Antagonism of acetylcholine-mediated relaxation of rabbit pulmonary arteries by phorbol myristate acetate.
We studied the effect of 4-phorbol 12-myristate 13-acetate (PMA) on endothelium-dependent relaxation of rabbit isolated lobar pulmonary arteries contracted with phenylephrine. After full development of relaxation in response to 1.0 microM acetylcholine, addition of 10.0 nM PMA reversed relaxation rapidly and completely. This effect of PMA on acetylcholine-induced relaxation was unchanged when catalase was included in the medium. In separate groups of experiments, lobar pulmonary arteries were preincubated with 10.0 nM PMA for 20 min and then challenged with acetylcholine without washout of PMA. In these experiments PMA did not block completely the relaxation in response to addition of 1.0 microM acetylcholine. Log-concentration response curves for 0.01 to 31.6 microM acetylcholine vs. relaxation as percentage of phenylephrine-induced tone exhibited rightward shifts and depression of maxima after pretreatment with PMA. The EC50 for acetylcholine-induced relaxation was increased from 57 +/- 9.0 to 377 +/- 6.30 nM (values are mean +/- S.E.). Relaxation of lobar pulmonary arteries induced by 10.0 nM A23187 was much less sensitive to treatment with PMA than relaxation induced by acetylcholine. At least for the low concentration of PMA used here, these data are consistent with the following: 1) PMA blocks acetylcholine-induced relaxation by disrupting the link between acetylcholine receptor occupancy and the formation or release of the endothelium-derived relaxing factor, 2) PMA does not directly block the relaxant action of endothelium-derived relaxing factor on vascular smooth muscle and 3) the effect of PMA on acetylcholine-induced relaxation is not mediated by hydrogen peroxide or derived oxygen radicals.
D000109:Acetylcholine / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D001685:Biological Factors / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002374:Catalase / Q000378:metabolism; D005609:Free Radicals; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009569:Nitric Oxide; D011651:Pulmonary Artery / Q000187:drug effects*; D011817:Rabbits; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014664:Vasodilation / Q000187:drug effects*
D001685:Biological Factors; D005609:Free Radicals; D009569:Nitric Oxide; D000001:Calcimycin; D002374:Catalase; D000109:Acetylcholine; D013755:Tetradecanoylphorbol Acetate