Spontaneous Histamine Release Research Articles

Colorectal mucosal histamine release by mucosa oxygenation in comparison with other established clinical tests in patients with gastrointestinally mediated allergy

This study evaluated colorectal mucosal histamine release in response to blinded food challenge-positive and -negative food antigens as a new diagnostic procedure. 19 patients suffering from gastrointestinally mediated allergy confirmed by blinded oral provocation were investigated on grounds of their case history, skin prick tests, serum IgE detection and colorectal mucosal histamine release by ex vivo mucosa oxygenation. Intact tissue particles were incubated/stimulated in an oxygenated culture with different food antigens for 30 min. Specimens challenged with anti-human immunoglobulin E and without any stimulus served as positive and negative controls, respectively. Mucosal histamine release (% of total biopsy histamine content) was considered successful (positive), when the rate of histamine release from biopsies in response to antigens reached more than twice that of the spontaneous release. Histamine measurement was performed by radioimmunoassay. The median (range) of spontaneous histamine release from colorectal mucosa was found to be 3.2 (0.1%-25.8%) of the total biopsy histamine content. Food antigens tolerated by oral provocation did not elicit mast cell degranulation 3.4 (0.4%-20.7%, P = 0.4), while anti-IgE and causative food allergens induced a significant histamine release of 5.4 (1.1%-25.6%, P = 0.04) and 8.1 (1.5%-57.9%, P = 0.008), respectively. 12 of 19 patients (63.1%) showed positive colorectal mucosal histamine release in accordance with the blinded oral challenge responding to the same antigen (s), while the specificity of the functional histamine release to accurately recognise tolerated foodstuffs was found to be 78.6%. In comparison with the outcome of blinded food challenge tests, sensitivity and specificity of history (30.8% and 57.1%), skin tests (47.4% and 78.6%) or antigen-specific serum IgE determinations (57.9% and 50%) were found to be of lower diagnostic accuracy in gastrointestinally mediated allergy. Functional testing of the reactivity of colorectal mucosa upon antigenic stimulation in patients with gastrointestinally mediated allergy is of higher diagnostic efficacy.

Spontaneous histamine secretion during isolation of rat cardiac mast cells

To test the hypothesis that spontaneous release of histamine occurring during an isolation protocol may modify responses of rat cardiac mast cells (connective tissue-type mast cells) to secretagogues. We assessed two protocols for enzymatic dispersion utilizing collagenase, hyaluronidase, and deoxyribonuclease; with protease (Protocol 1, n = 8) or without protease (Protocol 2, n = 3). Spontaneous release of histamine was quantified following mechanical and enzymatic dispersion of the whole heart. Total histamine loss (Mean +/- SEM) was 963+/-92 and 833+/-60 ng/g of tissue weight following Protocols 1 and 2. Percentages of histamine release from cell isolates following Protocol 1 were 40+/-5%, 41+/-6%, and 51+/-7% at 0, 30, and 300 microg/mL of compound 48/80. Enzymatic dispersion of cardiac mast cells affects their response to secretagogues.

Consequences of eicosapentaenoic acid (n-3) and arachidonic acid (n-6) supplementation on mast cell mediators.

Mast cells are important players in the pathogenesis of atopic diseases. These cells release immediate-phase and late-phase mediators of inflammation. Fatty acids are incorporated in cellular membranes and therefore seem to influence mediator production and release. A study was conducted to assess the effects of eicosapentaenoic acid (EPA, 20:5n-3) and arachidonic acid (AA, 20:4n-6) on mast cell mediators in a canine mastocytoma cell line (C2). Cells were cultured in a basic medium (Dulbecco's modified Eagle's medium/HAM's F12 1 : 1, DEH), DEH supplemented with 14.0 microm EPA (DEH-EPA) or 14 microm AA (DEH-AA). The DEH-AA cultured cells had increased spontaneous and mastoparan-stimulated PGE2 production and histamine release. Furthermore, the tryptase activity was increased. The DEH-EPA cultured cells rendered elevated levels of PGE2 and histamine release compared with DEH only after stimulation. These levels were significantly lower in comparison to DEH-AA. The increased PGE2 production of C2 cultured in DEH-AA is the consequence of the AA enrichment, because AA is the precursor of PGE2. However, the different effects by AA and EPA on mast cell mediators possibly reflect the higher susceptibility of long chain polyunsaturated fatty acids (PUFA) to undergo lipid peroxidation, because it is known that altered cellular redox state influences mediator production and release.

Evaluation of spontaneous histamine release from colorectal mucosa in patients with colorectal adenoma, patients with gastrointestinally mediated allergy and in a healthy control group.

Evaluation of spontaneous histamine release from colorectal mucosa in patients with colorectal adenoma, patients with gastrointestinally mediated allergy and in a healthy control group.

Down-regulation of Th2 cytokine expression by glucocorticoids in cultivated human lung mast cells

VOLUME 111, NUMBER 2 using dot blot analysis with the specific antibody, BB1. Ca 2+ fluxes were measured using Fluo-3. Inositol 1,4,5-trisphosphate (IP3) was measured by radio-receptor binding assay. RESULTS: Thrombin (250 U/ml) and trypsin (10 lag/ml) elevated intracetlular Ca 2§ ([Ca2+]i) in KU812 cells. Selective agonist peptides, to PAR-I (TFLLR, 100 gM) and PAR4 (AYPGKF, 300 ~tM) elevated [Ca2+]i but PAR2 selective peptides (SLIGRL, 50 gM and SLIGKV, 100 gM) caused no stimulation. PAR-I and PAR-4 selective peptides transiently increased IP 3 levels in KU812 cells, mRNA for PAR-I and PAR-4 was detected in KU812 cells and purified human basophils (n=3). Additionally mRNA for PAR-2 and -3 was faintly detected in one donor's basopbils. Agonist peptides failed to stimulate basogranulin release from basophils in four out of five experiments. CONCLUSIONS: These data suggest the expression of PAR-1 and PAR4 by human basophils and KU812 cells. PAR-2 and PAR-3 may be expressed by basophils in some individuals. Selective stimulation of PAR1 or PAR-4 is generally insufficient to induce degranulation. Funding: National Asthma Campaign 4 7 7 Down-regulation of Th2 Cytokine Expression by Glucocorticoids in Cultivated Human Lung Mast Cells J. G. Mohanty, J. M. Abboud, E. S. Schulman; Pulmonary and Critical Care Medicine, Drexel University College of Medicine, Philadelphia, PA. RATIONALE: In allergen-induced asthma, mast cells play a critical role through the release of various mediators including Th2 cytokines. Glucocorticoids are used for treatment of allergic disorders; however their effects on human lung mast cell (HLMC) function have not been ftdly studied. Recently, we developed techniques to culture partially purified HLMC over months using stem cell factor and interleukin (IL)-4, in which HLMC become homogeneous, proliferate and maintain a functional phenotype equivalent to freshly isolated cells. METHODS: HLMC were cultured overnight with or without triamcinolone (10-6 M) to examine its effects on the regulation ofTh2 cytokines expression. HLMC were stimulated by antibody cross-linking of the highaffinity IgE receptor (FceRI). At 20 min post stimulation, percent histamine release (HR) was measured; at 2 hour, total cellular RNA was isolated, and reverse transcriptase/polymererase chain reaction (RT-PCR) was performed to study cytokine gene expression. RESULTS: Spontaneous HR was 20-fold, with concurrent increases in IL-6 mRNA levels and DNA binding activity for key transcriptional regulators of the IL-6 promoter, NF-kB and AP-I. Comparisons of conditioned media and eosinophilfibroblasts co-culture using transwell barriers, indicated cell contact is unnecessary and the soluble nature of the mediators. Antibody neutralization of TGF-13 in the conditioned media produced only a 20% inhibition of fibroblast IL-6 secretion. Interestingly, neutralization of IL-113 and bFGF inhibited the IL-6 response by 60% and 15-20%, respectively. Antibody neutralization results were supported by the induction of fibroblast IL-6 secretion by recombinant IL-II3 (68-fold), TGF-I]I (2.5-tbld), and bFGF (l.5-fold). Neutralization of other potential eosinophil-derived mediators including GM-CSF, PDGF-BB, NGE and IL-4, had an insignificant effect. CONCLUSIONS: Our results suggest a major role for eosinophilderived IL-113, TGF-13 and bFGF in fibroblast activation and eosinophilassociated fibrotic responses, including subepithelial fibrosis in asthma. Funding: NIH, EMS Foundation

Effect of experimental influenza A infection on systemic immune and inflammatory parameters in allergic and nonallergic adult subjects

The economic impact and medical complication rate of viral upper respiratory infections are well documented, but many of the physiologic, inflammatory, and immune responses to respiratory viruses have only recently been investigated. A previous study demonstrated differential systemic immune and inflammatory responses in allergic rhinitis (AR) and nonallergic rhinitis (NAR) subjects during experimental infection with rhinovirus-39. The purpose of this study was to compare selected systemic immune and inflammatory responses to experimental influenza A virus (FLU) challenge in seronegative AR and NAR subjects. Peripheral blood was obtained at baseline (study day 0) and 3, 6, 18, and 31 days after intranasal FLU challenge and assayed for leukocyte histamine release, serum immunoglobulins, and plasma histamine. All subjects were infected, as manifested by viral shedding in nasal secretions and/or seroconversion. FLU infection induced decreases in spontaneous leukocyte histamine release and increases in anti-immunoglobulin E-induced leukocyte histamine release, which were evident at least 1 month after infection, but caused no significant changes in serum immunoglobulins or plasma histamine. There were no differences between AR and NAR subjects for any of the study parameters. The results show that intranasal challenge with FLU induces changes in leukocyte histamine release, but not other systemic immune and inflammatory responses.

Muscarinic control of histamine release from airways. Inhibitory M1-receptors in human bronchi but absence in rat trachea.

Isolated human bronchi and rat tracheae were incubated in organ baths to measure histamine release. The calcium ionophore A23187, 3 micromol/L in rat trachea and 10 micromol/L in human bronchi, stimulated histamine release by 145 +/- 50% (n = 6) and 270 +/- 48% (n = 7) above the prestimulation level, respectively. Acetylcholine (100 pmol/L; human bronchi) or oxotremorine (1, 100, 10,000 nmol/L; rat trachea) did not affect the spontaneous histamine release. In rat tracheae neither acetylcholine nor oxotremorine inhibited A23187-evoked histamine release, whereas 100 pmol/L acetylcholine significantly suppressed the evoked histamine release in human bronchi by 86%. For receptor characterization the following subtype-specific muscarinic receptor antagonists were applied: pirenzepine (M1 subtype), para-fluorohexahydrosiladifendiol (pFHHSiD; similar affinities at human cloned M1-, M3-, and M4-receptors), AF-DX 116 (M2 subtype), and clozapine (antagonist at cloned M1-, M2-, M3-receptors; agonist at cloned M4-receptors). Pirenzepine, pFHHSiD, AF-DX 116, and clozapine (100 nmol/L each) antagonized the inhibitory effect of 100 pmol/L acetylcholine by 83 +/- 20% (n = 6), 83 +/- 9% (n = 8), 50 +/- 14% (n = 6), and 35 +/- 7% (6). In conclusion, a species difference exists in the cholinergic control of histamine release between human and rat airways. In human airways muscarinic receptors most likely of the M1 subtype are involved in the inhibitory control of mast cell function, whereas such an inhibitory pathway does not exist in the rat trachea.

Influence of bronchial allergen challenge on histamine release by human basophils.

Basophils can be primed by cytokines such as interleukin (IL) -3, IL-5 or granulocyte macrophage-colony stimulating factor (GM-CSF). It has been described that the concentrations of these cytokines are enhanced at sites of allergic inflammation as well as systemic in allergic asthma. To investigate the priming status of basophils as detected by thapsigargin-induced histamine release during bronchial allergen challenge. Ten subjects allergic to house dust mite were challenged via an aerosol delivery system. Spontaneous leucocyte histamine release as well as histamine release induced by various stimuli was measured in vitro at several time points. In addition, lung function parameters, serum IL-5 and blood eosinophil counts were evaluated. We found no effect of bronchial allergen challenge upon spontaneous leucocyte histamine release, nor upon histamine release induced by anti-immunoglobulin (Ig) E, house dust mite extract, C5a, fMLP, IL-3, PMA+ thapsigargin or IL-3+ thapsigargin. However, the priming status of basophils as measured by thapsigargin-induced histamine release was enhanced at 24 h after bronchial allergen challenge. Analysis of the individual data showed a heterogeneous initial response (30 min, 6 h) followed by a predominant increase at 24 h after allergen challenge. This increase in the thapsigargin-induced histamine release correlated with the increase in serum IL-5 levels at 24 h after allergen challenge. The priming status of human basophils as measured by thapsigargin-induced histamine release is enhanced 24 h after allergen challenge.

Simplified purification of human basophils

Studies of human basophils have been limited by the low number present in peripheral blood and the difficulties of purification to homogeneity with reasonable yield and functional status. Reproducible purification of human basophils to 96.5±0.5% with a yield of 40.8±5.3% was obtained by negative selection using immunomagnetic beads following initial separation by density gradient centrifugation. Isolated cells demonstrated complete viability by vital dye exclusion and spontaneous histamine release following incubation of <5%. Stimulation with anti-IgE or calcium ionophore A23187 caused histamine release and leukotriene C 4 production. Basophils demonstrated dose-dependent chemotaxis to monocyte chemotactic protein-3. This simplified methodology results in fully functional basophils in very high purity and good yield.

Basophils from patients with allergic asthma show a primed phenotype

Background: IL-3, IL-5, and GM-CSF are not able to induce histamine release in purified basophils of nonallergic donors. However, we have recently found that preincubation with 2 μmol/L thapsigargin, which induces a rise in intracellular free calcium ions, renders human basophils extremely sensitive for IL-3, IL-5, or GM-CSF, leading to enhanced histamine release. Histamine release was also induced in the reverse order (first cytokine and then thapsigargin). Objective: Because these cytokines are supposed to be increased in allergic inflammation, we examined whether basophils of patients with allergic asthma showed an enhanced response to thapsigargin. Methods: We measured the histamine release induced by thapsigargin in a group of allergic asthmatic subjects (n = 24) and compared this response with those of 3 control groups. The control groups consisted of healthy control subjects (group 1, n = 21); patients with a nonallergic, nonasthmatic lung disease (group 2, n = 22); and patients with nonallergic asthma (group 3, n = 9). Results: There was no difference in spontaneous histamine release. Also, no significant difference in histamine release was found when anti-IgE or formyl-methionyl-leucyl-phenylalanine was used as a stimulus. Histamine release induced by IL-3 alone or a combination of IL-3 and thapsigargin also did not differ. In contrast, basophils from the group with allergic asthma showed a significantly higher percentage of histamine release induced by thapsigargin (38.2% ± 13.2%) than did basophils from the 3 control groups (healthy control subjects, 22.5% ± 6.9%; subjects with lung disease, 24.9% ± 8.9%; subjects with nonallergic asthma 15.0% ± 3.0%; all mean ± SD). Conclusion: These data indicate that basophils in peripheral blood of subjects with allergic asthma have a primed phenotype and that thapsigargin-induced histamine release is a practical tool to study this phenomenon. (J Allergy Clin Immunol 1999;104:1000-7.)

Effect of Substance P on Histamine Secretion from Gut Mucosa in Inflammatory Bowel Disease

Background: Mast cell hyperplasia in the gut is a feature of inflammatory bowel disease (IBD), but the role of mast cells in this disease is still unclear. Since mast cell-nerve interactions might have some impact on intestinal inflammation, the present study investigated whether the neuropeptide substance P causes histamine secretion from human gut mucosal mast cells. Methods: Four hundred and eighteen colorectal endoscopic samples from 20 patients with IBD and 10 controls were studied. Colorectal biopsy samples were cultured in an oxygenated medium for spontaneous histamine release or were stimulated with substance P, anti-human immunoglobulin E, and a combination of substance P and anti-human immunoglobulin E. Histamine release was measured using a highly sensitive and specific radioimmunoassay. Results: Substance P failed to induce mast cell activation in histologically normal mucosa from controls. In contrast, mucosal specimens taken from inflamed IBD tissue or from uninvolved Crohn disease tissue showed a considerably enhanced rate of histamine secretion towards substance P, alone or in combination with anti-IgE. Unaffected mucosa with ulcerative colitis appeared insensitive towards substance P. Conclusions: The neuropeptide substance P was shown to preferentially enhance mucosal mast cell mediator secretion in active IBD. Thus, it appears likely that mast cell-nerve interactions are involved in as yet uninvestigated neurovegetative histamine-releasing processes of the gut in IBD.

Tumor necrosis factor alpha (TNF- α) modulates rat mast cell reactivity

Nowadays there is growing evidence that some cytokines regulate biological functions of the mature mast cells. Therefore, we have studied whether TNF- α, the cytokine of multifunctional activities, could directly stimulate rat peritoneal mast cells to histamine secretion and whether it could modulate rat mast cell reactivity in anaphylactic (with ConA) and anaphylactoid (with compound 48/80) reactions. We have established that rat recombinant TNF- α does not activate rat mast cells to histamine release. However, TNF- α-treatment causes the decrease of spontaneous histamine release up to 85% (TNF- α concentration: 2×10 −9 M). Pretreatment of mast cells with TNF- α inhibits ConA-stimulate release of histamine with the percent release decreasing up to 33.7% of the control value (TNF- α concentration: 5×10 −9 M) and this decrease is statistically significant. Pretreatment of mast cells with TNF- α reduces compound 48/80-dependent histamine release as well and the percent release of histamine fell to 64.7% of the control value. We have concluded that TNF- α may play a significant role in regulation of mast cell secretory activity.

Factors determining spontaneous histamine release from human basophils purified with Percoll gradients and Dynabeads.

Identification of factors influencing histamine release from purified and cultured basophil leukocytes is important for proper interpretation of results obtained on histamine release. This paper describes factors that influence spontaneous histamine secretion from human basophil leukocytes purified on Percoll gradients, followed by negative selection with Dynabeads. Anti-IgE and recombinant human interleukin-3 were used as model stimulants, and the purified basophil leukocytes were stimulated for 10 min and 6 h. The effect of the following conditions was examined: Percoll temperature, cell-suspension density, and serum in the media. The results showed that low Percoll temperature, high cell-suspension density, and the presence of serum in the media decreased spontaneous histamine release and increased maximal net histamine release upon stimulation.

Analysis of the effect of a 60 Hz AC field on histamine release by rat peritoneal mast cells.

Reports have indicated effects of electromagnetic fields on inflammatory processes in vivo. To begin a systematic approach toward separating and examining the many components of such responses, we created and tested a temperature-controlled device to develop 5 mT 60 Hz magnetic fields for studies of the effects of fields on mast cells, a key component in acute inflammatory responses. Such fields have been reported to modulate cell activity, including changes in membrane function, in various systems. The magnetic field was generated using a solenoid and calibrated with an induction probe. Tests of mast cell function were determined by histamine release response to stimulation by compound 48/80, using both an "expose then test" and a "test during exposure" protocol. Aliquots not treated with 48/80 were used to evaluate field treatment effects on spontaneous histamine release. Freshly harvested rat peritoneal mast cells were exposed to the magnetic field for periods of 30 min to 2 h at 37 degrees C. They showed no significant degranulation during treatment, nor did they show reduced sensitivity to the degranulating agent 48/80. These observations are consistent with a model in which such processes are exclusively reflexive by the cells using field-independent membrane systems. This observation is very useful and was needed before examining longer term exposures in which gene expression in the cells might be influenced; this is the first such report of in vitro exposure of purified mast cells under these conditions and will further the study of the effects of electromagnetic fields on cell types active in acute inflammation.

In vitro reactivity of mast cells in urticaria pigmentosa skin.

The aim of our study was to evaluate the sensitivity of skin mast cells from urticaria pigmentosa (UP) patients to substance P (SP), tumor necrosis factor alpha (TNF-alpha) and anti-IgE, and to compare the sensitivity of these cells with that of skin mast cells from healthy human donors. Mast cells for in vitro functional studies were obtained using an enzymatic dispersion technique from skin biopsies (from 11 patients with UP and 11 healthy donors), and the reactivity of these cells was estimated on the basis of histamine release. Our observations indicated that UP skin mast cells and healthy skin mast cells had similar sensitivities to challenge with TNF-alpha at a concentration 10(-7) M (16.4% vs 15.2%) and with anti-IgE at a dilution 1:100 (41.0% vs 37.0%). However, UP mast cells showed considerably higher sensitivity to challenge with SP at a concentration 10(-4) M than healthy skin mast cells (20.0% vs 6.8%), and the difference was statistically significant (P < 0.001). UP skin mast cells also demonstrated significantly higher spontaneous histamine release than healthy skin mast cells (32.1% vs 12.4%, P < 0.001). Our findings indicating UP skin mast cell sensitivity to SP might suggest that mechanisms involving neurogenic inflammation could contribute to the course of this disease.

Spontaneous histamine release from mast cells and basophils is controlled by the cellular environment.

Spontaneous histamine release from mast cells and basophils is controlled by the cellular environment.

Effects of Pasteurella haemolytica leukotoxin and lipopolysaccharide on histamine, prostanoid, and leukotriene release by bovine lung parenchyma in vitro

SUMMARY Objective To identify the effect of Pasteurella haemolytica lipopolysaccharide (LPS) and leukotoxin (LKT) on spontaneous and calcium ionophore-induced histamine and inflammatory mediator release from isolated bovine lung parenchyma. Sample Population Lungs from 8 healthy cattle. Procedure Isolated bovine lung parenchyma was incubated in vitro for 2 hours with LKT or LPS, and spontaneous and induced release of inflammatory mediators was determined. Results LKT and LPS increased spontaneous release of histamine and leukotriene B4. In addition, incubation with LPS increased spontaneous release of prostaglandin E2. Moreover, a differential effect of the 2 toxins on calcium ionophore-induced inflammatory mediator release was observed. LKT specifically primed isolated lung parenchyma to release leukotriene B4 and thromboxane B2 in response to calcium ionophore, whereas LPS did not alter the profile of prostanoids released by bovine lung tissue exposed to calcium ionophore. Conclusions Pasteurella haemolytica toxins have a direct effect on bovine lung parenchyma, causing release of inflammatory mediators, which contribute to response to infection. Furthermore, bacterial toxins (LKT in this study) may sensitize tissues to the effects of other irritant stimuli, amplifying the inflammatory response. (Am J Vet Res 1997;58:1227–1231)

Acetylcholine via muscarinic receptors inhibits histamine release from human isolated bronchi.

Human bronchi were incubated in organ baths to measure histamine release. The calcium ionophore A23187 (10 mumol/L; 1 min) stimulated histamine release by 148 +/- 28% (n = 11) above the prestimulation level but was ineffective in epithelium-denuded bronchi. Neither bradykinin (0.1 mumol/L) nor compound 48/80 (10 micrograms/ml) triggered the release of histamine from epithelium-intact bronchi. Acetylcholine did not affect spontaneous histamine release (about 2 nmol/g x 5 min) but inhibited A23187-evoked histamine release in an atropine-sensitive manner. Already a concentration as low as 0.1 nmol/L acetylcholine was effective, the maximal inhibition (by 89%) occurred at 100 nmol/L, whereas a concentration of 10 mumol/L acetylcholine was ineffective. Oxotremorine (1 nmol/L), a stable agonist at muscarinic receptors, suppressed stimulated histamine release completely. Physostigmine (0.1 mumol/L), an acetylcholinesterase inhibitor, reduced A23187-evoked histamine release by 58%. Antihuman IgE antibody stimulated histamine release by 127 +/- 30% (n = 6) above the prestimulation level. Acetylcholine (100 nmol/L) inhibited also the immunologically evoked histamine release by 70%. In conclusion, the present experiments provide a model to characterize mast cells that are localized in or close to the airway surface epithelium. Acetylcholine via muscarinic receptors strongly inhibits the releasability of these mucosal mast cells being among the first cells to interact with inhaled antigens and environmental agents. The inhibitory action of physostigmine indicates the involvement of endogenous, probably non-neuronal acetylcholine expressed in airway epithelial cells.

Functional studies of skin mast cells in lichen planus.

In order to identify possible functional differences between mast cells obtained from the skin of lichen planus (LP) patients and healthy donors, biopsies from lesional skin of 11 lichen planus patients and from normal skin of 7 healthy donors were sampled. Mast cells were obtained from the skin using an enzymatic dispersion technique. The cells were challenged in vitro with substance P (SP), tumor necrosis factor alpha (TNF-alpha) and anti-IgE. Their reactivity was estimated on the basis of histamine release. LP skin mast cells and healthy skin mast cells showed similar sensitivity to stimulation with TNF-alpha at a concentration of 10(-7) M (15.2% histamine release, as a proportion of total cellular content vs 15.9%) and to stimulation with anti-IgE at a dilution of 1:100) (38.8% vs 37.0%). Spontaneous histamine release was also very similar in both the populations of mast cells (10.2% vs 12.7%, respectively). However, LP skin mast cells showed significantly higher (P < 0.01) sensitivity towards stimulation with SP at a concentration of 10(-4) M than healthy skin mast cells (15.9% histamine release vs 7.0%). This finding could suggest that neurogenic inflammatory mechanisms contribute to the pathogenesis of LP.

Effect of H1-antihistamines on histamine release from dispersed canine cutaneous mast cells

Abstract Objective Because of the implication of histamine in canine atopic dermatitis, H1-antihistamines may provide a valid alternative to glucocorticoid therapy. In vitro study of these drugs prior to clinical testing can allow the most promising compounds to be selected for trials and render trials with drugs of doubtful efficacy unnecessary. Sample Population Isolated canine cutaneous mast cells. Procedure Cells were preincubated with antihistamines at increasing concentrations and incubated with concanavalin A (1,000 µg/ml), calcium ionophore A23187 (1 µM), and substance P (100 µM). Compound 48/80 was not used because it proved to be cytotoxic. Results Generally, significant prodegranulating effect was not observed for most of the studied agents. Only terfenadine increased spontaneous histamine release at concentrations &gt; 30 µM. Cetirizine did not block histamine release at any of the studied concentrations. Ketotifen had a low inhibitory effect only at the highest concentration (100 µM) after concanavalin A- (23.6 ± 2.8%) and calcium ionophore A23187- (29.8 ± 3.0%) induced release. Terfenadine caused a concentration-dependent inhibitory effect after ionophore A23187- (48.1 ± 2.2%) and concanavalin A- (28.9 ± 2.3%) activation, but was inactive against substance P-induced release. In contrast, loratadine had potent dose-dependent inhibition of concanavalin A- and ionophore A23187-induced histamine release, with maximal effect of 85.6 ± 3.1 % and 62.6 ± 4.7%, respectively, at 100 µM concentration. After substance P activation, histamine release was only slightly inhibited by loratadine (14.8 ± 1.1%). Conclusions This study documents the behavior of isolated canine cutaneous mast cells in the presence of nonimmunologic stimulation. Using this in vitro method, we were able to determine that loratadine is the only antihistamine that has potent inhibition of histamine release from dog cutaneous mast cells without a substantial prodegranulating effect. Loratadine is, therefore, a good candidate for clinical testing. (Am J Vet Res 1997;58:293–297)