Potentiation by viral respiratory infection of ovalbumin-induced guinea-pig tracheal hyperresponsiveness: role for tachykinins.

1. We investigated whether virus-induced airway hyperresponsiveness in guinea-pigs could be modulated by pretreatment with capsaicin and whether viral respiratory infections could potentiate ovalbumin-aerosol-induced tracheal hyperresponsiveness. 2. Animals were inoculated intratracheally with bovine parainfluenza-3 virus or control medium 7 days after treatment with capsaicin (50 mg kg-1, s.c.). Four days after inoculation, tracheal contractions were measured to increasing concentrations of substance P, histamine and the cholinoceptor agonist, arecoline. 3. In tracheae from virus-infected guinea-pigs, contractions in response to substance P, histamine and arecoline were significantly enhanced (P < 0.01) by 144%, 46% and 77%, respectively. Capsaicin pretreatment inhibited the hyperresponsiveness to substance P partly (62%) and to histamine and arecoline completely. 4. In another series of experiments animals were first sensitized with ovalbumin (20 mg kg-1, i.p.). After 14 days animals were exposed to either saline or ovalbumin aerosols for 8 days. After 4 aerosol exposures (4 days) animals were inoculated with either parainfluenza-3 virus or control medium. One day after the last ovalbumin aerosol, tracheal contraction in response to increasing concentrations of substance P, histamine and arecoline was measured. 5. Tracheae from ovalbumin-aerosol-exposed control inoculated animals showed a similar degree of airway hyperresponsiveness to saline-aerosol-exposed virus-treated guinea-pigs. Virus inoculation of ovalbumin-treated animals significantly potentiated the tracheal contractions to substance P compared to either of the treatments alone. The contractions in response to histamine and arecoline were only slightly enhanced. 6. In conclusion, sensory nerves and/or tachykinins are involved in virus-induced airway hyperresponsivenessin guinea-pigs and viral respiratory infections can potentiate the increase in tracheal responsiveness to bronchoconstrictor agonists after ovalbumin exposure.

Capsaicin pretreatment of guinea pigs in vivo prevents ovalbumin-induced tracheal hyperreactivity in vitro.

The role of substance P-containing sensory nerves in the development of tracheal hyperreactivity to histamine and arecoline was investigated in an allergic model of asthma. Male Hartley-strain guinea pigs were sensitized to ovalbumin (20 mg/kg i.p.) and 14 days later exposed to either saline or ovalbumin (2%) aerosols for 8 consecutive days. One day after the last aerosol exposure the animals were killed and the tracheas were removed. Isotonic muscle shortening in response to increasing doses of histamine and arecoline was measured. Capsaicin (50 mg/kg s.c.) or vehicle pretreatment was performed 7 days prior to sensitization. Tracheas from vehicle-pretreated sensitized and ovalbumin-aerosol exposed animals had increased reactivity to both histamine and arecoline compared to saline-aerosol exposed animals. Capsaicin pretreatment did not alter tracheal reactivity in the saline-aerosol exposed group. Capsaicin pretreatment prevented the increase in tracheal reactivity caused by both agonists in sensitized and ovalbumin-aerosol exposed guinea pigs. These results suggest that capsaicin-sensitive sensory nerves are important for the development of increased tracheal reactivity in an allergic model of asthma.

Effect of anti-IL-5 and IL-5 on airway hyperreactivity and eosinophils in guinea pigs.

Chronic ovalbumin challenge of sensitized guinea pigs induces bronchoalveolar lavage (BAL) eosinophilia, neutrophilia, and tracheal hyperreactivity. In the present study, the influence of monoclonal antibody to murine interleukin-5 (anti-IL-5) on these phenomena is examined. In ovalbumin-sensitized guinea pigs treated with isotype-matched control antibody and challenged daily with ovalbumin for 8 days, the number of BAL eosinophils and neutrophils is increased significantly six- and fivefold, respectively, compared with saline-challenged animals. The maximal contractions of tracheal rings to histamine and arecoline in ovalbumin-challenged animals are enhanced significantly to 155% compared with saline-challenged animals. In sensitized guinea pigs treated with anti-IL-5, the BAL eosinophil number is markedly inhibited compared with control antibody treatment in both saline- and ovalbumin-challenged animals. In contrast, the number of neutrophils is not affected by anti-IL-5 treatment. In guinea pigs treated with anti-IL-5, the development of hyperreactivity to histamine and arecoline after ovalbumin challenge is completely inhibited. The contractions to histamine and arecoline of tracheal rings isolated from guinea pigs treated with recombinant murine IL-5 for 3 or 7 days are enhanced significantly to approximately 140% compared with controls. Treatment with IL-5 for 7 days tends to increase the number of eosinophils in BAL fluid. It can be concluded that IL-5 is involved in airway eosinophilia and in the development of hyperreactivity in this animal model, but other cytokines may contribute. Development of IL-5 synthesis inhibitors and/or receptor antagonists could provide another therapeutic class of anti-asthma drugs.

Agonist interactions at the calcium pools in skinned and unskinned canine tracheal smooth muscle.

We studied the functionally discrete calcium sources used by acetylcholine, 5-hydroxytryptamine, histamine and high K+ in the dog tracheal smooth muscle. The extracellular calcium dependence of their responses was assessed by altering the calcium and by pretreatment with the calcium antagonist, nifedipine. The intracellular calcium pool was assessed by studying the interactions between caffeine and the agonists in both skinned and unskinned preparations. The extent of overlap for the different calcium pools between the various agonists was determined by studying the dose-response relationships of these agents before and after pretreatment with another agonist, i.e., the conditioning agonist, in zero calcium conditions. The rank order of sensitivity to calcium removal and to nifedipine was histamine greater than KCl greater than 5-hydroxytryptamine greater than acetylcholine. Caffeine-induced atenuation of the agonist responses was predominantly through physiological antagonism. However, the caffeine responses in unskinned fibres were augmented by pretreatment with the agonists through both nifedipine-sensitive (as with KCl) and -insensitive (as with acetylcholine) mechanisms. The responses to acetylcholine and caffeine were inhibited by theophylline and forskolin. In the skinned muscle fibres, the pCa-tension relationship suggested high calcium sensitivity, a significant caffeine-sensitive calcium pool, and no evidence of calcium release by exogenous inositol trisphosphate. The results are consistent with multiple extracellular and intracellular calcium sources for the agonist responses. We observed considerable overlap of the calcium sources used by these agonists. Of the four agonists studied, histamine appeared to inhibit the release and sequestration of calcium utilized by the other agonists most effectively.

Pharmacological characterization of airway smooth muscle responses to antigen in ascaris-sensitive dogs.

The dog model of ascaris airway sensitivity was chosen because of its frequency and its immunologic similarity to the human atopic asthmatic state. We studied the mediators of the antigen-induced airway response in vitro and the alterations in the in vivo and in vitro responsiveness to spasmogens evoked by antigen challenge. A myogenic basis of altered reactivity was suggested by the following: tetrodotoxin-insensitive spontaneous active tone; phasic contractions of airway smooth muscle; and responsiveness to leukotrienes C4 and D4. The pharmacologic characteristics of the antigen-induced airway smooth muscle contraction in vitro were similar to those induced by arachidonic acid and the leukotrienes only in some respects but were clearly different from those induced by compound 48/80. This suggested a predominant role for arachidonate lipoxygenase products. Histamine appeared to play a minor role in the antigen response. Comparisons were made between antigen-induced responses of actively and passively sensitized airways tissues. In the latter, histamine release appeared to contribute to the initial antigen-induced contraction and, unlike in actively sensitized airways, the responses were easily desensitized to repeated challenge. Alterations of airway responsiveness were demonstrated in vivo to acetylcholine and 5-HT following antigen challenge of highly ascaris-sensitive dogs. In vitro studies of passively sensitized muscle showed selectively enhanced response to 5-HT following antigen challenge. These studies support the presence of altered myogenic properties of airway smooth muscle and nonspecific increased airway responsiveness in this animal model.