title: Mechanism of smooth muscle relaxation by tiropramide.
abstract: Experiments on rabbit isolated colon show that a carbachol-induced contraction is accompanied by a decrease in cAMP content of the smooth muscle. (+/-)-alpha-(Benzoylamino)-4-[2-(diethylamino)-ethoxy]-NN-di-propylbenzen-propanamid (tiropramide, CR 605), a new tyrosine derivative with antispastic properties, increases cAMP concentrations within the same dose range that produces smooth muscle relaxation with or without carbachol (0.1 microM). These effects are potentiated by 1 mM theophylline, a phosphodiesterase inhibitor. In a purified microsomal preparation from rabbit colon smooth muscle, corresponding to sarcoplasmic reticulum, tiropramide induced a dose-dependent increase Ca2+ binding in the presence of ATP and Mg2+. Tiropramide inhibited phosphodiesterase activity in rabbit colon homogenates in a range of doses about ten times that producing relaxation, cAMP content enhancement and increase Ca2+ binding to sarcoplasmic reticulum. The effects of tiropramide on the carbachol-stimulated rabbit colon in the presence of theophylline, indomethacin of PGE1 are more in agreement with an action of tiropramide as inhibitor of cAMP catabolism than as a result of a prostaglandin-mediated effect. These observations suggest that the smooth muscle relaxant activity of tiropramide arises from drug-induced increase of cAMP concentrations possibly because of inhibition of cAMP catabolism. This effect is accompanied by the binding to the sarcoplasmic reticulum of Ca2+, preventing its interaction with the contractile proteins of the smooth muscle. A direct effect of tiropramide-enhanced cAMP content on contractile proteins in the smooth muscle cannot be excluded.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D003106:Colon / Q000187:drug effects; D000242:Cyclic AMP / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D010276:Parasympatholytics / Q000494:pharmacology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D011458:Prostaglandins E / Q000494:pharmacology; D011817:Rabbits; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D010276:Parasympatholytics; D010726:Phosphodiesterase Inhibitors; D011458:Prostaglandins E; D014443:Tyrosine; D000242:Cyclic AMP; C031173:tiropramide; D002118:Calcium; D007213:Indomethacin