Regulation of Adenosine Cyclic 3',5'-Monophosphate and Guanosine Cyclic 3',5'-Monophosphate Levels and Contractility in Bovine Tracheal Smooth Muscle

Abstract

The effects of various agents on cyclic 3',5'-AMP and cyclic 3',5'-GMP levels and mechanical activity of bovine tracheal smooth muscle were examined. Carbachol, acetylcholine, and histamine caused muscle contraction and increased cyclic GMP levels several fold in a dose-dependent manner; contraction preceded the increase in cyclic GMP. Serotonin and high K+ concentrations contracted muscle to the same degree as carbachol, while cyclic GMP increases were smaller than that due to carbachol. The effects of carbachol and histamine were blocked by atropine and diphenhydramine, respectively. The calcium ionophore A-23187 also increased cyclic GMP levels and caused contraction. Guanylate cyclase activators-sodium azide, hydroxylamine, sodium nitrite, nitroglycerin, and sodium nitroprusside-increased cyclic GMP levels and relaxed tracheal smooth muscle. None of these agents had any effect on cyclic AMP levels. The presence of Ca2+ in the incubation medium was not required for cyclic GMP increases with these latter agents. However, it was required in order to see increases in cyclic GMP with carbachol, histamine, and A-23187. Adremergic agonists relaxed muscle preparations and increased cyclic AMP levels 2-3-fold. Both these effects were blocked by propranolol. Inhibitors of cyclic nucleotide phosphodiesterases relaxed muscle preparations and were associated with increases in both cyclic AMP and cyclic GMP. Prostaglandins E1 and F2α had little or no effect on mechanical activity or cyclic nucleotide levels. The addition of 1 mM 8-bromo-cyclic GMP or 8-bromo-AMP relaxed muscle preparations. A variety of other nucleotides had no effect. These results support the hypothesis that cyclic AMP plays a role in relaxation of tracheal muscle induced by adrenergic agents. However, with a variety of other agents, we found that contraction or relaxation occurred with increases either in cyclic GMP alone or in both cyclic AMP and cyclic GMP. Thus the roles of cyclic AMP and cyclic GMP in smooth muscle mechanical activity remain obscure. ACKNOWLEDGMENTS We thank Daniel Macklin and Joanne Holmes for their technical assistance, and Cathy Bostron for typing this manuscript.