The Effect of Thyroid and Thyroxine on the Concentration of Creatine in the Heart, Muscle, Liver, and Testes of the Albino Rat

Concerning the Relation of Environmental Temperature to Resistance to Thyroid and Thyroxine, and the Creatine Content of the Heart and Other Tissues in Experimental Hyperthyroidism

“…These changes, which appeared more degenerative than functional, were essentially alike in the thyroid or thyroxine treated rats and in the untreated controls. P a r t y on the basis of the data of Fieschi and Gavazzeni (15), Buell, Strauss and Andrus (16), and on that of a limited number of observations of the changes in phosphocreatine by one of us (10), it may be suggested tentatively that in thyrotoxicosis, the glycogen and phosphocreatine mechanisms are primarily affected and that the depletion of total creatine follows the loss of phosphocreatine. In acute intoxications, such as occur at high temperatures, death from heart failure may thus occur when the phosphocreatine of the myocardium has fallen to a fraction of normal, but before the total creatine content has become markedly reduced.…”

“…At the termination of each experiment, the organs were removed, weighed and preserved for microscopic study. To add to the data previously reported (10,13), and for reasons to be considered presently, estimations were made of the creatine content of the myocardium, liver, testes and the muscles of the hind limbs. The influence of external temperature on the resistance to thyroid and thyroxine is illustrated by the data charted in Text-fig.…”

“…A conspicuous effect of hyperthyroidism in the rat, induced by the administration of thyroid or thyroxine, is the marked reduction of the creatine content of the myocardium (10), frequently to about 50 per cent of normal. There is apparently a critical level below which the creatine concentration cannot be readily depressed.…”