Effect of triac and beta-adrenergic blocking agents on the myocardium of developing rats

Triiodothyroacetic acid, triac, when given to rats during pregnancy, causes hypertrophy and intracellular disarray in the hearts of their offspring and concurrent treatment with dl propranolol can prevent the latter abnormality. Further experiments have been carried out to test the effect of dl oxprenolol and d propranolol on triac-induced myofibrillar disarray. Administration of dl oxprenolol at the same time as triac prevented disarray but a higher dose than that of dl propranolol was required to produce this effect. Disarray was also prevented by d propranolol. Selective consideration of the membrane stabilising, beta blocking and agonist activities of dl oxprenolol and d and dl propranolol leads to the conclusion that although direct or indirect beta stimulation by triac may play a small part in its disruptive effect on the developing myocardium, its main deleterious action can be blocked by membrane stabilisation.