Effect of phenoxybenzamine on myocardial cell necroses and blood levels of catecholamines in pigs subjected to stress.

The degree of myocardial cell necroses after stress was investigated in 6 pigs, weighing 70 to 90 kg. The stress was induced by a myorelaxant, succinylcholine, for about 12 min. The alpha-adrenoceptor blocking agent phenoxybenzamine (PBZ) was given orally 3 times a day in a total dose of 50 to 60 mg per day for 6 to 7 days before the stress. The plasma levels of noradrenaline and adrenaline were assayed in blood samples drawn before, during, and immediately after the period of stress. Heart cell necroses were found in all the cases. The activity of the sympathetic-adrenomedullary system, indicated by the plasma levels of catecholamines, was intense during the stress. When the present results were compared with those of earlier studies the degree of heart cell necroses was significantly smaller after PBZ in control pigs but significantly higher than after the beta-adrenoceptor blocking agent propranolol given for about a week. PBZ exerts a number of different actions, as briefly discussed, some of them appearing to be harmful for the heart during stress while others appear to be protective for the heart.