Topic:Histamine
Histamine is an organic compound involved in various physiological processes in horses, including immune response, gastric acid secretion, and neurotransmission. It is synthesized from the amino acid histidine and is stored in mast cells and basophils, which release histamine in response to allergens or tissue injury. In horses, histamine plays a role in allergic reactions and inflammatory responses, influencing conditions such as equine asthma and urticaria. The compound interacts with specific histamine receptors, which mediate its effects on target tissues. This page compiles peer-reviewed research studies and scholarly articles that explore the synthesis, function, and clinical implications of histamine in equine health.
Effects of a histamine type 2 receptor antagonist, BMY-26539-01, on equine gastric acid secretion. A dose-response study was undertaken of the effects of a newly developed histamine type 2 receptor antagonist, BMY-26539-01, on gastric acid secretion in 4 fasted horses. Doses of 0.1 mg/kg, 0.3 mg/kg, 0.5 mg/kg, or placebo were administered in a randomly assigned treatment sequence. Hydrogen ion concentration and pH were variable during baseline measurements in all 4 animals; however, following BMY-26539-01 administration, mean pH increased and hydrogen ion concentration decreased in a dose-related pattern. At the 0.3 mg/kg and 0.5 mg/kg dose levels, pH remained elevated for > 4 h and >...
Comparative responses of bronchial rings to mediators of airway hyperreactivity in healthy horses and those affected with summer pasture-associated obstructive pulmonary disease. To compare responses of bronchial rings obtained from healthy horses and horses affected with summer pasture-associated obstructive pulmonary disease (SPAOPD) to selected mediators of airway hyperreactivity in vitro. Methods: Bronchial rings from 6 healthy horses and 6 horses affected with SPAOPD. Methods: Bronchial rings obtained from each group of horses were mounted in organ baths and attached to force transducers interfaced with a polygraph. After applying 2g of tension, each ring was allowed to equilibrate for 45 minutes in Tyrode's solution at 37 C. Cumulative concentration-response rela...
Effect of pyloric blockade and infusion of histamine or pentagastrin on gastric secretion in horses. To determine the origin of the nonacid (nonparietal) component of gastric secretions in horses induced by pentagastrin infusion. Methods: 6 horses. Methods: A Latin square design was used, involving 6 horses, 3 treatments, and 2 duodenal intubation conditions (catheter with balloon to obstruct pylorus [B] or without balloon allowing movement of contents between stomach and duodenum [NB]). Each horse had an indwelling gastric cannula and a catheter positioned in the duodenum. Gastric and duodenal contents were collected during 15-minute periods. Each experiment consisted of serial collection pe...
Evidence of histamine receptor function in isolated horse penile dorsal arteries. The effect of histamine (10(-9)-10(-3) M) on horse penile dorsal artery was evaluated. Precontracted vessels showed a biphasic response (relaxation-contraction) to histamine, while at basal tone, histamine only induced a contractile effect. The H1 receptor agonist, 2-pyridylethylamine (PEA) (10(-9)-10(-3) M), induced concentration-dependent relaxation in precontracted rings and provoked vasoconstriction at basal tone. Mepyramine (10(-9)-10(8) M), an H1 receptor antagonist, competitively antagonized the relaxant response to histamine (pA2 = 9.7) and PEA (pA2 = 9.2). At basal tone, mepyramine (1...
Thoracoabdominal asynchrony failed to grade airway obstructions in foals. Respiratory inductive plethysmography (RIP) can be used to obtain a valid measure of tidal volume in humans. This device also compares the contributions to ventilation of the thorax and abdomen. Although thoracoabdominal asynchrony is a prominent clinical feature for patients with airway obstruction, the accuracy of the RIP device to assess the severity of obstruction is unclear. This study analyzes how well RIP variables reflect the degree of a fixed external inspiratory plus expiratory resistive load in foals. Foals were employed because the species and age group are commonly afflicted with ...
Forced expiration: a test for airflow obstruction in horses. The purpose of this study was to assess whether our method of inducing forced expiration detects small airway obstruction in horses. Parameters derived from forced expiratory flow-volume (FEFV) curves were compared with lung mechanics data obtained during spontaneous breathing in nine healthy horses, in three after histamine challenge, and in two with chronic obstructive pulmonary disease (COPD) pre- and posttherapy with prednisone. Parameters measured in the healthy horses included forced vital capacity (FVC = 41.6 +/- 5.8 liters; means +/- SD) and forced expiratory flow (FEF) at various perc...
Actions and interactions of ADP, 5- HT, histamine and PAF on equine platelets. Platelets are thought to play a role in equine diseases such as acute laminitis and verminous arteritis and may be involved in allergic disease. Mediators implicated in the pathophysiology of these conditions activate platelets and responses may be enhanced by interactions between mediators. The present study compared platelet aggregation, thromboxane production and release of radiolabelled [(3)H]5- HT in response to 5- HT, histamine, ADP and PAF alone and in combination in vitro.PAF caused concentration-related aggregation, [(3)H]5- HT release and thromboxane production. In contrast, ADP caus...
Signalling pathway for histamine activation of non-selective cation channels in equine tracheal myocytes. 1. The signalling pathway underlying histamine activation of non-selective cation channels was investigated in single equine tracheal myocytes. Application of histamine (100 microM) activated the transient calcium-activated chloride current (ICl(Ca)) and sustained, low amplitude non-selective cation current (ICat). The H1 receptor antagonist pyrilamine (10 microM) blocked activation of ICl(Ca) and ICat. Simultaneous application of histamine (100 microM) and caffeine (8 mM) during H1 receptor blockade activated ICl(Ca), but not ICat. Neither the H2 receptor antagonist cimetidine (20 microM) nor...
A preliminary study of the effect of inhaled nitric oxide on lung mechanics in the standing horse with histamine-induced bronchoconstriction. The effect of inhaled nitric oxide on pulmonary mechanics was studied in normal standing horses with histamine-induced bronchoconstriction. The respiratory health status of 6 normal horses was established on the basis of history, clinical and bronchoalveolar lavage examination. Intrathoracic pressures were estimated using distal oesophageal pressures. Respiratory gas flows were measured using a heated pneumotachograph. Pulmonary mechanics variables were determined from these measurements on a breath by breath basis. Bronchoconstriction was induced by nebulizing a 0.75% w/v solution of histamin...
Sulfidoleukotriene generation from peripheral blood leukocytes of horses affected with insect bite dermal hypersensitivity. Sulfidoleukotrienes (sLT) generated in vitro after incubation of equine peripheral blood leukocytes (PBL) with different inducing agents were determined in 18 healthy and 16 insect bite dermal hypersensitivity (IDH)-affected horses. PBL from these 32 horses were stimulated with Concanavalin A, Parascaris equorum, Culicoides nubeculosus and Simulium extracts, and with a six-Grass mix. The cells of all but four horses generated sLT after incubation with Concanavalin A; these four horses did also not produce sLT with the other inducing agents. Of the 28 remaining horses (12 affected with IDH and ...
The use of compound 48/80 as a positive control in equine intradermal allergy testing. The macroscopic and microscopic effects following the intradermal injection of the mast cell degranulator compound 48/80 were investigated in horses. It was found that a 1000 μg mL-1 solution of compound 48/80 could be used as an alternative to histamine as a positive control in equine intradermal allergy tests. An inflammatory cell infiltration was noted on histological examination, following compound 48/80 injection. This inflammatory cell pattern was similar to that noted for Type-I hypersensitivity.
Airway responses to histamine aerosol in clinically normal foods. To describe the spectrum of nonspecific airway reactivity in a group of clinically normal foals. Methods: 12 clinically normal mixed-breed foals, 48 to 92 days old, without history of clinical lung disease. Methods: Nonspecific airway reactivity was determined by measuring the extent of changes in dynamic compliance during nebulization of incrementally increasing concentrations of histamine aerosol. Degree of airway reactivity was expressed as the dose of histamine that evoked a decrease in dynamic compliance (Cdyn) to 65% of the after saline nebulization value (PC65Cdyn) or increase in pulmon...
Pre- and postjunctional effects of inflammatory mediators in horse airways. In addition to their direct contractile effects, histamine (Hist), serotonin [5-hydroxytryptamine (5-HT)], and leukotriene (LT) D(4), in low concentrations, dramatically augment electrical field stimulation (EFS)-induced smooth muscle contractions in equine airways. To determine the mechanism of their action, we studied, in trachealis strips, the effect of these mediators on both cholinergically induced tension and the release of ACh from cholinergic nerves. All three mediators synergistically augmented the contraction of the trachealis that was due to release of endogenous ACh, i.e., EFS-indu...
In vitro allergen-induced degranulation of pulmonary mast cells from horses with recurrent airway obstruction (heaves). To determine the capacity of pulmonary mast cells (PMC) to degranulate in response to various potential allergens and other secretagogues in horses with recurrent airway obstruction (heaves) and clinically normal horses before and after exposure to moldy hay. Methods: 5 horses with heaves and 5 clinically normal horses. Methods: Heaves was characterized as an increased clinical respiratory score and maximum change in transpulmonary pressure of > 20 cm H2O after exposure. Bronchoalveolar lavage was performed during each period. Washed and resuspended cells were exposed for 20 minutes at 37 C wi...
Mediators of anaphylaxis but not activated neutrophils augment cholinergic responses of equine small airways. Neutrophilic inflammation in small airways (SA) and bronchospasm mediated via muscarinic receptors are features of chronic obstructive pulmonary disease in horses (COPD). Histamine, serotonin, and leukotrienes (LTs) are reported to be involved in the exacerbation of COPD, and currently, histamine has been shown to increase tension response to electrical field simulation (EFS) in equine SA. We tested the effects of these mediators and the effects of activated neutrophils on the cholinergic responses in SA. Histamine, serotonin, and LTD4 had a synergistic effect on EFS responses and only an addi...
Comparison of forced oscillation with the conventional method for histamine bronchoprovocation testing in horses. To compare response of horses to histamine bronchoprovocation (HBP), using total respiratory resistance (Rrs) measured by forced oscillatory mechanics (FOM) with dynamic compliance (Cdyn) and pulmonary resistance (RL) measured by the esophageal balloon method. Methods: 10 horses with various degrees of airway reactivity. Methods: The 2 methods for measuring airway responses to HBP were performed on separate days. Endpoints compared were increase of 150 or 200% of baseline Rrs (PC150Rrs, PC200Rrs) and to 150% of baseline RL (PC150RL) or decrease to 65% of baseline Cdyn (PC65Cdyn). Frequency dep...
Responses of guinea-pig lung parenchymal strips to tracheobronchial lavage fluid from horses affected with summer pasture-associated obstructive pulmonary disease. The response of parenchymal strips from guinea-pig lungs to tracheobronchial lavage fluid (TBLF) collected from 8 normal horses and from 8 affected with summer pasture-associated obstructive pulmonary disease (SPAOPD) was determined. TBLF was collected during the summer (July) and winter (February) seasons. The serum/TBLF urea nitrogen ratio was used to standardize the mediator concentration in the TBLF. Four strips were used from each guinea-pig. The first strip did not receive any antagonist and served as the control. The second, third and fourth strips received antagonists of PGE2, LTD4 and...
Biphasic responses of equine colonic vessel rings to vasoactive inflammatory mediators. 1. The role of endothelium in modulating equine colonic vessel responses to histamine (HST), 5-hydroxytryptamine (5-HT), bradykinin (BK) and acetylcholine (ACh) was evaluated in vitro. 2. Segments of mesenteric arteries and veins were collected from the left ventral colon of six adult horses destined for euthanasia for reasons unrelated to cardiovascular or gastrointestinal systems. Vessels were gently cleansed and cut into 4 mm wide rings. 3. Three vessel conditions namely endothelium intact, endothelium removed and N omega-nitro-L-arginine methyl ester (L-NAME)-treated were used for both art...
Histamine-induced gastric acid secretion in horses. To determine gastric secretory responses in horses treated with histamine and to determine the dose of histamine needed to elicit maximal gastric secretion. Methods: 6 adult horses with an indwelling gastric cannula. Methods: Gastric contents were collected in 15-minute periods, and volume, pH, hydrogen ion concentration, hydrogen ion output, sodium concentration, and sodium output were determined. Values were determined without any treatment (baseline), after administration of pyrilamine maleate (1 mg/kg of body weight, i.v., given during a 15-minute period), and during 1-hour infusions of hi...
Inhibition of antigen-induced cutaneous responses of ponies with insect hypersensitivity by the histamine-1 receptor antagonist chlorpheniramine. A whole-body extract of Culicoides impunctatus induced a biphasic increase in oedema formation in ponies with insect hypersensitivity, with maxima after one and eight hours. The Culicoides antigen did not induce similar responses in ponies with no previous history of the disease. In insect-hypersensitive ponies the local administration of chlorpheniramine (12 micrograms) completely inhibited oedema formation in response to histamine (0.04 microgram) and to Culicoides antigen (0.5 microgram) at one hour, and the response to Culicoides antigen at eight hours was inhibited by 63 per cent. Chlorph...
Histamine-induced adherence and migration of equine eosinophils. To examine effects of histamine on equine eosinophil adherence in vitro and to determine the histamine receptor subtype(s) and cell surface adhesion molecules that mediate this response. In addition, to determine the receptor subtypes involved in histamine-induced eosinophil migration. Methods: 8 healthy ponies. Methods: Effects of histamine on equine eosinophil adherence to serum- or fibronectin-coated plastic, and migration in a microchemotaxis assay were examined. In some experiments, eosinophils were pretreated with histamine receptor antagonists or monoclonal antibodies raised against cel...
Pulmonary eosinophilia associated with increased airway responsiveness in young racing horses. Horses are known to acquire small airway disease (SAD), an allergen-induced naturally occurring syndrome of reversible obstructive lung disease accompanied by airway hyperresponsiveness and increased inflammatory cell numbers on bronchoalveolar lavage (BAL). This disorder has received scant attention in young racehorses. The purpose of the present report was to examine the effect of BAL eosinophilia in young racehorses on clinical examination, BAL, hematology, airway responsiveness, and on pulmonary function at rest and after a standardized exercise challenge. Five (3 males, 2 females; age 2.6...
Evaluation of an in vitro degranulation challenge procedure for equine pulmonary mast cells. Pulmonary mast cells (PMC) are important components of the inflammatory process in equine allergic lung diseases such as heaves. Very little, however, is known of the degranulation kinetics of these cells and thus, their pathophysiologic role remains largely speculative. The purpose of this study was to develop a repeatable protocol for in vitro equine PMC degranulation. Five mature horses (sex: 2 M, 3 F; age: 8.8 +/- 6.5 y), historically free of pulmonary disease and normal on clinical respiratory examination, arterial blood gas analysis, pulmonary mechanics testing and histamine inhalation c...
Association between bronchoalveolar lavage cytologic features and airway reactivity in horses with a history of exercise intolerance. To correlate indices of airway reactivity to bronchoalveolar lavage (BAL) fluid cytologic features in horses with a recent decline in exercise tolerance. Methods: 20 actively working horses from 2 to 24 years old. Methods: Bronchoalveolar lavage fluid samples were obtained and analyzed. Forced oscillatory mechanics (1-7 Hz) technique was used for measurements of total respiratory system resistance (RRS), compliance (CRS), and resonant frequency (fres). Changes in RRS (1 Hz) during histamine challenge were used to generate histamine dose-response curves, from which the provocative concentration...
Differential superoxide anion generation by equine eosinophils and neutrophils. Equine eosinophils and neutrophils are believed to play an important part in the protection of horses against parasitic and bacterial invasion. Eosinophils may also play a key role in the pathogenesis of equine inflammatory conditions such as the allergic skin disease, insect hypersensitivity. The factors which stimulate the respiratory burst of equine eosinophils and neutrophils are poorly understood. The first aim of the present study was to determine the effects of the phorbol ester, phorbol myristate acetate (PMA), which is believed to activate intracellular protein kinase C, and opsonised...
In vitro responses of equine small airways and lung parenchyma. In vitro responses of equine small peripheral airways (SA) and lung parenchyma (LP) were studied. We examined their contractile and relaxant responses and investigated effects of histamine, and endogenous prostanoids as these mediators may play a role in development or recurrent airway obstruction in horses (heaves). SA and LP electrical field stimulation (EFS) induced nearly maximal and partial frequency-dependent contractions, respectively. These contractions were virtually abolished in SA but only partially inhibited in LP by atropine (ATR) and tetrodotoxin (TTX). Methacholine (MCh) contrac...
Role of endothelium and nitric oxide in the response of equine colonic arterial rings to vasoconstrictor agents. To determine the in vitro contractile responses of equine colonic arteries to angiotensin II, histamine, serotonin, norepinephrine, prostaglandin F2 alpha, vasopressin, and a thromboxane-B2-analogue. Methods: The tension generated in colonic arterial rings placed in organ baths with oxygenated Tyrode's solution at 37 degrees C after exposure to the previously mentioned chemical agents was measured using force-transducers interfaced with a polygraph. Methods: Large colon arterial rings collected from eight horses. Methods: The rings were allowed to equilibrate for 45 minutes after applying 2 g ...
High-performance liquid chromatographic determination of imidazole dipeptides, histidine, 1-methylhistidine and 3-methylhistidine in equine and camel muscle and individual muscle fibres. The combined solid-phase extraction (Isolute PRS columns) and reversed-phase gradient HPLC method presented provides a sensitive, reproducible and selective quantification of carnosine, balenine, homocarnosine, histidine, 1-methylhistidine and 3-methylhistidine in equine and camel muscle and individual muscle fibres. Recoveries were 91-115%. Lower limits of detection were 0.005-0.010 mmol kg-1 dry muscle. The compounds were isolated from other physiological amino acids and small peptides and resolved within a single chromatographic run of 55 min. Concentrations of these compounds in equine myo...
Effects of intermittent feed deprivation, intermittent feed deprivation with ranitidine administration, and stall confinement with ad libitum access to hay on gastric ulceration in horses. To determine the effect of decreasing gastric acidity in a feed-deprivation protocol on induction of gastric ulcers, and to determine whether stall confinement may be a factor contributing to gastric ulceration in horses. Methods: 8 adult horses, 4 geldings and 4 mares, 3 to 8 years old, and 7 adult horses, 5 geldings and 2 mares, 4 to 11 years old. Methods: Gastric ulceration was induced in horses by alternating 24-hour periods of feed deprivation and ad libitum access to hay, for a total of 96 hours' feed deprivation. This protocol was repeated with the horses receiving the histamine type-2 ...
The effects of three models of airway disease on tidal breathing flow-volume loops of thoroughbred horses. The effects of histamine and methacholine aerosols and of a fixed inspiratory resistance on tidal breathing flow-volume loops (TBFVL) were investigated using 18 unsedated, standing, healthy thoroughbred horses. The data were first analysed using traditional flow-volume loop indices and then reduced using standardized factor scoring coefficients obtained in a previous study in this laboratory using similar experimental techniques. On the basis of resting TBFVL analysis, the degree of pulmonary dysfunction caused by inhalation of histamine and methacholine aerosols with concentrations of 10 and ...