Selective inhibitors for phosphodiesterase 3 and 4 in antigen-induced increase of cough reflex sensitivity in guinea pigs

Effects of the selective phosphodiesterase 3 (PDE3) inhibitor olprinone and the selective PDE4 inhibitor SB207499 were investigated on antigen-induced increase of cough reflex sensitivity and normal cough response to capsaicin in guinea pigs. Number of coughs elicited by inhalation of capsaicin (10(-8), 10(-6) and 10(-4)M) was counted 24h after an antigen challenge in actively sensitized guinea pigs, and then bronchoalveolar lavage (BAL) was performed. Olprinone (1 or 10mg/kg) or SB207499 (1 or 10mg/kg) was given twice intraperitoneally: One hour after the antigen challenge and 1h before the capsaicin provocation. SB207499, but not olprinone, significantly reduced both antigen-induced increase of cough response to inhaled capsaicin in sensitized animals and normal cough response in non-sensitized animals. SB207499, but not olprinone, also reduced the antigen-induced BAL eosinophilia. PDE4 inhibitors may be useful in treating cough associated with airway allergy via inhibiting both allergic airway inflammation and the common pathway of cough reflex.     

Effects of macrolides on antigen-induced increases in cough reflex sensitivity in guinea pigs

BackgroundMacrolides are antibiotics that have anti-inflammatory activities. Hence, they are used for both acute and chronic inflammatory airway diseases. However, the effects of these agents on allergic airway disorders presenting with an isolated chronic cough, such as non-asthmatic eosinophilic bronchitis and eosinophilic tracheobronchitis with cough hypersensitivity (atopic cough), still remain to be elucidated.ObjectiveTo determine if macrolides are effective in the management of chronic cough caused by eosinophilic airway inflammation.MethodsThe cough reflex sensitivity to inhaled capsaicin was measured at 48 h after challenge with an aerosolized antigen in actively sensitized guinea pigs. The 14-, 15- or 16-membered macrolides (erythromycin, azythromycin, or josamycin, respectively) were given intraperitoneally every 12 h after the antigen challenge. Bronchoalveolar lavage and the resection of the tracheal tissue were performed immediately after the measurement of the cough response to capsaicin.ResultsThe antigen-induced increase in the number of coughs elicited by capsaicin inhalation was significantly reduced by treatments with erythromycin and azythromycin, but not with josamycin. Erythromycin dose-dependently inhibited the increases in the substance P, prostaglandin E₂ and leukotriene B₄ levels, but not the histamine levels, in the bronchoalveolar lavage fluid. However, erythromycin did not influence the antigen-induced decrease in the neutral endopeptidase (NEP) activity in the tracheal tissue.ConclusionsBoth 14- and 15-membered, but not 16-membered, macrolides could reduce the antigen-induced cough reflex hypersensitivity by inhibiting the antigen-induced release of the afferent sensory nerve sensitizers. These macrolides may be therapeutically useful for the treatment of isolated chronic cough based on cough reflex hypersensitivity in allergic airway diseases such as non-asthmatic eosinophilic bronchitis and atopic cough.     

Effects of pirfenidone on increased cough reflex sensitivity in guinea pigs

Pirfenidone, an antifibrotic drug with anti-inflammatory and antioxidant effects, delays fibrosis in idiopathic pulmonary fibrosis (IPF). Patients with IPF have a greater cough reflex sensitivity to inhaled capsaicin than healthy people, and cough is an independent predictor of IPF disease progression; however, the effects of pirfenidone on cough reflex sensitivity are unknown.After challenge with an aerosolized antigen in actively sensitized guinea pigs, pirfenidone was administered intraperitoneally, and the cough reflex sensitivity was measured at 48 h after the challenge. Bronchoalveolar lavage (BAL) was performed, and the tracheal tissue was collected.Pirfenidone suppressed the capsaicin-induced increase in cough reflex sensitivity in a dose-dependent manner. Additionally, increased levels of prostaglandin E₂, substance P, and leukotriene B₄, but not histamine, in the BAL fluid were dose dependently suppressed by pirfenidone. The decrease in neutral endopeptidase activity in the tracheal tissue was also alleviated by pirfenidone treatment. The total number of cells and components in the BAL fluid was not influenced.These results suggest that pirfenidone ameliorates isolated cough based on increased cough reflex sensitivity associated with allergic airway diseases, and potentially relieve chronic cough in IPF patients who often have increased cough reflex sensitivity. Prospective studies on cough-relieving effects of pirfenidone in patients with IPF are therefore warranted.     

Effect of whole-body x-irradiation on antigen-induced airway response in sensitized guinea pigs.

The objectives of this study were to test the hypothesis that x-irradiation inhibits the late asthmatic response (LAR) without influencing the early asthmatic response (EAR) and to examine the mechanism of the inhibitory effect. Twenty sensitized guinea pigs were irradiated at a dose of 8 Gy. The next day, one-half of the animals were injected intravenously with spleen cells (2 x 10(8)) collected from unirradiated sensitized guinea pigs, whilst the other half were injected with vehicle only. Ten additional unirradiated sensitized guinea pigs also received vehicle only. Antigen inhalation challenge took place two days later. Pulmonary resistance was measured for 6 h after antigen exposure, and bronchoalveolar lavage and lung fixation were then undertaken. The area under the percentage pulmonary resistance curve 2-6 h after allergen inhalation was used for analysis of the LAR, while the maximal percentage change in pulmonary resistance was used for analysis of the EAR. Irradiation abolished the LAR (364.4+/-49.4 versus 62.8+/-10.4) without inhibiting the EAR (229.3+/-27.2 versus 278.7+/-40.2) and significantly inhibited the accumulation of eosinophils and lymphocytes in the airways. Transfer of spleen cells restored the LAR (334.4+/-66.8) and the recruitment of cells to the levels seen in unirradiated sensitized guinea pigs. In addition, transfer of only CD4+ T-lymphocytes separated from the spleen cells restored the LAR (439.4+/-62.1) and the cell infiltration into the airways. These inhibitory effects of x-irradiation were due to decreases in numbers of CD4+ T-lymphocytes.     

Prolactin responses to histamine H2 receptor antagonists

We have compared the effects of cimetidine and SK&F 92994, a new more potent histamine H2 receptor antagonist, on serum prolactin, and also assessed the effect of the H2 receptor agonist impromidine on the response to cimetidine. As previously reported, cimetidine 200 mg given as an iv bolus dose produced a marked rise in serum prolactin, but 50 mg and 200 mg of SK&F 92994 given by the same route had no effect. Iv infusion of impromidine 10 microgram kg-1h-1 failed to modify the prolactin response to cimetidine. It is concluded that the rise in serum prolactin following iv administration of cimetidine may be due to a specific property of cimetidine. An effect mediated via histaminergic pathways within the central nervous system, although less likely, cannot be excluded.     

The effect of histamine H2 receptor antagonists on platelet aggregation in man

The in vivo and in vitro effects on the aggregatory response of human platelets to ADP and collagen of a series of imidazole and non-imidazole histamine H2 receptor antagonists, and imidazole derivatives, have been studied. Bolus i.v. administration of the antagonists cimetidine and oxmetidine was without effect. However, inhibition of platelet aggregation was observed in vitro with oxmetidine, metiamide and to a lesser extent burimamide, but not with cimetidine or the non-imidazole antagonist ranitidine. Of the imidazole derivatives only imidazole and its 1-methyl analogue significantly affected platelet aggregation. The relationship between potency as a histamine H2 receptor antagonist, the presence of an imidazole ring structure and the antiaggregatory effectiveness of these compounds is discussed. Although certain antagonists clearly inhibit platelet aggregation in vitro, effects are only seen at drug concentrations exceeding those achieved under normal therapeutic conditions; thus the clinical significance of these observations remains to be determined.     

Effect of intraduodenally administered histamine on gastric acid secretion in rats and guinea pigs

We examined the effect of histamine administered intraduodenally as well as subcutaneously or intravenously on the gastric acid secretion in rats and guinea pigs, using a newly devised cannula. Intraduodenally administered histamine dihydrochloride caused a significant dose-dependent increase in the gastric acid secretion in rats. The maximal acid secretion, which corresponded to that after subcutaneous (20 mg/kg) or intravenous (10 mg/kg/hr) administration of histamine, was observed within 30 min after intraduodenal administration (40 mg/kg). The plasma concentrations of histamine determined 30 min after intraduodenal, subcutaneous, and intravenous administration of histamine were nearly the same. Pretreatment with aminoguanidine sulfate (diamine oxidase inhibitor) at 30 mg/kg significantly increased the gastric acid secretion caused by intraduodenal histamine. The gastric acid secretion stimulated by intraduodenal histamine was significantly inhibited by cimetidine, pirenzepine, and omeprazole, but remained unchanged with tripelennamine. Intraduodenal histamine (20 mg/kg) also maximally stimulated the gastric acid secretion in guinea pigs. The response was comparable to that with subcutaneous histamine (1 mg/kg). We conclude that intraduodenal histamine has the ability to stimulate gastric acid secretion in both rats and guinea pigs.     

Endogenous tachykinins in antigen-induced acute bronchial responses of guinea pigs.

Because tachykinins (TKs) cause severe bronchoconstriction in humans and animals, this study was carried out to examine whether depletion of TKs can prevent or ameliorate antigen-induced immediate bronchial constriction. Forty-five guinea pigs were randomly divided into six groups: control, antigen challenge, TK depletion + antigen challenge, ganglionic (Ggl) blockade, Ggl blockade + antigen challenge, and TK depletion + Ggl blockade + antigen challenge. Control animals received no treatment. Animals of all antigen challenge groups were sensitized with ovalbumin 10 days before the study. TK depletion was performed via 5-day pretreatment of capsaicin, which began 11 days before the study. On the day of the study, pulmonary resistance (RI), dynamic compliance (Cdyn), and breathing patterns were measured for 15 min just before (baseline) and for 30 min after intravenous injection of either saline (control) or ovalbumin (antigen challenge). In controls, saline injection did not produce any significant change within 30 min, whereas antigen challenge significantly increased RL at 4-15 min and significantly decreased Cdyn at 6-15 min, suggesting antigen-induced bronchoconstriction. Following TK depletion, antigen challenge produced pulmonary changes similar to those without depletion. Ggl blockade reduced RL and breathing frequency, and increased Cdyn and tidal volume; the blockade, however, did not significantly alter (in terms of % baseline) antigen challenge-induced changes in RL, Cdyn, or breathing patterns. These results suggest that TKs and reflexes via Ggl do not appear to be important contributing factors for antigen-induced immediate bronchial constriction in this animal model.     

Inflammatory mediators involved in antigen-induced airway microvascular leakage in guinea pigs

Antigen challenge of ovalbumin (OA)-sensitized guinea pigs results in significant (p less than 0.05) increases in vascular permeability to Evans blue (EB) dye in the airways, esophagus, and bladder. Mean values +/- SEM in ng EB/mg wet weight tissue for unsensitized versus sensitized animals were: trachea, 23.6 +/- 6.6 versus 92.5 +/- 11.1; main bronchi, 31.1 +/- 12.2 versus 153.1 +/- 14.9; "central" intrapulmonary airways (ipa), 34.6 +/- 11.2 versus 101.3 +/- 6.2; and "peripheral" ipa, 26.2 +/- 6.8 versus 93.5 +/- 13.6. We investigated the involvement of several mediators of inflammation in this process. FPL 55712, a sulfidopeptide leukotriene receptor antagonist, caused significant inhibition of leakage in trachea (to 55.1 +/- 9.8) and main bronchi (91.7 +/- 15.8). Blockade of the cyclooxygenase and lipoxygenase pathways with BW 755C, but not of the cyclooxygenase pathway alone with indomethacin, also significantly reduced EB dye extravasation in trachea (55.1 +/- 18.0), main bronchi (71.7 +/- 23.0), and "central" ipa (62.7 +/- 16.4). The histamine antagonists, chlorpheniramine and cimetidine, only inhibited microvascular leakage in main bronchi (94.4 +/- 20.0). PAF-receptor blockade with the ginkgolide mixture BN 52063 had no effect. Nedocromil sodium, a mast cell stabilizer and an inhibitor of inflammatory cell activation, caused significant inhibition throughout the airways: trachea, 50.4 +/- 10.6; main bronchi, 72.0 +/- 15.3; "central" ipa 61.0 +/- 8.6; "peripheral" ipa 41.9 +/- 12.2. Thus, histamine and lipoxygenase products (in particular, leukotrienes), but not PAF, may mediate the antigen-induced increase in vascular permeability to different degrees in differing regions of the respiratory tract in guinea pigs.     

Effect of nociceptin in acid-evoked cough and airway sensory nerve activation in guinea pigs

RATIONALE: Nociceptin/orphanin FQ has been reported to inhibit capsaicin- and mechanically provoked cough in animal models, but the mechanism of this effect has not been elucidated. OBJECTIVES: The objectives of this study were to determine whether nociceptin inhibits acid-evoked cough in conscious animals and to evaluate the mechanism of this effect. METHODS: We tested the effect of nociceptin on acid-induced cough in conscious guinea pigs and acid-induced nerve activation in airway-specific vagal sensory neurons using calcium imaging techniques and the gramicidin-perforated patch clamp technique. MEASUREMENTS AND MAIN RESULTS: Nociceptin (3 mg/kg, intraperitoneal) effectively inhibited acid-evoked cough in guinea pigs by nearly 70%. Acid (pH 5) increased intracellular free calcium in acutely dissociated vagal jugular ganglionic neurons. The acid-induced increase in intracellular calcium was inhibited by a selective transient receptor potential vanilloid-1 antagonist, 5-iodo-resiniferatoxin (1 microM, approximately 80% reduction). The inhibitory effect of 5-iodo-resiniferatoxin on acid-induced increases in calcium was mimicked by nociceptin (0.1 microM). In gramicidin-perforated patch clamp recordings on airway-specific capsaicin-sensitive jugular ganglion neurons, acid (pH 5) induced two distinct inward currents. A transient current was evoked that was inhibited by amiloride and a sustained current was evoked that was inhibited by 5-iodo-resiniferatoxin. Nociceptin selectively inhibited only the sustained component of acid-induced inward current. CONCLUSION: These results indicate that the inhibitory effect of nociceptin on acid-induced cough may result from a direct inhibitory effect on peripheral C-fiber activity caused by the selective inhibition of acid-induced transient receptor potential vanilloid-1 activation.     

Bronchial biopsy and sequential bronchoalveolar lavage in atopic cough: In view of the effect of histamine H1-receptor antagonists

We have shown that some patients presenting with chronic bronchodilator-resistant non-productive cough have global atopic tendency, airway cough hyper-sensitivity without non-specific bronchial hyperresponsiveness and eosinophilic inflammation of the trachea and bronchi, abbreviated as atopic cough (AC). Histamine H₁ receptor antagonists are effective in relieving the cough in some patients with AC but not in others in whom corticosteroids are needed to improve the cough. The aim of the present study was to compare the intensity of eosinophil infiltration in biopsied bronchial submucosa and sequential bronchoalveolar lavage (SBAL) fluids between two subgroups of patients with AC: (i) group A, successfully treated with histamine H₁ receptor antagonists; and (ii) group B, requiring corticosteroids. Sequential BAL was performed using three 50 mL aliquots of physiologic saline solution and then bronchoscopic bronchial biopsy was performed in group A (n = 9) and B (n = 9) patients. Sequential BAL was also performed in normal controls (NC; n = 13). The first SBAL fraction was analyzed as bronchial lavage fluid (BLF) and the mixed fluid of the second and third SBAL fractions as bronchoalveolar lavage fluid (BALF). The number of eosinophils in the bronchial subepithelium was significantly (P = 0.0134) greater in group B patients (median 8.3 cells/mm²; range 3.6–21.9 cells/mm²) compared with group A (median 3.6 cells/mm²; range 0–10.0 cells/mm²). However, There were no significant differences in the number or percentage of eosinophils in BLF or BALF between group A, group B and NC subjects. These findings confirm that eosinophils do not infiltrate the peripheral airways of AC and suggest that corticosteroids are required to relieve the cough in more severe illness of AC, in which submucosal eosinophilic inflammation of the central bronchi is more intensive compared with the milder illness successfully treated with histamine H receptor antagonists.     

The effects of H1 and H2 histamine receptor antagonists on the development of endotoxemia in the conscious, unrestrained rat

This study was designed to use the H2 antagonist cimetidine and the H1 antagonist diphenhydramine alone and in combination to clarify the role of histamine in the development of endotoxin shock. The jugular vein and the carotid artery of male Sprague-Dawley rats were cannulated during enflurane anesthesia. After recovery, blood pressure, heart rate, and respiration rate were continuously monitored. Animals were pretreated with saline, a combination of the H1 and H2 receptor antagonists diphenhydramine (20 mg/kg) and cimetidine (80 mg/kg), or individual doses of diphenhydramine or cimetidine. After pretreatment an endotoxin bolus (40 mg/kg) was given. Arterial blood samples (0.35 ml) were taken before endotoxin and after endotoxin at 60 and 240 min for measurement of pH, PO2, PCO2, hematocrit, glucose, and lactate. Pathological examinations were made at 240 min. Four additional groups of animals (N = 10) were studied for the effect of each of the treatment modes on 24-hr survival rate. Treatment with cimetidine plus diphenhydramine prevented the endotoxin-induced blood pressure fall, increase in heart rate, and hypoglycemia; increased the 24-hr survival rate from 10 to 60%; and inhibited the small intestinal pathology found in control rats. Treatment with diphenhydramine alone produced similar results except that there was a gradual blood pressure decrease later in shock. The results obtained from the cimetidine-treated groups were much the same but there was a slight, transient decrease in blood pressure early after endotoxin and the survival rate was increased to 90%. These results demonstrate that in the conscious rat antagonism of the H1 and/or H2 receptors modifies hemodynamic and metabolic responses and the subsequent pathology, altering the course of endotoxin shock and survival. This study provides substantial evidence to implicate histamine as one of the key vasoactive mediators in the development of endotoxin shock.     

Effect of stobadine and histamine H1 and H2 blockers on histamine-induced contraction of guinea pig airways in vitro

Histamine, a nonselective histamine receptor agonist, activates simultaneously both H1 and H2 receptors in the guinea pig trachea and lung strip. The resulting contraction is due to the prevalence of H1 receptors, because they are blocked by the selective H1 antagonist diphenhydramine. The H2 receptor antagonists cimetidine and ranitidine increased the sensitivity of both tissues to histamine by affecting primarily the amplitude of contractions induced by high histamine concentrations. Since the lung strips were more sensitized by ranitidine and low concentrations of the other studied antagonists (diphenhydramine, dithiadene, stobadine) than the tracheal smooth muscle, it is inferred that the density of H2 receptors is higher in peripheral than central airways. From all the studied histamine receptor antagonists only dithiadene was able to unmask the relaxation induced by H2 receptor activation indicative of its highest H1 selectivity. In the light of the concentration-dependent antihistaminic effect of stobadine, i.e. potentiation in low and inhibition in high concentrations, stobadine is suggested to belong to antihistaminics with no histamine receptor subtype selectivity.     

Effect of the selective leukotriene B4 antagonist U-75302 on antigen-induced bronchopulmonary eosinophilia in sensitized guinea pigs

The selective leukotriene B4 (LTB4) antagonist, U-75302, 6-(6-(3-hydroxy-1E,5Z-undecadien-1-yl)-2-pyridinyl)-1,5-hexa nediol) was examined for its ability to inhibit the "late-phase" bronchopulmonary eosinophilia that occurs 6 to 24 h after inhalation of specific antigen in sensitized guinea pigs. Groups of 6 male guinea pigs, sensitized with ovalbumin, were pretreated with U-75302, 1.0, 10.0, or 30.0 mg/kg, or vehicle 1 h before and 7 h after antigen inhalation. Twenty-four hours after antigen provocation, the lungs were lavaged for the enumeration of inflammatory cell populations. Doses of U-75302 (1.0, 10.0 and 30.0 mg/kg) administered orally produced 12.2%, (p greater than 0.05), 43.2% (p less than 0.05), and 61.1% (p less than 0.05) inhibition, respectively, of the antigen-induced influx of eosinophils into the bronchial lumen. Neutrophil populations were not significantly affected by treatment with U-75302. In a separate study, we compared the histopathological changes that occurred following antigen challenge in U-75302-treated or vehicle-treated guinea pigs. Vehicle-treated, sensitized animals exhibited marked changes in the airway at 8 min, 6 h, and 24 h after antigen challenge. U-75302 treatment produced a significant reduction in eosinophil adherence to peribronchial/peribronchiolar capillaries followed by a dramatic and specific reduction of peribronchial eosinophil infiltration (81% reduction at 6 h and 79% reduction at 24 h). Neutrophil migration appeared unaffected. These data implicate LTB4 as a mediator of antigen-induced bronchopulmonary eosinophilia in the guinea pig.