RT Journal Article SR Electronic T1 Inhibitory effect of methacholine on drug-induced relaxation, cyclic AMP accumulation, and cyclic AMP-dependent protein kinase activation in canine tracheal smooth muscle. JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 409 OP 417 VO 233 IS 2 A1 T J Torphy A1 C Zheng A1 S M Peterson A1 R R Fiscus A1 G A Rinard A1 S E Mayer YR 1985 UL http://jpet.aspetjournals.org/content/233/2/409.abstract AB Functional antagonism between bronchoconstricting and bronchodilating pathways was examined in canine tracheal smooth muscle. Trachealis strips were contracted with either 0.3 microM (EC55) or 3.0 microM (EC80) methacholine before being relaxed by the cumulative addition of isoproterenol, prostaglandin E2, or forskolin. The EC50 for all three relaxants was increased 10-fold in tissues contracted with 3.0 microM methacholine vs. those contracted with 0.3 microM methacholine. Moreover, contracting tissues with the higher concentration of methacholine reduced the maximum relaxation induced by prostaglandin E2 and isoproterenol. Forskolin produced total relaxation regardless of the concentration of methacholine used and thus was a much more effective bronchodilator than either isoproterenol or prostaglandin E2. The inhibitory effect of methacholine on the relaxant response to these agents was paralleled by a reduction in drug-stimulated cyclic AMP-dependent protein kinase activity. Methacholine reduced the maximum activation of cyclic AMP-dependent protein kinase elicited by isoproterenol, prostaglandin E2 and submaximal concentrations of forskolin, which was a much more powerful enzyme activator than the other two agents. The ability of a maximum concentration of forskolin (30 microM) to activate cyclic AMP-dependent protein kinase was not inhibited by methacholine. Although methacholine also appeared to suppress drug-stimulated cyclic AMP accumulation, the inhibitory effect was only statistically significant in forskolin-treated tissues.(ABSTRACT TRUNCATED AT 250 WORDS)