Recent advances in endocrinology / by A.T. Cameron.

  • Alexander Thomas Cameron
Date:
1947
Catalogue details

Licence: In copyright

Credit: Recent advances in endocrinology / by A.T. Cameron. Source: Wellcome Collection.

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    sectomy (and thus removal of thyrotrophic stimulation) does not appear to lessen formation of diiodotyrosine, but does deerease formation of thyroxine. Leblond stresses the faet that under normal physiologieal eondi- tions, with minute amounts of available iodine, the thyroid ean abstraet about 50 per eent. of it, in eontrast with abstraetion of relatively minute amounts from large doses. Under physiologieal eireumstanees iodide is transformed to diiodotyrosine as it enters the thyroid, while later on thyroxine is slowly formed from this. When large doses of iodide are administered, initially the gland contains much iodide, which later changes to organic forms. Only iodide is taken up by the gland. Thus when diiodotyrosine is administered (and it has been recommended for therapeutic use) it is largely excreted, and the proportion taken up by the gland must be changed first to iodide. Morton and Chaikoff, using radioactive as tracer element, have shown that surviving tissue slices of thyroid from sheep, dog and rat will transform iodide into thyroxine and diiodo¬ tyrosine. When 300 to 350 mg. of rat thyroid were incubated in a bicarbonate-Ringer solution along with the iodine, subsequent tissue hydrolysis showed that 12 per cent, of the was present in thyroxine radicals and 70 per cent, in diiodotyrosine radicals. Dog and sheep thyroids produced a smaller degree of transforma¬ tion, but in similar ratio between the two. This in vitro incor¬ poration of iodine failed to occur with homogenized glands (cf. Chaikoff et al. (2) ). Most of the above results confirm conclusions reached by older methods. Radioactive studies have suggested the unexpected conclusion that tissues other than the thyroid retain a primitive ability to synthetize thyroxine or some compound with like activity (Chapman ; Morton, Chaikoff et al. ; Chapman et al.). The Function of the Thyroid It is generally considered that thyroid function is linked with oxidative processes of the body cells, yet it is not possible to demonstrate that all the manifold changes associated on the one hand with thyroid deficiency and on the other hand with thyroid hyperactivity can be accounted for directly or indirectly by a change in the level of cell oxidation. To appreciate this some of these effects must be listed. Experimental thyroidectomy produces in animals at all ages a
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