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.

Oral sapropterin acutely augments reflex vasodilation in aged human skin through nitric oxide-dependent mechanisms

Functional constitutive nitric oxide synthase (NOS) and its cofactor tetrahydrobiopterin (BH4) are required for full reflex cutaneous vasodilation and are attenuated in primary aging. Acute, locally administered BH4 increases reflex vasodilation through NO-dependent mechanisms in aged skin. We hypothesized that oral sapropterin (Kuvan, shelf-stable pharmaceutical formulation of BH4) would augment reflex vasodilation in aged human skin during hyperthermia. Nine healthy human subjects (76 ± 1 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 of sapropterin for measurement of plasma BH4. Three intradermal microdialysis fibers were placed in the forearm skin for local delivery of 1) lactated Ringer's solution, 2) 10 mM BH4, and 3) 20 mM N(G)-nitro-l-arginine methyl ester (l-NAME) to inhibit NOS. Red cell flux was measured at each site by laser-Doppler flowmetry (LDF) as reflex vasodilation was induced using a water-perfused suit. At 1°C rise in oral temperature, mean body temperature was clamped and 20 mM l-NAME was perfused at each site. Cutaneous vascular conductance was calculated (CVC = LDF/MAP) and expressed as a percentage of maximum (%CVCmax 28 mM sodium nitroprusside and local heat 43°C). Plasma concentrations of BH4 were significantly elevated 3 h after ingestion of sapropterin (0 h: 19.1 ± 2 pmol/ml vs. 3 h: 43.8 ± 3 pmol/ml; P < 0.001). Sapropterin increased NO-dependent vasodilation at control site (placebo: 14 ± 1 %CVCmax vs. sapropterin: 25 ± 4 %CVCmax; P = 0.004). Local BH4 administration increased NO-dependent vasodilation compared with control in placebo trials only (control: 14 ± 1 %CVCmax vs. BH4-treated: 24 ± 3 %CVCmax; P = 0.02). These data suggest oral sapropterin increases bioavailable BH4 in aged skin microvasculature sufficiently to increase NO synthesis through NOS and that sapropterin may be a viable intervention to increase skin blood flow during hyperthermia in healthy aged humans.

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

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

Nonuniform, age-related decrements in regional sweating and skin blood flow

Aging is associated with attenuated thermoregulatory function that varies regionally over the body. Decrements in vasodilation and sweating are well documented with age, yet limited data are available concerning the regional relation between these responses. We aimed to examine age-related alterations in the relation between regional sweating (RSR) and skin blood flow (SkBF) to thermal and pharmacological stimuli. Four microdialysis fibers were inserted in the ventral forearm, abdomen, thigh, and lower back of eight healthy aged subjects (64 ± 7 yr) and nine young (23 ± 3 yr) during 1) ACh dose response (1 × 10(-7) to 0.1 M, mean skin temperature 34°C) and 2) passive whole body heating to Δ1°C rise in oral temperature (Tor). RSR and SkBF were measured over each microdialysis membrane using ventilated capsules and laser-Doppler flowmetry. Maximal SkBF was measured at the end of both protocols (50 mM SNP). Regional sweating thresholds and RSR were attenuated in aged vs. young at all sites (P < 0.0001) during whole body heating. Vasodilation thresholds were similar between groups (P > 0.05). Attenuated SkBF were observed at the arm and back in the aged, representing 56 and 82% of those in the young at these sites, respectively (0.5 ΔTor). During ACh perfusion, SkBF (P = 0.137) and RSR were similar between groups (P = 0.326). Together these findings suggest regional age-related decrements in heat-activated sweat gland function but not cholinergic sensitivity. Functional consequences of such thermoregulatory impairment include the compromised ability of older individuals to defend core temperature during heat exposure and a subsequently greater susceptibility to heat-related illness and injury.

Oral clopidogrel improves cutaneous microvascular function through EDHF-dependent mechanisms in middle-aged humans

Platelet P₂Y₁₂-ADP and COX-1 receptor inhibition with oral clopidogrel (CLO) and low-dose aspirin (ASA), respectively, attenuates reflex-mediated cutaneous vasodilation, but little is known about how these medications affect local vasodilatory signaling. Reactive hyperemia (RH) results in vasodilation that is mediated by sensory nerves and endothelium-derived hyperpolarization factors (EDHF) through large-conductance calcium-activated potassium channels, whereas slow local heating (LH) elicits vasodilation largely through the production of nitric oxide (NO). We hypothesized that CLO and ASA would attenuate locally mediated cutaneous vasodilation assessed by RH and LH (0.5°C/min). In a randomized, cross-over, double-blind placebo-controlled study, nine healthy men and women (56 ± 1 yr) took CLO (75 mg), ASA (81 mg), and placebo for 7 days. Skin blood flow was measured (laser-Doppler flowmetry, LDF) and cutaneous vascular conductance (CVC) was calculated (LDF/mean arterial pressure) and normalized to maximal CVC (%CVCmax: 43°C and 28 mM sodium nitroprusside). RH response parameters, including area under the curve (AUC), total hyperemic response (THR), and the decay constant tau (λ) were calculated. NO-dependent vasodilation during LH was assessed by calculating the difference in %CVCmax between a control site and an NO synthase-inhibited site (10 mM l-NAME: intradermal microdialysis). CLO augmented the AUC and THR (AUCclo = 3,783 ± 342; THRclo = 2,306 ± 266% CVCmax/s) of the RH response compared with ASA (AUCASA = 3,101 ± 325; THRASA = 1,695 ± 197% CVCmax/s) and placebo (AUCPlacebo = 3,000 ± 283; THRPlacebo = 1,675 ± 170% CVCmax/s; all P < 0.0001 vs. CLO). There was no difference in the LH response or calculated NO-dependent vasodilation among treatments (all P > 0.05). Oral CLO treatment augments vasodilation during RH but not LH, suggesting that CLO may improve cutaneous microvascular function.

Effect of short-term heat acclimation on endurance time and skin blood flow in trained athletes

Background

To examine whether short-term, ie, five daily sessions, vigorous dynamic cycling exercise and heat exposure could achieve heat acclimation in trained athletes and the effect of heat acclimation on cutaneous blood flow in the active and nonactive limb.

Methods

Fourteen male badminton and table tennis athletes (age = 19.6 ± 1.2 years) were randomized into a heat acclimation (EXP, n = 7) or nonheat acclimation (CON, n = 7) group. For 5 consecutive days, the EXP group was trained using an upright leg cycle ergometer in a hot environment (38.4°C ± 0.4°C), while the CON group trained in a thermoneutral environment (24.1°C ± 0.3°C). For both groups, the training intensity and duration increased from a work rate of 10% below ventilatory threshold (VT) and 25 minutes per session on day 1, to 10% above VT and 45 minutes per session on day 5. Subjects performed two incremental leg cycle exercise tests to exhaustion at baseline and post-training in both hot and thermoneutral conditions. Study outcome measurements include: maximum oxygen uptake (VO_2max); exercise heart rate (HR); O₂ pulse; exercise time to exhaustion (t_max); skin blood flow in the upper arm (SkBF_a) and quadriceps (SkBF_q); and mean skin (T_sk).

Results

The significant heat-acclimated outcome measurements obtained during high-intensity leg cycling exercise in the high ambient environment are: (1) 56%–100% reduction in cutaneous blood flow to the active limbs during leg cycling exercise; (2) 28% drop in cutaneous blood flow in nonactive limbs at peak work rate; (3) 5%–10% reduction in heart rate (HR); (4) 10% increase in maximal O₂ pulse; and (5) 6.6% increase in t_max.

Conclusion

Heat acclimation can be achieved with five sessions of high-intensity cycling exercise in the heat in trained athletes, and redistribution of cutaneous blood flow in the skin and exercising muscle, and enhanced cardiovascular adaptations provide the heat-acclimated athletes with the capability to increase their endurance time in the hot environment.

Topical anaesthesia does not affect cutaneous vasomotor or sudomotor responses in human skin

(1) The effects of local sensory blockade (topical anaesthesia) on eccrine sweat glands and cutaneous circulation are not well understood. This study aimed to determine whether topical lidocaine/prilocaine alters eccrine sweat gland and cutaneous blood vessel responses. (2) Sweating (capacitance hygrometry) was induced via forearm intradermal microdialysis of five acetylcholine (ACh) doses (1 × 10(-4) to 1 × 10(0) m, 10-fold increments) in control and treated forearm sites in six healthy subjects. Nitric oxide-mediated vasodilatory (sodium nitroprusside) and adrenergic vasoconstrictor (noradrenaline) agonists were iontophoresed in lidocaine/prilocaine-treated and control forearm skin in nine healthy subjects during blood flow assessment (laser Doppler flowmetry, expressed as% from baseline cutaneous vascular conductance; CVC; flux/mean arterial pressure). (3) Non-linear regression curve fitting identified no change in the ED50 of ACh-induced sweating after sensory blockade (-1.42 ± 0.23 logM) compared to control (-1.27 ± 0.23 logM; P > .05) or in Emax (0.43 ± 0.08 with, 0.53 ± 0.16 mg cm(-2) min(-1) without lidocaine/prilocaine; P > .05). Sensory blockade did not alter the vasodilator response to sodium nitroprusside (1280 ± 548% change from baseline CVC with, 1204 ± 247% without lidocaine/prilocaine) or vasoconstrictor response to noradrenaline (-14 ± 4% change from baseline CVC with, -22 ± 14% without lidocaine/prilocaine; P > 0.05). (4) Cutaneous sensory blockade does not appear to alter nitric oxide-mediated vasodilation, adrenergic vasoconstriction, or cholinergic eccrine sweating dose-response sensitivity or responsiveness to maximal dose. Thus, lidocaine/prilocaine treatment should not affect sweat gland function or have blood flow implications for subsequent research protocols or clinical procedures.

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

Localized exogenous R-tetrahydrobiopterin (R-BH(4)) corrects the deficit in local heat-induced vasodilation (VD) in hypercholesterolemic (HC) human skin through one of two plausible mechanisms: by serving as an essential cofactor to stabilizing endothelial nitric oxide (NO) synthase (eNOS) or through generalized antioxidant effects. We used the stereoisomer S-BH(4), which has the same antioxidant properties but does not function as an essential NOS cofactor, to elucidate the mechanism by which R-BH(4) restores cutaneous VD in HC humans. Intradermal microdialysis fibers were placed in 20 normocholesterolemic (NC), 13 midrange cholesterolemic (MC), and 18 HC (LDL: 94 ± 3, 124 ± 3 and 179 ± 6 mg/dl, respectively) men and women to perfuse Ringer (control site) and R-BH(4). In 10 NC, 13 MC, and 9 HC subjects (LDL: 94 ± 3, 124 ± 3, 180 ± 10 mg/dl), S-BH(4) was perfused at a third microdialysis site. Skin blood flow was measured during a standardized local heating protocol to elicit eNOS-dependent VD. After cutaneous vascular conductance (CVC = LDF/MAP) plateaued, NO-dependent VD was quantified by perfusing N(G)-nitro-l-arginine methyl ester (l-NAME). Data were normalized as %CVC(max). Fully expressed VD (NC: 97.9 ± 2.3 vs. MC: 85.4 ± 5.4, HC: 79.9 ± 4.2%CVC(max)) and the NO-dependent portion (NC: 62.1 ± 3 vs. MC: 45.8 ± 3.9, HC: 35.7 ± 2.8%CVC(max)) were reduced in HC (both P < 0.01 vs. NC), but only the fully expressed VD was reduced in MC (P < 0.01 vs. NC). R-BH(4) increased the fully expressed (93.9 ± 3.4%CVC(max); P < 0.01) and NO-dependent VD (52.1 ± 5.1%CVC(max); P < 0.01) in HC but not in NC or MC. S-BH(4) increased full-expressed VD in HC (P < 0.01) but did not affect NO-dependent VD in HC or MC. In contrast S-BH(4) attenuated NO-dependent VD in NC (control: 62.1 ± 3 vs. S-BH(4): 41.6 ± 7%CVC(max); P < 0.001). Exogenous R-BH(4) restores NO-dependent VD in HC human skin predominantly through NOS coupling mechanisms but increases full expression of the local heating response through generalized antioxidant properties.

Autonomic markers of emotional processing: skin sympathetic nerve activity in humans during exposure to emotionally charged images

The sympathetic innervation of the skin primarily subserves thermoregulation, but the system has also been commandeered as a means of expressing emotion. While it is known that the level of skin sympathetic nerve activity (SSNA) is affected by anxiety, the majority of emotional studies have utilized the galvanic skin response as a means of inferring increases in SSNA. The purpose of the present study was to characterize the changes in SSNA when showing subjects neutral or emotionally charged images from the International Affective Picture System (IAPS). SSNA was recorded via tungsten microelectrodes inserted into cutaneous fascicles of the common peroneal nerve in ten subjects. Neutral images, positively charged images (erotica) or negatively charged images (mutilation) were presented in blocks of fifteen images of a specific type, each block lasting 2 min. Images of erotica or mutilation were presented in a quasi-random fashion, each block following a block of neutral images. Both images of erotica or images of mutilation caused significant increases in SSNA, but the increases in SSNA were greater for mutilation. The increases in SSNA were often coupled with sweat release and cutaneous vasoconstriction; however, these markers were not always consistent with the SSNA increases. We conclude that SSNA, comprising cutaneous vasoconstrictor and sudomotor activity, increases with both positively charged and negatively charged emotional images. Measurement of SSNA provides a more comprehensive assessment of sympathetic outflow to the skin than does the use of sweat release alone as a marker of emotional processing.

The physiological origin of task-evoked systemic artefacts in functional near infrared spectroscopy

A major methodological challenge of functional near-infrared spectroscopy (fNIRS) is its high sensitivity to haemodynamic fluctuations in the scalp. Superficial fluctuations contribute on the one hand to the physiological noise of fNIRS, impairing the signal-to-noise ratio, and may on the other hand be erroneously attributed to cerebral changes, leading to false positives in fNIRS experiments. Here we explore the localisation, time course and physiological origin of task-evoked superficial signals in fNIRS and present a method to separate them from cortical signals. We used complementary fNIRS, fMRI, MR-angiography and peripheral physiological measurements (blood pressure, heart rate, skin conductance and skin blood flow) to study activation in the frontal lobe during a continuous performance task. The General Linear Model (GLM) was applied to analyse the fNIRS data, which included an additional predictor to account for systemic changes in the skin. We found that skin blood volume strongly depends on the cognitive state and that sources of task-evoked systemic signals in fNIRS are co-localized with veins draining the scalp. Task-evoked superficial artefacts were mainly observed in concentration changes of oxygenated haemoglobin and could be effectively separated from cerebral signals by GLM analysis. Based on temporal correlation of fNIRS and fMRI signals with peripheral physiological measurements we conclude that the physiological origin of the systemic artefact is a task-evoked sympathetic arterial vasoconstriction followed by a decrease in venous volume. Since changes in sympathetic outflow accompany almost any cognitive and emotional process, we expect scalp vessel artefacts to be present in a wide range of fNIRS settings used in neurocognitive research. Therefore a careful separation of fNIRS signals originating from activated brain and from scalp is a necessary precondition for unbiased fNIRS brain activation maps.

Local tetrahydrobiopterin administration augments reflex cutaneous vasodilation through nitric oxide-dependent mechanisms in aged human skin

Functional constitutive nitric oxide synthase (NOS) is required for full expression of reflex cutaneous vasodilation that is attenuated in aged skin. Both the essential cofactor tetrahydrobiopterin (BH(4)) and adequate substrate concentrations are necessary for the functional synthesis of nitric oxide (NO) through NOS, both of which are reduced in aged vasculature through increased oxidant stress and upregulated arginase, respectively. We hypothesized that acute local BH(4) administration or arginase inhibition would similarly augment reflex vasodilation in aged skin during passive whole body heat stress. Four intradermal microdialysis fibers were placed in the forearm skin of 11 young (22 ± 1 yr) and 11 older (73 ± 2 yr) men and women for local infusion of 1) lactated Ringer, 2) 10 mM BH(4), 3) 5 mM (S)-(2-boronoethyl)-l-cysteine + 5 mM N(ω)-hydroxy-nor-l-arginine to inhibit arginase, and 4) 20 mM N(G)-nitro-l-arginine methyl ester (l-NAME) to inhibit NOS. Red cell flux was measured at each site by laser-Doppler flowmetry (LDF) as reflex vasodilation was induced. After a 1.0°C rise in oral temperature (T(or)), mean body temperature was clamped and 20 mM l-NAME was perfused at each site. Cutaneous vascular conductance was calculated (CVC = LDF/mean arterial pressure) and expressed as a percentage of maximum (%CVC(max); 28 mM sodium nitroprusside and local heat, 43°C). Vasodilation was attenuated at the control site of the older subjects compared with young beginning at a 0.3°C rise in T(or). BH(4) and arginase inhibition both increased vasodilation in older (BH(4): 55 ± 5%; arginase-inhibited: 47 ± 5% vs. control: 37 ± 3%, both P < 0.01) but not young subjects compared with control (BH(4): 51 ± 4%CVC(max); arginase-inhibited: 55 ± 4%CVC(max) vs. control: 56 ± 6%CVC(max), both P > 0.05) at a 1°C rise in T(or). With a 1°C rise in T(or), local BH(4) increased NO-dependent vasodilation in the older (BH(4): 31.8 ± 2.4%CVC(max) vs. control: 11.7 ± 2.0%CVC(max), P < 0.001) but not the young (BH(4): 23 ± 4%CVC(max) vs. control: 21 ± 4%CVC(max), P = 0.718) subject group. Together these data suggest that reduced BH(4) contributes to attenuated vasodilation in aged human skin and that BH(4) NOS coupling mechanisms may be a potential therapeutic target for increasing skin blood flow during hyperthermia in older humans.

Impact of 10 sessions of whole body cryostimulation on cutaneous microcirculation measured by laser Doppler flowmetry

The aim of the present study was to evaluate the basic and evoked blood flow in the skin microcirculation of the hand, one day and ten days after a series of 10 whole body cryostimulation sessions, in healthy individuals.

The study group included 32 volunteers – 16 women and 16 men. The volunteers underwent 10 sessions of cryotherapy in a cryogenic chamber. The variables were recorded before the series of 10 whole body cryostimulation sessions (first measurement), one day after the last session (second measurement) and ten days later (third measurement). Rest flow, post-occlusive hyperaemic reaction, reaction to temperature and arterio–venous reflex index were evaluated by laser Doppler flowmetry.

The values recorded for rest flow, a post-occlusive hyperaemic reaction, a reaction to temperature and arterio – venous reflex index were significantly higher both in the second and third measurement compared to the initial one. Differences were recorded both in men and women. The values of frequency in the range of 0,01 Hz to 2 Hz (heart frequency dependent) were significantly lower after whole-body cryostimulation in both men and women. In the range of myogenic frequency significantly higher values were recorded in the second and third measurement compared to the first one.

Recorded data suggest improved response of the cutaneous microcirculation to applied stimuli in both women and men. Positive effects of cryostimulation persist in the tested group for 10 consecutive days.

Altered thermal hyperaemia in human skin by prior desensitization of neurokinin-1 receptors

The neuropeptides substance P (SP) and calcitonin gene-related peptide are believed to be involved in the axon reflex-mediated component of cutaneous thermal hyperaemia, but no studies have specifically addressed this issue. The purpose of this study was to determine whether neurokinin-1 receptors, which preferentially bind SP, contribute to the axon reflex component of cutaneous thermal hyperaemia. Nine subjects were equipped with four microdialysis fibres, and each fibre received one of the following four treatments: (1) lactated Ringer's solution (control); (2) 10 mml-NAME to inhibit nitric oxide synthase; (3) 10 μm SP; or (4) 10 μm SP + 10 mml-NAME. Skin blood flow was monitored via laser-Doppler flowmetry, and local skin temperature was controlled using local heating devices. Sites 3 and 4 were perfused with 10 μm SP for 15 min at a rate of 4 μl min(-1), and the ensuing vasodilatation was allowed to return to baseline. Following SP-induced vasodilatation, all skin sites were locally heated from a baseline temperature of 33°C to 42°C at a rate of 0.5°C every 5 s. Cutaneous vascular conductance (CVC) was calculated as skin blood flow/mean arterial pressure and normalized to the maximal value (%CVC(max)) via 28 mm nitroprusside and local heating to 43°C. The initial peak did not differ between control (79 ± 3%CVC(max)) and SP-only sites (79 ± 2%CVC(max)). The initial peaks at the l-NAME (43 ± 3%CVC(max)) and SP + l-NAME sites (53 ± 3%CVC(max)) were significantly reduced compared with both the control and the SP-only sites (P < 0.001 for both), and l-NAME sites were attenuated compared with SP + l-NAME sites (P < 0.01). There was no observable nadir response at sites pretreated with SP. Compared with control sites (57 ± 4%CVC(max)), the nadirs at the l-NAME (14 ± 2%CVC(max)) and the SP + l-NAME sites (31 ± 5%CVC(max)) were significantly reduced (P < 0.01 for all conditions). l-NAME significantly reduced the nadir compared with SP + l-NAME (P < 0.01). Plateau CVC values did not differ between control (86 ± 3%CVC(max)) and SP sites (91 ± 1%CVC(max)). At l-NAME (36 ± 4%CVC(max)) and SP +l-NAME sites (56 ± 6%CVC(max)), plateau CVC was significantly reduced compared with control and SP-only sites (P < 0.01 for all conditions). The plateau at l-NAME sites was significantly reduced compared with SP + l-NAME sites (P < 0.01). These data suggest that neurokinin-1 receptors contribute to both the axon reflex component and the secondary plateau phase of cutaneous thermal hyperaemia.

Topiramate improves neurovascular function, epidermal nerve fiber morphology, and metabolism in patients with type 2 diabetes mellitus

PURPOSE

To assess the effects of topiramate on C-fiber function, nerve fiber morphology, and metabolism (including insulin sensitivity, obesity, and dyslipidemia) in type 2 diabetes.

PATIENTS AND METHODS

We conducted an 18-week, open-label trial treating patients with topiramate. Twenty subjects with type 2 diabetes and neuropathy (61.5 ± 1.29 years; 15 male, 5 female) were enrolled and completed the trial. Neuropathy was evaluated by total neuropathy scores, nerve conduction studies, quantitative sensory tests, laser Doppler skin blood flow, and intraepidermal nerve fibers in skin biopsies.

RESULTS

Topiramate treatment improved symptoms compatible with C-fiber dysfunction. Weight, blood pressure, and hemoglobin A(1c) also improved. Laser Doppler skin blood flow improved significantly after 12 weeks of treatment, but returned to baseline at 18 weeks. After 18 weeks of treatment there was a significant increase in intraepidermal nerve fiber length at the forearm, thigh, and proximal leg. Intraepidermal nerve fiber density was significantly increased by topiramate in the proximal leg.

CONCLUSION

This study is the first to demonstrate that it is possible to induce skin intraepidermal nerve fiber regeneration accompanied by enhancement of neurovascular function, translating into improved symptoms as well as sensory nerve function. The simultaneous improvement of selective metabolic indices may play a role in this effect, but this remains to be determined.

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.

Interactive effects between isometric exercise and mental stress on the vascular responses in glabrous and nonglabrous skin

Cutaneous vascular responses to mental arithmetic (MA) and handgrip exercise (HG) were studied independently and combined at different local skin temperatures (T (loc)). MA and HG induced (P < 0.05) vasoconstrictor responses in glabrous and nonglabrous skin at a higher level of T (loc), resulting in a nonadditive effect of these two stresses.

Cutaneous vasoconstriction contributes to hyperthermia induced by 3,4-methylenedioxymethamphetamine (ecstasy) in conscious rabbits

3,4-Methylenedioxymethamphetamine (MDMA; "Ecstasy") increases body temperature. This process could be associated with increased cutaneous blood flow, as normally occurs with exercise-induced hyperthermia. Alternatively, an MDMA-induced fall in cutaneous blood flow could contribute to the hyperthermia by diminishing normal heat transfer from the body to the environment. We investigated these possibilities by administering MDMA (1.5-6 mg/kg, i.v.) to conscious freely moving rabbits, determining effects on body temperature, cutaneous blood flow (measured by a Doppler ultrasonic probe that was chronically implanted around the ear pinna artery), and other cardiovascular parameters. MDMA caused a dose-dependent increase in body temperature (from 38.3 +/- 0.3 to 41.2 +/- 0.4 degrees C after 6 mg/kg; p < 0.01; n = 5), preceded and accompanied by a dose-dependent cutaneous vasoconstriction (from 29 +/- 6 to 5 +/- 1 cm/sec after 6 mg/kg; p < 0.01; n = 5). MDMA (3 mg/kg) did not change blood flow to the mesenteric vascular bed. Prior unilateral cervical sympathectomy reduced the increase in body temperature elicited by MDMA (6 mg/kg) from 2.0 +/- 0.2 to 1.3 +/- 0.2 degrees C (p < 0.01; n = 5). On the denervated side, ear pinna blood flow after MDMA injection was 13 +/- 3 cm/sec, compared with 3 +/- 1 cm/sec on the sympathetically intact side (p < 0.05; n = 5). Thus, sympathetically mediated cutaneous vasoconstriction is one mechanism whereby MDMA causes hyperthermia. Reversal of cutaneous vasoconstriction by appropriate pharmacological means could be of therapeutic benefit in humans suffering from life-threatening hyperthermia induced by MDMA.

Mechanisms of the cutaneous vasodilator response to local external pressure application in rats: involvement of CGRP, neurokinins, prostaglandins and NO

1. Local pressure-induced vasodilation (PIV) is a neural vasodilator response to non-nociceptive externally applied pressure in the skin, previously described in humans. We first determined whether PIV exists in rats and depends on capsaicin-sensitive fibres as it does in humans. We then examined the mediators involved in the efferent pathway of PIV. 2. Cutaneous blood flow was measured by laser Doppler flowmetry during 11.1 Pa s(-1) increases in local applied pressure in anaesthetized rats. The involvement of capsaicin-sensitive fibres in PIV was tested in rats treated neonatally with capsaicin. To antagonize CGRP, neurokinin-1, -2, or -3 receptors, different groups of rats were treated with CGRP(8 - 37), SR140333, SR48968 or SR142801, respectively. Prostaglandins involvement was tested with indomethacin treatment. To inhibit nitric oxide synthase (NOS) activity or specific neuronal NOS, rats were treated with N(G)-nitro-L-arginine or 7-nitroindazole, respectively. 3. PIV was found in rats, as in humans. PIV was abolished by neonatal treatment with capsaicin and by administration of CGRP(8 - 37) but remained unchanged with SR140333, SR48968 and SR142801 treatments. Prostaglandin inhibition resulted in a significant decrease in PIV. Inhibition of NOS abolished PIV, whereas inhibition of neuronal NOS caused a diminution of PIV. 4. These data suggest that PIV depends on capsaicin-sensitive fibres in rats, as in humans. It appears that CGRP plays a major role in the PIV, whereas neurokinins have no role. Furthermore, PIV involves a contribution from prostaglandins and depends on endothelial NO, whereas neuronal NO has a smaller role.

Effects of nociceptin and nocistatin on antidromic vasodilatation in hairless skin of the rat hindlimb in vivo

1. We tested whether nociceptin (NCE), the endogenous ligand of the opioid receptor-like 1 (ORL1) receptor, and nocistatin (NST), which reverses central NCE effects when applied intrathecally (i.t.), affect small-diameter afferent fibre-mediated vasodilatation in rat hairless skin. 2. Female Wistar rats were vagotomized. Ongoing sympathetic vasoconstrictor activity was abolished by bilateral section of the lumbar sympathetic trunk between ganglia L2 and L3. Sensory axons were selectively stimulated in the dorsal root L5 by 20 electrical impulses supramaximal for activating C-fibres at 1 Hz. Blood flow was measured on the plantar skin of the left hind paw in the L5 dermatome using laser Doppler flowmetry. 3. NCE injected intravenously (i.v.) as single boluses (1, 10 and 100 nmol kg(-1) 7 - 8 min before dorsal root stimulation (n=6) dose-dependently decreased blood pressure and local vascular resistance and suppressed antidromic vasodilatation maximally by 47% (P<0.01). When NCE was injected 2 min before stimulation (n=3), antidromic vasodilatation was reduced by 64% after NCE (1 nmol kg-1) and totally, or almost totally, abolished after the two higher doses. 4. NST (1 - 100 nmol kg(-1) i.v., n=6) was without significant effect on blood pressure and cutaneous vascular resistance. Applied 5 (n=6) or 2 min (n=3) before stimulation it also did not affect antidromic vasodilatation. NST (100 nmol kg(-1) i.v.) applied shortly before an equimolar dose of NCE did not antagonize NCE effects on vascular resistance, blood pressure and antidromic vasodilatation (n=4). 5. In conclusion, NCE inhibits antidromic vasodilatation, a component of neurogenic inflammation, in rat skin while NST is without effect. NST, at the small-diameter sensory ending, is not an effective antagonist of NCE.

Epidural anesthesia affects pulse oximeter readings and response time

We investigated the effects of epidural anesthesia on pulse oximeter readings (Spo₂) and response time because this type of anesthesia causes significant changes in microcirculation at measurement sites. Twenty patients were divided into lumbar epidural (L-EPI;n=10) and the cervical epidural (C-EPI;n=10) groups. Spo₂ and skin blood flow (SBF) were measured at the finger and toe simultaneously by pulse oximeter and laser Doppler flowmeter, respectively. Data were collected before and after epidural anesthesia for 1 min and the response time was calculated by the difference between the finger and toe using the breath-holding method. Epidural anesthesia increased SBF in the blocked area and decreased it in the nonblocked area in both groups (P<0.01, respectively). In the L-EPI group, Spo₂ was increased at the finger (P<0.05) and decreased at the toe (P<0.05). In the C-EPI group, Spo₂ at both the finger and toe was decreased by the anesthesia. ΔSpo₂ (Spo₂ at the finger minus Spo₂ at the toe) was increased in the L-EPI group (P<0.05) and decreased in the C-EPI group (P<0.01). The difference in the response time became larger in the C-EPI group and smaller or opposite in the L-EPI group after anesthesia. The difference in response time and SBF were significantly correlated (r=0.71;P<0.05). These results indicated that epidural anesthesia lowerd Spo₂ and shortened the response time through vasodilation in the blocked area and caused the opposite reactions in the nonblocked area through compensatory vasoconstriction.