RADIOACTIVE IODINE AS AN INDICATOR OF THE METABOLISM OF IODINE V. THE EFFECTS OF HYPOPHYSECTOMY ON THE DISTRIBUTION OF LABELED THYROXINE AND DIIODOTYROSINE IN THYROID GLAND AND PLASMA¹

The Behavior of Radioiodine in the Blood 1

“…The possibility of in vivo exchange occurring in the blood remains a remote possibility but such exchange could not be demonstrated in vitro. The observations of precipitable radioiodine in this case may be of some interest in connection with the demonstration by Chapman (14) and by Morton and associates (15) that iodine may be organically combined elsewhere in the body than in the thyroid.…”

Passage of exogenous thyroxine and of iodide between mother and foetus in pregnant rabbits

“…This, however, rests on the assumptions that the foetus does not make thyroxine in tissues other than its thyroid, and that the thyroid hormone normally circulating in the maternal plasma behaves in the same way as exogenous labelled thyroxine. It is not known whether the foetus can make thyroxine outside the thyroid at any stage of its development, but the possibility cannot be excluded, since there is some evidence that adult rats can make thyroxine in the absence of the thyroid (Morton, Chaikoff, Reinhardt & Anderson, 1943). The amount of non-radioactive thyroxine injected into the mother must, in some cases, have greatly exceeded the daily output of hormone from the animal's own thyroid.…”

The Use of Radioiodine in Physiological and Clinical Studies on the Thyroid Gland

“…The rate at which organic binding and coupling goes on depends on the state of activity of the gland, and is accelerated by thyrotropin (50) and exposure to cold (51), slowed by hypophysectomy (4,52), and influenced by the previous iodide level (36). The rate is also affected by the iodide concentration at any moment (32), as noted below.…”

“…This assumption is perhaps unnecessary, however, since it has been found repeatedly that diiodotyrosine is rapidly destroyed in the body. Thus, Leblond and Sue (4) when the radioactivity first appears in the proteinbound iodine, it is predominantly in the diiodotyrosine-like fraction; later, it is chiefly in the thyroxine-like component (50).…”

“…If radioactively labelled iodide is injected into thyroidectomized rats, small amounts of the iodine can be recovered in the various tissues of the body as diiodotyrosine and thyroxine (54). The subcutaneous injection of elemental iodine will exert thyroid hormone-like effects (55) and produce considerable iodination of tissue protein (56), but this represents a highly unphysiological situation.…”