Cholinergic mechanisms and bronchoconstriction in guinea-pigs

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Abstract
Seventy-four guinea-pigs have been actively sensitized against ovalbumin. The effects of bilateral cervical vagotomy and of cholinergic efferent blockade on the bronchoconstriction induced by inhaled acetylcholine, histamine or antigen have been quantified. Animals were curarized then tested during controlled ventilation to ensure constant conditions throughout the whole experiment by suppressing the post-vagotomy apneusis. Bronchial sensitivity was estimated by calculating the bronchoconstrictor dose-threshold provoking respiratory asynchronism. Corresponding variation of total lung resistance and dynamic compliance were also measured as indices of bronchial reactivity. The data obtained in 27 guinea-pigs indicated that the vagi section produced no significant effect on the direct bronchial response to histamine (P>0.5), to acetylcholine (P>0.1) or to antigen (P>0.5). In 47 guinea-pigs, atropine at doses 5 and 10 times higher than the acetylcholine blocking one did not alter the direct bronchial response to histamine (P>0.5). Higher doses induced a progressive decrease in bronchial sensitivity to antigen (.05<P> .01) which could be related to the repetitive administration of the antigen. According to the present results, peripheral cholinergic mechanisms play no significant role in guinea-pigs neither in histamine nor in anaphylactic bronchoconstriction. Curarization has no influence on resting bronchial tone.