Involvement of histamine H1- and H2-receptors in induced asthmas in dogs

A new pharyngitis model using capsaicin in rats

1. Application of capsaicin solution onto the rat pharyngeal mucosa caused a well-reproducible increase in vascular permeability in the pharynx. 2. Capsaicin-induced pharyngeal inflammation was unaffected by a histamine H1 blocker and non-steroidal anti-inflammatory agents, whereas dexamethasone was effective in its inhibition. 3. FK224, a dual antagonist of tachykinin NK1 and NK2 receptors, and FK888, a selective antagonist of NK1 receptor, significantly inhibited capsaicin-induced plasma exudation in the pharynx. 4. In capsaicinized animals, the application of capsaicin solution in the pharyngeal mucosa did not induce pharyngitis. 5. These results suggest that the mechanism of the capsaicin-induced pharyngitis primarily involves tachykinins.

Effects of mast cell stabilizers on a new bronchial asthma model using compound 48/80 in dogs

Development of a nonimmunologically induced experimental asthma model using compound 48/80 was attempted. Male mongrel dogs anesthetized with pentobarbital-Na were immobilized with decamethonium bromide under artificial respiration. Airway resistance was measured with a modified Konzett-Rössler method and expressed as a change in ventilation overflow (VO). Inhalation of compound 48/80 caused no change in VO even in high concentrations up to a 1% solution. Infusion of compound 48/80 into the bronchial artery at a dose of 0.2 mg/min for 10 min by using the right bronchial perfusion method caused a marked increase in VO accompanied by decreases in perfusion pressure and systemic blood pressure. The compound 48/80-induced bronchoconstriction was inhibited 58% by surgical vagotomy and was almost abolished by chlorpheniramine (10 mg/kg, intraduodenally (i.d.)). Disodium cromoglycate (inhalation of 1% solution along with 5 mg/kg, i.v.), tranilast (300 mg/kg, i.d.) and NCO-650, a new antiallergic drug (100 mg/kg, i.d.) significantly inhibited the compound 48/80-induced bronchoconstriction. These results indicate that compound 48/80 infusion into the bronchial artery produces an asthma-like bronchoconstriction, the main chemical mediator involved in this response would be histamine acting through H1-receptors, and effects of mast cell stabilizers can be evaluated with this model.

Functional depression of H2 histamine receptors in sheep with experimental allergic asthma

We tested the hypothesis that airway hyperresponsiveness to histamine in the allergic sheep is related to functional depression of H2 histamine receptors. Thirteen of 32 sheep responded with bronchoconstriction to inhaled Ascaris suum antigen (allergic sheep), and the remainder served as controls (nonallergic sheep). In the allergic sheep, 50 and 100 breaths of 5% histamine solution increased mean pulmonary resistance (RL) to 235% and 438% of baselines, respectively. The corresponding values in nonallergic sheep were 200% and 211%, indicating a greater response to the higher dose of histamine in allergic sheep. Selective H1-receptor stimulation with 50 breaths of histamine (pretreatment with the H2-receptor antagonist metiamide) failed to enhance the effect of histamine in allergic sheep (mean RL increased to 239% of baseline) whereas it enhanced the histamine response in nonallergic sheep (RL increased to 438% of baseline). Selective H2-receptor stimulation (pretreatment with the H1-receptor antagonist chlorpheniramine) caused histamine to decrease RL by 31% in the nonallergic sheep group; it blocked but did not reverse the histamine effect in the allergic sheep. Similar observations were made in a different group of animals when selective H1- or selective H2-receptor stimulation was produced by 100 breaths of histamine. The cutaneous wheal response to intradermal histamine dilutions of 0.0001. 0.001, 0.01, and 1 mg/ml was similar in both groups. In nonallergic sheep, both chlorpheniramine and metiamide blunted the cutaneous wheal response. In allergic animals, only chlorpheniramine blunted the cutaneous wheal response, whereas metiamide was without effect. We conclude that airway hyperresponsiveness to histamine in allergic sheep is related to a functional depression of H2 receptors and that such a defect is observed both in the airways as well as in the skin.