Abstract
Isometric tension responses of isolated porcine coronary artery rings were studied in the presence of concentrations of propranolol higher than those necessary to block effects mediated by β-adrenergic receptors. Propranolol (50-300 μM) inhibited contractions induced by 30mM KCl and by histamine, norepinephrine, and acetylcholine in a concen tration-dependent, noncompetitive fashion. The (+) propranolol isomer and the racemic mixture were equipotent inhibitors of contraction. Propranolol inhibition was partly reversed by increased extracellular Ca++. These effects of propranolol thus appeared to be independent of β-blockade and could be relevant to some of the drug's observed but still unexplained in vivo actions.
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