Comparison of the alpha-adrenergic agonists, phenylephrine and methoxamine in rabbit papillary muscles.
The positive inotropic effects of the alpha-adrenergic agonists, phenylephrine and methoxamine were compared in isolated rabbit papillary muscles. Phenylephrine in the presence of 10(-7)M propranolol produced a greater response than methoxamine. Antagonism by phentolamine was competitive for phenylephrine and apparently, noncompetitive for methoxamine. Based upon observed maximum following frequencies, 10(-4)M methoxamine had a greater cardiac depressant effect than 10(-4) phenylephrine. It was suggested that phenylephrine with a beta-adrenergic antagonist possessed advantages over methoxamine as an agonist for studying cardiac alpha-adrenergic receptors in rabbit papillary muscles.
D000818:Animals; D005260:Female; D008297:Male; D008729:Methoxamine / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects*; D010210:Papillary Muscles / Q000187:drug effects*; D010656:Phenylephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D011433:Propranolol; D011817:Rabbits; D011941:Receptors, Adrenergic / Q000187:drug effects*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D013268:Stimulation, Chemical
D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D011433:Propranolol; D008729:Methoxamine