The Rôle of Thyroxin Iodine and Total Organic Iodine in the Calorigenic Action of Whole Thyroid Gland

Abstract

In a previous communication (1) we have shown that thyroxin polypeptide has a calorigenic action identical to that of pure racemic thyroxin when the two are given, intravenously, in doses containing equal quantities of iodine. It was further shown that thyroxin polypeptide is as active when taken by mouth as when given intravenously. These facts can be taken advantage of for the further study of thyroid physiology. The present paper deals with the calorigenic activity of certain brands of whole thyroid gland, the calorigenic action of thyroxin polypeptide being used as a basis of comparison. The ultimate object is not to study the pharmacology of these drugs per se but to discover in what form the natural hormone circulates and is effective.It is known that the organic iodine of whole thyroid gland is found partly in the form of thyroxin and partly in the form of diiodotyrosin (2). It has been shown by Thompson (3) and others (4) that diiodotyrosin exerts no calorigenic action in human myxedema even when given in very large doses. One would suppose therefore that the calorigenic action of whole thyroid would be determined by its thyroxin iodine rather than by its total organic iodine content. The data here presented prove that this supposition is incorrect.Three patients with full-blown, untreated, spontaneous myxedema were given, daily, 15 grains (1.0 gram) of a lot of Armour and Company's thyroid, which had been found by analysis, according to Harington and Randall's method (5), to contain 0.05 per cent of thyroxin or so-called active iodine (the acid insoluble fraction) and 0.22 per cent of total organic iodine.' The dosage of thyroid chosen contained 0.49 mgm. of thyroxin 1 At the outset of this investigation we were forced, in selecting our analytical method, to choose between the procedure of Harington and Randall (5) and of Leland and Foster (7). The latter method involves a twenty-four-hour alkaline hydrolysis, and gives lower values for thyroxin content. W. W. Palmer and co-workers (8) have recently published data which indicate that the lower figures may be more accurate.In view of the comparative newness of both procedures, it seemed to us 683

The Calorigenic Action of D- And L-Thyroxin

“…The role of physical properties such as solubility or optical activity must be identified. The possibility of enhancement of physiologic potency brought about by alteration in physical state has been mentioned in previous communications (1) (2). In the first paper of this series (1) it was shown that racemic crystalline thyroxin and optically active thyroxin polypeptide had equal calorigenic activity when given in equal iodine dosage.…”

Serum Iodine in Hypothyroidism Before and During Thyroid Therapy 12

“…This hypothesis involves 3 assumptions: that all the dried thyroid is absorbed from the alimentary tract; that it is quantitatively as effective as the natural hormone; and lastly, that the hypothyroid patient's own gland contributes no hormone. Although complete intestinal absorption has not been proved directly, it is strongly suggested by the fact that in the treatment of human hypothyroidism, desiccated thyroid is even more effective than intravenous thyroxine in iodoequivalent amounts (19). The validity of the second assumption has already been discussed.…”

The Effect of Diiodotyrosine on the Basal Metabolism in Myxedema 1

“…The reason for the apparent difference in the effect of very large doses of diiodotyrosine in tadpoles and man is not clear. Means, Lerman and Salter (27) have recently advanced the hypothesis that diiodotyrosine assumes calorigenic properties when linked with amino-acids in iodothyreoglobulin.…”