Effects of H1 antagonists on the cutaneous vascular response to histamine and bradykinin: a study using scanning laser Doppler imaging

Role of Bradykinin Type 2 Receptors in Human Sweat Secretion: Translational Evidence Does Not Support a Functional Relationship

Bradykinin increases skin blood flow via a cGMP mechanism but its role in sweating in vivo is unclear. There is a current need to translate cell culture and nonhuman paw pad studies into in vivo human preparations to test for therapeutic viability for disorders affecting sweat glands. Protocol 1: physiological sweating was induced in 10 healthy subjects via perfusing warm (46-48°C) water through a tube-lined suit while bradykinin type 2 receptor (B2R) antagonist (HOE-140; 40 μM) and only the vehicle (lactated Ringer's) were perfused intradermally via microdialysis. Heat stress increased sweat rate (HOE-140 = +0.79 ± 0.12 and vehicle = +0.64 ± 0.10 mg/cm2/min), but no differences were noted with B2R antagonism. Protocol 2: pharmacological sweating was induced in 6 healthy subjects via intradermally perfusing pilocarpine (1.67 mg/mL) followed by the same B2R antagonist approach. Pilocarpine increased sweating (HOE-140 = +0.38 ± 0.16 and vehicle = +0.32 ± 0.12 mg/cm2/min); again no differences were observed with B2R antagonism. Last, 5 additional subjects were recruited for various control experiments which identified that a functional dose of HOE-140 was utilized and it was not sudorific during normothermic conditions. These data indicate B2R antagonists do not modulate physiologically or pharmacologically induced eccrine secretion volumes. Thus, B2R agonist/antagonist development as a potential therapeutic target for hypo- and hyperhidrosis appears unwarranted.

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.

Genetic Variation along the Histamine Pathway in Children with Allergic versus Nonallergic Asthma

Histamine is an important mediator in the pathogenesis of asthma. Variation in genes along the histamine production, response, and degradation pathway may be important in predicting response to antihistamines. We hypothesize that differences exist among single-nucleotide polymorphisms (SNPs) in genes of the histamine pathway between children with allergic versus nonallergic asthma. Children (7-18 yr of age; n = 202) with asthma were classified as allergic or nonallergic based on allergy skin testing. Genotyping was performed to detect known SNPs (n = 10) among genes (HDC, HNMT, ABP1, HRH1, and HRH4) within the histamine pathway. Chi square tests and Cochran-Armitage Trend were used to identify associations between genetic variants and allergic or nonallergic asthma. Significance was determined by P < 0.05 and false-positive report probability. After correction for race differences in genotype were observed, HRH1-17 TT (6% allergic versus 0% nonallergic; P = 0.04), HNMT-464 TT (41% allergic versus 29% nonallergic; P = 0.04), and HNMT-1639 TT (30% allergic versus 20% nonallergic; P = 0.04) were overrepresented among children with allergic asthma. Genotype differences specifically among the African-American children were also observed: HRH1-17 TT (13% allergic versus 0% nonallergic; P = 0.04) and HNMT-1639 TT (23% allergic versus 3% nonallergic; P = 0.03) genotypes were overrepresented among African-American children with allergic asthma. Our study suggests that genetic variation within the histamine pathway may be associated with an allergic versus nonallergic asthma phenotype. Further studies are needed to determine the functional significance of identified SNPs and their impact on antihistamine response in patients with asthma and allergic disease.

Effects of loratadine and cetirizine on serum levels of neuropeptides in patients with chronic urticaria

H1-receptor inhibiting drugs, namely loratadine and cetirizine, were frequently used in treatment of chronic urticaria. Urticarial weal and flare reactions, a neurogenic reflex due to neuropeptides, were reported to be more effectively inhibited by cetirizine than loratadine. The aim of this study was to determine and compare the effects of systemic loratadine and cetirizine treatments on serum levels of selected neuropeptides in chronic urticaria. Treatment groups of either systemic loratadine or cetirizine (10 mg/d), consisting of 16 and 22 patients, respectively, were included. Serum levels of stem cell factor (SCF), neuropeptide Y (NPY), calcitonin gene-related peptide (CGRP), nerve growth factor (NGF), vasoactive intestinal peptide (VIP), and substance P (SP) were detected before and after one week of treatment with antihistamines. Serum NPY and VIP levels were significantly decreased when compared before and after treatment with antihistamines (P < 0.001 and P < 0.01, respectively). SCF and NGF values were also decreased after antihistamine treatment (P < 0.05). Post-treatment levels of CGRP were significantly higher compared with pretreatment values, while no significant difference was detected between pre and post treatment levels of SP. Cetirizine was significantly more effective than loratadine on lowering serum levels of SCF among the other neuropeptides. Systemic loratadine and cetirizine treatments in patients with chronic urticaria precisely caused variations in serum levels of neuropeptides. The predominant effect of cetirizine compared to loratadine on reducing serum SCF levels might be explained with anti-inflammatory properties of cetirizine.

Laser doppler blood flow imaging using a CMOS imaging sensor with on-chip signal processing

The first fully integrated 2D CMOS imaging sensor with on-chip signal processing for applications in laser Doppler blood flow (LDBF) imaging has been designed and tested. To obtain a space efficient design over 64 × 64 pixels means that standard processing electronics used off-chip cannot be implemented. Therefore the analog signal processing at each pixel is a tailored design for LDBF signals with balanced optimization for signal-to-noise ratio and silicon area. This custom made sensor offers key advantages over conventional sensors, viz. the analog signal processing at the pixel level carries out signal normalization; the AC amplification in combination with an anti-aliasing filter allows analog-to-digital conversion with a low number of bits; low resource implementation of the digital processor enables on-chip processing and the data bottleneck that exists between the detector and processing electronics has been overcome. The sensor demonstrates good agreement with simulation at each design stage. The measured optical performance of the sensor is demonstrated using modulated light signals and in vivo blood flow experiments. Images showing blood flow changes with arterial occlusion and an inflammatory response to a histamine skin-prick demonstrate that the sensor array is capable of detecting blood flow signals from tissue.

Comparison of the efficacy of fexofenadine 120 and 240 mg/day on chronic idiopathic urticaria and histamine-induced skin responses in Japanese populations

BACKGROUND

H1-antihistamines are the first-line treatment of chronic idiopathic urticaria (CIU), but CIU is occasionally refractory to the conventional treatment doses. Guidelines in Europe recommend increasing doses as second-line therapy; however, more supportive evidences for these guidelines are required to justify this management strategy.

METHODS

In this study, the authors evaluated the effect of conventional and double doses of fexofenadine HCl on CIU and on histamine-induced skin responses by iontophoresis using visual and laser Doppler imaging scales in healthy donors.

RESULTS

Cutaneous manifestations in CIU and histamine-induced flare and itch in healthy donors were attenuated more extensively by a double dose of fexofenadine HCl compared with a conventional dose.

CONCLUSION

The above findings support the management strategy that increasing the dose of non-sedative antihistamines is the second-line treatment choice for refractory CIU even in Japanese populations.

Platelet-activating factor (PAF) induces wheal and flare skin reactions independent of mast cell degranulation

BACKGROUND

Platelet-activating factor (PAF) causes wheal and flare responses which are abrogated by H1-antihistamines giving rise to the hypothesis that PAF-induced wheal development is secondary to histamine release from dermal mast cells. But is this hypothesis correct?

METHODS

Wheal and flare responses were induced by intradermal injection of PAF, codeine and histamine in 14 healthy volunteers. Dermal histamine and PGD2 contractions were measured using microdialysis.

RESULTS

PAF, unlike histamine and codeine, did not cause a statistically significant rise in mean histamine levels with ten persons showing negligible histamine release. Codeine caused a significant but variable histamine release, ranging from 29 to 282 ng/ml. Codeine, but not PAF or histamine, caused a small but statistically significant release of PGD2.

CONCLUSION

Wheal and flare reactions in human skin induced by PAF are not associated with histamine release and, therefore, appear to be independent of mast cell degranulation.

Effects of bepotastine and fexofenadine on histamine-induced flare, wheal and itch

BACKGROUND

Urticaria is mainly caused by mast cell-derived histamine through the histamine H(1) receptor. Antihistamines are occasionally used on demand upon a recurrence of urticaria; therefore, rapidly acting agents should be explored. The onset of action is assumed to depend on time to maximum concentration (T(max)), but the speed of action needs to be evaluated not only through blood concentration analysis but also by measuring in vivo effectiveness.

METHODS

In this study, we chose two representative second-generation antihistamines (bepotastine and fexofenadine) with relatively short T(max) values and evaluated their effects on histamine-induced skin responses using both visual and laser Doppler imaging scales.

RESULTS

Suppression of histamine-induced flare and itch was observed 3 and 6 h after administration of both antihistamines. Attenuation of itch was seen 30 min after the administration of each drug and thereafter until 6 h. In addition, bepotastine suppressed flare formation after only 30 min following application.

CONCLUSION

These results suggest that antihistamines suppress histamine-induced itch and flare, followed by wheal formation, and that bepotastine suppresses skin symptoms sooner after administration than fexofenadine does, which is relatively consistent with the T(max) results.

Determination of histamine in microdialysis samples from Guinea pig skin by high-performance liquid chromatography with fluorescence detection

AIM

To develop a sensitive and selective liquid-chromatographic method for the determination of histamine in microdialysis samples from guinea pig skin following allergenic provocation.

METHODS

The novel fluorescence derivatization method is based on an intramolecular excimer-forming reaction between 2 amino moieties of histamine and 2 molecules of 4-(1-pyrene)butanoyl chloride (PBC) yielding the corresponding dipyrene-labeled derivative.

RESULTS

The PBC derivative of histamine was separated within 20 min, and the detection limit (signal-to-noise ratio = 3) of histamine was 0.6 fmol/20 μl volume injected. The basal extracellular levels of histamine in guinea pig skin microdialysates were 20.6 ± 1.7 fmol/10 μl. Subcutaneous administration of histamine liberator compound 48/80 (3 mg/kg) increased the extracellular histamine levels in the skin dialysates by about 860%, whereas ovalbumin challenge (2 mg/kg i.v.) in the sensitized guinea pigs increased the extracellular histamine levels by about 3,030%.

CONCLUSION

The novel technique for histamine determination in microdialysis samples from the guinea pig skin may be utilized in preclinical research of antihistaminergic drugs and evaluation of allergenic properties of various dermal preparations such as transdermal drug delivery systems.

Kruppel-like factor 2 regulates endothelial barrier function

OBJECTIVE

A central function of the endothelium is to serve as a selective barrier that regulates fluid and solute exchange. Although perturbation of barrier function can contribute to numerous disease states, our understanding of the molecular mechanisms regulating this aspect of endothelial biology remains incompletely understood. Accumulating evidence implicates the Kruppel-like factor 2 (KLF2) as a key regulator of endothelial function. However, its role in vascular barrier function is unknown.

METHODS AND RESULTS

To assess the role of KLF2 in vascular barrier function in vivo, we measured the leakage of Evans blue dye into interstitial tissues of the mouse ear after treatment with mustard oil. By comparison with KLF2(+/+) mice, KLF2(+/-) mice exhibited a significantly higher degree of vascular leak. In accordance with our in vivo observation, adenoviral overexpression of KLF2 in human umbilical vein endothelial cells strongly attenuated the increase of endothelial leakage by thrombin and H(2)O(2) as measured by fluorescein isothiocyanate dextrans (FITC-dextran) passage. Conversely, KLF2 deficiency in human umbilical vein endothelial cells and primary endothelial cells derived from KLF2(+/-) mice exhibited a marked increase in thrombin and H(2)O(2)-induced permeability. Mechanistically, our studies indicate that KLF2 confers barrier-protection via differential effects on the expression of key junction protein occludin and modification of a signaling molecule (myosin light chain) that regulate endothelial barrier integrity.

CONCLUSIONS

These observations identify KLF2 as a novel transcriptional regulator of vascular barrier function.

Morphine is an arteriolar vasodilator in man

AIM

The mechanisms of action of morphine on the arterial system are not well understood. The aim was to report forearm vascular responses, and their mediation, to intra-arterial morphine in healthy subjects.

METHODS

Three separate protocols were performed: (i) dose ranging; (ii) acute tolerance; (iii) randomized crossover mechanistic study on forearm blood flow (FBF) responses to intrabrachial infusion of morphine using venous occlusion plethysmography. Morphine was infused either alone (study 1 and 2), or with an antagonist: naloxone, combined histamine-1 and histamine-2 receptor blockade or during a nitric oxide clamp.

RESULTS

Morphine caused an increase in FBF at doses of 30 microg min(-1)[3.25 (0.26) ml min(-1) 100 ml(-1)][mean (SEM)] doubling at 100 microg min(-1) to 5.23 (0.53) ml min(-1) 100 ml(-1). Acute tolerance was not seen to 50 microg min(-1) morphine, with increased FBF [3.96 (0.35) ml min(-1) 100 ml(-1)] (P = 0.003), throughout the 30-min infusion period. Vasodilatation was abolished by pretreatment with antihistamines (P = 0.008) and the nitric oxide clamp (P < 0.001), but not affected by naloxone. The maximum FBF with pretreatment with combined H1/H2 blockade was 3.06 (0.48) and 2.90 (0.17) ml min(-1) 100 ml(-1) after 30 min, whereas with morphine alone it reached 4.3 (0.89) ml min(-1) 100 ml(-1).

CONCLUSIONS

Intra-arterial infusion of morphine into the forearm circulation causes vasodilatation through local histamine-modulated nitric oxide release. Opioid receptor mechanisms need further exploration.

Molecular mechanisms of endothelial hyperpermeability: implications in inflammation

Endothelial hyperpermeability is a significant problem in vascular inflammation associated with trauma, ischaemia-reperfusion injury, sepsis, adult respiratory distress syndrome, diabetes, thrombosis and cancer. An important mechanism underlying this process is increased paracellular leakage of plasma fluid and protein. Inflammatory stimuli such as histamine, thrombin, vascular endothelial growth factor and activated neutrophils can cause dissociation of cell-cell junctions between endothelial cells as well as cytoskeleton contraction, leading to a widened intercellular space that facilitates transendothelial flux. Such structural changes initiate with agonist-receptor binding, followed by activation of intracellular signalling molecules including calcium, protein kinase C, tyrosine kinases, myosin light chain kinase, and small Rho-GTPases; these kinases and GTPases then phosphorylate or alter the conformation of different subcellular components that control cell-cell adhesion, resulting in paracellular hypermeability. Targeting key signalling molecules that mediate endothelial-junction-cytoskeleton dissociation demonstrates a therapeutic potential to improve vascular barrier function during inflammatory injury.

The histamine H1 receptor is not involved in local control of mammary blood flow in dairy cows

Low concentrations of the essential amino acid histidine in circulation have been shown to increase mammary blood flow and it has been suggested that this effect is mediated by histamine. The hypotheses tested in this experiment were that interstitial histamine concentrations in the mammary gland are related to arterial His concentrations and that mammary blood flow is reduced by extracellular histamine via H(1) receptors. The hypotheses were tested by infusing saline or chlorpheniramine, a blocker of the H(1) histamine receptor, into the arterial supply of the mammary glands of lactating cows infused with 44 g/h of amino acid mixtures with or without His for 10 h. Infusates were administered in a 2 x 2 factorial arrangement within a 4 x 4 Latin square to 4 multiparous Holstein cows in mid lactation. Exclusion of His from the infusate decreased protein content in milk from the infused udder half from 3.98 to 3.77%, and increased arterial alpha-aminonitrogen concentration from 3.2 to 3.4 mM. Neither the decreased arterial His concentration nor the H(1) blocker affected plasma flow to the infused udder half. We conclude that histamine is not involved in the regulation of mammary blood flow. The H(1) blocker decreased milk production in the infused udder half from 4.6 to 3.5 kg without affecting protein, fat, and lactose percentages, suggesting an inhibition of milk ejection. Cows on chlorpheniramine ate less feed during the infusion than saline-infused cows, which resulted in lower arterial concentrations and mammary uptakes of acetate. The efficiency of plasma triacylglycerol uptake across the mammary glands was decreased by chlorpheniramine but net uptake of long-chain fatty acids was not affected. The mechanism by which an amino acid deficiency influences mammary blood flow does not involve histamine signaling through the H(1) receptor and remains unidentified.

Rapid flare development evoked by current frequency-dependent stimulation analyzed by full-field laser perfusion imaging

We analyzed, with a new imaging technique, the rapid axon reflex flare responses in human skin upon transcutaneous delivery of electrical stimuli at 1, 5, 10 and 50 Hz in single bursts of five pulses each. Two-dimensional perfusion images covering an area of 8 x 8 cm(2) were captured at 25 Hz and their averages saved at 0.5 Hz. The stimulation caused an axon reflex flare (maximum 3 cm(2), 20 s after stimulation) that gradually resolved within 2 min. Maximum flare responses developed at 5 Hz, whereas pain ratings increased with stimulation frequency. The highest neuropeptide release at 5 Hz correlates to the discharge characteristics of mechanoinsensitive C-fibers, whereas the maximum pain intensity at 50 Hz may be attributed to the activation of A-delta fibers.

Repeated cycles of electrical stimulation decrease vasoconstriction and axon-reflex vasodilation to noradrenaline in the human forearm

AIM

To investigate whether desensitization to the vasomotor effects of noradrenaline is a specific effect of electrical stimulation.

METHODS

Three sites on the forearm of 10 healthy volunteers were stimulated with 0.2 mA direct current for 2 min twice daily for 10 days. Noradrenaline and histamine were then displaced from ring-shaped iontophoresis chambers into two of the pretreated sites and two untreated sites on the contralateral forearm. Axon-reflex vasodilation was measured from the centre of the ring described by the iontophoresis chamber with a laser Doppler flowmeter. One or two days later, noradrenaline and vasopressin were introduced into pretreated and untreated sites by iontophoresis, and vasoconstriction at sites of administration was measured in the heated forearm.

RESULTS

The pretreatment blocked vasoconstriction to noradrenaline [median increase in flow 1%, interquartile range (IR) -41 to 52%; median decrease at the untreated site 53%, IR. -70 to -10%; P < 0.05], but did not block vasoconstriction to vasopressin (median decrease 42% at the untreated site and 45% at the pretreated site). Axon-reflex vasodilation to noradrenaline was diminished at the pretreated site (median increase in flow 33%, IR 2-321%; untreated site 247%, IR 31-1087%; P < 0.05). However, axon-reflex vasodilation to histamine did not differ significantly between the pretreated site (median increase 1085%) and the untreated site (median increase 1345%).

CONCLUSIONS

The conditioning pretreatment appears to evoke a specific decrease in responsiveness to noradrenaline. Repeated cycles of electrical stimulation may downregulate neural and vascular responses to noradrenaline by repetitively activating cutaneous sympathetic nerve fibres.

Histamine Is Released following Aminolevulinic Acid-Photodynamic Therapy of Human Skin and Mediates an Aminolevulinic Acid Dose-Related Immediate Inflammatory Response

Acute skin inflammation occurs following topical aminolevulinic acid-photodynamic therapy (ALA-PDT), but its nature and mediation are ill defined. As we observed an urticarial response, a potential role for histamine was explored. In 13 healthy volunteers, we assessed the time course and dose-response of the acute cutaneous response(s) to ALA-PDT, the impact of H(1) antihistamine blockade, and measured dermal histamine release. An ALA dose series was iontophoresed into ventral forearm skin and exposed to red light. All participants exhibited an immediate urticarial response, both wheal and flare correlating with log ALA dose. Subsequently, a dose-related erythema developed at treatment sites by 3 hours and persisted at 24 hours. H(1) blockade with oral cetirizine doubled the median minimal urticating dose of ALA and reduced the slope of dose-response for wheal and flare, whereas at the highest ALA dose, mean wheal and flare areas reduced by 68 and 60%, respectively. In contrast, cetirizine did not influence the 24 hour minimal phototoxic dose or erythema dose-response. Histamine release after ALA-PDT mirrored the urticarial response, levels peaking within 30 minutes and returning to baseline by 24 hours. Thus, two discrete acute inflammatory responses to topical ALA-PDT occur in human skin; histamine mediates the immediate response, but does not appear involved in the delayed phototoxicity.

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.

Laser Doppler imager (LDI) scanner and intradermal injection for in vivo pharmacology in human skin microcirculation: responses to acetylcholine, endothelin-1 and their repeatability

AIMS

The purpose of this study was to evaluate the repeatability of forearm skin blood flow responses to intradermal injections of acetylcholine (ACh) and endothelin-1 (ET-1) using a double injection technique (DIT) and a laser Doppler imager (LDI) scanner in the human skin microcirculation.

METHODS

We used a laser Doppler imager (Moor LDI V3.01) to continuously monitor the change in skin blood flow during intradermal administration of physiological saline (0.9% NaCl), acetylcholine (ACh 10(-7), 10(-8), 10(-9) M) and endothelin-1 (ET-1 10(-14), 10(-16), 10(-18) M) in 10 healthy male subjects. Subjects were examined on 3 different days for assessment of interday and interobserver repeatability. Injections of either drug were randomly placed on different sites of the forearm. Laser Doppler images were collected before and after injection at 2.5 min intervals for 30 min. Data were analysed after the completion of each experiment using Moor Software V.3.01. Results are expressed as changes from baseline in arbitrary perfusion units (PU).

RESULTS

ACh caused a significant vasodilation (P < 0.0001 anova, mean +/- SE: 766 +/- 152 PU, ACh 10(-9) M; 1868 +/- 360 PU, ACh 10(-8) M; 4188 +/- 848 PU, ACh 10(-7) M; mean of days 1 and 2, n = 10), and ET-1 induced a significant vasoconstrictive response (P < 0.0001 anova, -421 +/- 83 PU, ET-1 10(-18) M; -553 +/- 66 PU, ET-1 10(-16) M; -936 +/- 90 PU, ET-1 10(-14) M; mean of days 1 and 2, n = 10). There was no difference on the response to either drug on repeated days. Bland-Altman analyses showed a close agreement of responses between days with repeatability coefficients of 1625.4 PU for ACh, and 386.0 PU for ET-1 (95% CI: ACh, -1438 to 1747 PU, ET-1, -399 to 358 PU) and between observers with repeatability coefficients of 1057.2 PU for ACh and 255.8 PU for ET-1 (95% CI: ACh, -1024 to 1048 PU, ET-1, -252 to 249 PU). The variability between these responses was independent of average flux values for both ACh and ET-1. There was a significant correlation between responses measured in the same site, in the same individual on two different days by the same observer (ACh, r = 0.94, P < 0.0001; ET-1, r = 0.90, P < 0.0006), and between responses measured by two different observers (ACh, r = 0.94, P < 0.0001; ET-1, r = 0.91, P < 0.0003).

CONCLUSION

We have shown that interday and intraobserver responses to intradermal injections of ET-1 and ACh, assessed using the DIT in combination with an LDI scanner, exhibited good reproducibility and may be a useful tool for studying the skin microcirculation in vivo.

Regulation of wheal and flare by tea tree oil: complementary human and rodent studies

When applied 20 min after injection of histamine into human forearm skin, tea tree oil (TTO) reduces the developing cutaneous vascular response. In this study, the effect of TTO on inflammatory microvascular changes was dissected at the base of an experimental blister on rat skin. 1,8-Cineole, representing 2% of TTO, reduced vascular changes induced by sensory neuropeptides released when the distal portion of a cut sciatic nerve was electrically stimulated. The pre-terminal modulatory effect of 1,8-Cineole was confirmed in tests in sensory-denervated rats. Terpinen-4-ol (approximately 40% TTO) reduced substance P-induced microvascular changes and protein extravasation by a direct nitric oxide-mediated effect on the microvasculature, without sensory nerve involvement. alpha-Terpineol (3% of TTO) regulated both pre- and post-sensory nerve terminals. In human skin, terpinen-4-ol applied 10 min after histamine injection, but not alpha-terpineol or 1,8-cineole, regulated the developing wheal and flare suggesting that the histamine-induced responses in humans (at the dose used in this study, 50 microL of 330 microM histamine) are in large part determined by histamine directly affecting the vasculature via post-terminal-mediated events. The underlying strength of these studies is the use of a well-established rat physiologic model to differentiate the mechanism of regulation of microvascular changes by modulatory agents.

Tissue spectroscope: a novel in vivo approach to real time monitoring of tissue vitality

Optical monitoring of various tissue physiological and biochemical parameters in real-time represents a significant new approach and a tool for better clinical diagnosis. The Tissue Spectroscope (TiSpec), developed and applied in experimental and clinical situations, is the first medical device that enables the real-time monitoring of three parameters representing the vitality of the tissue. Tissue vitality, which is correlated to the oxygen balance in the tissue, is defined as the ratio between O(2) supply and O(2) demand. The TiSpec enables the monitoring of microcirculatory blood flow (O(2) supply), mitochondrial NADH redox state (O(2) balance), and tissue reflectance, which correlates to blood volume. We describe in detail the theoretical basis for the monitoring of the three parameters and the technological aspects of the TiSpec. The comparison between the TiSpec and the existing single parameter monitoring instruments shows a statistically significant correlation as evaluated in vitro as well as in various in vivo animal models. The results presented originated in a pilot study performed in vivo in experimental animals. Further research is needed to apply this technology clinically. The clinical applications of the TiSpec include two situations where the knowledge of tissue vitality can improve clinical practice. The major application is the monitoring of "nonvital" organs of the body [i.e., the skin, gastrointestinal (G-I) tract, urethra] in emergency situations, such as in the operating rooms and intensive care units. Also, the monitoring of specific (vital) organs, such as the brain or the heart, during surgical procedure is of practical importance.

Investigation into the mechanisms by which nedocromil sodium, frusemide and bumetanide inhibit the histamine-induced itch and flare response in human skin in vivo

BACKGROUND

In a previous study, iontophoresis of nedocromil sodium into human skin in vivo was shown to reduce histamine-induced itch and flare. In asthma, the Na+/K+/2Cl- cotransporter inhibitors, frusemide and bumetanide, have been reported to have many similar actions to nedocromil sodium.

OBJECTIVE

To compare the effects of these drugs in the histamine-induced itch, flare and weal response in human skin in vivo and elucidate their site of action.

METHODS

Nedocromil sodium, frusemide bumetanide and reversed osmosis water (control), were introduced by iontophoresis into the forearm skin of 10 volunteers in each of two single-blind studies. In study 1, histamine (20 microL of 100 microM) or vehicle was injected into the area of iontophoresis 10 min later. In study 2, histamine or vehicle was injected 5 mm outside the area of iontophoresis so the flare developed over the area of iontophoresis. Itch was scored on a visual analogue scale every 20 s for 5 min, flare areas were assessed using scanning laser Doppler imaging up to 10 min and weal was assessed by planimetry at 10 min.

RESULTS

In study 1, nedocromil sodium, frusemide and bumetanide reduced itch scores by 36%, 48% and 34%, respectively, and flare areas by 17%, 26% and 15% respectively (all P<0.05). Weal areas and blood flux in the flare were unaffected. In study 2, itch scores, flare areas and weal areas were not inhibited. Also, blood flux values in areas of drug and water iontophoresis were not different.

CONCLUSION

This study has provided evidence to support the hypothesis that nedocromil sodium, frusemide and bumetanide inhibit sensory nerve activation to reduce the itch and flare responses induced by histamine in human skin in vivo. It is likely that inhibition of a Na+/K+/2Cl- cotransporter in the sensory nerve membrane is a possible mechanism of action.

Role of histamine release in nonspecific vasodilatation during anodal and cathodal iontophoresis

Nonspecific vasodilatation during iontophoresis is an important confounding factor in experimental pharmacology. In this investigation, we studied the involvement of sensory nerves and histamine-related reactions in causing nonspecific vasodilatation in a model of anodal and cathodal iontophoresis of sodium chloride. Firstly, we applied a mixture of local anesthetic (EMLA) cream to confirm its suppressive effect on nonspecific vasodilatation and to measure its efficacy in three different dosages (duration: 1, 2, and 3 h). We then investigated the role of histamine in nonspecific vasodilatation by giving an oral antihistamine drug (cetirizine) to subjects who had and had not been given EMLA. We found substantial suppression of the nonspecific vasodilatation in all EMLA-treated groups (all dosages) compared with untreated controls (with suppression rates of 60-65%). Dosage had no significant effect. A further suppression of nonspecific vasodilatation was seen after oral cetirizine during anodal and cathodal iontophoresis in both EMLA-treated and untreated groups. The antihistamine effect was most pronounced during anodal iontophoresis. These results suggest a histaminergic increase in perfusion that may be independent of neurogenic mechanisms and depend on polarity (anode or cathode). Local nerve blocks (EMLA) together with cetirizine may therefore be used to reduce nonspecific vasodilatation in both anodal and cathodal iontophoresis.

Tea tree oil reduces histamine-induced skin inflammation

BACKGROUND

Tea tree oil is the essential oil steam-distilled from Melaleuca alternifolia, an Australian native plant. In recent years it has become increasingly popular as an antimicrobial for the treatment of conditions such as tinea pedis and acne.

OBJECTIVES

To investigate the anti-inflammatory properties of tea tree oil on histamine-induced weal and flare.

METHODS

Twenty-seven volunteers were injected intradermally in each forearm (study and control assigned on an alternating basis) with histamine diphosphate (5 microg in 50 microL). Flare and weal diameters and double skin thickness were measured every 10 min for 1 h to calculate flare area and weal volume. At 20 min, 25 microL of 100% tea tree oil was applied topically to the study forearm of 21 volunteers. For six volunteers, 25 microL paraffin oil was applied instead of tea tree oil.

RESULTS

Application of liquid paraffin had no significant effect on histamine-induced weal and flare. There was also no difference in mean flare area between control arms and those on which tea tree oil was applied. However, mean weal volume significantly decreased after tea tree oil application (10 min after tea tree oil application, P = 0.0004, Mann-Whitney U-test).

CONCLUSIONS

This is the first study to show experimentally that tea tree oil can reduce histamine-induced skin inflammation.

Vascular responses in the skin: an accessible model of inflammation

The skin is the most accessible organ of the human body in which to study the inflammatory process. Until recently, changes in vascular perfusion and permeability could only be superficially visualized. A novel combination of techniques has now provided the appropriate tools with which to study this more extensively in humans.

Are cysteinyl leukotrienes involved in allergic responses in human skin?

BACKGROUND

Cysteinyl leukotrienes have been suggested to be involved in producing the symptoms of both the early and late phases of the allergic response in the lung and other tissues.

OBJECTIVE

To use scanning laser Doppler imaging, microdialysis and immunocytochemistry to explore the mediator and cellular mechanisms of the dermal allergic response.

METHODS

Thirteen atopic volunteers received intradermal injections into the forearm of grass pollen or D. pteronyssinus extract. Changes in dermal blood flow up to 8 h were monitored by scanning laser Doppler imaging. The release of histamine, PGD2 and LTC4/D4/E4 was assessed by dermal microdialysis. Skin biopsies were taken at 6 h to determine numbers of mast cells, eosinophils, basophils, Langerhans' cells, and monocytes/macrophages, and the expression of COX-1, COX-2, 5-LO and FLAP.

RESULTS

Allergen provocation produced an immediate weal and flare response followed by an erythematous induration peaking at 6 h. During the first hour, c. 84 pmoles of histamine and c. 0.3 pmoles of PGD2 were recovered by microdialysis (both P < 0.001) but LTC4/D4/E4 was undetectable. No histamine, PGD2 or LTC4/D4/E4 was detectable at later times. Immunocytochemical examination of biopsies taken at 8 h showed increased numbers of eosinophils and basophils and in COX-2, 5-LO and FLAP, but not COX-1. Expression of 5-LO and FLAP was associated primarily with eosinophils.

CONCLUSIONS

These findings suggest that inflammatory cells recruited to the site of allergen injection are not activated to release detectable amounts of cysteinyl leukotrienes. Hence, it is unlikely that the late-phase erythematous induration is mediated by this autocoid.

H1-antihistamines: inverse agonism, anti-inflammatory actions and cardiac effects

This review addresses novel concepts of histamine H1-receptor function and attempts to relate them to the anti-inflammatory effects of H1-antihistamines. Furthermore, the molecular mechanisms underlying the cardiotoxic effects of H1-antihistamines are discussed. H1-receptors are G-protein-coupled-receptors (GPCRs), the inactive and active conformations of which coexist in equilibrium. The degree receptor activation in the absence of histamine is its 'constitutive activity'. In this two-state model, histamine acts as an agonist by combining with and stabilizing the activated conformation of the H1-receptor to shift the equilibrium towards the activated state. Drugs classified previously as antagonists act as either inverse agonists or neutral antagonists. Inverse agonists combine with and stabilize the inactive conformation of the receptor to shift the equilibrium towards the inactive state. Thus, they may down-regulate constitutive receptor activity, even in the absence of histamine. Neutral antagonists combine equally with both conformations of the receptor, do not affect basal receptor activity but do interfere with agonist binding. All H1-antihistamines examined to date are inverse agonists. As the term 'H1-receptor antagonists' is obviously erroneous, we suggest that it be replaced by 'H1-antihistamines'. The observations that H1-receptors modulate NF-kappaB activation and that there are complex interactions between GPCRs, has allowed us to postulate receptor dependent-mechanisms for some anti-inflammatory effects of H1-antihistamines, e.g. inhibition of ICAM-1 expression and the effects of bradykinin. Finally, the finding that blockade of HERG1 K+ channels is the mechanism by which some H1-antihistamines may cause cardiac arrhythmias has allowed the development of preclinical tests to predict such activity.

Laser Doppler, speckle and related techniques for blood perfusion mapping and imaging

Laser Doppler velocimetry uses the frequency shift produced by the Doppler effect to measure velocity. It can be used to monitor blood flow or other tissue movement in the body. Laser speckle is a random interference effect that gives a grainy appearance to objects illuminated by laser light. If the object consists of individual moving scatterers (such as blood cells), the speckle pattern fluctuates. These fluctuations provide information about the velocity distribution of the scatterers. It can be shown that the speckle and Doppler approaches are different ways of looking at the same phenomenon. Both these techniques measure at a single point. If a map of the velocity distribution is required, some form of scanning must be introduced. This has been done for both time-varying speckle and laser Doppler. However, with the speckle technique it is also possible to devise a full-field technique that gives an instantaneous map of velocities in real time. This review article presents the theory and practice of these techniques using a tutorial approach and compares the relative merits of the scanning and full-field approaches to velocity map imaging. The article concludes with a review of reported applications of these techniques to blood perfusion mapping and imaging.

Comparison of the effects of levocetirizine and loratadine on histamine-induced wheal, flare, and itch in human skin

BACKGROUND

This randomized, double-blind, crossover study compared the effects of the R-enantiomer of cetirizine, levocetirizine, with those of loratadine on the wheal, flare, and itch response to histamine in human skin.

METHODS

Levocetirizine (5 mg), loratadine (10 mg), or placebo was taken orally 4 h before the intradermal injection of histamine (20 microl, 100 microM) or the control vehicle into the forearm skin of healthy volunteers. Flare areas were assessed by scanning laser Doppler imaging before and at 30-s intervals for a period of 9 min. Wheal areas were measured by planimetry at 10 min. Itch was scored every 30 s with a visual analogue scale.

RESULTS

After placebo administration, the mean peak flare area was 23.01+/-1.94 cm(2), the wheal area 248+/-27 mm(2), and the cumulative itch score 28.8+/-4.6% (mean+/-SEM). Levocetirizine reduced the flare, wheal, and itch by 60%, 68%, and 91%, respectively (all P<0.001, Student's t-test for paired data). The effects of loratadine were variable and not statistically significant.

CONCLUSION

Levocetirizine (5 mg) is a potent inhibitor of the effects of histamine in human skin with an efficacy that exceeded that of loratadine (10 mg) when single doses of the drugs were administered 4 h before the test.

Nociceptor activation and protein extravasation induced by inflammatory mediators in human skin

Protein extravasation (PE) is known to play an important role in inflammatory conditions. In this study we used dermal microdialysis to apply inflammatory mediators (histamine, bradykinin, serotonin) to human skin. Locally induced PE was compared to pain ratings and axon reflex erythema measured simultaneously. Linear microdialysis capillaries (outer diameter 0.4 mm; cut-off 3000 kDa) were inserted intracutaneously at a length of 1.5 cm in the volar forearm of healthy volunteers. The capillaries were perfused with Ringer's solution at a constant flow rate of 4 microl/min. The perfusate was sampled at 15-min intervals and was analysed for total protein concentration. After a baseline of 60 min, the perfusion was switched to inflammatory mediators for 30 min and then back to vehicle again. Sensations evoked by the stimulation were assessed on a visual analogue scale and visible axon reflex erythema was measured planimetrically.Dose-dependent increases in PE could be assessed for all inflammatory mediators tested. Bradykinin (10(-7)M) induced a significant PE, whereas serotonin was effective only at a concentration of 10(-3)M. While serotonin in lower concentrations induced moderate burning pain and an axon reflex flare but no PE, bradykinin provoked PE without pain or axon reflex flare at a concentration of 10(-7)M. Application of histamine similarly evoked PE at lower concentrations as compared to the induction of itch sensation and axon reflex flare. It is concluded that there is no link between nociceptor activation and protein extravasation induced by inflammatory mediators in healthy human skin.

Nedocromil sodium inhibits histamine-induced itch and flare in human skin

This study was designed to test the hypothesis that nedocromil sodium inhibits sensory nerve function to reduce flare and itch in human skin. Nedocromil sodium (2%) or water (control) was introduced into the volar forearm skin of eight non-atopic volunteers by iontophoresis (8 mC) and histamine (20 microl of 1 microM and 300 nM) injected intradermally 10 min later at the same site. Itch was assessed on a visual analogue scale every 20 s for 5 min. Weal and flare areas and mean blood flux within the flare were assessed by scanning laser Doppler imaging at 10 min. The results showed that nedocromil sodium reduced itch scores, totalled over 5 min, by approximately 74.0% (P<0.005) and flare areas by approximately 65% (P<0.03). Neither weal areas nor blood flux within were reduced. These data demonstrate that nedocromil sodium is effective in reducing neurogenic itch and flare in the skin. We suggest that its mechanism of action is modulation of sensory neurone activation or conduction in the skin.

Inhibition by glucocorticoids of the mast cell-dependent weal and flare response in human skin in vivo

1. This study examines the relative contributions made by inhibition of mast cell degranulation, reduction of mast cell recruitment and maturation, and lowering the responsiveness of the vasculature to histamine, in the inhibition by glucocorticoids of the weal and flare in human skin. 2. One forearm of healthy human volunteers was treated for 24 h (n=6) or daily for 21 days (n=10) with 0.05% clobetasol propionate. The other arm served as control. Weal and flare responses were elicited by intradermal injection of 20 microl of 0.3 mM codeine. The areas of the responses were measured using scanning laser Doppler imaging. Microdialysis was used to assess histamine release. Mast cell numbers and tissue histamine content were assessed in 4-mm punch biopsies. Histamine (20 microl of 1 microM i.d.) was used to assess the status of the vasculature. 3. No significant effects were seen at 24 h. At 21 days, clobetasol reduced the areas of the codeine-induced weal and flare responses by 59 and 58% respectively (both P=0.006). Mast cell numbers were reduced by 47%, (P=0.014) and total tissue histamine content by 52% (P=0.006). Codeine-induced histamine release was reduced by 44% (P=0.022). The weal, but not the flare, induced by histamine was significantly inhibited (P=0.019). Echography revealed a 15% thinning of the skin by clobetasol. 4. These results demonstrate that reduction of the weal and flare responses to codeine following clobetasol treatment, results primarily from reduced mast cell numbers and tissue histamine content rather than inhibition by corticosteroids of mast cell degranulation.

Microdialysis in clinical drug delivery studies

The introduction of in vivo microdialysis (MD) to clinical pharmacological studies has opened the opportunity to obtain previously inaccessible information about the drug distribution process to the clinically relevant target site. The aim of this review is to provide a comprehensive overview of the current literature about MD in drug delivery studies from a clinical perspective. In particular the application of MD in clinical--antimicrobial, oncological and transdermal--and neurological research will be described and the scope of MD in pharmacokinetic-pharmacodynamic (PK-PD) studies will be discussed. It is concluded that MD has a great potential for both academic and industrial research, and may become the method of choice for drug distribution studies in humans.

Cetirizine inhibits bradykinin-induced cutaneous wheal and flare in atopic and healthy subjects

BACKGROUND

Kinins are vasoactive mediators involved in allergic reactions. When applied on the skin or in the nose, bradykinin (BK) elicits inflammation that is poorly affected by previous H1-blockade. The aim of this study was to compare the possible effect of cetirizine (an H1-antagonist) on wheal and flare responses to BK, histamine, and compound 48/80 in atopic and healthy subjects.

METHODS

In a randomized, double-blind, crossover study, eight atopic and eight healthy subjects received cetirizine (10 mg/day) or placebo for 3 days before cutaneous tests. Intradermal tests (IDT) and prick tests (PT) were performed with BK (20 nmol/ml for IDT and 20 micromol/ml for PT), histamine (100 microg/ml IDT and 100 mg/ml PT), and compound 48/80 (100 microg/ml IDT and 100 mg/ml PT) as positive controls and saline as negative control. The skin responses were monitored by measurement of wheal and flare areas.

RESULTS

BK, histamine, and 48/80 induced wheal and flare reactions in all placebo-treated subjects. Histamine elicited larger wheal and flare reactions than BK and 48/80. IDT with BK induced four- to six-fold larger wheal and flare reaction than PT. No differences in BK-induced wheal and flare were observed between atopic and healthy subjects. In atopic subjects, cetirizine induced a significant reduction of flare reactions after the BK test (80% for IDT, and 94% for PT [P<0.01]). Moreover, cetirizine reduced significantly BK-induced wheals by 70% for IDT (P<0.01) and 65% for PT (P<0.01). A similar inhibiting effect of cetirizine was also observed in healthy subjects.

CONCLUSIONS

These findings showed that the wheal and flare reactions induced by BK challenge were markedly inhibited by previous intake of cetirizine. The mechanism by which this effect is mediated cannot be established at present.

Mast cell mediators other than histamine induce pruritus in atopic dermatitis patients: a dermal microdialysis study

While histamine is the crucial mediator of pruritus in type 1 allergic reactions, its role in atopic dermatitis (AD) is unclear. In this study, the role of mast cell mediators in protein extravasation and pruritus was evaluated using intradermal microdialysis. The microdialysis capillaries were used to apply the mast cell degranulating substance compound 48/80 (C48/80; 0.05%) or histamine (0.01%) and also to deliver H1-blockers (cetirizine, 200 microg mL-1) in nine AD patients and nine controls. Large pore size membranes (3000 kDa) enabled simultaneous analysis of protein extravasation. Itch sensation was measured psychophysically and weal and flare reaction were evaluated planimetrically. Protein extravasation induced by histamine and C48/80 was significantly reduced in AD patients. Blockade of H1-receptors by cetirizine significantly reduced C48/80-induced protein extravasation in AD patients and controls to an identical level. C48/80-induced pruritus was abolished by cetirizine in controls, whereas pruritus in AD patients was unchanged after H1 blockade. We conclude that mast cell mediators others than histamine are involved in C48/80-induced pruritus in AD patients. Whether the reduced capacity of AD patients to induce protein extravasation is of pathophysiological relevance for pruritus remains to be established.

Clinical pharmacology of the H1-receptor antagonists cetirizine and loratadine in children

H1-receptor antagonists are widely used in children but are not as well-studied in children as they are in adults. Our objective was to determine the onset and duration of action and the relative potency of the H1-receptor antagonists cetirizine and loratadine in children. We performed a prospective, randomized, placebo-controlled, double-blind, crossover, single-dose study of cetirizine and loratadine using suppression of the histamine-induced wheal and flare as the primary outcome. In 15 allergic children, mean age 9 years, compared with baseline, cetirizine (10 mg) suppressed the wheals and flares significantly from 0.25 to 24 h, achieving nearly 100% of flare suppression from 2 to 24 h, inclusive, and loratadine (10 mg) suppressed the wheals and flares significantly from 0.75 to 24 h, inclusive. Cetirizine suppressed the wheals and flares significantly more than loratadine from 0.25 to 1 h, inclusive, and at 0.5, 1, 2, 3, 5, 6, 7, and 24 h, respectively. Placebo also suppressed the wheal and flare significantly at some assessment times. Cetirizine and loratadine both have excellent antihistaminic activity in children, with a rapid onset of action and a 24-h duration of action in this population.

Cetirizine inhibits bradykinin-induced cutaneous wheal and flare in atopic and healthy subjects

BACKGROUND

Kinins are vasoactive mediators involved in allergic reactions. When applied on the skin or in the nose, bradykinin (BK) elicits inflammation that is poorly affected by previous H1-blockade. The aim of this study was to compare the possible effect of cetirizine (an H1-antagonist) on wheal and flare responses to BK, histamine, and compound 48/80 in atopic and healthy subjects.

METHODS

In a randomized, double-blind, crossover study, eight atopic and eight healthy subjects received cetirizine (10 mg/day) or placebo for 3 days before cutaneous tests. Intradermal tests (IDT) and prick tests (PT) were performed with BK (20 nmol/ml for IDT and 20 micromol/ml for PT), histamine (100 microg/ml IDT and 100 mg/ml PT), and compound 48/80 (100 microg/ml IDT and 100 mg/ml PT) as positive controls and saline as negative control. The skin responses were monitored by measurement of wheal and flare areas.

RESULTS

BK, histamine, and 48/80 induced wheal and flare reactions in all placebo-treated subjects. Histamine elicited larger wheal and flare reactions than BK and 48/80. IDT with BK induced four- to sixfold larger wheal and flare reaction than PT. No differences in BK-induced wheal and flare were observed between atopic and healthy subjects. In atopic subjects, cetirizine induced a significant reduction of flare reactions after the BK test (80% for IDT, and 94% for PT [P < 0.01]). Moreover, cetirizine reduced significantly BK-induced wheals by 70% for IDT (P < 0.01) and 65% for PT (P < 0.01). A similar inhibiting effect of cetirizine was also observed in healthy subjects.

CONCLUSIONS

These findings showed that the wheal and flare reactions induced by BK challenge were markedly inhibited by previous intake of cetirizine. The mechanism by which this effect is mediated cannot be established at present.

Pruritus: more scratch than itch

Itch is one of the major symptoms of skin disease although it remains poorly studied. Little is known about its mediators or the neurological processes involved in either the detection of an itch stimulus or the induction of the main response to itch, scratch. This lack of knowledge may be due to the subjective nature of the sensation itself and the related difficulties in quantifying it, and is compounded by the absence of a convincing animal model. Defining itch as that sensation which provokes the desire to scratch provides two approaches to measurement, that of itch itself, and the behavioural response, scratch. The measurement of itch itself traditionally involves the use of questionnaires or visual analogue scale, both of which rely on the dubious assumption that the subject is able to relate their experiences accurately. By contrast experimental induction of itch and measurement of areas of allokinesis around application sites may provide a more reliable and repeatable method of itch quantification. Recent advances in two areas that may prove relevant are discussed: new technological improvements in movement meters and compatible software; and some recently described animal models.

Experimental models of skin inflammation

The skin is the most accessible organ of the body in which to view the inflammatory process and its pharmacological modulation. However, there are relatively few studies in which the response of the dermal vasculature to inflammatory stimuli has been assessed quantitatively or the chemical mediators of the response measured directly. The mechanisms underlying these responses remain unclear despite the fact that altered microvascular function plays an important part in a number of clinical conditions. This paper describes recent studies in which an experimental model of inflammation in the skin has been used to investigate the pharmacological mechanisms underlying microvascular responses. As allergen-induced cutaneous weal and flare responses are mediated mainly by histamine, we first set out to characterize the vascular responses using the intradermal injection of histamine as a first step, experimental model of allergic skin disease. To quantify the inflammatory responses and to explore the mediator mechanisms underlying them we have combined the techniques of scanning laser Doppler imaging of blood flux and dermal microdialysis to make simultaneous measurements of changes in skin blood flow and the release of mediators within the weal and flare response to intradermal injection of histamine in human skin, in vivo.