The effect of the nitric oxide synthase inhibitor N-nitro-L-arginine-methyl ester on neuropeptide-induced vasodilation and protein extravasation in human skin

Migraine headache pathophysiology

In both episodic and chronic migraine, headache is the most disabling symptom that requires medical care. The migraine headache is the most well-studied symptom of migraine pathophysiology. The trigeminal system and the central processing of sensory information transmitted by the trigeminal system are of considerable importance in the pathophysiology of migraine headache. Glutamate is the main neurotransmitter that drives activation of the ascending trigeminal and trigeminothalamic pathways. The neuropeptide, calcitonin gene-related peptide (CGRP) that is released by the trigeminal system, plays a crucial role in the neurobiology of headache. Peripheral and central sensitizations associated with trigeminal sensory processing are neurobiologic states that contribute to both the development of headache during a migraine attack and the maintenance of chronic migraine.

Thermal dysregulation in patients with multiple sclerosis during SARS-CoV-2 infection. The potential therapeutic role of exercise

Thermoregulation is a homeostatic mechanism that is disrupted in some neurological diseases. Patients with multiple sclerosis (MS) are susceptible to increases in body temperature, especially with more severe neurological signs. This condition can become intolerable when these patients suffer febrile infections such as coronavirus disease-2019 (COVID-19). We review the mechanisms of hyperthermia in patients with MS, and they may encounter when infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Finally, the thermoregulatory role and relevant adaptation to regular physical exercise are summarized.

Skin microdialysis: methods, applications and future opportunities-an EAACI position paper

Skin microdialysis (SMD) is a versatile sampling technique that can be used to recover soluble endogenous and exogenous molecules from the extracellular compartment of human skin. Due to its minimally invasive character, SMD can be applied in both clinical and preclinical settings. Despite being available since the 1990s, the technique has still not reached its full potential use as a tool to explore pathophysiological mechanisms of allergic and inflammatory reactions in the skin. Therefore, an EAACI Task Force on SMD was formed to disseminate knowledge about the technique and its many applications. This position paper from the task force provides an overview of the current use of SMD in the investigation of the pathogenesis of chronic inflammatory skin diseases, such as atopic dermatitis, chronic urticaria, psoriasis, and in studies of cutaneous events during type 1 hypersensitivity reactions. Furthermore, this paper covers drug hypersensitivity, UVB-induced- and neurogenic inflammation, and drug penetration investigated by SMD. The aim of this paper is to encourage the use of SMD and to make the technique easily accessible by providing an overview of methodology and applications, supported by standardized operating procedures for SMD in vivo and ex vivo.

Shared Fate of Meningeal Mast Cells and Sensory Neurons in Migraine

Migraine is a primary headache disorder which has complex neurogenic pathophysiological mechanisms still requiring full elucidation. The sensory nerves and meningeal mast cell couplings in the migraine target tissue are very effective interfaces between the central nervous system and the immune system. These couplings fall into three categories: intimacy, cross-talk and a shared fate. Acting as the immediate call-center of the neuroimmune system, mast cells play fundamental roles in migraine pathophysiology. Considerable evidence shows that neuroinflammation in the meninges is the key element resulting in the sensitization of trigeminal nociceptors. The successive events such as neuropeptide release, vasodilation, plasma protein extravasation, and mast cell degranulation that form the basic characteristics of the inflammation are believed to occur in this persistent pain state. In this regard, mast cells and sensory neurons represent both the target and source of the neuropeptides that play autocrine, paracrine, and neuro-endocrine roles during this inflammatory process. This review intends to contribute to a better understanding of the meningeal mast cell and sensory neuron bi-directional interactions from molecular, cellular, functional points of view. Considering the fact that mast cells play a sine qua non role in expanding the opportunities for targeted new migraine therapies, it is of crucial importance to explore these multi-faceted interactions.

Cutaneous active vasodilation as a heat loss thermoeffector

Human skin is the interface between the human body and the environment. As such, human temperature regulation relies largely on cutaneous vasomotor and sudomotor adjustments to appropriately thermoregulate. In particular, changes in skin blood flow can increase or decrease the convective heat transfer from internal tissues to the periphery where it can increase or prevent heat loss to the environment. Thermoregulatory control of the cutaneous vasculature is largely due to cutaneous sympathetic nerves. Sympathetic adrenergic nerves mediate vasoconstriction of the skin, similar to other vascular beds, whereas active vasodilator nerves in nonglabrous skin respond to changes in internal and peripheral temperatures and can profoundly increase skin blood flow. Activation of these vasodilator nerves is known as cutaneous active vasodilation and has been the subject of much recent research. This research has uncovered a highly complex system that involves the activation of multiple receptors and vasodilator pathways in a synergistic and sometimes redundant manner. This complexity and redundancy has left our understanding of cutaneous active vasodilation incomplete; however, the employment of new techniques and use of new pharmacologic agents have introduced many new insights into cutaneous active vasodilation.

Understanding migraine: Potential role of neurogenic inflammation

Neurogenic inflammation, a well-defined pathophysiologial process is characterized by the release of potent vasoactive neuropeptides, predominantly calcitonin gene-related peptide (CGRP), substance P (SP), and neurokinin A from activated peripheral nociceptive sensory nerve terminals (usually C and A delta-fibers). These peptides lead to a cascade of inflammatory tissue responses including arteriolar vasodilation, plasma protein extravasation, and degranulation of mast cells in their peripheral target tissue. Neurogenic inflammatory processes have long been implicated as a possible mechanism involved in the pathophysiology of various human diseases of the nervous system, respiratory system, gastrointestinal tract, urogenital tract, and skin. The recent development of several innovative experimental migraine models has provided evidence suggestive of the involvement of neuropeptides (SP, neurokinin A, and CGRP) in migraine headache. Antidromic stimulation of nociceptive fibers of the trigeminal nerve resulted in a neurogenic inflammatory response with marked increase in plasma protein extravasation from dural blood vessels by the release of various sensory neuropeptides. Several clinically effective abortive antimigraine medications, such as ergots and triptans, have been shown to attenuate the release of neuropeptide and neurogenic plasma protein extravasation. These findings provide support for the validity of using animal models to investigate mechanisms of neurogenic inflammation in migraine. These also further strengthen the notion of migraine being a neuroinflammatory disease. In the clinical context, there is a paucity of knowledge and awareness among physicians regarding the role of neurogenic inflammation in migraine. Improved understanding of the molecular biology, pharmacology, and pathophysiology of neurogenic inflammation may provide the practitioner the context-specific feedback to identify the novel and most effective therapeutic approach to treatment. With this objective, the present review summarizes the evidence supporting the involvement of neurogenic inflammation and neuropeptides in the pathophysiology and pharmacology of migraine headache as well as its potential significance in better tailoring therapeutic interventions in migraine or other neurological disorders. In addition, we have briefly highlighted the pathophysiological role of neurogenic inflammation in various other neurological disorders.

Randomized placebo-controlled trial of sucrose analgesia on neonatal skin blood flow and pain response during heel lance

OBJECTIVES

To evaluate the effect of oral sucrose on skin blood flow (SBF; perfusion units; PU) measured by Laser Doppler Imager (LDI) in term newborns and pain response (Neonatal Infant Pain Scale score; NIPS score) during heel lance; (2) determine SBF changes during heel lance; and (3) the relationship between SBF and NIPS.

MATERIALS AND METHODS

Term infants ≤7 days old (n=56) undergoing routine heel lance were randomized to pretreatment with 2.0 mL oral 24% sucrose (n=29) or sterile water (n=27) in a double-blinded, placebo-controlled trial. SBF was assessed by LDI scans and NIPS scores at 10 minutes before lance, immediately after lancing, and 5 minutes after blood extraction. Mean SBF and median NIPS scores were compared between groups using General Linear Model or Kruskal-Wallis. Regressions examined the relationship between SBF immediately after heel lance and NIPS score.

RESULTS

Mean SBF and median NIPS scores immediately after heel lance were lower in sucrose-treated infants (167.9±15.5 vs. 205.4±16.0 PU, P=0.09; NIPS 1 [interquartile range 0 to 4] vs. NIPS 3 [interquartile range 0 to 6], P=0.02), although no significant difference in mean SBF. During heel lance NIPS score was predictive of SBF. An increase of 1 in NIPS score was associated with 11 PU increase in SBF (R=0.21; P=0.09) for sucrose, and 16 PU increase for placebo-treated infants (R=0.20; P=0.014).

CONCLUSIONS

Increased SBF assessed by LDI is a pain response among term neonates after routine heel lance, which was not completely attenuated by oral sucrose administration. Increased SBF is associated with NIPS scores. Sucrose analgesic efficacy evidenced by decreased NIPS scores for the sucrose group. Association of SBF with NIPS scores suggests that LDI is potentially useful for assessing newborn procedural pain.

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.

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

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

Retrodialysis: a review of experimental and clinical applications of reverse microdialysis in the skin

Microdialysis is a method that has been used for decades to recover endogenous mediators, metabolites and drugs from the interstitial space in several tissues of both animals and humans. The principle of microdialysis is the flux of compounds across a semipermeable membrane. The application of microdialysis as a method of drug delivery is a process referred to as retrodialysis, i.e. the introduction of a substance into the extracellular space via a microdialysis probe. Thus, microdialysis also offers opportunities to deliver mediators and drugs to target tissues by adding solutes to the perfusion medium. In this context, retrodialysis combines a method for minimally invasive delivery with a sampling method to study biological processes in health and disease. The aim of this review is to give insight into the use of retrodialysis by outlining examples of retrodialysis studies focusing on applications in skin in animal studies, human experimental investigations and clinical settings.

Sensory nerves and nitric oxide contribute to reflex cutaneous vasodilation in humans

We tested the hypothesis that inhibition of cutaneous sensory nerves would attenuate reflex cutaneous vasodilation in response to an increase in core temperature. Nine subjects were equipped with four microdialysis fibers on the forearm. Two sites were treated with topical anesthetic EMLA cream for 120 min. Sensory nerve inhibition was verified by lack of sensation to a pinprick. Microdialysis fibers were randomly assigned as 1) lactated Ringer (control); 2) 10 mM nitro-L-arginine methyl ester (L-NAME) to inhibit nitric oxide synthase; 3) EMLA + lactated Ringer; and 4) EMLA + L-NAME. Laser-Doppler flowmetry was used as an index of skin blood flow, and blood pressure was measured via brachial auscultation. Subjects wore a water-perfused suit, and oral temperature was monitored as an index of core temperature. The suit was perfused with 50°C water to initiate whole body heat stress to raise oral temperature 0.8°C above baseline. Cutaneous vascular conductance (CVC) was calculated and normalized to maximal vasodilation (%CVC(max)). There was no difference in CVC between control and EMLA sites (67 ± 5 vs. 69 ± 6% CVC(max)), but the onset of vasodilation was delayed at EMLA compared with control sites. The L-NAME site was significantly attenuated compared with control and EMLA sites (45 ± 5% CVC(max); P < 0.01). Combined EMLA + L-NAME site (25 ± 6% CVC(max)) was attenuated compared with control and EMLA (P < 0.001) and L-NAME only (P < 0.01). These data suggest cutaneous sensory nerves contribute to reflex cutaneous vasodilation during the early, but not latter, stages of heat stress, and full expression of reflex cutaneous vasodilation requires functional sensory nerves and NOS.

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.

A qualitative and quantitative proteomic study of human microdialysate and the cutaneous response to injury

The extracellular fluid space is the site of intercellular communication and represents an important source of mediators that can shed light on the parenchymal environment. Sampling of this compartment using continuous microdialysis allows assessment of the temporal changes in extracellular mediators involved in tissue homeostasis and disease processes. However, novel biomarker identification is limited by the current need to utilize specific, targeted molecular assays. The aim of our study was to explore the use of qualitative and quantitative proteomic approaches to define the protein content of dermal dialysate. Timed dermal dialysate samples were collected from healthy human volunteers for 5 h following probe insertion, using a 3,000-kDa MWCO membrane perfused at a rate of 3 μl/min. Dialysate proteins were identified using GeLC-MS/MS and iTRAQ approaches and functions assigned according to the Gene Ontology classification system. More than 80 proteins (size range 11-516 kDa) originating from both extracellular and intracellular fluid space were identified using the qualitative approach of GeLC-MS/MS. Quantitative iTRAQ data were obtained for 27 proteins with relative change ratios between consecutive timed samples showing changes of >1.5-fold. Interstitial proteins can be identified and measured using shotgun proteomic techniques and changes detected during the acute inflammatory response. Our findings provide a platform from which to explore novel protein biomarkers and their modulation in health and disease.

Retrograde tracing of spinal cord connections to the cervix with pregnancy in mice

In contrast to the uterus, the cervix is well innervated during pregnancy and the density of nerve fibers increases before birth. To assess neural connections between the cervix and the spinal cord, the cervix of pregnant mice was injected with the trans-synaptic retrograde neural tract tracer pseudorabies virus (PRV). After 5 days, the virus was present in nerve cells and fibers in specific areas of the sensory, autonomic, and motor subdivisions of the thoracolumbar spinal cord. In nonpregnant controls, the virus was predominantly distributed in laminae I-III in the dorsal gray sensory areas with the heaviest label in the substantia gelatinosa compared with the autonomic or motor areas. Labeled cells and processes were sparse in other regions, except for a prominent cluster in the intermediolateral column (lamina VII). Photomicrographs of spinal cord sections were digitized, and the total area with the virus was estimated. Compared with nonpregnant controls, the area with PRV was significantly decreased in all the spinal cord subdivisions in pregnant mice except in the intermediolateral column. However, areas with the virus were equivalent in mice injected with PRV at 4 days or 1 day before birth. These findings suggest that the predominant innervation of the murine cervix is from the sensory regions of the thoracolumbar spinal cord, and that these connections diminish with pregnancy. The results raise the possibility that the remaining connections from sensory and autonomic subdivisions, particularly the intermediolateral column, of the thoracolumbar spinal cord may be important for increased density of nerve fibers in the cervix as pregnancy nears term.

Use of sensory methods for detecting target engagement in clinical trials of new analgesics

The translation of analgesic efficacy seen in preclinical pain models into the clinic is problematic and is associated with a number of factors that may result in the failure of clinical trials to detect the effect of investigational therapeutic agents. The use of translational pain biomarkers in phase I trials can potentially reduce some of these risks by measuring the interaction between the drug and its target (termed target engagement) in humans. To serve this purpose, sensory tests and other measures of pharmacological activity in nociceptive pathways need to be identified, based on the preclinical profile of the drug being tested and the feasibility of human assessments. Here we discuss some examples to assess the utility of sensory and related pain biomarkers in the early phase of evaluation of novel analgesics for confirmation of target engagement in humans. The emphasis is on the TRPV1 antagonists, but some other target mechanisms are also discussed in examining the validity of this approach.

Responses of nitric oxide-cGMP release in acupuncture point to electroacupuncture in human skin in vivo using dermal microdialysis

OBJECTIVES

The aim of this study was to examine the release of nitric oxide (NO) and cGMP in response to electroacupuncture (EA) stimulation in the acupuncture point (acupoint), compared to the non-meridian control area.

METHODS

Thirty samples of dermal microdialysis data were collected from 24 volunteers at pericardium (PC) 4 and control area. EA was applied to PC 3 by using a 5-V pulse with a duration of 1.0 milliseconds at 10 Hz for 15 minutes. Dialysate samples were continuously collected 20 minutes each before, during, and after EA for two hours. Total nitrite and nitrate (NO(x)(-)) and cGMP in the dialysate were quantified in a blinded fashion.

RESULTS

Dialysate NO(x)(-) concentrations were decreased during a 120-minute dialysis in all groups, but reduced NO(x)(-) levels were attenuated predominantly in PC 4 acupoint at 20-40 minutes after EA PC 3. cGMP concentrations were significantly enhanced in acupoint PC 4 by EA PC 3, but not in the non-meridian area.

CONCLUSION

We suggest that the attenuation of NO(x)(-) reduction during dialysis reflects an increase in NO release induced by EA stimulation in acupoint and that cGMP mediates the signaling functions of NO to improve local microcirculation, which, at least in part, contributes to the effects of acupuncture.

Skin vasodilator response to local heating in multiple system atrophy

Local heating of nonglabrous skin increases skin blood flow (SkBF) in two phases. The initial peak (P1) is mediated by a sensory-axon reflex and the plateau phase (P2) by local production of substances such as nitric oxide. We evaluated the SkBF response to local heating in 15 multiple system atrophy (MSA) patients with autonomic failure and 12 age-matched healthy controls. The mean ratio of SkBF at P1 to that at baseline (SkBF(P1)/SkBF(base) ratio) in MSA was significantly lower than that in controls (P < 0.01). The mean ratio of SkBF at P2 seemed to be slightly reduced in the MSA patients, compared with controls, although there was no significant difference. The P1 phase is thought to be mediated by a sensory-axon reflex modulated by sympathetic nerve activity. These findings are indicative of the skin sympathetic vasomotor dysfunction in MSA.

Diminished skin vasodilator response to local heating in patients with long-standingsubacute myelo-optico-neuropathy

BACKGROUND

Local heating of non-glabrous skin increases skin blood flow (SkBF) in two phases: the initial peak (P1) is mediated by sensory axon reflex, and the plateau phase (P2) is thought to be mediated by local production of substances including nitric oxide. We evaluated P1 and P2 responses in subacute myelo-optico-neuropathy (SMON).

METHODS

SkBF response to local heating from 32 degrees C (5 min of baseline) to 42 degrees C (at least for 30 min) of the dorsal surface of the hand skin were measured in 7 SMON patients (67.6+/-10.0 years) and 7 normal control volunteers (65.0+/-7.4 years) participated.

RESULTS

Mean values of SkBF at P1 (SkBFP1) and SkBF during P2 (SkBFP2) were significantly lower in SMON patients than in controls (p<0.05, p<0.05). Mean SkBFP1/SkBF at baseline (SkBFbase) and SkBFP2/SkBFbase ratios were significantly lower in SMON patients than in controls (p<0.01 and p<0.05, respectively).

CONCLUSIONS

The SkBF response to local heating was diminished in SMON patients. This may reflect the involvement of the spinal cord, peripheral sensory nerves, and sympathetic post-ganglionic nerves in SMON.

Evidence of enhanced non-enzymatic generation of nitric oxide on the skin surface of acupuncture points: An innovative approach in humans

The present study quantified total nitrate and nitrite (NOx-) collected from the skin surface along acupuncture points (acupoints) and determined whether non-enzymatic reduction of nitrate by bacteria is involved in chemical generation of nitric oxide (NO) on acupoints. A small plastic tube (0.5 x 7 cm) cut in half lengthwise was taped to the forearm or leg in 50 healthy volunteers. NO-collecting solutions with NO-scavenging compounds, hemoglobin or 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide, was placed inside the tubing attached to the skin surface for 20 min. The concentrations of NOx- in the collected samples were quantified by using chemiluminescence. NOx- concentration was significantly enhanced in four acupoints on the pericardium meridian and in two acupoints on the bladder meridian compared with those collected on non-meridian control areas. The time intervals of NOx- levels were significantly higher at the first 20 min of acupoint collection, but the concentrations were similar among the study groups collected at 20-40, 40-60, and 60-80 min. NOx- concentrations and numbers of bacteria colonies detected on the skin surface were markedly reduced by pretreatment of skin with sodium hypochlorite compared to water treatment. This is the first evidence showing that NO has been successfully quantified on skin acupoints by a non-invasive device in humans. We conclude that NO is physiologically released from the skin surface with a higher level at acupoints, and that the non-enzymatic reduction of nitrate by bacteria is involved in chemical generation of NO on skin acupoints in addition to l-arginine-derived NO synthesis.

Preserved reflex cutaneous vasodilation in cystic fibrosis does not include an enhanced nitric oxide-dependent mechanism

In humans, vasoactive intestinal peptide (VIP) may play a role in reflex cutaneous vasodilation during body heating. We tested the hypothesis that the nitric oxide (NO)-dependent contribution to active vasodilation is enhanced in the skin of subjects with cystic fibrosis (CF), compensating for sparse levels of VIP. In 2 parallel protocols, microdialysis fibers were placed in the skin of 11 subjects with CF and 12 controls. Lactated Ringer was perfused at one microdialysis site and NG-nitro-L-arginine methyl ester (2.7 mg/ml) was perfused at a second microdialysis site. Skin blood flow was monitored over each site with laser-Doppler flowmetry. In protocol 1, local skin temperature was increased 0.5 degrees C every 5 s to 42 degrees C, and then it maintained at 42 degrees C for approximately 45 min. In protocol 2, subjects wore a tube-lined suit perfused with water at 50 degrees C, sufficient to increase oral temperature (Tor) 0.8 degrees C. Cutaneous vascular conductance (CVC) was calculated (flux/mean arterial pressure) and scaled as percent maximal CVC (sodium nitroprusside; 8.3 mg/ml). Vasodilation to local heating was similar between groups. The change (Delta%CVCmax) in CVC with NO synthase inhibition on the peak (9+/-3 vs. 12+/-5%CVCmax; P=0.6) and the plateau (45+/-3 vs. 35+/-5%CVCmax; P=0.1) phase of the skin blood flow response to local heating was similar in CF subjects and controls, respectively. Reflex cutaneous vasodilation increased CVC in CF subjects (58+/-4%CVCmax) and controls (53+/-4%CVCmax; P=0.37) and NO synthase inhibition attenuated CVC in subjects with CF (37+/-6%CVCmax) and controls (35+/-5%CVCmax; P=0.8) to a similar degree. Thus the preservation of cutaneous active vasodilation in subjects with CF is not associated with an enhanced NO-dependent vasodilation.

Neurokinin-1 receptor desensitization attenuates cutaneous active vasodilatation in humans

To date, the neurotransmitter(s) and pathways involved in cutaneous active vasodilatation are not fully understood. The purpose of this study was to determine the potential involvement of neurokinin-1 (NK(1)) receptors to active vasodilatation. Our experimental model exploited our previous findings that repeated microdialysis infusions of substance P desensitize the NK(1) receptors and that substance P-induced vasodilatation contains a substantial nitric oxide (NO) component. Eleven subjects were equipped with four microdialysis fibres on the ventral forearm. Site 1 served as a control and received a continuous infusion of Ringer solution. Site 2 received a continuous infusion of 10 mM L-NAME to inhibit NO synthase. Site 3 received a 10 microm dose of substance P to desensitize the NK(1) receptors prior to whole-body heating. Site 4 received a 10 microm dose of substance P combined with 10 mM L-NAME. Red blood cell (RBC) flux was measured via laser-Doppler flowmetry, and cutaneous vascular conductance (CVC) was calculated as RBC flux/mean arterial pressure and normalized to maximal vasodilatation via 28 mM sodium nitroprusside. Substance P was infused for 15 min at 4 microl min(-1) in sites 3 and 4, and skin blood flow was allowed to return to baseline (approximately 45-60 min). Subjects then underwent a period of whole-body heat stress to raise oral temperature 0.8-1.0 degrees C above baseline. Pretreatment with substance P increased CVC to 48 +/- 2% CVC(max), which was significantly greater than for sites pretreated with substance P combined with L-NAME (27 +/- 2% CVC(max); P < 0.001). During whole-body heating, CVC in control sites increased to 69 +/- 3% CVC(max). Sites pretreated with substance P (48 +/- 3% CVC(max)) were significantly reduced compared to control sites (P < 0.001). The CVC response to whole-body heat stress in L-NAME sites was significantly reduced (32 +/- 3% CVC(max); P < 0.001) compared to both control sites and sites pretreated with substance P. The CVC response to whole-body heating was nearly abolished in sites pretreated with substance P combined with L-NAME (20 +/- 2% CVC(max)) and was significantly reduced compared to the other three sites (all P < 0.001). These data suggest NK(1) receptors contribute to active vasodilatation and that combined NK(1) receptor desensitization and NO synthase inhibition further diminishes active vasodilatation.

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.

Neuropeptide (Calcitonin Gene-Related Peptide) Induction of Nitric Oxide in Human Keratinocytes in vitro

Nitric oxide (NO) is an important signaling molecule in both the central nervous system and the periphery, where it is involved in neurotransmission, vascular and bronchial tone, inflammation, and cutaneous immune function. More recently, NO has been implicated in intracellular signaling and may have a role in cellular differentiation, cytokine expression, and apoptosis. The experiments described herein examined the effect of calcitonin gene-related protein (CGRP), a cutaneous nerve neuropeptide, on NO production in human keratinocytes in vitro. CGRP stimulated two distinct increases in NO production: one within 30 minutes and a second at 24 hours. CGRP stimulated a modest increase in inducible nitric oxide synthase (iNOS) at 3-6 hours. Experimental evidence suggested that CGRP stimulated both constitutive NOS activity and generation of NO via nitrosothiol degradation within the first hour. Production of NO was paralleled by a decrease in nitrosothiol levels for 2 hour, suggesting that immediate NO release may originate from pre-existing stores. Nitrosothiols are ubiquitous molecules that comprise an important NO pool and have intracellular regulatory roles, particularly linked to oxidative stress. The present data indicate that, in addition to its known cAMP signaling pathway, CGRP may act to regulate keratinocyte biology through intracellular NO by modulation of S-nitrosothiol stores and stimulation of NOS activity.

Mechanisms of Raynaud's disease

Raynaud's phenomenon is due to transient cessation of blood flow to the digits of the hands or feet. An attack of Raynaud's phenomenon is classically manifested as triphasic color changes. The white phase is due to excessive vasoconstriction and cessation of regional blood flow. This phase is followed by a cyanotic phase, as the residual blood in the finger desaturates. The red phase is due to hyperemia as the attack subsides and blood flow is restored. An attack is frequently associated with pain and/or paresthesia due to sensory nerve ischemia. Variants of Raynaud's phenomenon include acrocyanosis and primary livedo reticularis, each of which is associated with reduced skin blood flow, exacerbated by cold or emotional upset. Raynaud's phenomenon in the absence of other disorders is primary Raynaud's phenomenon, or Raynaud's disease. The mechanisms of Raynaud's disease include increased activation of the sympathetic nerves, in response to cold or emotion; an impaired habituation of the cardiovascular response to stress may contribute. In addition, there appears to be a local fault, which is likely multifactorial. This local fault is due to an alteration in vascular function rather than vascular structure. The alteration in vascular function may be related to increased sensitivity to cold of the adrenergic receptors on the digital artery vascular smooth muscle. In some cases, locally released or systemically circulating vasoconstrictors may participate, including endothelin, 5-hydroxytryptamine and thromboxane. A deficiency or increased degradation of nitric oxide, possibly due to increased oxidative stress, may be involved in some cases. These recent pathophysiological insights may lead to new therapeutic options.

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.

The Vasorelaxant Effect of Adrenomedullin, Proadrenomedullin N-Terminal 20 Peptide and Amylin in Human Skin

In this study we aimed to assess in vivo, the vasodilator effects of adrenomedullin, proadrenomedullin N-terminal 20 peptide (PAMP) and amylin in human skin vasculature and compare the responses to the effects mediated by the endogenous neuropeptides calcitonin gene-related peptide (CGRP) and substance P and to examine the mRNA expression of calcitonin receptor-like receptor (CL-R) and receptor-activity modifying proteins, RAMP1, RAMP 2 and RAMP3 in human subcutaneous arteries. Changes in skin blood flow of the forearm were measured using a Laser Doppler Imager after intradermal injection of the peptides. The mRNA expression was assessed by real-time reverse transcriptase-polymerase chain reaction (real-time PCR). CGRP, adrenomedullin and amylin induced concentration-dependent, long-lasting increases in skin blood flow. The response to PAMP was shorter in duration appearing similar to the transient response induced by substance P. PAMP (10(-6)-10(-5) M) caused distinct itch sensation and local erythema. This effect could be abolished when combining the histamine H1-receptor antagonist mepyramin and PAMP. Real-time PCR data showed a higher level of mRNA for RAMP2 than CL-R, RAMP1 and RAMP3 in the tissue. Though the PCR data demonstrated the presence of mRNA for both CGRP1 and adrenomedullin receptors the rank order of potency (CGRP>adrenomedullin>amylin) for the blood flow increase indicated vasodilatation for these peptides was induced by activation of CGRP1 receptors. Intradermal injection of CGRP, adrenomedullin and amylin induces long lasting dilatation of human skin vasculature by activation of CGRP1 receptors. PAMP induces transient vasodilatation. PAMP but not CGRP, adrenomedullin and amylin causes itch sensation and local erythema. The transient effect on vasodilatation as response to PAMP is discussed.

Maximum skin hyperaemia induced by local heating: possible mechanisms

BACKGROUND

Maximum skin hyperaemia (MH) induced by heating skin to > or = 42 degrees C is impaired in individuals at risk of diabetes and cardiovascular disease. Interpretation of these findings is hampered by the lack of clarity of the mechanisms involved in the attainment of MH.

METHODS

MH was achieved by local heating of skin to 42-43 degrees C for 30 min, and assessed by laser Doppler fluximetry. Using double-blind, randomized, placebo-controlled crossover study designs, the roles of prostaglandins were investigated by inhibiting their production with aspirin and histamine, with the H1 receptor antagonist cetirizine. The nitric oxide (NO) pathway was blocked by the NO synthase inhibitor, NG-nitro-L-arginine methyl esther (L-NAME), and enhanced by sildenafil (prevents breakdown of cGMP).

RESULTS

MH was not altered by aspirin, cetirizine or sildenafil, but was reduced by L-NAME: median placebo 4.48 V (25th, 75th centiles: 3.71, 4.70) versus L-NAME 3.25 V (3.10, 3.80) (p = 0.008, Wilcoxon signed rank test). Inhibition of NO production (L-NAME) resulted in a more rapid reduction in hyperaemia after heating (p = 0.011), whereas hyperaemia was prolonged in the presence of sildenafil (p = 0.003). The increase in skin blood flow was largely confined to the directly heated area, suggesting that the role of heat-induced activation of the axon reflex was small.

CONCLUSION

NO, but not prostaglandins, histamine or an axon reflex, contributes to the increase in blood flow on heating and NO is also a component of the resolution of MH after heating.

The role of endothelial nitric oxide in the Substance P induced vasodilation in bovine dental pulp

Vasodilation, an important response in neurogenic inflammation, involves release of Substance P (SP) from the sensory nerve endings. It is now well known that SP causes edema formation and vascular relaxation in nondental tissues, however, the SP vasodilatory mechanism in the dental pulp is not completely understood. Endothelium-dependent relaxation is mediated by nitric oxide (NO) release with consecutive intracellular cyclic-GMP elevation in many vascular preparations. Recently, it has been shown in different vascular systems that SP-induced vasodilation is mediated by cyclic-GMP production through different pathways involving endothelial NO or direct endothelial-independent pathways. In the present study, the role of endothelial NO in SP induced vasodilation in the dental pulp was investigated to better understand the inflammatory mechanisms. Freshly extracted bovine dental pulp was used to measure NO production. Sodium nitroprusside (SNP), L-NAME and SP were utilized to induce and to inhibit NO production in endothelial cells. Released NO byproducts were measured with chemiluminescence assay technique. The present data demonstrate that SP induces NO production by activating NOsynthase (NOS) in endothelial cells. The NOS inhibitor L-NAME blocks NO production completely. In conclusion, in the bovine dental pulp, SP-induced vascular relaxation can be mediated by inducing NOS, and subsequently NO production in endothelial cells.

Neurokinin-1 receptor desensitization to consecutive microdialysis infusions of substance P in human skin

The neuropeptide substance P is known to be localized in nerve terminals in human skin and substance P-induced vasodilatation is believed to be partially dependent on nitric oxide (NO) and H1 histamine receptor activation. Unlike other neuropeptides investigated in human skin, substance P-induced vasodilatation has been shown to decline during continuous infusion, possibly suggestive of an internalization of neurokinin-1 (NK1) receptors, which are highly specific to substance P. However, questions remain regarding these mechanisms in human skin. Fifteen subjects participated in this series of studies designed to investigate the effect of consecutive infusions and possible mechanisms of substance P-induced vasodilatation in human skin. Two concentrations of substance P (10 microm and 20 microm) were tested via intradermal microdialysis in two groups of subjects. Site 1 served as a control and received substance P only. Site 2 received substance P combined with 10 mm L-NAME to inhibit NO synthase. Site 3 received substance P combined with 500 microm pyrilamine, an H1 receptor antagonist. Site 4 received substance P combined with 10 mm L-NAME plus 500 microm pyrilamine. Red blood cell (RBC) flux was measured via laser-Doppler flowmetry to provide an index of skin blood flow. Cutaneous vascular conductance was calculated as RBC flux/mean arterial pressure and was normalized to maximal vasodilatation via 28 mm sodium nitroprusside. Substance P was perfused through each microdialysis fibre at a rate of 4 microl min(-1) for 15 min. The subsequent increase in skin blood flow was allowed to return to baseline (approximately 45-60 min) and a stable 5 min plateau was used as a new baseline (post-infusion baseline). A second dose of substance P was then delivered to the skin and skin blood flow was monitored for 45-60 min. Substance P produced a dose-dependent increase in skin blood flow with the concentrations of substance P tested, which was significantly attenuated in the presence of L-NAME and the combination of L-NAME plus pyrilamine. However, substance P-induced vasodilatation was unaffected in the presence of pyrilamine. There was no significant difference between the L-NAME-only sites and the L-NAME plus pyrilamine sites. Importantly, the second dose of substance P did not produce a significant increase in skin blood flow compared to the initial baseline or the post-infusion baseline. These data suggest substance P-induced vasodilatation delivered via microdialysis contains an NO component but does not contain an H1 receptor activation component at the doses tested. Additionally, these data provide evidence for NK1 receptor desensitization as there was no observable increase in skin blood flow following a second administration of substance P. This may provide a useful model for studying the role of substance P in the control of skin blood flow in humans.

Microdialysis of large molecules

Microdialysis has been used in many tissues, including skin, brain, adipose tissue, muscle, kidney, and gastrointestinal tract, to recover low-molecular mass endogenous mediators, metabolites, and xenobiotics from the interstitial space. Recently, molecules of larger molecular mass, such as plasma proteins, cytokines, growth factors, and neuropeptides, have also been recovered successfully using larger-pore membranes. Microdialysis recovery of large molecules offers the opportunity to identify patterns of protein expression in a variety of tissue spaces and to evaluate clinically useful biomarkers of disease. From this may develop a better understanding of the disease process and its diagnosis and more targeted approaches to therapy.

Minimal role for H1 and H2 histamine receptors in cutaneous thermal hyperemia to local heating in humans

The precise mechanism(s) underlying the thermal hyperemic response to local heating of human skin are not fully understood. The purpose of this study was to investigate a potential role for H1 and H2 histamine-receptor activation in this response. Two groups of six subjects participated in two separate protocols and were instrumented with three microdialysis fibers on the ventral forearm. In both protocols, sites were randomly assigned to receive one of three treatments. In protocol 1, sites received 1) 500 microM pyrilamine maleate (H1-receptor antagonist), 2) 10 mM L-NAME to inhibit nitric oxide synthase, and 3) 500 microM pyrilamine with 10 mM NG-nitro-L-arginine methyl ester (L-NAME). In protocol 2, sites received 1) 2 mM cimetidine (H2 antagonist), 2) 10 mM L-NAME, and 3) 2 mM cimetidine with 10 mM L-NAME. A fourth site served as a control site (no microdialysis fiber). Skin sites were locally heated from a baseline of 33 to 42 degrees C at a rate of 0.5 degrees C/5 s, and skin blood flow was monitored using laser-Doppler flowmetry (LDF). Cutaneous vascular conductance was calculated as LDF/mean arterial pressure. To normalize skin blood flow to maximal vasodilation, microdialysis sites were perfused with 28 mM sodium nitroprusside, and control sites were heated to 43 degrees C. In both H1 and H2 antagonist studies, no differences in initial peak or secondary plateau phase were observed between control and histamine-receptor antagonist only sites or between L-NAME and L-NAME with histamine receptor antagonist. There were no differences in nadir response between L-NAME and L-NAME with histamine-receptor antagonist. However, the nadir response in H1 antagonist sites was significantly reduced compared with control sites, but there was no effect of H2 antagonist on the nadir response. These data suggest only a modest role for H1-receptor activation in the cutaneous response to local heating as evidenced by a diminished nadir response and no role for H2-receptor activation.

Microdialysis--a model for studying chronic wounds

Microdialysis has been used for more than 20 years as a method of sampling the interstitial fluid space. It has been used in both animals and human tissues, in vivo. The principle of microdialysis is based on the passive diffusion of a compound along its concentration gradient. One major advantage of this sampling technique is that it is simple, relatively cheap, and minimally invasive. Consequently, microdialysis has been employed in a variety of research and clinical settings to recover endogenous molecules and metabolites from the tissue space. It has also been used to measure the tissue penetration of xenobiotics and to follow their temporal and spatial distribution. Most recently, microdialysis has begun to be used as a diagnostic tool and its application to clinical investigation at the bedside explored. This review describes the principles of the technique of microdialysis and its current uses in both an experimental and clinical setting. It goes on to consider current methods of wound fluid sampling and the range of bioactive molecules that have been detected in wound fluid recovered using these techniques. Finally, the use of microdialysis as a novel method for sampling wound fluid in vivo and its ability to provide a fluid that is unaffected by the sampling method and that is representative of the wound environment is discussed.

H1 but not H2 histamine receptor activation contributes to the rise in skin blood flow during whole body heating in humans

Recent evidence suggests a role for vasoactive intestinal polypeptide (VIP) in active vasodilatation and it has been shown that VIP-mediated vasodilatation includes a nitric oxide (NO) and histamine component. Thus, the purpose of this study was to determine the role of H1 and H2 histamine receptors and to examine a potential interaction between NO and histamine receptors in cutaneous active vasodilatation. Eleven subjects were instrumented with four microdialysis fibres. Site 1 served as a control and site 2 was perfused with l-NAME to inhibit nitric oxide synthase. Site 3 was perfused with either the H1 antagonist pyrilamine maleate or the H2 antagonist cimetidine. Site 4 was perfused with l-NAME plus pyrilamine maleate or l-NAME plus cimetidine. Laser-Doppler flowmetry (LDF) was used as an index of skin blood flow and cutaneous vascular conductance (CVC) was calculated as LDF/mean arterial pressure and normalized to maximal vasodilatation achieved via 28 mm sodium nitroprusside infusion. During whole body heating, subjects' sublingual temperature increased a minimum of 0.8 degrees C. In the H1 antagonist studies, CVC in l-NAME, pyrilamine, and combined l-NAME plus pyrilamine sites was significantly reduced compared with control (P < 0.001). The l-NAME and combined l-NAME plus pyrilamine sites were significantly reduced compared with pyrilamine only sites (P < 0.05) but no significant differences were observed between sites. In the H2 receptor antagonist studies, CVC in control sites was not significantly different from cimetidine sites. There was no difference between the l-NAME and combined l-NAME plus cimetidine sites but these sites were significantly attenuated compared with control and cimetidine only sites (P < 0.05). These data suggest the rise in skin blood flow during whole body heating contains an H1 histamine receptor component but do not support an H2 histamine receptor component. Furthermore, part of the NO-dependent component of active vasodilatation can be explained by H1 receptor activation.

Nicotine increases initial blood flow responses to local heating of human non-glabrous skin

Nicotine affects the regulation of skin blood flow (SkBF), but the mechanisms involved are not well understood. We tested the hypothesis that acute exposure to nicotine inhibits both the initial neurally mediated component and the later sustained component of SkBF responses to local heating of non-glabrous skin in humans. SkBF (measured by laser-Doppler) responses to local heating of forearm skin from 32 to 42 degrees C were measured in 11 chronic smokers. Heating occurred at one site over 15 min (RAMP) and over 90 s (STEP) at another site, and was maintained for an additional 30 min. STEP heating was also applied to a site pretreated with bretylium via iontophoresis to inhibit noradrenergic neurotransmission. Responses were measured before and after acute administration of nicotine via cigarettes or nasal spray in two experimental sessions. Nicotine decreased resting skin blood flow (P < 0.05); this response was inhibited by bretylium. During RAMP, nicotine increased the initial SkBF at 42 degrees C (by approximately 12%, P < 0.05). For STEP, nicotine increased the initial peak response (by approximately 25%, P < 0.05), and decreased the sustained plateau value (by approximately 10%, P < 0.05). In skin pretreated with bretylium, the increase caused by nicotine in the initial peak value persisted, but the plateau value was not different from pre-nicotine. These data suggest that in abstinent cigarette smokers, nicotine augments initial responses to both gradual and rapid non-painful heating of non-glabrous skin by sensitizing the sensory nerves that mediate the axon reflex associated with rapid vasodilatation. In contrast, nicotine decreases SkBF responses to prolonged heating by activating noradrenergic nerves.

Mechanisms of vasoactive intestinal peptide-mediated vasodilation in human skin

Vasoactive intestinal peptide (VIP) is known to induce histamine release in human skin and to include a nitric oxide (NO)-dependent dilation in several other vascular beds. However, the relative contribution of histamine and NO to VIP-mediated vasodilation in human skin is unknown. Forty-three subjects volunteered to participate in two studies designed to examine the mechanism of VIP-mediated vasodilation in human skin. Study 1 examined the contribution of NO in the skin blood flow response to eight doses of VIP ranging from 25 to 800 pmol. In addition, study 1 examined a specific role for NO in VIP-mediated dilation. Study 2 examined the relative contribution of NO and histamine to VIP-mediated dilation via H1 and H2 histamine receptors. Infusions were administered to skin sites via intradermal microdialysis. Red blood cell flux was measured by using laser-Doppler flowmetry (LDF), and cutaneous vascular conductance (CVC; LDF/mean arterial pressure) was calculated and normalized to maximal vasodilation. VIP-mediated vasodilation includes a NO-dependent component at doses above 100 pmol, where NO synthase inhibition significantly attenuates CVC (P < 0.05). Inhibition of H1 receptors attenuates the rise in CVC to exogenous VIP (P < 0.05); however, combined H1-receptor inhibition and NO synthase inhibition further reduced VIP-mediated vasodilation compared with either H1 inhibition or NO synthase inhibition alone (P < 0.05). In contrast to H1-receptor inhibition, H2-receptor inhibition did not affect vasodilation to exogenous VIP. Thus, in human skin, VIP-mediated vasodilation includes a NO-dependent component that could not be explained by H1- and H2-receptor activation.