title: Which of caffeine's chemical relatives are able to evoke contractures in mammalian heart?
abstract: At concentrations between 0.5 mM and 10 mM caffeine, theophylline, theobromine, imidazole, 2-methyl imidazole, 5-amino-4-imidazole carboxamide, naphazoline, antazoline, and tolazoline in normal MacEwen solution induce contractures in rat and guinea pig myocardium. 9-Methylxanthine, 1,3,9-trimethylxanthine, hypoxanthine, or 2-imidazolidone, when similarly applied, do not. These observations, and similar results from frog heart, can be interpreted assuming that an unsaturated position 9 nitrogen in a xanthine molecule or in the equivalent position of an imidazole group is necessary for the release of calcium into the sarcoplasm to be initiated and therefore for a contraction to develop. The site of action of these compounds is likely to be the sarcoplasmic reticulum.
mesh_terms: D000818:Animals; D002110:Caffeine / Q000031:analogs & derivatives / Q000494:pharmacology*; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000187:drug effects; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects*; D051381:Rats; D013329:Structure-Activity Relationship; D013696:Temperature; D013805:Theobromine / Q000494:pharmacology; D013806:Theophylline / Q000494:pharmacology; D016276:Ventricular Function; D014970:Xanthines / Q000494:pharmacology
chemical_list: D007093:Imidazoles; D014970:Xanthines; D002110:Caffeine; D013806:Theophylline; D013805:Theobromine