The effects of some beta-adrenoreceptor blocking drugs on the uptake and release of noradrenaline by the heart.

1. The potencies of some beta-adrenoreceptor blocking drugs in reducing noradrenaline uptake by the isolated heart were compared with their potencies in reducing the release of noradrenaline from the heart by tyramine.2. Of the drugs tested, propranolol, pronethalol and dichloroisoprenaline were the most potent in blocking uptake and release of noradrenaline, although none was at potent as cocaine; MJ 1999 and I.C.I. 50172 were only weakly effective.3. Pronethalol and dichloroisoprenaline each reduced release of noradrenaline by tyramine in the concentration range (10(-7)-10(-6)M) where blockade of responses to tyramine was apparent; with these drugs both reduction of noradrenaline release and beta-receptor blockade contribute to the reduction in responses to tyramine.4. Potency of beta-receptor blocking drugs in reducing noradrenaline uptake is unrelated to potency in blocking beta-receptors; Kö 592 blocks beta-receptors without affecting noradrenaline uptake.