Comparison of the effects of forskolin and isoprenaline on tracheal, cardiac and skeletal muscles from guinea-pig.
Forskolin, a potent activator of adenylate cyclase, and isoprenaline, an unselective beta-adrenoceptor agonist, were studied in vitro on tissues from guinea-pig with respect to relaxation of the carbachol-contracted trachea, increase in the force of contraction of the papillary muscle and depression of subtetanic contractions of the soleus muscle, three well-characterized beta-adrenoceptor-mediated effects. Forskolin and isoprenaline relaxed the trachea and increased the force of contraction of the papillary muscle. Isoprenaline but not forskolin caused a depression of the subtetanic contraction of the soleus muscle. Forskolin did not seem to potentiate the effects of isoprenaline on the tissues studied; the combined effects appeared to be a mere addition. Forskolin did not increase the efficacy of the partial agonist prenalterol either. It is concluded that there is no simple relation between c-AMP generation and the functional response to beta-adrenoceptor agonists. Forskolin should not be used uncritically to probe beta-adrenoceptor-mediated effects.
D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology*; D005576:Colforsin; D004224:Diterpenes / Q000494:pharmacology*; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009132:Muscles / Q000187:drug effects*; D009200:Myocardial Contraction / Q000187:drug effects; D010210:Papillary Muscles / Q000187:drug effects; D011217:Practolol / Q000031:analogs & derivatives / Q000494:pharmacology; D011294:Prenalterol; D014132:Trachea / Q000187:drug effects
D002316:Cardiotonic Agents; D004224:Diterpenes; D005576:Colforsin; D007545:Isoproterenol; D011294:Prenalterol; D011217:Practolol