the inhibitory effects of nitric oxide on adrenergic vasoconstriction.

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.

Augmented Endothelial-Specific L-Arginine Transport Blunts the Contribution of the Sympathetic Nervous System to Obesity Induced Hypertension in Mice

Augmenting endothelial specific transport of the nitric oxide precursor L-arginine via cationic amino acid transporter-1 (CAT1) can prevent obesity related hypertension. We tested the hypotheses that CAT1 overexpression prevents obesity-induced hypertension by buffering the influence of the sympathetic nervous system (SNS) on the maintenance of arterial pressure and by buffering pressor responses to stress. Wild type (WT; n=13) and CAT1 overexpressing mice (CAT+; n=13) were fed a normal or a high fat diet for 20 weeks. Mice fed a high fat diet were returned to the control diet before experiments commenced. Baseline mean arterial pressure (MAP) and effects of restraint-, shaker- and almond feeding-stress and ganglionic blockade (pentolinium; 5 mg/kg; i.p.) on MAP were determined in conscious mice. Fat feeding increased body weight to a similar extent in WT and CAT+ but MAP was greater only in WT compared to appropriate controls (by 29%). The depressor response to pentolinium was 65% greater in obese WT than lean WT (P < 0.001), but was similar in obese and lean CAT+ (P = 0.65). In lean WT and CAT+, pressor responses to shaker and feeding stress, but not restraint stress, were less in the latter genotype compared to the former (P ≤ 0.001). Pressor responses to shaker and feeding stress were less in obese WT than lean WT (P ≤ 0.001), but similar in obese and lean CAT+. The increase in MAP in response to restraint stress was less in obese WT (22 ± 2%), but greater in obese CAT+ (37 ± 2%), when compared to respective lean WT (31 ± 3%) and lean CAT+ controls (27 ± 2%; P ≤ 0.02). We conclude that CAT1 overexpression prevents obesity-induced hypertension by reducing the influence of the SNS on the maintenance of arterial pressure but not by buffering pressor responses to stress.

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.

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.

Forehead versus forearm skin vascular responses at presyncope in humans

Facial pallor is commonly observed at presyncope in humans, suggestive of reductions in facial skin blood flow (SkBF). Yet, cutaneous vasoconstriction is usually minimal at presyncope when measured at the forearm. We tested the hypothesis that reductions in forehead SkBF at presyncope are greater than in the forearm. Forehead and forearm SkBF (laser-Doppler) and blood pressure (Finometer or radial artery catheterization) were measured during lower body negative pressure (LBNP) to presyncope in 11 normothermic and 13 heat-stressed subjects (intestinal temperature increased ∼1.4°C). LBNP reduced mean arterial pressure from 91 ± 5 to 57 ± 7 mmHg during normothermia (P ≤ 0.001) and from 82 ± 5 to 57 ± 7 mmHg during heat stress (P ≤ 0.001). During normothermia, LBNP decreased forehead SkBF 55 ± 14% compared with 24 ± 11% at the forearm (P = 0.002), while during heat stress LBNP decreased forehead SkBF 39 ± 11% compared with 28 ± 8% in the forearm (P = 0.007). In both conditions, most (≥68%) of the decreases in SkBF were due to decreases in blood pressure. However, a greater contribution of actively mediated reductions in SkBF was observed at the forehead, relative to the forearm during normothermia (32 ± 13% vs. 11 ± 11%, P = 0.031) and heat stress (30 ± 13% vs. 10 ± 13%, P = 0.004). These data suggest that facial pallor at presyncope is due to a combination of passive decreases in forehead SkBF secondary to reductions in blood pressure and to active decreases in SkBF, the latter of which are relatively greater than in the forearm.

Comparison of Elaeagnus angustifolia Extract and Sildenafil Citrate on Female Orgasmic Disorders: A Randomized Clinical Trial

BACKGROUND

Orgasmic disorder can create a feeling of deprivation and failure and provide mental problems, incompatibility and marital discord. This study aimed to compare the effects of Elaeagnus angustifolia flower extract and sildenafil citrate on female orgasmic disorder in women in 2013.

METHODS

In this randomized clinical trial, 125 women between 18-40 years old who suffered from orgasmic disorder were divided into three E. angustifolia, sildenafil citrate and control groups. The data were gathered using Female Sexual Function Index and through measurement of TSH and prolactin. The first intervention group had to consume 4.5 gr E. angustifolia extract in two divided doses for 35 days and the second one had to use 50 mg sildenafil citrate tablets for 4 weeks one hour before their sexual relationship. However, the control group had to consume the placebo. The data were analyzed using paired t-test, one-way ANOVA, and Bonferroni posthoc test and p<0.05 was considered significant.

RESULTS

The frequency of orgasmic disorder before the intervention was 41.5%, 40.5%, and 57.1% in E. angustifolia, sildenafil citrate, and control groups, respectively (p=0.23). However, these measures were respectively 29.3%, 16.7%, and 50% after the intervention (p=0.004). A significant difference between the two groups regarding sexual satisfaction after the intervention (p=0.003) compared to the beginning of the study (p=0.356). Besides, the highest reduction of changes after the intervention (58.82%) was observed in the sildenafil citrate group.

CONCLUSION

Both E. angustifolia extract and sildenafil citrate were effective in reduction of the frequency of orgasmic disorder in women.

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.

Analysis of the degree of insulin resistance in post menopausal women by using skin temperature measurements and fasting insulin and fasting glucose levels: a case control study

INTRODUCTION

In addition to being associated with the termination of the reproductive life in women, menopause coincides with an increase in several co-morbidities which include insulin resistance. An increase in the insulin resistance is associated with an increased risk of diabetes, cardiovascular disease and breast cancer.

AIM

To analyze the degree of insulin resistance in post menopausal women by using skin temperature measurements and to confirm the insulin resistance from the fasting insulin and the fasting glucose levels.

METHODS

The insulin insensitivity was assessed by using skin temperature measurements and this was further proved by assessing the fasting insulin and the fasting glucose levels, and by incorporating the values for the Homeostatic model assessment (HOMA) and the Quantitative insulin sensitivity check index (QUICKI).

STATISTICAL ANALYSIS

This was a case control study and the association was found by applying Fischer's exact test and the P value was estimated. The statistical significance was set at p < 0.05. Student's t test was applied to determine the significant difference in the skin temperature measurements.

RESULTS

By using the HOMA index, only 15 subjects out of the 25 post menopausal women were identified to be insulin resistant. 11 of them were also identified by QUICKI. No premenopausal woman from the recruited population showed insulin resistance with the HOMA and the QUICKI indices. The skin temperature measurements showed significant correlations with the HOMA and the QUICKI indices. There was a significant decrease (p value < 0.0001) in the skin temperature in the postmenopausal women as compared to that in the premenopausal women. The mean ± SD was found to be 0.3834 ± 0.1666 in the premenopausal women, and it was 2.192 ± 3.943 in the postmenopausal women.

CONCLUSION

This study suggests a linear correlation between the skin temperature measurements and the insulin resistance. An increased prevalence of insulin resistance was seen in the postmenopausal women as compared to the premenopausal women.

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.

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.

Effect of whole body heat stress on peripheral vasoconstriction during leg dependency

The venoarteriolar response (VAR) increases vascular resistance upon increases in venous transmural pressure in cutaneous, subcutaneous, and muscle vascular beds. During orthostasis, it has been proposed that up to 45% of the increase in systemic vascular tone is due to VAR-related local mechanism(s). The objective of this project was to test the hypothesis that heat stress attenuates VAR-mediated cutaneous and whole leg vasoconstriction. During normothermic conditions, measurements of cutaneous blood flow (laser-Doppler flowmetry) and femoral artery blood flow (Doppler ultrasound) were obtained from both legs during supine and leg-dependent conditions. These measurements were repeated following a whole body heat stress (increase in internal temperature of 1.4 +/- 0.2 degrees C). Before leg dependency, cutaneous (CVC) and femoral vascular conductances (FVC) were significantly elevated in both legs during heat stress relative to normothermia (P < 0.001). During leg dependency the absolute decrease in CVC was attenuated during heat stress (P < 0.01) while the absolute decrease in FVC was unaffected (P = 0.90). When CVC and FVC data were analyzed as a relative change from their respective baseline values, heat stress significantly attenuated the magnitude of vasoconstriction due to leg dependency in the cutaneous and femoral circulations (P < 0.001 for both variables). These data suggest that an attenuated local vasoconstriction, evoked via the venoarteriolar response, may contribute to reduced blood pressure control and thus reduced orthostatic tolerance that occurs in heat-stressed individuals.

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.

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.

Nitric oxide inhibits cutaneous vasoconstriction to exogenous norepinephrine

Previously, we found that nitric oxide (NO) inhibits cutaneous vasoconstrictor responsiveness evoked by whole body cooling, as well as an orthostatic stress in the heat-stressed human (Shibasaki M, Durand S, Davis SL, Cui J, Low DA, Keller DM, Crandall CG. J Physiol 585: 627-634, 2007). However, it remains unknown whether this response occurs via NO acting through presynaptic or postsynaptic mechanisms. The aim of this study was to test the hypothesis that NO is capable of impairing cutaneous vasoconstriction via postsynaptic mechanisms. Skin blood flow was monitored over two forearm sites where intradermal microdialysis membranes were previously placed. Skin blood flow was elevated four- to fivefold through perfusion of the NO donor sodium nitroprusside at one site and through perfusion of adenosine (primarily non-NO mechanisms) at a second site. Once a plateau in vasodilation was evident, increasing concentrations of norepinephrine (1 x 10(-8) to 1 x 10(-2) M) were administrated through both microdialysis probes, while the aforementioned vasodilator agents continued to be perfused. Cutaneous vascular conductance was calculated by dividing skin blood flow by mean arterial blood pressure. The administration of norepinephrine decreased cutaneous vascular conductance at both sites. However, the dose of norepinephrine at the onset of vasoconstriction (-5.9 +/- 1.3 vs. -7.2 +/- 0.7 log M norepinephrine, P = 0.021) and the concentration of norepinephrine resulting in 50% of the maximal vasoconstrictor response (-4.9 +/- 1.2 vs. -6.1 +/- 0.2 log M norepinephrine dose; P = 0.012) occurred at significantly higher norepinephrine concentrations for the sodium nitroprusside site relative to the adenosine site, respectively. These results suggested that NO is capable of attenuating cutaneous vasoconstrictor responsiveness to norepinephrine via postsynaptic mechanisms.

Decoding rule from vasoconstrictor skin sympathetic nerve activity to nonglabrous skin blood flow in humans at normothermic rest

Although an importance of vasoconstrictor skin sympathetic nerve activity (SNA) in control of cutaneous circulation is widely recognized, the decoding rule that translate dynamic fluctuations of vasoconstrictor skin SNA into skin blood flow is not fully understood. In 10 male subjects who rested in supine position under normothermic condition, we measured skin blood flow index (by laser-Doppler flowmetry) at the dorsum pedis, and vasoconstrictor skin SNA (by microneurography) that was confirmed to innervate the same region as the flow index. We determined the transfer and coherence functions from the neural activity input to the flow and quantified the contribution and predictability from the input to output by system engineering technique. The results showed that in frequency-domain analysis, the transfer function from vasoconstrictor skin SNA to skin blood flow had low-pass filter characteristics with 3.6+/-0.1s of pure time delay. The coherence function was approximately 0.5 between 0.01 and 0.1Hz and less above 0.1Hz. In time-domain analysis, the predictability from the SNA to the skin blood flow was approximately 50%. These findings indicate that at normothermic rest, the decoding rule from vasoconstrictor skin SNA to skin blood flow of skin is characterized by low-pass filter with 3-4s of pure time delay, and that the vasoconstrictor skin SNA contributes to a half of fluctuation of skin blood flow in the condition. The incomplete dependence of skin blood flow on vasoconstrictor skin SNA may confirm nonneural mechanisms to control cutaneous circulation even at normothermic rest.

Endogenous nitric oxide attenuates neutrally mediated cutaneous vasoconstriction

Cutaneous vasoconstrictor responsiveness may be impaired by substance(s) directly or indirectly responsible for cutaneous active vasodilatation. In this study, we tested the hypothesis that endogenous nitric oxide (NO) attenuates the reduction in cutaneous vascular conductance (CVC) during an orthostatic challenge combined with whole-body heating, as well as during whole-body cooling. In protocol 1, healthy subjects were pretreated with an intradermal injection of botulinum toxin A (BTX) to block the release of neurotransmitters from nerves responsible for cutaneous active vasodilatation. On the experimental day, a microdialysis probe was placed at the BTX-treated site as well as at two adjacent untreated sites. NG-nitro-l-arginine methyl ester (L-NAME, 10 mm) was perfused through the probe placed at the BTX-treated site and at one untreated site. After confirmation of the absence of cutaneous vasodilatation at the BTX site during whole-body heating, adenosine was infused through the microdialysis probe at this site to increase skin blood flow to a level similar to that at the untreated site. Subsequently, 30 and 40 mmHg lower-body negative pressures (LBNPs) were applied. The reduction in CVC to LBNP was greatest at the BTX-treated site (15.0 +/- 2.4% of the maximum level (% max)), followed by the L-NAME-treated site (11.3 +/- 2.6% max), and then the untreated site (3.8 +/- 3.0% max; P < 0.05 for all comparisons). In protocol 2, two microdialysis membranes were inserted in the dermal space of one forearm. Adenosine alone was infused at one site while the other site received adenosine and L-NAME. The reduction in CVC in response to whole-body cooling was significantly greater at the L-NAME-treated site than at the adjacent adenosine alone site. These results suggest that endogenous NO is capable of attenuating cutaneous vasoconstrictor responsiveness.

The role of baseline in the cutaneous vasoconstrictor responses during combined local and whole body cooling in humans

Previous work showed that local cooling (LC) attenuates the vasoconstrictor response to whole body cooling (WBC). We tested the extent to which this attenuation was due to the decreased baseline skin blood flow following LC. In eight subjects, skin blood flow was assessed using laser-Doppler flowmetry (LDF). Cutaneous vascular conductance (CVC) was expressed as LDF divided by blood pressure. Subjects were dressed in water-perfused suits to control WBC. Four forearm sites were prepared with microdialysis fibers, local heating/cooling probe holders, and laser-Doppler probes. Three sites were locally cooled from 34 to 28 degrees C, reducing CVC to 45.9 +/- 3.9, 42 +/- 3.9, and 44.5 +/- 4.8% of baseline (P < 0.05 vs. baseline; P > 0.05 among sites). At two sites, CVC was restored to precooling baseline levels with sodium nitroprusside (SNP) or isoproterenol (Iso), increasing CVC to 106.4 +/- 12.4 and 98.9 +/- 10.1% of baseline, respectively (P > 0.05 vs. precooling). Whole body skin temperature, apart from the area of blood flow measurement, was reduced from 34 to 31 degrees C. Relative to the original baseline, CVC decreased (P < 0.05) by 44.9 +/- 2.8 (control), 11.3 +/- 2.4 (LC only), 29 +/- 3.7 (SNP), and 45.8 +/- 8.7% (Iso). The reductions at LC only and SNP sites were less than at control or Iso sites (P < 0.05); the responses at those latter sites were not different (P > 0.05), suggesting that the baseline change in CVC with LC is important in the attenuation of reflex vasoconstrictor responses to WBC.

Does local heating-induced nitric oxide production attenuate vasoconstrictor responsiveness to lower body negative pressure in human skin?

We tested the hypothesis that local heating-induced nitric oxide (NO) production attenuates cutaneous vasoconstrictor responsiveness. Eleven subjects (6 men, 5 women) had four microdialysis membranes placed in forearm skin. Two membranes were perfused with 10 mM of N(G)-nitro-L-arginine (L-NAME) and two with Ringer solution (control), and all sites were locally heated to 34 degrees C. Subjects then underwent 5 min of 60-mmHg lower body negative pressure (LBNP). Two sites (a control and an L-NAME site) were then heated to 39 degrees C, while the other two sites were heated to 42 degrees C. At the L-NAME sites, skin blood flow was elevated using 0.75-2 mg/ml of adenosine in the perfusate solution (Adn + L-NAME) to a similar level relative to control sites. Subjects then underwent another 5 min of 60-mmHg LBNP. At 34 degrees C, cutaneous vascular conductance (CVC) decreased (Delta) similarly at both control and L-NAME sites during LBNP (Delta7.9 +/- 3.0 and Delta3.4 +/- 0.8% maximum, respectively; P > 0.05). The reduction in CVC to LBNP was also similar between control and Adn + L-NAME sites at 39 degrees C (control Delta11.4 +/- 2.5 vs. Adn + L-NAME Delta7.9 +/- 2.0% maximum; P > 0.05) and 42 degrees C (control Delta1.9 +/- 2.7 vs. Adn + L-NAME Delta 4.2 +/- 2.7% maximum; P > 0.05). However, the decrease in CVC at 42 degrees C, regardless of site, was smaller than at 39 degrees C (P < 0.05). These results do not support the hypothesis that local heating-induced NO production attenuates cutaneous vasoconstrictor responsiveness during high levels of LBNP. However, elevated local temperature, per se, attenuates cutaneous vasoconstrictor responsiveness to LBNP, presumably through non-nitric oxide mechanisms.

Relationship between muscle sympathetic nerve activity and systemic hemodynamics during nitric oxide synthase inhibition in humans

Large interindividual differences exist in resting sympathetic nerve activity (SNA) among normotensive humans with similar arterial pressure (AP). We recently showed inverse relationships of resting SNA with cardiac output (CO) and vascular adrenergic responsiveness that appear to balance the influence of differences in SNA on blood pressure. In the present study, we tested whether nitric oxide (NO)-mediated vasodilation has a role in this balance by evaluating hemodynamic responses to systemic NO synthase (NOS) inhibition in individuals with low and high resting muscle SNA (MSNA). We measured MSNA via peroneal microneurography, CO via acetylene uptake and AP directly, at baseline and during increasing systemic doses of the NOS inhibitor NG-monomethyl-l-arginine (l-NMMA). Baseline MSNA ranged from 9 to 38 bursts/min (13 to 68 bursts/100 heartbeats). l-NMMA caused dose-dependent increases in AP and total peripheral resistance and reflex decreases in CO and MSNA. Increases in AP with l-NMMA were greater in individuals with high baseline MSNA ( PANOVA < 0.05). For example, after 8.5 mg/kg of l-NMMA, in the low MSNA subgroup ( n = 6, 28 ± 4 bursts/100 heartbeats), AP increased 9 ± 1 mmHg, whereas in the high-MSNA subgroup ( n = 6, 58 ± 3 bursts/100 heartbeats), AP increased 15 ± 2 mmHg ( P < 0.01). The high-MSNA subgroup had lower baseline CO and smaller decreases in CO with l-NMMA, but changes in total peripheral resistance were not different between groups. We conclude that differences in CO among individuals with varying sympathetic traffic have important hemodynamic implications during disruption of NO-mediated vasodilation.

Nitric oxide and noradrenaline contribute to the temperature threshold of the axon reflex response to gradual local heating in human skin

The initial skin blood flow response to rapid local heating is an axon reflex, which may be mediated by calcitonin gene-related peptide and substance P released from C-fibres. We investigated the role of nitric oxide (NO) and noradrenaline on the temperature threshold for the axon reflex during gradual local heating. 36 subjects participated in two studies. Using microdialysis, we examined the following interventions: NO synthase inhibition (10 mM N(G)-nitro-L-arginine methyl ester, L-NAME); low-dose NO infusion (1.0 microM sodium nitroprusside, SNP); adrenergic blockade (10 mM bretylium tosylate); and low-dose (0.1 microM) noradrenaline infusion. Laser-Doppler flowmetry was used to measure red blood cell flux. Skin was heated at a rate of 0.1 degrees C min(-1) from 33 degrees C to 40 degrees C. Compared to control skin sites, the axon reflex response was shifted to a higher temperature in 4 subjects in the L-NAME sites (control, 37.0 +/- 0.3 degrees C, n = 16; L-NAME, 39.8 +/- 0.1 degrees C, n = 4; P < 0.001) and absent in 12 subjects. The response was also absent in L-NAME plus low-dose SNP sites and not altered by low-dose SNP infusion alone. Adrenergic blockade, with and without low-dose noradrenaline infusion, also abolished the axon reflex response in all subjects. Low-dose noradrenaline infusion alone shifted the axon reflex to a significantly lower temperature threshold compared to control sites (control, 38.2 +/- 0.5 degrees C; noradrenaline, 37.7 +/- 0.4 degrees C, P < 0.05, n = 5). These results suggest that endogenous NO and noradrenaline contribute to the temperature threshold of the axon reflex response during gradual local heating of the skin.

Bicyclic monoterpene diols stimulate release of nitric oxide from skin cells, increase microcirculation, and elevate skin temperature

Bicyclic monoterpene diols (BMTd) stimulate nitric oxide synthesis in melanoma and neuronal cells, representing cell types arising from embryonic neural crest tissue. This study shows that an equimolar mixture of the BMTd's 2,3-cis/exo-pinanediol and 2,3-cis/exo-camphanediol stimulates nitric oxide synthesis in epithelial cells of the skin, specifically normal human epidermal keratinocytes (NHEK) and normal human microvascular endothelial cells (HMVEC). A 1 mM mixture increased nitric oxide 3-fold in HMVEC in the first 24 h after treatment, and a 2 mM mixture produced an equivalent increase in NHEK. We hypothesized that an increase in nitric oxide in skin would lead to an increase in microcirculation, thereby increasing skin temperature. We found that twice daily application of 1mM BMTd lotion significantly increased arm skin temperature by 0.5 degrees C in 14 days compared to placebo, while a 2 mM mixture significantly increased skin temperature by 0.3 degrees C in 7 days (P < or = 0.05; ANOVA). A single application of a 2 mM BMTd mixture applied 30 min before a 30 min cold challenge (6 degrees C), maintained facial skin temperature 1.4 degrees C above untreated control sites (P < or = 0.05; ANOVA). We also tested whether BMTd treatment would benefit people with dark circles under their eyes. Twenty-six panelists with dark undereye circles completed 2-week, twice daily application of a lotion containing the 1mM mixture to one eye while the other eye was untreated. Seven of 26 subjects showed a reduction of darkness of undereye circles (P < or = 0.05; paired t test). Application of 2 mM BMTd lotion to lips resulted in a significant increase in their redness, as measured by the erythema index (P < or = 0.05; ANOVA). These results show that a mixture of BMTd's increases nitric oxide, and application to skin increases microcirculation and skin temperature.

The involvement of nitric oxide in the cutaneous vasoconstrictor response to local cooling in humans

Cutaneous vascular conductance (CVC) declines in response to local cooling (LC). Previous work indicates that at least part of the vasoconstrictor response to LC may be through an inhibitory effect on nitric oxide synthase (NOS) activity. In this study we further tested that notion. A total of eight (6 male, 2 female) subjects participated (Part 1 n = 7; Part 2 n = 5, 4 of whom participated in Part 1). Skin blood flow was monitored by laser-Doppler flowmetry. Control of local skin and body temperatures was achieved with Peltier cooler/heater probe holders and water perfused suits, respectively. Microdialysis fibres were inserted aseptically. Saline, L-NAME (20 mM; to inhibit NOS activity) and sodium nitroprusside (SNP 10 microM) were infused by microdialysis. Bretylium tosylate (BT), to block adrenergic function, was administered by iontophoresis. CVC was calculated from blood flow and blood pressure. Part 1 was designed to determine the relative roles of the NO and the adrenergic systems. The infusion of L-NAME elicited a 35 +/- 4% decrease in CVC at the L-NAME and BT + L-NAME sites (P < 0.05); subsequent slow LC (34-24 degrees C) for 35 min caused a significant (P < 0.05) decrease in CVC at control sites (68 +/- 4%) and at the BT treated sites (39 +/- 5%). LC caused a further 23 +/- 5% of initial baseline decrease in CVC at the L-NAME treated sites (P < 0.05). Importantly, CVC at the BT + L-NAME sites was unaffected by LC (P > 0.05). Part 2 was designed to test whether LC influences were specific to the NOS enzymes. Two sites were pretreated with both BT and L-NAME. After 50 min, SNP was added as an NO donor to restore baseline CVC at one site. The same LC process as in Part 1 was applied. There was a 24 +/- 10% decrease (P < 0.05) in CVC at sites with baseline CVC restored, while, as in Part 1, there was no change (P > 0.05) at sites treated with BT + L-NAME only. These data suggest that the vasoconstriction with slow LC is due to a combination of increased noradrenaline release and decreased activity of both NOS per se and of process(es) downstream of NOS.

Rate dependency and role of nitric oxide in the vascular response to direct cooling in human skin

Local cooling of nonglabrous skin without functional sympathetic nerves causes an initial vasodilation followed by vasoconstriction. To further characterize these responses to local cooling, we examined the importance of the rate of local cooling and the effect of nitric oxide synthase (NOS) inhibition in intact skin and in skin with vasoconstrictor function inhibited. Release of norepinephrine was blocked locally (iontophoresis) with bretylium tosylate (BT). Skin blood flow was monitored from the forearm by laser-Doppler flowmetry (LDF). Cutaneous vascular conductance (CVC) was calculated as the ratio of LDF to blood pressure. Local temperature was controlled over 6.3 cm2 around the sites of LDF measurement. Local cooling was applied at -0.33 or -4 degrees C/min. At -4 degrees C/min, CVC increased (P < 0.05) at BT sites in the early phase. At -0.33 degrees C/min, there was no early vasodilator response, but there was a delay in the onset of vasoconstriction relative to intact skin. The NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) (intradermal microdialysis) decreased (P < 0.05) CVC by 28.3 +/- 3.8% at untreated sites and by 46.9 +/- 6.3% at BT-treated sites from the value before infusion. Rapid local cooling (-4 degrees C/min) to 24 degrees C decreased (P < 0.05) CVC at both untreated (saline) sites and L-NAME only sites from the precooling levels, but it transiently increased (P < 0.05) CVC at both BT + saline sites and BT + L-NAME sites in the early phase. After 35-45 min of local cooling, CVC decreased at BT + saline sites relative to the precooling levels (P < 0.05), but at BT + L-NAME sites CVC was not reduced below the precooling level (P = 0.29). These findings suggest that the rate of local cooling, but not functional NOS, is an important determinant of the early non-adrenergic vasodilator response to local cooling and that functional NOS, adrenergic nerves, as well as other mechanisms play roles in vasoconstriction during prolonged local cooling of skin.