title: Possible role of adenosine in the relaxant effect of amrinone on guinea-pig ileum.
abstract: In isolated segments of guinea-pig ileum, amrinone (0.3 mM-0.3 M) caused a transient contraction followed by a concentration-dependent relaxation. Theophylline (0.1-0.5 mM) mimicked the effects of amrinone but apparently inhibited relaxation induced by the latter. However the total decrease of muscle tension measured in preparations exposed to amrinone before and after theophylline treatment was quantitatively comparable. Dipyridamole (0.1 microM) potentiated the relaxing effect of amrinone. The stimulatory response of the ileum to high concentrations of adenosine (10-50 mM) was abolished by amrinone. In preparations treated with adenosine deaminase (10 U/ml) the basal tone was decreased and both amrinone and theophylline were ineffective. In rat ileum, amrinone exerted a marked relaxing effect that was abolished by adenosine deaminase. Thus amrinone appears to cause relaxation of intestinal smooth muscle from different species by hindering the stimulatory effect of endogenous adenosine. The possible intracellular localization of the amrinone-adenosine interaction site is discussed.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000241:Adenosine / Q000502:physiology*; D000243:Adenosine Deaminase / Q000378:metabolism; D000676:Amrinone / Q000494:pharmacology*; D000818:Animals; D004176:Dipyridamole / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D009125:Muscle Relaxants, Central; D009130:Muscle, Smooth / Q000187:drug effects*; D051381:Rats; D013806:Theophylline / Q000494:pharmacology
chemical_list: D009125:Muscle Relaxants, Central; D004176:Dipyridamole; D013806:Theophylline; D000243:Adenosine Deaminase; D000676:Amrinone; D000241:Adenosine; D000109:Acetylcholine