A novel double-isotope technique for the enzymatic assay of plasma histamine: application to estimation of mast cell activation assessed by antigen challenge in asthmatics

Urinary metabolomics analysis reveals the anti-diabetic effect of stachyose in high-fat diet/streptozotocin-induced type 2 diabetic rats

As a new platform of systems biology, metabolomics provides a powerful approach to discover therapeutic biomarkers and mechanism of metabolic disease. Type 2 diabetes mellitus (T2DM) is a global metabolic disease, thus, a urinary metabolomics profiling was analyzed to study the anti-diabetic effects and mechanism of stachyose (ST) on high-fat diet- and low dose streptozotocinc-induced T2DM rats. The results showed that ST treatment regulated the level of insulin, low-density lipoprotein cholesterol, and triglycerides, which demonstrates improvement in T2DM on ST treatment. Urinary samples from the ST and T2DM group were enrolled in metabolomics study, 21 differential metabolites were identified from urinary metabolomics analysis, indicating that the ST treatment partly exerted the anti-diabetes activity by regulating energy metabolism, gut microbiota changes and inflammation. A metabolomics strategy is both suitable and reliable for exploring the anti-diabetes effects and understanding the mechanisms of ST treatment against T2DM.

Diagnostic role of serum tryptase in anaphylactic deaths in forensic medicine: a systematic review and meta-analysis

Postmortem diagnosis of sudden death due to anaphylaxis can be very difficult due to the non-specific pathological findings in forensic practice. Postmortem serum tryptase has been used as an indicator of possible ante-mortem anaphylaxis. Though many previous studies have been conducted to explore the diagnostic significance of serum tryptase for lethal anaphylaxis, inconsistent results were documented. In this study, we made a retrospective study and presented a systematic review and meta-analysis that aims to summarize the diagnostic significance of postmortem serum tryptase in the deceased with and without anaphylactic shock and to calculate a cutoff value for future reference in the identification of deaths due to anaphylactic shock. A complete literature search in the PubMed, Cochrane Library, CNKI and Embase databases (published prior to March 1st, 2017) was performed. The quality of the eligible literature was evaluated according to the Newcastle-Ottawa Quality Assessment Scale (NOS), and the relevant data was extracted. The procedure of meta-analysis was performed by RevMan 5.3 software. Subgroup analysis was performed according to different causes of death. A total of nine studies with 296 patients were identified. The NOS of each included study was equal to 7. The results indicated that high concentrations of tryptase were significantly associated with anaphylactic shock when compared to the other causes of death. The weighted mean difference (WMD) was 29.53 (95% CI = 7.58-51.47, p = 0.008). Similar results were detected in the subgroup analysis when compared to deaths due to cardiovascular disease (CVD). However, no obvious elevation of tryptase in decedents with CVD compared to the other cause of death was observed (WMD = 4.42, 95% CI = -0.94-9.79). We concluded that high serum tryptase is a promising diagnostic biomarker for deaths due to anaphylactic shock, especially when it is higher than 30.4 μg/L.

Basophil activation testing

Both the treatment of patients with allergic diseases and the study of allergic disease mechanisms depend on a wide variety of assays that in various ways assess the presence and function of IgE antibody. The study of allergic diseases could benefit from the study of its 2 principle cellular participants, mast cells and basophils, but the basophil is more accessible than mast cells for ex vivo studies. Its functionality is tested by using 2 predominant methodologies: the secretion of mediators of allergic inflammation and the expression of proteins on the plasma membrane after stimulation. Each approach has benefits. There are also many operational details to consider regardless of which general approach is taken, and proper interpretation of the methods requires a good understanding of the reagents used and the receptors expressed on basophils and a detailed understanding of the factors regulating aggregation of cell-surface IgE.

Application of metabolomics approaches to the study of respiratory diseases

Metabolomics is the global unbiased analysis of all the small-molecule metabolites within a biological system, under a given set of conditions. These methods offer the potential for a holistic approach to clinical medicine, as well as improving disease diagnosis and understanding of pathological mechanisms. Respiratory diseases including asthma and chronic obstructive pulmonary disorder are increasing globally, with the latter predicted to become the third leading cause of global mortality by 2020. The root causes for disease onset remain poorly understood and no cures are available. This review presents an overview of metabolomics followed by in-depth discussion of its application to the study of respiratory diseases, including the design of metabolomics experiments, choice of clinical material collected and potentially confounding experimental factors. Particular challenges in the field are presented and placed within the context of the future of the applications of metabolomics approaches to the study of respiratory diseases.

Biochemical diagnosis of systemic mast cell disorders

Systemic mastocytosis is characterized by an abnormal proliferation of tissue mast cells. Symptoms of mastocytosis are primarily attributed to the release of mast cell mediators during episodes of systemic activation of the excessive numbers of mast cells. Thus, biochemical evidence for the release of increased quantities of mast cell secretory products can suggest or confirm, depending on the clinical situation, a diagnosis of systemic mastocytosis. A major advantage of the biochemical approach to the diagnosis of systemic mast cell disease is that it has allowed the recognition of a class of patients in whom episodes of systemic mastocyte activation can be unequivocally documented biochemically but in whom clear-cut evidence of abnormal mast cell proliferation is lacking by current histologic criteria. Although the release of increased quantities of mast cell mediators can be demonstrated during episodes of mast cell activation in such patients, mediator levels are usually normal at quiescent times. By contrast, patients with proliferative mast cell disease (mastocytosis) usually exhibit chronic overproduction of mast cell mediators. Mast cell secretory products that can be measured in an attempt to obtain biochemical evidence of systemic mast cell activation include histamine, prostaglandin D2, tryptase, and heparin. The analytical approaches to assessing release of those individual mast cell products are evaluated. In general, the diagnosis and investigation of patients with systemic mast cell activation can best be accomplished by concerted use of histologic examination of key tissues together with analysis of chemical markers of the mast cell.

Polarized TH1 responses by liposome-entrapped allergen and its potential in immunotherapy of allergic disorders

BACKGROUND

The conventional immunotherapy used for treating allergic individuals may at times lead to varying degrees of anaphylactic reaction. Liposomes have been proposed as a vehicle for safe and effective allergen-specific immunotherapy as multiple injections of liposome-entrapped allergen (LEA) have been shown to reduce specific IgE response and induce specific IgG response in BALB/c mice.

OBJECTIVE AND METHODS

To elucidate the effect of LEA on polarization of T-cell responses, its effect on the relative production of TH1/TH2 type cytokines (namely IL-2, IL-4 and IFN-gamma by commercially available ELISA kits and immunoglobulin profile as measured by ELISA) were studied. Histamine release on challenge of immunized mice was measured to examine the efficacy of LEA in preventing anaphylactic reactions.

RESULTS

Measurement of cytokine levels in serum and spleen cell culture supernatants of BALB/c mice injected repeatedly with either free allergen (FA) or LEA (three mice per group) indicate that LEA preferentially induces a TH1-type of response dominated by IFN-gamma and IL-2 production. Further, it was also shown that immunization of mice with FA or LEA and subsequent challenge with a large dose of the sensitizing allergen leads to fatal systemic reactions in 50-65% of the animals treated with FA, whereas no mortality was observed in mice injected with LEA. Analysis of IgG subclasses in sera of mice immunized with LEA revealed a sixfold higher production of IgG1 antibodies than mice immunized with FA. Serum IgG2a, IgG2b, IgG3 and IgM responses were also enhanced in the group of mice immunized with LEA in comparison with mice injected with FA.

CONCLUSION

The results indicate that LEA confers protection against anaphylaxis to mice due to their ability to induce a high IFN-gamma:IL-4 ratio which may lead to decreased synthesis of IgE and reduced histamine release on challenge with FA.

Markers of mast cell degranulation

Mast cells are the primary effector cells of immediate hypersensitivity reactions in humans. Upon mast cell activation both preformed and newly synthesized mediators are secreted. Histamine can be measured by fluorometric assays, radioenzymatic assays, and immunoassays. These methods have been applied to plasma and urine to detect histamine that had been released in vivo and to release histamine in vitro from basophils and mast cells. Another mast cell constituent is tryptase, which is a more selective marker of mast cells, because negligible amounts are found in basophils. beta-Tryptase is stored in secretory granules and is actively released when mast cells degranulate. alpha-Protryptase remains in the proenzyme form and is constitutively released from mast cells, and consequently its level in serum reflects total numbers of mast cells. alpha-Protryptase levels are elevated in serum at baseline in subjects with systemic mastocytosis, whereas beta-tryptase is elevated in serum from subjects with systemic anaphylaxis. These markers serve as precise clinical indicators of the involvement of mast cells in human disease.

Modulation of pentagastrin-induced histamine release by histamine H3 receptors in the dog

BACKGROUND

The histamine H3 receptor has been shown to inhibit pentagastrin-induced gastric acid secretion in dogs. Since pentagastrin releases histamine in dogs, we have now assessed whether the effects of H3-receptor ligands may be indirectly mediated by changes in gastric histamine release.

METHODS

Pentagastrin infusions (1 or 6 micrograms/kg/h), alone or together with the H3-receptor agonist (R) alpha-methylhistamine (1.2 mumol/kg/h) or the antagonist thioperamide (0.1 mumol/kg/h), were performed in dogs. One group (anaesthetized) was used for enzyme immunoassays of plasma histamine and, when required. (R) alpha-methylhistamine in the gastrosplenic vein, and another group (non-anaesthetized) for measurement of gastric acid secretion.

RESULTS

Histamine levels were increased five- and eight-fold after 1 and 6 micrograms/kg/h pentagastrin, respectively, whereas acid output was nearly maximal at the lower dosage. (R) alpha-methylhistamine, at a plasma concentration of 0.15 microM, inhibited histamine release by 78% (P < 0.007) and 37% (not significant) and the total acid output by 44% (P < 0.05) and 19% (not significant) after infusion of 1 and 6 micrograms/kg/h pentagastrin, respectively. Thioperamide, together with pentagastrin in low dose, significantly increased histamine release by 212% (P < 0.05), whereas acid output increased by 34% (not significant).

CONCLUSIONS

The histamine H3 receptor mediates a negative feedback control of pentagastrin-induced release of gastric histamine. It is tonically activated by endogenous histamine after pentagastrin in low dosage. The control of acid secretion by the H3 receptor seems to involve modulation of endogenous histamine release, possibly by means of enterochromaffin-like cells.

Humoral immunity to aerosolized staphylococcal enterotoxin B (SEB), a superantigen, in monkeys vaccinated with SEB toxoid-containing microspheres

Staphylococcal enterotoxin B (SEB) toxoid-containing microspheres were tested for efficacy in rhesus monkeys as a vaccine candidate for respiratory SEB toxicosis and toxic shock. Forty monkeys were randomly separated into 10 groups of four monkeys each: 9 groups were vaccinated with the microspheres via combinations of mucosal and nonmucosal routes, and 1 group served as nonvaccinated controls. Both vaccinated and nonvaccinated monkeys were then challenged with a high lethal dose of SEB aerosol. Monkeys primed with an intramuscular dose of the microspheres followed by an intratracheal booster all survived the SEB challenge. Overall, monkeys with an intratracheal booster generally had the highest antibody levels, which is consistent with their high survival rate and lower rate of illness. Protective immunity was correlated with antibody levels in both the circulation and the respiratory tract. The protection was not due to the depletion or anergy of SEB-reactive T cells, since SEB-induced proliferation in cultures of circulating lymphocytes was not significantly reduced after the microsphere vaccination. It is evident that the nonsurvivors did not die of systemic anaphylaxis or hypersensitivity because the monkeys did not die immediately after SEB challenge and there were no significant differences in histamine levels between the vaccinated and control monkeys before and after SEB challenge. The antibodies seemed to neutralize the SEB that got into the airway and the circulation.

Eicosanoid release in allergen-induced bronchoconstriction in dogs. Its relationship to airways hyperreactivity and pulmonary inflammation

In vitro studies have demonstrated the release of histamine, PGD2, TXB2, PGE2, PGF2 alpha, 6-keto-PGF1 alpha and the peptidoleukotrienes from sensitized lung. We have assessed the release of these mediators following antigen challenge in vivo. Antigen challenge of allergic dogs resulted in an acute bronchoconstriction and an increase in bronchial reactivity to histamine and an increase in neutrophil and eosinophil numbers recovered by bronchoalveolar lavage (BAL), 2 and 24 h later. The acute response was associated with histamine and PGD2 release but there was no increase in the levels of other eicosanoids in recovered BAL. Bronchial hyperreactivity and pulmonary inflammation, 2 and 24 h post-challenge was not associated with a concommitant (antigen specific) increase in BAL fluid eicosanoid levels. We conclude that although PGD2 is released during the acute response to antigen the subsequent changes (hyperreactivity and inflammation) are not characterised by a maintained elevation in eicosanoid levels detectable by BAL.

The effect of terfenadine on unilateral nasal challenge with allergen

To investigate the role of H1 receptor-mediated effects in allergic rhinitis, we challenged 12 allergic volunteers with allergen 2 hours after administration of either placebo or 60 mg of terfenadine. Filter paper discs were used for the unilateral administration of allergen and the collection of nasal secretions. Secretion weights, levels of histamine in recovered nasal secretions, and nasal airway resistance (NAR) were measured for each nostril separately, and the number of sneezes was counted. After placebo treatment, allergen challenge led to significant increases in ipsilateral and contralateral secretion weights, ipsilateral histamine levels, ipsilateral NAR, and sneezing. Contralateral histamine levels were not elevated. H1 antagonism with terfenadine markedly reduced the number of sneezes and partially decreased ipsilateral and contralateral secretion weights, without affecting the increase in NAR. Terfenadine premedication also lowered the amount of histamine in ipsilateral secretions after allergen challenge. Performing identical nasal challenges with a 10-fold lower dose of antigen produced similar results. Previous studies showed that terfenadine had no effect on methacholine provocation and completely abolished ipsilateral and contralateral secretion weights after histamine challenge. We conclude that sneezing after allergen challenge is caused almost exclusively by a reflex initiated through H1 receptors and that H1 antagonism has no influence on allergen-induced increases in NAR. Unilateral allergen challenge leads to bilateral increases in secretion weights, which are only partially inhibited by terfenadine, suggesting the involvement of mediators other than histamine in the nasonasal reflex. As reported earlier, terfenadine also decreases allergen-induced histamine release after challenge with the highest dose of antigen.

The effect of immunotherapy on the cutaneous late phase response to antigen

BACKGROUND

This study used the skin chamber model to evaluate prospectively the effect of immunotherapy (IT) on the cutaneous early and late phase response (LPR) to epicutaneous antigen challenge.

METHODS

Nine subjects with allergic rhinitis were studied at three time points: before starting IT, after 3 months of IT, and after 6 months of IT. Skin chamber histamine content was measured hourly for 12 hours, and cell counts performed hourly during hours 6 to 12. An intradermal skin test was placed, and the reaction was measured hourly for 12 hours. Skin biopsy specimens were obtained 8 hours after intradermal placement and evaluated for cellular infiltrate and major basic protein deposition. Serum antigen-specific IgG and IgE levels were measured at each time point to confirm physiologic effect of IT.

RESULTS

Six months of IT significantly (p < 0.05) decreased both early and LPR skin test reactivity and skin chamber histamine for hours 1 to 3, 4 to 6, and 9 to 12. Skin chamber LPR cellular influx decreased significantly (p < 0.05) for neutrophils only. Decrease in LPR histamine after 6 months of IT was significantly correlated with both decrease in mononuclear cells (R2 = 0.817, p = 0.002) and decrease in neutrophils (R2 = 0.813, p = 0.009). Also significantly correlated were decrease in LPR skin test reactivity, with percent change in skin chamber mononuclear cells (R2 = 0.800, p = 0.009) and decrease in early skin test reactivity (R2 = 0.675, p = 0.01). Biopsy specimens showed no consistent change in either dermal cellular infiltrate or deposition of major basic protein.

CONCLUSION

IT significantly attenuates cutaneous histamine release and skin test reactivity and is accompanied by a decrease in skin chamber LPR neutrophil influx without significantly altering the dermal infiltrate at 8 hours.

Cutaneous late-phase response in food-allergic children and adolescents with atopic dermatitis

Food hypersensitivities contribute to disease exacerbation in a sub-group of children with atopic dermatitis (AD). It has been shown that only selected foods are capable of causing clinical reactions when ingested, whereas other foods, to which the patient is equally sensitive by skin-prick testing, may be tolerated. The purpose of this study was to examine the cutaneous late-phase response (LPR) to food antigens in food-allergic patients with AD and to determine if the skin reacted differently to 'relevant foods' (foods eliciting positive skin-prick tests and positive oral challenges) than to 'non-relevant foods' (foods eliciting positive skin tests but negative oral challenges). Using blister chambers adfixed to the skin, six children with AD were challenged epicutaneously with foods to which they had previously been shown to be sensitive. Histamine and PGD2 were measured hourly for 10-12 hr in parallel with quantitation of the cellular traffic. There appeared to be no difference in any of the measured parameters between relevant foods and non-relevant foods, and the patterns of the LPR cells and mediators were similar to those previously described with aero-allergens in patients with respiratory allergy. Histamine rose to 13.0 +/- 24 ng/ml (P < 0.005) during the first hours, declined to < 1 ng/ml by the fifth hour, and then rose a second time to 6.72 +/- 3.4 ng/ml (P < 0.05) during the 12th hour. PGD2 rose to an average of 312 pg/ml (P < 0.05) during the first 3 hr followed by a decline to baseline.(ABSTRACT TRUNCATED AT 250 WORDS)

Cutaneous IgE-mediated inflammatory lesion size is inhibited by an H1 antagonist (terfenadine) while mediator release is unaffected in vivo and in vitro

We are interested in understanding the pathogenesis of the cutaneous IgE-mediated late phase reaction. A double-blind, placebo-controlled, randomized cross-over study with 10 subjects of the effect of the non-sedating antihistamine, terfenadine (Selddane), on the cutaneous reaction to antigen (ragweed or mixed grass) administered intradermally and over denuded blister bases was performed. The activity of terfenadine on anti-IgE-induced mediator release from the skin mast cell, lung mast cell and basophil was also examined in vitro. Terfenadine significantly inhibited the size of the cutaneous reaction at every hour between hours 1 and 9 (hr 9, control 2250 +/- 500 mm2 vs drug 1250 +/- 250 mm2, P < 0.01, n = 10) and showed some inhibitory effect at hours 10-12. While terfenadine blocks histamine release after nasal antigen challenge the release of mediators at skin blister sites was unaffected. The infiltration of leucocytes into the blister supernatant was unaffected by terfenadine although previous studies have shown significant inhibition with another antihistamine, cetirizine. In vitro, terfenadine, like other antihistamines, was found to have inhibitory activity on anti-IgE-induced mediator release at concentrations of 10(-4)-10(-5) M in lung and skin mast cells and basophils. We conclude that the effects of the newer antihistamines on cellular movement into the skin may be diverse, that terfenadine may show organ specificity in vivo and that terfenadine significantly decreases both the early and late gross inflammatory response of the skin to antigen. We cannot, as yet, explain the mechanism(s) by which this occurs.

Narcotic-induced histamine release: a comparison of morphine, oxymorphone, and fentanyl infusions

This study, using an improved histamine assay, repeated previous studies that demonstrated large doses of morphine for induction of anesthesia in patients undergoing coronary artery bypass grafting were associated with histamine release. Thirty randomized patients received infusions of either morphine, 1 mg/kg, oxymorphone, 0.2 mg/kg, or fentanyl, 50 micrograms/kg, over a 10-minute period for induction of anesthesia prior to surgery. There were no significant changes in plasma histamine levels in individual patients or among drug groups. The discrepancy between the present histamine results and those previously reported using similar protocols is due, in part, to variations in plasma histamine measurements that can occur using the less reproducible, older assays for histamine. During routine inductions, large doses of morphine, oxymorphone, or fentanyl administered by infusion do not appear to stimulate release of clinically significant plasma levels of histamine.

Mouse splenic and bone marrow cell populations that express high-affinity Fc epsilon receptors and produce interleukin 4 are highly enriched in basophils

Splenic and bone marrow cells from normal mice, and from mice that have been polyclonally activated by injection of anti-IgD antibody, contain cells that produce interleukin 4 (IL-4) in response to crosslinkage of Fc epsilon receptors (Fc epsilon R) or Fc gamma R or to ionomycin. Isolated Fc epsilon R+ cells have recently been shown to contain all of the IL-4-producing capacity of the nonlymphoid compartment of spleen and bone marrow. Here, purified Fc epsilon R+ cells are shown to be enriched in cells that contain histamine and express alcian blue-positive cytoplasmic granules. By electron microscopy, the vast majority of cytoplasmic granule-containing cells are basophils; they constitute approximately 25% and approximately 50%, respectively, of Fc epsilon R+ spleen and bone marrow cells from anti-IgD-injected mice. The Fc epsilon R- populations contain cells that form colonies typical of mast cells. The Fc epsilon R+ populations also contain cells that, upon culture with IL-3, form colonies of alcian blue-positive cells, but (in contrast to colonies derived from Fc epsilon R- populations) the colonies are small, and all the cells die within 2-3 weeks. The Fc epsilon R+ cells synthesize histamine during a 60-hr culture with IL-3, while the Fc epsilon R- cells do not. These results indicate that IL-4-producing Fc epsilon R+ cells are highly enriched in basophils.

Comparison of methods for intestinal histamine application: histamine in enterosoluble capsules or via a duodeno-jenunal tube. Influence of fast and histamine-restrictive diet

The study was conducted to investigate whether introduction of histamine in enterosoluble capsules produced the same amount of urinary histamine metabolites as that found after application of histamine through a duodeno-jejunal tube. Secondly, to examine whether a histamine-restrictive or a fast diet affected the amount of urinary metabolites. Fifteen healthy subjects were challenged four times with 100 mg of histamine. Results were monitored by the urinary recovery of 1,4-methylimidazole acetic acid (MIAA) from 24 h before to 72 h after challenge. Urine was collected in 24-h samples except on the first day after challenge when separation into 0-2h-, 2-4 h- and 4-24 h-fractions was made. MIAA was measured by high performance liquid chromatography (HPLC). The results showed that during the first 2 h after challenge the recovery of MIAA was higher with tubes than with capsules. Measurements from all other intervals did not differ significantly between the two challenge regimens. Fast (water only) and histamine-restrictive diet versus non-restrictive diet did not affect the urinary MIAA. MIAA was significantly higher overall during the first 24 h after challenge than in any other fraction. We conclude that oral administration of enterosoluble capsules is an easy and appropriate method for intestinal histamine challenge. Fast and histamine-restrictive diets are not necessary, but subjects should record unexpected responses in a food and symptom diary.

Interleukin-1 is released at sites of human cutaneous allergic reactions

Interleukin-1 (IL-1) promotes cell recruitment and influences allergic mediator release. We analyzed histamine, prostaglandin D2, IL-1, and leukocytes accumulating hourly for 12 hours at skin-chamber sites after local ragweed challenge in eight allergic subjects with cutaneous late-phase reactions. Ragweed induced a peak of histamine at 1 hour (p less than 0.02), which diminished, and then steadily increased (p less than 0.02). Prostaglandin D2 levels peaked by the second hour (p less than 0.02) and then decreased, approaching prechallenge levels by 12 hours. Leukocyte infiltration (predominantly neutrophils) was detectable 3 to 4 hours after challenge, although selective enrichment of mononuclear cells, eosinophils, and basophils ws observed at later hours (p less than 0.02). IL-1 bioactivity was detected in fluids 10 to 12 hours after challenge but not at control sites (p less than 0.05). Analysis of IL-1 beta levels by RIA revealed an initial peak at 1 hour of 0.90 ng/ml (p less than 0.02) and a second elevation of up to 0.75 ng/ml during the later hours (p less than 0.04). Ragweed challenge of three nonatopic subjects did not change levels of the above-mentioned mediators or cells. Bioactivity in chamber fluids from antigen-challenged sites of atopic subjects was significantly neutralized by an anti-IL-1 beta antiserum, although treatment with anti-IL-1 alpha and anti-IL-1 beta was needed for complete neutralization, IL-1 released locally during cutaneous allergic reactions may contribute to IgE-dependent cutaneous inflammation.

A comparative study of releasing and nonreleasing human basophils: nonreleasing basophils lack an early component of the signal transduction pathway that follows IgE cross-linking

Basophils from approximately one fifth of the population were found to be unresponsive (nonreleasers), in terms of both histamine and leukotriene release, to an IgE cross-linking stimulus, such as anti-IgE antibody. Although unresponsive to any IgE-mediated stimulation, these basophils responded to non-IgE-mediated stimuli, such as the phorbol ester, 12-o-tetradecanoyl phorbol-13 acetate, the calcium ionophore, A23187, and to formyl-methionyl-leucyl-phenylalanine peptide. These stimuli produced equal dose-response curves in both releaser (basophils able to respond with greater than 5% histamine release to anti-IgE antibody) and nonreleaser basophils. Nonreleaser basophils possessed statistically similar densities of cell-surface IgE antibody (287,000 versus 400,000 IgE molecules per basophil for releaser and nonreleaser basophils, respectively), and with 12-o-tetradecanoyl phorbol-13 acetate as a probe of anti-IgE-induced cross-linking, the IgE on nonreleaser basophils was found to be cross-linked by the polyclonal anti-IgE antibody used for these studies. Interleukin-3 (IL-3) has previously been demonstrated to enhance markedly both histamine and leukotriene release in human basophils. However, IL-3 was unable to convert nonreleasing basophils into releasing basophils, as measured by anti-IgE antibody. IL-3 equivalently enhanced formyl methionine peptide-induced release in both releaser and nonreleaser basophils, suggesting that the lack of an effect on anti-IgE-induced release was not due to a lack of IL-3 receptors. Although there are several possible interpretations of these data, these results and results of our previous studies of protein kinase C activation and cytosolic Ca++ elevations in human basophils suggest that nonreleasing basophils have a defect in early signal transduction, possibly involving the influx of Ca++.

Inflammatory mediator release on conjunctival provocation of allergic subjects with allergen

To evaluate the role of inflammatory mediators in the pathogenesis of the ocular allergic response, 23 subjects with positive histories of allergies to either cat dander or ragweed pollen and positive skin tests to the appropriate allergen extract were recruited and were subjected to conjunctival provocation. The tear duct of the left eye of each subject was blocked with a collagen plug while the right eye was left unplugged. In all cases, the eye was initially provoked with saline and subsequently with the appropriate allergen extract. Nonallergic subjects, or allergic subjects provoked with nonrelevant allergen, were used as control subjects. After each provocation, symptoms were recorded, and tears were collected with preweighed strips of filter paper (Schirmer strip). Each strip was placed into a tared tube containing fluid appropriate for the optimal preservation of the mediator to be measured. It was therefore possible to calculate the weight of tears collected and to express mediator levels per milliliter of tears. All allergic subjects demonstrated a positive symptomatic response to allergen challenge, whereas the control subjects remained asymptomatic. Blockage of the tear duct did not significantly alter the response. For allergic subjects, the levels of histamine, kinins, prostaglandin D2, albumin, and TAME-esterase activity were all significantly (p less than 0.005 in each case) greater after allergen challenge than after saline challenge. Furthermore, levels of each of these mediators after allergen challenge (expressed as increases above levels after saline provocation) were significantly greater for allergic subjects than for control subjects (p less than 0.005 in each case). Thus, the clinical response to conjunctival provocation with allergen is associated with increases in the levels of inflammatory mediators in tears.

Cutaneous late-phase response to allergen. Mediator release and inflammatory cell infiltration

To better define the inflammatory infiltrates and kinetics of mediator release during the cutaneous late-phase reaction (LPR), we examined skin biopsies at 8 h, and skin chamber cell counts and mediator release for 12 h after antigen challenge. Compared with the control sites, the antigen-stimulated biopsy sites contained 14 times as many basophils (P less than 0.01) and six times as many eosinophils (P less than 0.001) with one to two fold more mononuclear cells (P less than 0.03) and neutrophils (P less than or equal to 0.01). Similar changes were found in the skin chambers. Although there were neutrophils in the control chamber, they were only twice as numerous in the antigen challenged site (P less than 0.01). Eosinophils were 35-fold (P less than or equal to 0.03) more prevalent in the antigen chamber than the control chamber for hours 8-12 and basophils were noted starting in the eighth hour and were 20-fold (P less than or equal to 0.03) more concentrated in the antigen chamber during the next 4 h. The mononuclear cells were not significantly different between antigen and control blisters. With respect to inflammatory mediators, there was an initial peak of histamine (13.2 +/- 2.9 ng/ml) in the blister fluid at 1 h. The level then fell to approximately 2 ng/ml, followed by a secondary rise starting at the eighth hour and increasing to 9.8 +/- 2.8 ng/ml by the twelfth hour. This secondary increase in histamine correlated significantly (r = 0.81, P less than 0.05) with the observed influx of basophils. PGD2 in the blister fluid rose to 371+/-25 pg/ml during the first 4 h and then slowly decreased to half this level during the last 4 h. Thus, the cutaneous LPR has been shown to manifest a secondary increase in histamine levels and a markedly specific increase in eosinophils and basophils with mediator release apparently being derived from the latter cells.

Time course of appearance and disappearance of human mast cell tryptase in the circulation after anaphylaxis

Tryptase, a neutral protease of human mast cells, is a potentially important indicator of mast cell involvement in various clinical conditions. The current study examined the time course of appearance and disappearance of tryptase in the circulation after an anaphylactic event and the stability of both endogenous and exogenous tryptase in terms of freeze-thawing and temperature. The peak level of tryptase after an experimentally induced systemic anaphylactic reaction occurred 1-2 h after the initiating bee sting in each of three subjects, in contrast to histamine levels which peaked at 5-10 min. In some cases elevated levels of tryptase may not be detected during the initial 15-30 min. Tryptase levels then declined under apparent first order kinetics with a t1/2 of approximately 2h. Similar disappearance kinetics were observed for two subjects presenting in the emergency room with immediate type reactions, one with severe asthma after indomethacin ingestion, the other with systemic anaphylaxis after a bee sting. Histamine levels declined rapidly and were back to baseline by 15-60 min. Measured levels of tryptase in serum or plasma were not diminished by up to four freeze-thaw cycles. Incubation of serum samples taken from subjects with elevated levels of tryptase at 22 and 37 degrees C indicated that greater than 50% of endogenous tryptase was still detected after 4 d. Purified tryptase added to serum or plasma and incubated as above was less stable: approximately 50% of exogenous tryptase in serum and approximately 15% in plasma was detected after 2d of incubation. Therefore, optimally samples should be stored frozen, but even those stored at room temperature for up to 4 d should be satisfactory. The best time to obtain samples for tryptase determinations is 1-2 h after the precipitating event, but depending on the magnitude of the initial response elevated levels of tryptase may be present in the circulation for several hours.

Analysis of histamine and N tau-methylhistamine in plasma by gas chromatography-negative ion-chemical ionization mass spectrometry

Current methods of quantitation of histamine and its major metabolite N tau-methylhistamine are inaccurate and insensitive to the very low concentrations that exist in plasma samples. Therefore, an accurate and sensitive method for quantification in plasma has been developed using the stable isotope dilution assay with negative ion-chemical ionization mass spectrometry. For histamine, after the addition of [2H4]histamine to 2 ml of plasma, the plasma sample is deproteinized, extracted into butanol, back extracted into HCl, derivatized to the pentafluorobenzyl derivative (CH2C6F5)3-histamine, purified on silica gel columns, and then quantified with negative ion-chemical ionization mass spectrometry by selected ion monitoring of the ratio of ions m/z 430/434. For N tau-methylhistamine, after the addition of N tau-[2H3]methylhistamine to 2 ml of plasma, the plasma sample is deproteinized, extracted into butanol, back extracted into HCl, derivatized to the heptafluorobutyryl derivative (C3F7CO2)2-N tau-methylhistamine, purified on silica gel columns, and then quantified with negative ion-chemical ionization mass spectrometry by selected ion monitoring of the ratio of ions m/z 497/500. The precision of the histamine assay is 3.1% and the accuracy is 95.5 +/- 2.5% while the precision of the N tau-methylhistamine assay is 1.9% and the accuracy is 106.8 +/- 1.9%. The lower limits of sensitivity are 1 pg for histamine and 6 pg for N tau-methylhistamine injected on column. Using the assay in three normal human volunteers, plasma concentrations of histamine were 130, 92, and 85 pg/ml, and of N tau-methylhistamine were 229, 228, and 216 pg/ml. This assay provides a very sensitive and accurate method of quantitation of histamine and N tau-methylhistamine in plasma samples.

Urinary leukotriene E4 after antigen challenge and in acute asthma and allergic rhinitis

The leukotrienes LTC4, D4, and E4 are potent bronchoconstrictor agents and are thought to have an important role in asthma. Urinary LTE4, a stable urinary end-product of LTC4 and LTD4, was measured, by means of high-performance liquid chromatography and radioimmunoassay. LTE4 excretion followed a log-normal distribution in twenty-nine healthy controls, with a geometric mean of 23.8 (95% confidence interval 19.9-28.2) ng/mmol creatinine. Urine was collected from eight atopic subjects for 3 h after antigen inhalation and a control urine collection was made a week later at the same time of day. Urinary LTE4 was significantly higher after antigen challenge than in the control sample (153.7 [87.1-271.3] vs 23.5 [13.7-69.5] ng/mmol creatinine; p less than 0.01). Urinary LTE4 was also measured in twenty patients with severe acute asthma and nine patients with seasonal allergic rhinitis. Mean urinary LTE4 was higher in the asthmatic patients (78.3 [46.5-131.8] ng/mmol creatinine) than in normal subjects (p less than 0.01), although there was substantial overlap into the normal range. The urinary LTE4 values of the rhinitis patients were within the normal range whether or not they had symptoms. LTC4 and LTD4 were also found in bronchoalveolar lavage fluid from one of the three atopic subjects challenged with antigen before lavage, and in a single patient who underwent lavage after admission with severe acute asthma. These studies provide evidence that leukotrienes are released in vivo in man after antigen challenge and in acute asthma.

Combined H1 and H2 receptor blockade attenuates the cardiovascular effects of high dose atracurium in rabbits

Large doses of atracurium (1.5 mg/kg) (six times the ED95) have been reported to provide adequate conditions for rapid sequence endotracheal intubation within 60 seconds in humans. However, this dose can result in significant histamine release and systemic hypotension. We therefore studied the efficacy of histamine receptor blockade in attenuating this response. Four groups of five rabbits were pretreated as follows: Group I--control, Group II--H1 blockade (1 mg/kg diphenhydramine), Group III--H2 blockade (cimetidine 4 mg/kg), and Group IV--H1 and H2 blockade (diphenhydramine 1 mg/kg and cimetidine 4 mg/kg). All rabbits were anesthetized and then 1.8 mg/kg (six times the rabbit ED95) atracurium was administered. Group I rabbits experienced a decrease in MAP of 12.2 mmHg after one minute, a change that was significantly greater than Group IV in which MAP decreased by 0.8 mmHg (p less than 0.001). H1 or H2 receptor blockade alone was associated with intermediate changes in MAP not significantly different from control. We conclude that combined H1 and H2 receptor blockade attenuates the cardiovascular effects associated with large doses of atracurium in the rabbit and that this combination of antagonist drugs might have similar effectiveness in humans.

Leukotriene E4 release in cold urticaria

Cold urticaria is a rare condition characterized by abnormal wealing following exposure to cold. It has been suggested that lipid-derived mediators may be involved in the pathogenesis of this condition. We have investigated whether the inflammatory reaction in cold urticaria is associated with the release of cysteinyl-leukotrienes. Leukotriene E4 (LTE4; a stable metabolic product of LTC4 and LTD4) and histamine were measured in the blood draining the site of a cold-challenge in five patients with clinical histories of cold urticaria. Three of the patients showed a typical clinical response to the challenge, and this was associated with an increase in the concentration of LTE4 and histamine. No increase in LTE4 or histamine levels were observed following cold challenge in the non-responding individuals.

Histamine and Nt-methylhistamine in the circulation during intravenous infusion of histamine in normal volunteers

Plasma levels of histamine and Nt-methylhistamine were measured simultaneously by high performance liquid chromatography during the intravenous infusion of histamine acid phosphate in six normal volunteers. Progressive, dose-related increases in plasma histamine were noted, reaching a maximum value of 3.1 +/- 0.14 ng ml-1 corresponding to a maximum infusion rate of 180 ng kg-1 min-1 (means +/- SEM). Increases in plasma histamine were accompanied by a significant dose-related fall in mean diastolic blood pressure (baseline 74.0 +/- 4.4 mm Hg falling to 60.0 +/- 3.3 mm Hg at maximum infusion rate, p less than 0.001) and an increase in pulse rate (baseline 76.3 +/- 2.8 beats min-1 rising to 89.24 beats min-1 at maximum infusion rate, p less than 0.05). All subjects exhibited facial flushing, the threshold plasma histamine level for this effect being 1.3 +/- 0.15 ng ml-1 corresponding to an infusion rate of 60 ng kg-1 min-1. Elevation of plasma Nt-methylhistamine was seen in only one subject, who exhibited a level of 0.5 ng ml-1 at the highest infusion rate. These results suggest that measurements of plasma Nt-methylhistamine are unlikely to provide a useful index of histamine release into the circulation.

Optimization of histamine radio enzyme assay with purified histamine-N-methyltransferase

The radio enzyme assay for histamine based on the transmethylation with purified histamine-N-methyltransferase and utilizing [3H-methyl]-S-adenosylmethionine as the methyl donor has been optimized to measure low histamine concentrations, for example in plasma. The pH-optimum for the assay is pH 8.3 in Tris-glycine buffer at 20 degrees C. An incubation time of 90 min is necessary using an enzyme concentration of 5.8 micrograms/ml. EDTA and dithiothreitol were included in the assay to keep the histamine-N-methyltransferase active as agents that oxidize -SH groups were found to be inhibitory to the reaction. The present assay is sensitive to about 0.5 nmol/l of histamine in a sample volume of 50 microliter (about 3 pg/sample).

Establishment of an immature mast cell line from a patient with mast cell leukemia

A cell line showing many characteristics of immature mast cells has been established from the peripheral blood of a patient with mast cell leukemia. Cultured cells contain low levels of histamine, are stained metachromatically by toluidine blue, and contain chloroacetate esterase, aminocaproate esterase and tryptase activities. The cells lack T and B lymphocyte, as well as myeloid cell markers, and do not possess IgE receptors. Solid tumors of metachromatically positive cells have been successfully induced and serially passed in nude mice using 5-azacytidine transformed cells. This cell line may be useful for future studies of mast cells and their constituents.

The relationship between mast cell-mediator release and bronchial reactivity in allergic asthma

The relationship between mast cell-mediator release and nonspecific bronchial reactivity was investigated in allergen-induced asthma. Two groups of subjects with asthma, one group with markedly reactive airways (provocative concentration of methacholine causing a 20% fall in FEV1, 0.07 mg/ml) and the other group with less reactive airways (provocative concentration of methacholine causing a 20% fall in FEV1, 3.83 mg/ml), had allergen bronchoprovocation. After challenge, bronchoconstriction was measured as change in specific airway conductance (SGaw), and mast cell-mediator release was measured as change in both plasma histamine and serum neutrophil chemotactic activity (NCA). In the group with more reactive airways, allergen challenge, while it produced a mean fall in SGaw of 58.1%, was not associated with any significant increase in plasma histamine from a mean resting level of 3.69 nmol/L-1. In contrast, a comparable mean fall in SGaw of 52.4% in the group with less reactive airways was associated with a significant (p less than 0.005) increase in plasma histamine from 1.17 to 3.60 nmol/L-1, maximal 5 minutes after allergen challenge. There were, however, significant increments in serum NCA in both groups with asthma after allergen challenge. The changes in NCA in the group with less reactive airways (136.7 +/- 38.1% above baseline; p less than 0.01; 1% sera dilution) were significantly greater (p less than 0.05) than changes identified in the group with more reactive airways (68.3% above baseline; p less than 0.01; 20% sera dilution). These findings directly support the concept that both mast cell-mediator release and nonspecific bronchial reactivity are separate factors that influence the airway response to inhaled allergen in asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

The inflammatory theory of asthma

In summary, these observations suggest a model for asthma which is summarized in Table III. Initially, mast cells and possibly other bronchial cells, e.g., alveolar macrophages, are activated either in an IgE-dependent or, in intrinsic asthma, in an IgE-independent fashion. These cells release two sets of mediators which may be either preformed or newly synthesized. One set of mediators is responsible for the immediate bronchospastic response. This bronchospasm is transient, readily reversible, and not associated with either airway inflammation or bronchial hyperreactivity. The second set of mediators, however, promote chemotaxis and activation of neutrophils and eosinophils. The subsequent bronchial inflammation causes damage and desquamation of the respiratory epithelium. The increased exposure of irritant receptors results in hyperreactive airways. In addition, these inflammatory cells induce mast cell degranulation and recurrent bronchospasm. Thus, after the initial exposure to allergen, a vicious cycle of inflammation, hyperreactivity and recurrent mast cell degranulation develops, ultimately leading to the pathological picture of chronic asthma.

Single-step procedure for the extraction and purification of leukotrienes B4, C4 and D4

A rapid and simple method for the on-line concentration and high-performance liquid chromatographic (HPLC) purification of the leukotrienes in good yield from biological fluids is described. Readily available antisera are used in conjunction with this system to give a specific and sensitive assay for leukotrienes B4, C4 and D4 with sub-nanogram limits of detection. Tritium-labelled leukotrienes are used as internal standards, both to locate the leukotrienes post-HPLC and to accurately determine recoveries.

The effects of cremophor EL in the anaesthetized dog

The effects of cremophor EL were studied in 13 anaesthetized, paralyzed and ventilated dogs. Twenty per cent cremophor EL in a dose of 4.3 +/- 0.92 ml was infused at a rate of 30 ml X hr-1. In seven dogs, thoracopulmonary compliance, heart rate, systemic arterial pressure (SAP), pulmonary pressures (PAP, PCWP, RAP), cardiac output (CO) and platelet and white cell counts, were measured before the injection of cremophor EL, at the end of infusion and 5, 10, 30 and 150 minutes after the end of infusion. In six dogs, SAP, CO, and blood volume were measured before the injection of cremophor EL, at the end of infusion and 10, 30, 90 and 150 minutes after the end of infusion. Plasma histamine and catecholamines were assayed before the injection of cremophor EL and 2, 5, 10, 30, 90 and 150 minutes after starting the infusion. Cremophor EL induced a marked, sustained and significant decrease in SAP at the end of infusion and at 5, 10 and 30 minutes after the completion of the infusion (-68, -71, -70 and -43 per cent respectively), in PCWP, RAP and CO (-78 per cent at the end of infusion, -32 per cent 150 minutes after the end of infusion). Heart rate and systemic vascular resistance did not vary significantly. Pulmonary vascular resistance increased at the end of infusion, five and ten minutes after the end of infusion (+734, +548 and +439 per cent respectively). Plasma volume decreased 10 and 30 minutes after the end of infusion (-28 and -30.5 per cent respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood histamine levels in cotton-dust exposed workers in a textile mill of Ahmedabad

Blood histamine levels were measured by the bioassay of histamine (on an isolated strip of guinea pig ileum) in workers exposed to cotton dust in a textile mill in Ahmedabad. Byssinotic subjects showed very high levels of blood histamine as compared to nonbyssinotic and control subjects. The blood histamine levels were not well correlated to the dust concentrations or duration of exposure but rather to the day of the week (ie, first, second, third, etc., after weekend break) on which the samples were collected. The blood histamine levels were high on the first day of the work week, when byssinotics complained most of their symptoms.

Treatment of nocturnal asthma: the role of sustained-release theophylline and oral beta-2-mimetics

In two double-blind, multiple-dose cross-over studies the therapeutic effects of SR theophylline preparations given once each night (mean 11.2 mg/kg per day) versus twice daily in equal doses (mean 10.3 mg/kg per day) (study I) and SR-terbutaline in equal doses (mean 0.25 mg/kg per day) versus SR theophylline in unequally divided daily doses (mean 5.3 mg/kg morning dose, 10.6 mg/kg evening dose) study II) were compared in 19 patients with nocturnal asthma. At the end of each treatment period drug serum concentrations and PEFR were measured every 2 hr over a 24-hr period. With the twice-daily, equally divided regimen, serum theophylline concentrations were lower at night than during the day (mean 9.4 +/- 0.9 versus 11.3 +/- 1.0 mg/l). With the single evening administration, serum theophylline concentrations were considerably higher at night (Cmax 16.3 +/- 1.4 mg/l) and the circadian variation of PEFR was significantly reduced. PEFR was higher during night and early morning (283 +/- 14 versus 217 +/- 11 l/min, P less than 0.005). During daytime in study II, PEFR values were slightly higher with theophylline than terbutaline. There was no significant difference in peak flow between either treatment during the night and early morning. However, additional use of inhaled beta-2-mimetics because of asthmatic attacks occurred more often during terbutaline (79 times in 8/10 patients) than theophylline treatment (29 times in 5/10 patients). Symptom scores, number of attacks and side-effects clearly favor the theophylline regimen. We conclude that for patients with nocturnal asthma a once-nightly dose of SR theophylline can be sufficient for stabilization of the airways.

A direct and sensitive determination of histamine in acid-deproteinized biological samples by high-performance liquid chromatography

A convenient method for the routine measurement of histamine (HA) in biological samples was developed. This method does not require any preliminary purification or concentration of HA, and features high sensitivity, specificity, and reliability. The method consists of the direct application of the acid-deproteinized sample to high-performance liquid chromatography on a sulfonated polystyrene column with detection by means of a postcolumn fluorogenic reaction with o-phthaladehyde. The detection limit was found to be 0.1 pmol (signal-to-noise ratio = 3). The coefficient of variation for measurements of 10 pmol of standard histamine was 1.1%. Each chromatography takes only 10 min and therefore more than 50 samples can be measured in a day. The high sensitivity of the method allows it to be applied even to samples of very low HA concentration such as human plasma without any procedure for concentration of the sample, and further, only 0.1 ml of the sample is necessary for determination. The method was applied to compare the HA levels of the whole blood and plasma of man and various animals. Applications of the method to the supernatant of rat peritoneal mast cell incubates and to extracts of mouse brain and stomach are also described.

Release of prostaglandin D2 into human airways during acute antigen challenge

Among the many possible mediators of the early asthmatic response, prostaglandin D2, a bronchoconstrictor, is the principal cyclooxygenase metabolite of arachidonic acid that is released upon the activation of mast cells and is also synthesized by human alveolar macrophages. We performed bronchoalveolar lavage in five patients with chronic stable asthma, before and up to nine minutes after local provocative challenge with Dermatophagoides pteronyssinus. The lavage fluid was analyzed for products of arachidonic acid metabolism. Prostaglandin D2 levels in all five patients rose an average of 150-fold, from less than 8 to 332 +/- 114 pg per milliliter (mean +/- SEM; P less than 0.050), after local instillation of the antigen. Levels of 15-hydroxyeicosatetraenoic acid, which may also have a role in the pulmonary allergic response, were detectable in lavage fluid before challenge and increased after provocation with the antigen in four of the five patients. The activity of beta-glucuronidase, an enzyme released by macrophages and mast cells upon stimulation, tended to increase in the lavage fluid after provocation in all patients. These studies provide evidence that the release of prostaglandin D2 into the airways is an early event after the instillation of D. pteronyssinus in patients who are sensitive to this antigen.

Prostaglandin D2 and histamine release in cold urticaria

Prostaglandin (PG) D2 and histamine concentrations have been measured in blood draining cold-challenged forearm skin in patients with cold urticaria. Local venous concentrations of both histamine and PGD2 rose in four patients who developed a whealing response. Plasma histamine concentration increased from a mean resting value of 0.24 +/- 0.09 (SD) ng/ml to peak values of 16.9 to 96.6 ng/ml. Resting concentrations of PGD2 were below the limit of detection (5 pg/ml) in three patients and 62 and 27 pg/ml in the fourth. Peak plasma PGD2 concentration after challenge ranged from 166 to 279 pg/ml. Time course of histamine and PGD2 release was similar with peak concentrations at 6 and 10 minutes, respectively. The maximum clinical response occurred between 10 and 20 minutes after challenge. Our findings demonstrate that PGD2 is produced in association with mast cell degranulation in man, but the amount, relative to histamine, is low. Despite its high potency in production of inflammatory effects, PGD2 probably has only minor direct effects in cold urticaria, although it may act to potentiate other mediators.

Histamine is released from skin by substance P but does not act as the final vasodilator in the axon reflex

We have explored in man the hypothesis that histamine released from dermal mast cells by neurotransmitters from afferent nerves contributes to vasodilatation of the axon reflex. The ability of substance P to release histamine from human skin in vivo, and the effects of a histamine H1-receptor antagonist on capsaicin-induced axon reflex flares were studied. Intradermal injections of substance P (50 pmol) produced a weal and flare response which was associated with increased histamine concentration in blood draining the site (mean plasma histamine concentration before injection 0.17 +/- 0.02 ng ml-1 (+/- s.e.mean), concentration one minute after injection 1.26 +/- 0.28 ng ml-1, n = 6). Terfenadine, an H1-receptor antagonist, had no effect on the flare response to intradermal injection of capsaicin at a dose which inhibited by more than 60% the flare response to exogenous histamine and to histamine released from dermal mast cells by substance P. Substance P releases histamine from human skin in vivo. However, whatever the nature of the neurotransmitter released from afferent nerves during the axon reflex, it does not produce vasodilatation through release of histamine from dermal mast cells. Histamine may still contribute to the flare by initiation of the reflex.