Role of the cholinergic pathway in mediating platelet-activating factor-induced pulmonary dysfunctions in unsedated calves

The purpose of this study was to investigate the possible role of the choli nergic pathway in mediating platelet-activating factor (PAF)-induced pulmon ary dysfunctions in unsedated calves. In a placebo group, PAF infusion chal lenge induced significant dysfunctions in the pattern of breathing [a signi ficant increase in respiratory rate (RR) and a significant decrease in tida l volume (V-T)], the mechanics of breathing [a significant increase in tota l lung resistance (R-L) and a significant decrease in dynamic lung complian ce (C(L)dyn)] and gas exchange, whereas in atropine pre-treated calves, PAF infusion challenge induced a significant increase in RR, V-T and HR and a significant decrease in C(L)dyn. The R-L increase was prevented by atropine pre-treatment. On the basis of our findings, we suggest that, in cattle, t he PAF-induced pattern of breathing dysfunctions and the diffuse bronchocon striction and microvascular leakage of small airways are not mediated throu gh the cholinergic pathway. By contrast, our data suggest that PAF-induced bronchoconstriction of upper airways is at least partly mediated through mu scarinic receptors.