Effect of hypothyroid status on myocardial responses to sympathomimetic drugs.

The physiological relationship between thyroid hormone and the catecholamines has been investigated for many years (1, 2). In spite of numerous studies it is still not clear whether thyroid status alters the sensitivity of the heart to catecholamines. Coville (3) has reported that thyroid hormone increased the magnitude of the response to catecholamines, while some authors have failed to show that altering the thyroid status affects the response to catecholarnines (4, 5). Recently, it was tried to explore some effects of thyroidectomy on the response of alpha and beta adrenergic receptor mechanisms to catecholamines (6). A few workers have reported the existence of both alpha and beta receptors in the hearts of mammals (7, 8). Present studies reported here were made in an attempt to clarify some of the discrepancies in many reports by seeking a quantitative difference between different types of cardiac adrenergic receptor mechanisms after 6-propyl-2-thiouracil (PTU) treatment.