Role of the Cholinergic Pathway in Mediating Platelet‐Activating Factor‐induced Pulmonary Dysfunctions in Unsedated Calves

Abstract

The purpose of this study was to investigate the possible role of the cholinergic pathway in mediating platelet‐activating factor (PAF)‐induced pulmonary dysfunctions in unsedated calves. In a placebo group, PAF infusion challenge induced significant dysfunctions in the pattern of breathing [a significant increase in respiratory rate (RR) and a significant decrease in tidal volume (VT)], the mechanics of breathing [a significant increase in total lung resistance (RL) and a significant decrease in dynamic lung compliance (CLdyn)] and gas exchange, whereas in atropine pre‐treated calves, PAF infusion challenge induced a significant increase in RR, VT and HR and a significant decrease in CLdyn. The RL increase was prevented by atropine pre‐treatment. On the basis of our findings, we suggest that, in cattle, the PAF‐induced pattern of breathing dysfunctions and the diffuse bronchoconstriction and microvascular leakage of small airways are not mediated through the cholinergic pathway. By contrast, our data suggest that PAF‐induced bronchoconstriction of upper airways is at least partly mediated through muscarinic receptors.