title: Positive inotropic but no relaxant effects of phenylephrine in cat papillary muscle.
abstract: The effect of phenylephrine (30 micron) in the presence of propranolol (1 micron) on electrically induced isometric twitches and on KCl-contractures was studied in papillary muscles from reserpine-pretreated cats at 25 degrees C. Under these conditions phenylephrine has previously been shown to act solely via alpha-adrenoceptors and not to increase c-AMP. Phenylephrine increased force of contraction, time to peak tension and relaxation time. Contracture tension remained unaffected. These data indicate that the stimulation of cardiac alpha-adrenoceptors, in contrast to beta-adrenergic stimulation, does not lead to so-called relaxant effects. This qualitative difference between the two responses is probably due to the different capacity of both stimuli to increase c-AMP.
mesh_terms: D000818:Animals; D002415:Cats; D000242:Cyclic AMP / Q000378:metabolism; D004558:Electric Stimulation; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000378:metabolism; D010210:Papillary Muscles; D010656:Phenylephrine / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology
chemical_list: D010656:Phenylephrine; D011189:Potassium Chloride; D011433:Propranolol; D000242:Cyclic AMP