THE EFFECTS OF TRIIODOTHYRONINE ON HEMODYNAMIC RESPONSES TO EPINEPHRINE AND NOREPINEPHRINE IN MAN

¹ Section of Clinical Pharmacology and the Cardiovascular Research Laboratories, Departments of Internal Medicine and Pharmacology, and the Department of Preventive Medicine, University of Iowa College of Medicine, Iowa City, Iowa

The influence of triiodothyronine on hemodynamic responses to infusions of graded doses of epinephrine hydrochloride or norepinephrine bitartrate was studied in 14 normal male volunteers. Triiodothyronine produced a marked increase in sleeping pulse rate and oxygen consumption and a reduction in body weight and levels of serum cholesterol. Each subject was studied during a euthyroid session and during a hypermetabolic session. In group A (eight subjects), the increments in systolic and diastolic arterial pressures, mean right atrial pressure, heart rate, cardiac index and the changes in total systemic resistance during infusions of epinephnine (0.0375-0.30 µg/kg/min) were not significantly different in the two sessions. The absolute levels of mean arterial pressure during epinephrine were also similar in the two sessions. The increments in mean arterial pressure during epinephrine, however, were slightly greater during the euthyroid period. In group B (six subjects), the increments in systolic, mean and diastolic arterial pressures, mean right atrial pressure and total sustemic resistance and the reductions in heart rate and cardiac index during infusions of graded doses of norepinephrine (0.075-0.30 µg/kg/min) during the hypermetabolic session were not appreciably different from their responses during norepinephrine infusions when the subjects were euthyroid. These findings indicate that triiodothyronine does not augment hemodynamic responses to epinephrine and norepinephrine in man.