Influence of alpha- and beta-adrenergic antagonists on dopamine-induced responses in the isolated heart of Mercenaria mercenaria.
Agents with predominantly adrenergic antagonistic properties (the alpha-blockers, phentolamine and tolazoline, and the beta-blocker propranolol), and those with suspected alpha-blocking capabilities [hydralazine and 3,3'-(4,4'-biphenylene)bis(2,5-diphenyl-2H-tetrazolium chloride) (neotetrazolium chloride); I] were added individually to a bath containing an isolated Mercenaria mercenaria heart. Two and one-half minutes later, dopamine was added to the bath as the second drug and cardiac responses were noted. Pretreatment with saline controls, followed by dopamine 2.5 min later, produced results that were identical with those which occurred after the administration of dopamine alone, i.e., marked stimulation and cardiac arrest. Pretreatment with phentolamine and I were the only procedures that prevented dopamine-induced cardiac arrest. Phentolamine, tolazoline, and hydralazine generally produced positive inotropic responses when initially added to the bath, whereas propranolol mimicked the effects caused by the addition of dopamine alone or after saline pretreatment. The M. mercenaria heart appears to possess an adrenergic receptor of an alpha-configuration.
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000818:Animals; D049872:Bivalvia; D004298:Dopamine / Q000494:pharmacology*; D018492:Dopamine Antagonists; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects*
D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D018492:Dopamine Antagonists; D004298:Dopamine