Histamine Dose-response Curve Research Articles

ANTIHISTAMINIC ACTIVITY MODELS

Histamine is referred to as common allergic reactions and symptoms. Most of them are compared to histamine intolerance. Some common responses involved with this intolerance may vary but include headaches or migraines, nasal congestion or sinus problems, fatigue, hives, digestive problems, irregular menstrual cycle, nausea, and vomiting. Histamine is derived from a natural amino acid, S-histidine, through the histidine decarboxylase/ aromatic decarboxylase catalysis. Histamine is the compound that the mast cell generates for the immune response. Histamine promotes gastrointestinal secretion and induces capillary dilation, bronchial smooth muscle constriction, and reduced blood pressure. Antihistamines are medicinal products to treat allergic rhinitis and allergies. This includes the in vitro animal model and in-vivo tissue preparation antihistaminic activity. Animal models are significant instruments for understanding the pathological process of human illnesses in experimental medical science. Medicines associated with antihistamine include antiallergy, antivertigo, antimigraine, sedatives, antiemetic, etc. Elderly people are much more likely than youthful people to develop sleepiness from the use of antihistamines. The most common drugs used are cetirizine, levocetirizine, chlorpheniramine, diphenhydramine, loratadine, cimetidine, and fexofenadine. Animal models include histamine-induced bronchoconstriction, passive paw anaphylaxis, milk-induced leukocytosis and eosinophilia, clonidine, and haloperidol-induced catalepsy. While tissue models include isolated goat, and guinea-pig trachea chain preparation, as well as an isolated guinea pig, rat, mice ileum tissue preparation, and the dose-response curve of histamine, were plotted. The focus of the study had been on herbal plants and medicinal products, as they can effectively boost a variety of circumstances without significant adverse side effects. We can assess antihistaminic activity by using plant extracts or any synthetic drug.

Pharmacological screening of some newly synthesized triazoles for H1 receptor antagonist activity

The present work deals with the pharmacological screening of some newly synthesized triazoles. A series of 1,2,4-triazoles have been synthesized using benzoic acid or 4-chloro benzoic acid as the starting materials. The synthesized compounds were characterized by physical and spectral analysis viz., Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance, 13C nuclear magnetic resonance, Gas Chromatography-Mass Spectrometry and elemental analysis Carbon, Hydrogen and Nitrogen analysis in order to confirm the structure. Acute toxicity studies were carried out in accordance with the Organization for Economic Co-operation and Development guideline 425. The compounds were not found to be lethal even at a dose level of 2000 mg/kg. Pharmacological evaluation was done following three intact animal experiments and one experiment on the isolated tissue. Results of the study indicated that the compound 7bi and 7bj protected up to 60% against histamine-induced dyspnea. Antihistaminic nature of the test compounds 7bi, 7bj, 7ai, and 7bk were also confirmed by the loss of catalepsy after the administration of clonidine (1%, s.c.). During experiments on isolated tissue, suppression of dose-response curve of histamine indicates a noteworthy denouement in favor of the said effect.

Calcium influx and release mechanism(s) in histamine-induced myometrial contraction in buffaloes

The present study was undertaken to characterize the presence of histamine H1R using molecular biology tools and unravel the influx and release mechanism(s) involved in calcium signalling cascades in histamine-induced myometrial contraction in buffaloes. The presence of H1R mRNA transcript and immunoreactive membrane protein in buffalo myometrium was confirmed by RT-PCR and Western blot analysis. Further, histamine produced concentration-dependent (1nM–10μM) contraction in buffalo myometrium with a potency of 7.13±0.11. When myometrial strips were pre-incubated either with Ca2+ free solution or with nifedipine, a L-type Ca2+ channel blocker, dose response curve (DRC) of histamine was significantly (P<0.05) shifted towards right with decline in maximal contraction (Emax). Reduction in Emax of histamine in the presence of nifedipine (55.75±3.10%) was significantly (P<0.001) greater than that in the presence of ruthenium red (93.61±3.43%), a blocker of IP3-gated and RyR-sensitive Ca2+ channels. Moreover, histamine produced only 26.87±1.99% of the maximum contraction in the presence of both nifedipine and CPA (blocker of sarco-endoplasmic reticulum Ca2+-ATPase). Interestingly, following concurrent exposure to U-73122 (a PL-C inhibitor) and nifedipine, the DRC of histamine was significantly (P<0.05) shifted towards left with increase in maximal contraction (126.30±3.36%). Our findings in buffalo uterus thus suggest that influx of extracellular calcium plays a major role in histamine-induced myometrial contraction, while release of intracellular calcium through calcium-release channels of sarcoplasmic reticulum has a minor role. A possible involvement of non-selective cation channels in histamine-induced myometrial contraction cannot be ruled out, and therefore requires further investigations.

Evaluation of antihistaminic activity of Piper betel leaf in guinea pig

Piper betel Linn. leaves were evaluated for its antihistaminic activity, commonly known as Pan, Vidyache Pan or Tamboli. P. betel has a long history of use in India being applied in multiple therapeutic activities like antibacterial, treating eczema, lymphangitis, asthma, treating rheumatism. So selected, the plant P. betel is effective in histaminic activity related diseases, but antihistaminic activity of P. betel is still not scientifically investigated. In the present study, the pharmacological evaluation of ethanolic extract and essential oil extract of leaves of P. betel Linn. has been done for their antihistaminic activity on guinea pig. In isolated guinea pig tracheal chain preparation, there was a right side shift of dose response curve (DRC) of histamine. Chlorpheniramine maleate was used as a standard drug. Moreover extracts of P. beteldisturbed histamine aerosol induce bronchoconstriction in whole guinea pig, where essential oil was more effective comparatively to ethanolic extract. Thus from the results obtained in the present investigation, it can be concluded that ethanolic extract and essential oil of P. betel Linn possess antihistaminic activity. Key words: Piper betel leaf, H1-antagonist, guinea pig.

OC-044 Antisecretory effects ofLactobacillus rhamnosus-conditioned medium prompts the notion of lactobacilli species as probiotics of the upper gastrointestinal tract

<h3>Introduction</h3> The <i>Lactobacillus</i> genus has evolved over thousands of years together with humans through its<i>9</i> natural role in milk and dairy products. However, recent attention of the gastro-intestinal (GI) probiotic effect has concentrated on intestinal function rather than on gastric function. The antibacterial properties of Lactobacilli in controlling gastric colonisation by Helicobacter pylori are well recognised1 but little is known about the effects of these acidophilic bacteria on gastric physiology. Recent evidence that <i>Lactobacillus</i> species have been found in the stomachs of animals and humans suggests that they may also modulate acid secretion. <h3>Methods</h3> <i>Lactobacillus rhamnosus</i> (LRH) was chosen because its probiotic properties are well documented, it has been isolated from healthy human gastrointestinal mucosa and its genome was completely sequenced recently.2 LRH was grown in liquid medium for 48 h and conditioned medium (CM) was obtained by centrifugation and micro filtration. The effect of LRH CM was studied using a mouse gastric gland preparation with ¹⁴C-aminopirine accumulation as the indirect method for measurement of acid secretion. Culture medium alone was used as control. <h3>Results</h3> LRH CM inhibited 0.1 M histamine stimulated acid secretion by 100% at dilution of 1/40 while the control medium showed only marginal non-significant effect at this dilution (n=4). The IC₅₀ (50% of acid inhibition) was ∼1/120 dilution and at this concentration LRH CM did not cause a shift in the histamine dose response curves indicating that histamine H₂-receptor antagonism is not involved although the efficacy of the response was inhibited by 47.7% (n=5). Furthermore, LRH CM inhibited 0.01 M carbachol and 1.0 M cAMP stimulated acid secretion by 100% and 95%, respectively (n=5), the latter also being suggestive of a post receptor effect. This raises the possibility that bioactive bacterial products secreted into the culture medium act directly on the proton pump or other aspects of parietal cell physiology/metabolism. <h3>Conclusion</h3> This is the first report showing that <i>Lactobacillus</i> or its products exert a gastric antisecretory effect. This prompts the notion that colonisation of the gastric mucosa by these acidophilic bacteria or ingestion of their products may modulate acid secretion with the possibility of a beneficial impact on acid related diseases. Future <i>in vivo</i> and clinical studies on the role of <i>Lactobacillus sp</i> on gastric physiology are needed to explore the potential role of these probiotics in the stomach.

The Noncompetitive Antagonism of Histamine H1 Receptors Expressed in Chinese Hamster Ovary Cells by Olopatadine Hydrochloride: Its Potency and Molecular Mechanism

Calcium responses to various concentrations of histamine were monitored in Chinese hamster ovary cells stably expressing the human histamine H₁ receptor. The effects of various histamine H₁ receptor antagonists on the dose-response curve for histamine were evaluated. Olopatadine hydrochloride (olopatadine) inhibited the histamine-induced maximum response (pD₂’: 7.5) but had insignificant effects on histamine EC₅₀ values. This noncompetitive property exhibited by olopatadine, which was also observed in human umbilical vein endothelial cells, was the most striking among the antihistamines tested in this study. The geometrical isomer of olopatadine (E-isomer), which had a similar binding affinity to the histamine H₁ receptor as olopatadine, showed a mixed antagonistic profile (competitive and noncompetitive). These results indicate that the geometry around the double bond in the dimethylaminopropylidene group is critical for the potent noncompetitive property of olopatadine. Furthermore, binding mode analyses suggest that the protonated amine group in the dimethylaminopropylidene moiety of olopatadine forms an ionic bond with Glu 181 that is present in the second extracellular loop of the histamine H₁ receptor, whereas the amine group of the E-isomer does not. The second extracellular loop in aminergic G-protein-coupled receptors contributes to ligand binding and therefore the noncompetitive property of olopatadine may be explained by the interaction with Glu 181.

Prostaglandin E 2 sensitizes primary sensory neurons to histamine

1. Histamine is able to elicit a dose-dependent rise in intracellular Ca 2+ in a proportion of rat dorsal root ganglion (DRG) neurons. Pre-treatment with prostaglandin (PGE 2) prior to a histamine challenge increases the proportion of neurons responding to low concentrations of histamine (10–100 μM). 2. The dose-response curve for histamine is shifted to the left by approximately two orders of magnitude following 45 s pre-treatment with 1 μM PGE 2. 3. The phospholipase C (PLC) inhibitor 1-[6-[[17-β-3-methoxyestra-1,3,5(10)-trien-17-yl-]amino]hexyl]-1H-pyrrole-2,5-dione (U73122) completely blocked the response to histamine (100 μM) in non-sensitized cells but, after PGE 2 pre-treatment, this inhibitor reduced the proportion of cells responding to histamine by approximately a half. Removal of extracellular Ca 2+ blocked the response in the remaining cells so that, in this subgroup of histamine sensitive neurons, the PGE 2 sensitization is the result of activation of a Ca influx pathway. 4. The sensitization is dependent on an increase in cAMP as it is mimicked by pre-treatment with 8-bromo cyclic AMP (8-Br-cAMP) and by forskolin stimulation of adenylyl cyclase activity. It is inhibited by THFA (tetrahydrofuryl adenine) an inhibitor of adenylyl cyclase. The sensitization is also blocked by pre-treatment with N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H89), an inhibitor of protein kinase A. We conclude that the PGE 2 sensitization of DRG neurons to histamine is dependent on activation of the cAMP-protein kinase A cascade.

A Supraclinical Dose of Tramadol Stereoselectively Attenuates Endothelium-Dependent Relaxation in Isolated Rat Aorta

Tramadol, a combination of R(-) and S(+) enantiomers, inhibits both the acetylcholine-mediated response of muscarinic receptors and the muscarine-induced accumulation of cyclic guanosine monophosphate. Our goals in this in vitro study were to investigate the effects of tramadol on endothelium-dependent relaxation induced by acetylcholine, to determine whether this effect of tramadol is stereoselective, and to elucidate the associated cellular mechanism in rat aorta. In endothelium-intact rings precontracted with phenylephrine with or without naloxone, dose-response curves for acetylcholine, histamine, and calcium ionophore A23187 were generated in the presence and absence of tramadol (racemic, R(-) and S(+)). Sodium nitroprusside dose-response curves were generated in the presence and absence of racemic tramadol. Racemic tramadol (5 x 10(-5) 10(-4) M) attenuated acetylcholine-induced relaxation in the rings with or without naloxone. R(-) tramadol, 5 x 10(-5) M, attenuated acetylcholine-induced relaxation, whereas S(+) tramadol, 5 x 10(-5) M, did not. Racemic tramadol (10(-4) M) had no effect on dose-response curves for calcium ionophore A23187 or sodium nitroprusside. Taken together, these results indicate that tramadol, at a supraclinical dose (5 x 10(-5) M), stereoselectively attenuates endothelium-dependent relaxation via an inhibitory effect at levels proximal to nitric oxide synthase activation on a pathway involving nonspecific endothelial receptor activation.

Ascorbate enhancement of H1 histamine receptor sensitivity coincides with ascorbate oxidation inhibition by histamine receptors

Ascorbate has previously been shown to enhance both alpha(1)- and beta(2)-adrenergic activity. This activity is mediated by ascorbate binding to the extracellular domain of the adrenergic receptor, which also decreases the oxidation rate of ascorbate. H1 histamine receptors have extracellular agonist or ascorbate binding sites with strong similarities to alpha(1-) and beta(2)-adrenergic receptors. Physiological concentrations of ascorbate (50 microM) significantly enhanced histamine contractions of rabbit aorta on the lower half of the histamine dose-response curve, increasing contractions of 0.1, 0.2, and 0.3 microM histamine by two- to threefold. Increases in ascorbate concentration significantly enhanced 0.2 microM histamine (5-500 microM ascorbate) and 0.3 microM histamine (15-500 microM ascorbate) in a dose-dependent manner. Histamine does not measurably oxidize over 20 h in oxygenated PSS at 37 degrees C. Thus the ascorbate enhancement is independent of ascorbate's antioxidant effects. Ascorbate in solution oxidizes rapidly. Transfected histamine receptor membrane suspension with protein concentration at >3.1 microg/ml (56 nM maximum histamine receptor) decreases the oxidation rate of 392 microM ascorbate, and virtually no ascorbate oxidation occurs at >0.0004 mol histamine receptor/mol ascorbate. Histamine receptor membrane had an initial ascorbate oxidation inhibition rate of 0.094 min.microg protein(-1).ml(-1), compared with rates for transfected ANG II membrane (0.055 min.microg protein(-1).ml(-1)), untransfected membrane (0.052 min.microg protein(-1).ml(-1)), creatine kinase (0.0082 min.microg protein(-1).ml(-1)), keyhole limpet hemocyanin (0.00092 min.microg protein(-1).ml(-1)), and osmotically lysed aortic rings (0.00057 min.microg wet weight(-1).ml(-1)). Ascorbate enhancement of seven-transmembrane-spanning membrane receptor activity occurs in both adrenergic and histaminergic receptors. These receptors may play a significant role in maintaining extracellular ascorbate in a reduced state.

Disruption of microtubular network attenuates histamine-induced dilation in rat mesenteric vessels.

Cytoplasmic microtubules are important in many cellular homeostatic processes in the cell. They regulate cell shape and movement as well as serving as a network by which vesicles and membrane-bound organelles can travel. Lately, there have been many studies demonstrating that microtubules are involved in regulation of intracellular signaling and, therefore, affect vascular reactivity. In this study, we tested the hypothesis that microtubule disruption attenuates agonist-induced endothelium-dependent vasodilation. Isolated mesenteric arterial bed from normotensive rats was preconstricted with phenylephrine, and dose-response curves for histamine, acetylcholine (ACh), sodium nitroprusside (SNP), and pinacidil were performed before and after incubation with nocodazole or colchicine. Treatment of the vascular beds with nocodazole or colchicine significantly attenuated histamine relaxation but did not change the ACh-, SNP-, or pinacidil-induced vasorelaxation. Nocodazole did not cause an additional attenuation of the histamine-mediated dilation in mesenteric vessels in the presence of Nomega-nitro-L-arginine methyl ester, high extracellular K+, or K+ channel blockers. These data suggest that disruption of microtubules affects an essential endothelial component of histamine-mediated vasodilation in the mesenteric arterial bed. The mechanism(s) involved in this effect might be related to an impairment of endothelial NO synthesis, which might not be as important for the ACh as for the histamine vasodilator response in rat mesenteric vessels. These results demonstrate the importance of the microtubular system for endothelium-dependent NO-mediated smooth muscle relaxation.

Histaminolytic Agents in a Crude Venom Extract from the Sea Anemone Bunodosoma cavernata

A crude extract from the sea anemone Bunodosoma cavernata antoganized histamine-induced contractions of the ileum in a dose-related fashion and shifted the histamine dose-response curve to the right. Doubling the dose of histamine failed to surmount the antagonism. Similar results were obtained when ACh was used as the agonist. While the extract appeared to have no effect on 5-HT-induced contractions, it potentiated KCl-induced contraction of the ileum. Therefore, we suggest that the crude extract from B. cavernata contains histaminolytic agent(s) which inhibited histamine-induced contractions of the ileum. The action of the extract was probably non-selective since ACh-induced contractions were similarly inhibited. Furthermore, the histamine antagonism was probably of a non-competitive type since it was not surmounted by doubling the concentration of histamine. Finally, that the extract failed to inhibit 5-HT- and KCl-induced contractions appear to exclude a general toxic or local anaesthetic action on the tissue, and a receptor action is favoured.

Regulation of cerebral microvascular permeability by histamine in the anaesthetized rat.

1. The permeability response of slightly leaky pial venular capillaries to histamine was investigated using the single microvessel occlusion technique. 2. Histamine dose-response curves showed that concentrations between 5 nm and 5 microM increased permeability, while concentrations from 50 microM to 5 mM reduced it. 3. The H2 receptor antagonist cimetidine (2 microM) blocked the effects of lower concentrations of histamine, while the H1 receptor antagonist mepyramine (3 nM) blocked those of higher concentrations of histamine. 4. The effects of lower doses of histamine were mimicked by the H2 receptor agonist dimaprit, and the effects of higher doses of histamine were mimicked by the H1 receptor agonist alpha-2-(2-aminoethyl)pyridine (AEP). 5. Low concentrations of histamine, which normally increase the permeability of Lucifer Yellow (PLY), reduced it when co-applied with the phosphodiesterase 4 (PDE4) inhibitor rolipram. Rolipram also potentiated the response to AEP, but had no effect on that to dimaprit. 6. The effects of dimaprit were blocked by reducing extracellular Ca2+ from 2.5 mM to nominally Ca2+ free, or by applying the calcium entry blocker SKF 96365.

Association between bronchoalveolar lavage cytologic features and airway reactivity in horses with a history of exercise intolerance

SUMMARY Objective To correlate indices of airway reactivity to bronchoalveolar lavage (BAL) fluid cytologic features in horses with a recent decline in exercise tolerance. Animals 20 actively working horses from 2 to 24 years old. Procedure 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 concentrations that evoked a 75 or 100% increase in baseline RRS (PCRRS75 and PCRRS100, respectively) were determined. Age, sex, baseline lung mechanics, and BAL cytologic findings were correlated with PCRRS75 and PCRRS100. Results No horse of the study had clinical signs or history of obstructive pulmonary disease or increased percentage (&gt; 7%) of neutrophils in bronchoalveolar lavage fluid samples. Mean (± SEM) RRS, CRS, and fres were 0.67 ± 0.06 cm of H2O/L/s, 0.52 ± 0.04 L/cm H2O, and 2.46 ± 0.02 Hz, respectively. There was no correlation between age or sex, and RRS, CRS, fres, PCRRS75, or PCRRS100. There was a significant correlation (rs = −0.78, P &lt; 0.001) between percentage of BAL fluid mast cells and PCRRS75 or PCRRS100, but correlation with other cell types and indices of airway reactivity were not observed. Conclusion The strong association between mast cell percentage in BAL fluid and airway reactivity in this group suggests that mast cell products may contribute to bronchospasm, airway wall thickening, and/or loss of elastic recoil, which underlie airway hyperreactivity. Alternatively, mast cells may contribute to nonspecific airway reactivity in horses through unknown mechanisms. (Am J Vet Res 1998;59:176–181)

Inhibition of bronchospasm and ozone-induced airway hyperresponsiveness in the guinea-pig by CDP840, a novel phosphodiesterase type 4 inhibitor.

1. The activity of CDP840, a novel, potent and selective cyclic nucleotide phosphodiesterase type 4 (PDE 4) inhibitor, was evaluated in guinea-pig models (in vitro and in vivo) of bronchospasm, ozone-induced airway hyperresponsiveness (AHR) and non-cholinergic bronchoconstriction. Comparisons were made with (i) other PDE 4 inhibitors: CT1731 (S-enantiomer of CDP840), rolipram, RP73401 and (ii) the clinically used agents salbutamol and theophylline. 2. CDP840 relaxed isolated trachea, under basal tone (EC50 4.5 +/- 1.1 microM) being 17 fold less potent than rolipram (EC50 0.26 +/- 0.13 microM) but attaining the same Emax (83 +/- 6% of the response to 300 microM papaverine). 3. CDP840 relaxed tracheae pre-contracted with carbachol (IC25 39 +/- 9 microM) and histamine (IC25 4 +/- 1 microM) producing monophasic curves. Stereoselectivity was not observed with CT1731 against either carbachol (IC25 33 +/- 11 microM) or histamine (IC25 17 +/- 10 microM). Aminophylline was 1.6 fold (carbachol) and 11 fold (histamine) less potent than CDP840. Rolipram and RP73401 produced tri-phasic relaxation curves but were of similar potency (at the IC25 level) to CDP840 against carbachol (rolipram 18 +/- 5 microM, RP73401 39 +/- 1 microM) whereas against histamine they were approximately 20 fold more potent (rolipram 0.2 +/- 0.1 microM, RP73401 0.2 +/- 0.1 microM). In producing > 30% (carbachol) and > 60% (histamine) relaxation these inhibitors had similar potency and were poor compared to salbutamol. 4. Pre-incubation with CDP840 (10 microM) did not antagonize histamine-induced contraction of isolated trachea; however, it did cause a slight potentiation of the subsequent relaxation to salbutamol (IC50 23 +/- 1 to 15 +/- 2 nM). 5. Pretreatment (1 h) with either CDP840 (1 mg kg-1, i.p. or 3 mg kg-1, i.v.) or rolipram (1 mg kg-1, i.p.) did not bronchodilate or antagonize bronchospasm due to inhaled histamine in anaesthetized, ventilated guinea-pigs. Salbutamol (1 mg kg-1, i.p.) did not bronchodilate but caused a parallel 7 fold rightward shift in the histamine dose-response curve. 6. Stimulation of the vagus nerve in the presence of atropine resulted in a frequency-related bronchoconstriction. CDP840 and rolipram (i.v.) inhibited the response being approximately equipotent (EC50 approximately 10 micrograms kg-1). Neither drug inhibited bronchospasm to inhaled substance P. 7. CDP840 (1-10 micrograms kg-1 i.p.) dose relatedly inhibited ozone-induced bronchoconstriction. CT1731 (1 mg kg-1), rolipram (1 mg kg-1), RP73401 (10 micrograms kg-1) and aminophylline (10 mg kg-1) had no effect. Ozone-induced AHR to inhaled histamine was inhibited by CDP840 in a dose-related manner, 10 micrograms kg-1 abolishing the AHR. This effect was stereoselective as CT1731 was approximately 30 fold less potent than CDP840. Rolipram was approximately 100 fold less potent and RP73401 and aminophylline had no effect. CDP840 was orally active being approximately 10 fold less potent compared to i.p. administration. 8. CDP840 is a poor spasmolytic and anti-spasmogenic agent in response to exogenous mediators; however, it potently inhibits vagally mediated non-cholinergic bronchoconstriction and ozone-induced AHR to histamine. It is possible that regulation of cyclic AMP by PDE 4 contributes to neuronal sensitivity in the airways. Furthermore, CDP840 may suppress AHR without being an overt bronchodilator. Such a profile of activity may have therapeutic benefit in airways diseases such as asthma.

Hypotensive effect of 13-hydroxylinoleic acid in the rat: mediation via the release of a CGRP-like mediator from capsaicin-sensitive nerves.

1. The effect of 13-hydroxylinoleic acid (13-HODE) on changes in blood pressure in the rat was measured. 2. 13-HODE (0.1 - 100 micrograms kg-1) had no direct effect on blood pressure in the rat and had no effect on histamine (0.1 - 1000 micrograms kg-1)-induced changes in blood pressure. In contrast, it was found that 13-HODE itself induced a decrease in diastolic arterial blood pressure when it was injected intravenously after either a single dose of histamine (10, 100 or 1000 micrograms kg-1) or after a dose-response curve of histamine (0.1 - 1000 micrograms kg-1). 3. This hypotensive effect of 13-HODE was not observed after administration of the endothelium-dependent vasodilator, acetylcholine (0.1 - 10 micrograms kg-1), the endothelium-independent vasodilator, sodium nitroprusside (0.1 - 100 micrograms kg-1) or the inflammatory mediator, leukotriene B4 (0.1 - 300 micrograms kg-1). However, prior injection of bradykinin (0.1 - 100 micrograms kg-1) allowed a dose-dependent hypotensive effect of 13-HODE to be revealed. 4. The hypotensive effect of 13-HODE after histamine and bradykinin could be inhibited by neonatal capsaicin treatment of the rats (50 mg kg-1, s.c. on day 1 and 2 after birth). 5. Ruthenium red (120 micrograms kg-1 min-1), an inhibitor of excitatory effects on sensory nerves, and the CGRP antagonist, CGRP8-37 (1-3 micrograms kg-1 min-1) also inhibited the hypotensive effect of 13-HODE. 6. It is concluded that the hypotensive effect of 13-HODE in the rat after histamine and bradykinin is due to the release of a CGRP-like substance from sensory nerves. These results highlight the possibility that endogenous 13-HODE could be involved in the neurogenic regulation of blood pressure.

Effect of ozone exposure on antigen-induced airway hyperresponsiveness in guinea pigs.

Airway hyperresponsiveness can be induced by several stimuli including antigen and ozone, both of which may be present in the air of polluted cities. Though the effect of ozone on the bronchoconstrictor response to antigen has been well described, the combined effect of these stimuli on airway hyperresponsiveness has not yet been studied. Sensitized guinea pigs with or without ozone exposure for 1 h at 3 ppm, 18 h prior to study, were challenged with a dose-response curve to histamine (0.01-1.8 micrograms/kg, iv) followed by an antigen challenge (ovalbumin, 50 micrograms/kg, iv), and then by a second histamine dose-response curve 1 h later. Airway responses were measured as the increase in pulmonary insufflation pressure. In sensitized guinea pigs, the histamine ED50 significantly decreased after antigen challenge, demonstrating the development of airway hyperresponsiveness. Sensitized guinea pigs exposed to ozone showed airway hyperresponsiveness to histamine when compared with nonexposed animals, and such hyperresponsiveness was further enhanced after antigen challenge. We conclude that in this guinea pig model of acute allergic bronchoconstriction both antigen challenge and ozone induce airway hyperresponsiveness, while ozone exposure does not modify the development of antigen-induced hyperresponsiveness.

Histamine-induced modulation of nociceptive responses

Because previous studies suggest an antinociceptive role for the neuromodulator histamine (HA) in the periaqueductal grey or the nearby dorsal raphe (PAG/DR), a detailed pharmacological investigation of the effects of intracerebral HA on the hot-plate nociceptive test was performed in rats. Intracerebral microinjections of HA (1 μg) into the PAG/DR or into the median raphe evoked a mild, reversible antinociceptive response; injections into lateral or dorsal midbrain evoked either a delayed response or no response, respectively. In the PAG/DR, the HA dose-response curve had an inverted U-shape, showing that HA can induce both antinociceptive (0.3–3 μg) and pro-nociceptive (10–30 μg) responses. Larger doses of HA (e.g., 100 μg) produced irreversible and highly variable antinociceptive responses that were accompanied by behavioral and histopathological changes; such effects, indicative of toxicity, were not observed after 0.3 μg of HA, the peak antinociceptive dose. HA (0.3 μg) antinociception was completely inhibited by intracerebral co-administration of the opiate antagonist naloxone (1 ng), the H 1-receptor antagonist temelastine (20 pg), and the H 2-receptor antagonist tiotidine (1 ng); none of these drugs altered nociceptive scores in the absence of HA. These results show that: (1) HA, a neurotransmitter in the PAG, can evoke antinociception in the absence of other behavioral or toxic effects; and (2) HA antinociception depends on the activation of both opiate and HA receptors in the PAG/DR. Since previous studies have shown that: 1. (1) systemic morphine increases the release of HA in the PAG/DR, 2. (2) systemic morphine analgesia is inhibited by PAG/DR injections of the H 2 antagonist tiotidine, the present results (showing antagonism of HA antinociception by intracerebral tiotidine treatment) strongly support the conclusion that histaminergic mechanisms in the PAG/DR mediate a portion of systemic morphine antinociception.

Mechanisms of augmented vascular responses to histamine in atherosclerotic rabbit common carotid arteries

The vascular responsiveness to histamine, 2-pyridylethylamine and dimaprit was investigated in isolated and perfused atherosclerotic rabbit common carotid arteries enclosed by a hollow silastic collar. The constrictor effects of histamine were significantly enhanced in atherosclerotic arteries, although those of 2-pyridylethylamine were not changed. The dilator effects of histamine and dimaprit, which were completely inhibited after pretreatment with cimetidine, were not influenced by removal of the endothelium but significantly depressed in atherosclerotic arteries. The dose-response curves for histamine in the control group pretreated with cimetidine were shifted to the left and responses reached almost the same level as those of the atherosclerotic group. From these results, it is concluded that histamine-induced vasoconstrictions are enhanced in atherosclerotic arteries, and that the mechanism of the hyperreactivity to histamine might be an attenuation of the vasodilatations mediated via histamine H 2 receptors in vascular smooth muscle.

Secretagogue-induced [14C]aminopyrine uptake in isolated equine parietal cells

Summary Equine oxyntic mucosal cells were obtained by sequential exposure to pronase and collagenase. Acid production by parietal cells was assessed by uptake of [14C]aminopyrine (ap), a weak base that accumulates in intracellular acidic spaces. Incubation for various times revealed a maximal ap uptake at 10 minutes for histamine and carbachol. Similar secretagogue responses were observed for parietal cells from the mucosal cell preparation or after enrichment by elutriation. Histamine and isobutyl-methylxanthine (ibmx) stimulated AP uptake with a dose-dependent response and maximal effective concentration of 100 μM. Carbachol, 1 to 100 μM, and pentagastrin (pg), 1 to 1,000 μM, were ineffective stimulants of ap uptake. The ap uptake values for 100 μM ibmx, 1 μM carbachol, or 100 nM pg were 77 ± 6%, 50 ± 3-2%, and 40 ± 4.5%, respectively, of that observed with maximal stimulation by 100 μM histamine (mean ± sem, n = 4 to 14). Uptake of ap by nonstimulated control cells was 36 ± 3.6% of maximal histamine stimulation. The ap accumulations during control conditions and after stimulation with 100 μM histamine and IBMX, 1 μM carbachol, or 100 nM pg were 1.18 ± 0.39, 2.81 ± 0.85, 1.93 ± 0.48, 1.44 ± 0.36, and 1.23 ± 0.33 pmol of ap/105 parietal cells, respectively. Individual histamine dose-response curves were shifted to the right by increasing ranitidine and cimetidine concentrations (0.1 to 50 μM). These results indicate that isolated equine parietal cells are maximally stimulated by histamine and minimally stimulated by carbachol and pg.

Bronchial provocation tests in small animals: a quantified and automated procedure.

Bronchial provocation tests using aerosols in laboratory animals are difficult to standardize and quantify, because the amount of drug actually reaching the airways is unknown. To improve the quantification of aerosolized inhaled stimuli, we designed an apparatus that allows, in anesthetized intubated ventilated animals, control of temperature and hygrometry of inspired air, computerized measurement of pulmonary resistance, and fully automated delivery of a known amount of aerosolized drug directly into the trachea. Calibration of the aerosol delivery involved direct measurement of liquid delivered at the tip of the tracheal cannula. Despite all our efforts at standardization and full automation of all steps, reproducibility of aerosol delivery was poor, with stroke-by-stroke differences of 26 or 42%, according to whether an air-jet or an ultrasonic nebulizer was used. Histamine dose-response curves performed in 15 guinea pigs with this device confirmed marked differences among animals and also disclosed large intraindividual changes in bronchial responsiveness.