CARDIOVASCULAR EFFECTS OF THYROXINE TREATMENT IN NORMAL RATS

Abstract

Metabolic rate, blood pressure, weight and rate of the heart, cardiac output, and work were determined at weekly intervals in groups of normal rats receiving thyroxine. The measurements were made before and during the infusion of polyvinylpyrrolidone into the right side of the heart. The maximum values of cardiac output and work obtained during infusion were considered to be an approximate measure of the strength of the heart. Cardiac output and work in thyroxine-treated rats far exceeded the normal values before as well as during infusion. The greater strength was not merely the consequence of the greater size of the heart which developed in the course of thyroxine treatment. Hearts of similar size — coming from larger normal rats or from smaller normal rats with cardiac hypertrophy due to aortic constriction — did significantly less work than the hearts of thyroxine-treated rats.