Effect of unilateral vagus blockade on antigen-induced airway obstruction

Muscarinic acetylcholine receptors and airway diseases

Parasympathetic nerves provide the dominant autonomic innervation of the airways. Release of acetylcholine from parasympathetic nerves activates postjunctional muscarinic receptors present on airway smooth muscle, submucosal glands, and blood vessels to cause bronchoconstriction, mucus secretion, and vasodilatation, respectively. Acetylcholine also feeds back onto prejunctional muscarinic receptors to enhance or inhibit further acetylcholine release. In asthma and chronic obstructive pulmonary disease, bronchoconstriction and mucus secretion is increased and the airways are hyperresponsive to contractile agents. These changes are due to increased parasympathetic nerve activity. The number and function of postjunctional muscarinic receptors in the airways are unchanged in animal models of asthma. Rather, it is the supply of acetylcholine to the postjunctional cells (smooth muscle and submucosal gland) that is increased. The increase in acetylcholine release occurs because prejunctional, inhibitory M(2) muscarinic receptors on the parasympathetic nerves are dysfunctional. M(2) muscarinic receptor dysfunction and subsequent airway hyperreactivity have been demonstrated to occur in animals in response to a variety of triggers, including antigen challenge, virus infection, ozone exposure, and vitamin A deficiency. In humans, there is evidence that loss of M(2) muscarinic receptor function is related to asthma. The mechanisms by which neuronal M(2) muscarinic receptor function is lost and its relevance to human airway disease are discussed in this review.

Bronchodilator and antiallergic effects of thiazinamium chloride in guinea pigs, rats, cats and dogs

This study characterized the in vivo pulmonary pharmacology of thiazinamium chloride administered largely by the aerosol route in different animal species. The compound has greater anticholinergic but weaker antihistaminic activity than promethazine, the parent compound. It was less potent than atropine or ipratropium as an anticholinergic and had a shorter duration of action, but unlike these compounds it had long-lasting antihistaminic activity. It is effective in both IgG- and IgE-induced models of passive lung anaphylaxis in guinea pigs and rats, respectively. In Ascaris-induced allergic asthma in the conscious dog it produced a dose-related inhibition of the antigen-induced bronchospasm. No major side effects were observed in acute oral and inhalation toxicity studies in guinea pigs or rhesus monkeys. The results demonstrate that thiazinamium chloride is a safe, potent and efficacious bronchodilator after aerosol administration, with a rapid onset and moderate duration of action in animal models.