Atropine modification of the pulmonary effects of chemical mediators in the guinea pig.

The actions of histamine, slow-reacting substance of anaphylaxis (SRS-A), Bradykinin, and prostaglandin F2alpha on pulmonary mechanics in the unanesthetized guinea pig were separated into direct and secondary cholinergic airway effects on the basis of alteration of their actions by atropine. The effects of SRS-A (500 and 3,000 units/kg) on compliance were not significantly altered by atropine, while the effects of bradykinin (3.0 and 30 mug/kg) on compliance were decreased only at 3.0 mug/kg by atropine. The effects of both of these agents on resistance were decreased by atropine, suggesting that SRS-A and bradykinin act directly on the peripheral airways and by secondary cholinergic mechanisms on both central and peripheral airways. The effects of histamine (3.0 mug/kg) on both compliance and resistance were abolished by atropine, suggesting an action mainly via cholinergic pathways; while at a higher dose, 9.0 mug/kg, there was both a direct and a cholinergic action. The effects observed 20 sec after the administration of prostaglandin F2alpha (PGF2alpha) were not altered by atropine suggesting a direct action on airways, while both the compliance and resistance changes observed 3-8 min after PGF2alpha were abolished by atropine suggesting that the latter effects were mediated solely by cholinergic mechanisms