CHAPTER VI 

 THE THYROID AND PARATHYROIDS (continued) 



Nature of the Autacoid Substances produced by the Thyroid 



The active principle of the thyroid which is concerned with metabolism 

 has been usually assumed to be represented by the non-proteid nitrogenous 

 material known as iodo-thyrin, or by the compound of this with protein 

 (iodo-thyro-globulin). The former was prepared from thyroid by Baumann 

 (1895), and found by him to contain a marked amount of iodine (03 to 

 0"9 per mille of dry substance). In confirmation of this assumption, the 

 experiments of Reid Hunt, Marine, and others show that the production 

 of the autacoid is promoted by administration of iodides, and that there is 

 a certain relation between the physiological activity of the gland and its 

 iodine content. But the fact that even when the desiccated thyroid con- 

 tains a considerable amount of iodine it is sometimes found to have no 

 action suggests that Baumann's substance may not be the actual autacoid, 

 although it may be associated with it. . We are, in fact, still in the dark as 

 to the true nature of this autacoid, and it seems better to express our 

 ignorance by a term which implies no theory, leaving the question of its 

 identity with iodo-thyrin or iodo-thyro-globulin open. I propose, therefore, 

 provisionally to apply the word thyrine to denote the active principle, 

 whether it be identical with or contained in the iodo-thyrin of Baumann 

 or not. 



As we have already seen, the autacoid of the parathyroid (parathyrine) 

 is probably of chalonic, i.e. of inhibitory nature, serving to keep in check 

 the activity of certain tissues, especially of nerve-cells. On the other hand, 

 the autacoid of the thyroid (thyrine) acts like a hormone in increasing 

 their excitability. This increase of excitability is especially well marked 

 in connexion with the sympathetic. The question arises : Is this a direct 

 effect on the sympathetic system, or is it indirect through the adrenals, 

 which are stimulated to increased secretory activity by excess of thyroid 

 in the blood ? The answer is not easy. But it may be stated that although 

 certain symptoms of hyperthyroidism are similar to those produced by 

 excess of adrenalin in the blood, others are not so. This is the case 

 with the flushing of the skin, which is due to vascular dilatation; 

 whereas adrenalin ordinarily produces vasoconstriction. Further, excess 

 of adrenalin in the blood leads to glycosuria, which is not as a general 

 rule seen in exophthalmic goitre, nor is glycosuria a necessary result of 



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