CARDIAC AND VASCULAR EFFECTS OF SYMPATHOMIMETIC DRUGS AFTER ADMINISTRATION OF TRI-IODOTHYRONINE AND RESERPINE.

In spinal cats treated with tri-iodothyronine, the effects of sympathomimetic drugs on cardiac contraction were diminished. Ouabain failed to restore the effects on the contractile force of the heart. The effects of sympathomimetic drugs on the force of contraction of papillary muscle were not reduced by tri-iodothyronine, but the threshold for induction of automaticity was lowered. There was no evidence that in cats treated with reserpine the sensitivity of peripheral vessels to sympathomimetic agents is decreased and that blood pressure changes are merely secondary to changes in cardiac contraction.