Cardiac responsiveness after acute withdrawal of chronic propranolol treatment in rats

1. This study examined possible effects of chronic beta-adrenergic blockade on (a) rat myocardial beta-adrenergic receptors and (b) the responsiveness of isolated atria and right ventricular strips to various agents. 2. Following withdrawal of propranolol or saline treatment, significant left shifts were noted in the inotropic responses of propranolol-treated right ventricular strips to isoproterenol and norepinephrine. 3. This supersensitivity could not be demonstrated in left atrial inotropic or right atrial chronotropic responses. 4. Treatment and withdrawal did not alter (a) the inotropic responsiveness of right ventricular strips to extracellular calcium, methoxamine, ouabain, glucagon, 3-isobutyl-l-methylxanthine, acetylcholine or methacholine, or (b) beta-adrenergic receptors in ventricular membranes.