The effect of trimepranol on the binding of [3H] norepinephrine in myocardial subcellular fractions of the dog.

The effect of Trimepranol on the binding of 3H norepinephrine to myocardial particles from dogs (to fractions 1,000 g and 78,000 g resp.) has been studied and compared with the effect of propranolol, isoprenaline, phentolamine and ephedrine. Displacement of 3H norepinephrine by propranolol and isoprenaline was found in both fractions. Trimepranol, in low concentrations, inhibited the binding of 3H norepinephrine; in higher concentrations the binding of 3H norepinephrine was stimulated. Phentolamine and ephedrine were without effect in both fractions. The problem of specificity of adrenergic binding sites is discussed.