THE METABOLISM OF 3:3'-DIIODOTHYRONINE IN MAN*

Publisher Website
Google Scholar
Abstract
MONOIODOTYROSINE, diiodotyrosine, 3:5:3′-triiodothyronine and thyroxine are native substances in the thyroid gland. Normally, the latter two are secreted into the blood as the definitive thyroid hormones, but mono- and diiodotyrosine escape into the blood only under unusual circumstances (1). The metabolic fate of each of these substances has been observed after intravenous administration in man. Mono- and diiodotyrosine are rapidly degraded (2, 3), whereas thyroxine and triiodothyronine disappear more slowly—thyroxine with a half-time of approximately seven days (4) and triiodothyronine with a half-time of two to three days (5). Recently, evidence has been offered for the existence of 3:3′-diiodothyronine (3:3′-Th) in the thyroglobulin of the rat (6, 7), where it is said to account for as much as 25 per cent of the iodine previously attributed to thyroxine. Similarly it is said to account for as much as 25 per cent of the plasma iodine which previous methods of chromatographic separation had failed to resolve (8). The present studies describe the fate and excretion of 3:3′-Th after intravenous administration to subjects with and without thyroid disease. It will be shown that this substance is rapidly degraded. Its iodine appears in the urine almost entirely as free iodide.