THE EFFECT OF THYROXIN, CORTICOSTEROIDS, AND EPINEPHRINE ON ATRIAL RATE

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

Rate of contraction of atria isolated from normal, hyperthyroid, hyperthyroid adrenalectomized, hyperthyroid adrenalectomized corticosterone-treated, euthyroid adrenalectomized, hypothyroid, hypothyroid adrenalectomized, and hypothyroid adrenalectomized corticosteronetreated rats was studied. The rate of contraction was modified by the addition of graded doses of epinephrine. The following observations were made: the rate of contraction varied according to thyroid activity, atria from hypothyroid rats contracting slowest and those from thyroxin-treated rats fastest. The maximal atrial rates obtained by adding epinephrine varied directly with the level of thyroid activity. Adrenalectomy significantly reduced control rates of atria from hyperthyroid animals, but did not lower the rate of atria from euthyroid and hypothyroid animals significantly. The rates of atria from adrenalectomized hypothyroid and euthyroid animals responded to epinephrine with significantly lower rates than did the atria from hypothyroid and euthyroid animals not previously adrenalectomized.

Corticosterone treatment abolished the effect of adrenalectomy in the hyperthyroid group. Corticosterone treatment in the hypothyroid group resulted in a significantly higher control rate than seen in the atria from hypothyroid nonadrenalectomized animals.