THYROXIN, RESERPINE, EPINEPHRINE AND TEMPERATURE ON ATRIAL RATE

¹ Division of Anesthesiology, College of Medicine, University of Florida, Gainesville, Florida

Rate of contraction of atria isolated from normal, reserpine-treated, hyperthyroid, hyperthyroid reserpine-treated, athyroid, and athyroid reserpine-treated rats was studied. The rate of contraction was modified by changes in temperature and by the addition of epinephrine. The following observations were made.

The rate of contraction varied according to the thyroid activity, atria from athyroid rats contracting slowest and those from thyroxin-treated rats fastest. Atria from hyperthyroid rats accelerated faster than those from athyroid or euthyroid rats in response to warming from 28° to 36°C and to epinephrine. The maximum atrial rates obtained by warming and by adding epinephrine varied directly with the level of the thyroid activity.

The rates of atria obtained from athyroid, euthyroid and hyperthyroid rats pretreated with reserpine were significantly lower than the rates in the corresponding nonreserpine treated groups of rats. Reserpine did not affect the acceleration during warming. It did augment the accelerating effect of epinephrine in atria from euthyroid rats but did not alter the effect of epinephrine in athyroid and hyperthyroid atria.

An abundance or absence of thyroid hormone appeared to be of greater significance in the control of atrial rate of contraction than the presence or absence of the reserpine effect.

Very high doses of epinephrine slowed the rate of atrial contraction in all groups.