[Cardiac function and adrenergic regulation in incipient hyperthyroidism]

The authors investigated in 14 euthyroid women the action of triiodothyronine administered for 7 days, 100 micrograms per day. It was revealed that after the administration of triiodothyronine the duration of the preejection period of the systole was reduced as well as the index of the preejection period and the index of the electromechanical systole, and the weight declined. At the same time the authors recorded a drop of the plasma noradrenaline and adrenaline level, of the serum cholesterol and thyroxine concentration. The serum triiodothyronine level increased and correlated inversely with the duration of the preejection period. Triiodothyronine administration had no effect on the heart rate, Q-Kd interval, blood pressure and plasma concentration of cyclic adenosine monophosphate. The authors conclude from the findings that in triiodothyronine-induced hyperthyroidism the first cardiac effect of the administered hormone is enhanced contractility of the heart, this change being due to the direct effect of triiodothyronine not mediated by catecholamines.