title: Blockade of the rate and force responses to phenylephrine on rat atria with labetalol.
abstract: Evidence suggests that the combined alpha and beta adrenergic agonist phenylephrine influences cardiac tissue through stimulation of both alpha and beta adrenoceptors. Phenylephrine effected a positive inotropic and chronotropic response in paced (1 Hz) left and spontaneously beating right atria, respectively. In the presence of the combined alpha and beta adrenoceptor antagonist labetalol (5 x 10(-6)M) the rate and force responses to phenylephrine were completely abolished. The data suggest that phenylephrine exerts its inotropic and chronotropic effects through both alpha and beta adrenoceptors in such a way that both adrenoceptors must be blocked in order to completely abolish the responses induced by the dual agonist.
mesh_terms: D000818:Animals; D004983:Ethanolamines / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects*; D066298:In Vitro Techniques; D007741:Labetalol / Q000494:pharmacology*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D010656:Phenylephrine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D051381:Rats
chemical_list: D004983:Ethanolamines; D010656:Phenylephrine; D007741:Labetalol