Abstract
Employing propranolol as a non-selective beta-blocker, atenolol, acebutolol and metoprolol as selective betal-blockers, butoxamine as a selective beta2-blocker, labetalol as an alpha- and beta-blocker, and phentolamine as an alpha-blocker, we compared the effects of these adrenoceptor-blocking agents to reduce the degree of the myocardial injury induced by epinephrine in mice. Epinephrine in a single dose of 4mg/kg/day, s.c., daily for 7 days, caused widely extended lesions, necrosis and fibrosis in the myocardial fibers, and degeneration in the residual myocaridal fibers. The adrenoceptor-blocking agents in a dose of 10mg/kg/day, s. c., given 30 minutes prior to epinephrine to each mouse daily for 7 days, had reduced the degree of the myocardial injury induced by epinephrine. The blockers, all, effectively suppressed the injury. Although metoprolol and butoxamine were less effective on the protection of the cardiotoxicity than phentholamine, the other blockers prevented the cardiotoxicity with the same degree as phentolamine did. These findings suggest that not only alpha- but also beta1- and beta2-adrenoceptors play critical roles in producing the myocardial injury.
