Direct cardiac actions of phenylephrine when used in assessment of baroreflex function in the rat.
In pentobarbitone-anaesthetised wistar rats, the baroreflex bradycardia in response to the vasopressor agent phenylephrine was converted to a tachycardia by propranolol. In pithed wistar rats, phenylephrine produced a marked tachycardia which was mediated largely by beta-adrenoreceptors since propranolol markedly antagonised the response. A component of the tachycardia was mediated by alpha 1-adrenoreceptors since the tachycardia to phenylephrine in the presence of propranolol was antagonised by prazosin and mimicked by the alpha 1-adrenoreceptor agonist amidephrine. It is concluded that phenylephrine is not a useful agent for assessment of baroreflex function in the rat due to its marked cardiac stimulant actions.
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D004983:Ethanolamines / Q000494:pharmacology; D006321:Heart / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D010656:Phenylephrine / Q000494:pharmacology*; D011311:Pressoreceptors / Q000187:drug effects*; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012018:Reflex / Q000187:drug effects*
D004983:Ethanolamines; D010656:Phenylephrine; D001285:Atropine; C016980:amidephrine; D011433:Propranolol