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Secretion of Thyroxine and Non‐Thyroxine Iodine by the Normal Human Thyroid Gland. Influence of Carbimazole and Pharmacological Doses of Iodide
Author(s) -
Bürgi H.,
Andersen M. C.,
Schwander J.,
Kohler H.,
Stude H.
Publication year - 1973
Publication title -
european journal of clinical investigation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.164
H-Index - 107
eISSN - 1365-2362
pISSN - 0014-2972
DOI - 10.1111/j.1365-2362.1973.tb00342.x
Subject(s) - carbimazole , endocrinology , medicine , iodine , triiodothyronine , thyroid , iodide , hormone , chemistry , reverse triiodothyronine , wolff–chaikoff effect , secretion , thyroid function , graves' disease , organic chemistry
. In order to measure the effect of antithyroid agents on thyroxine and non‐thyroxine iodine secretion by the normal human thyroid gland, 12 normal persons were given tracer amounts of iodide‐ 125 I. 7 to 11 days later thyroxine‐ 131 I was injected I.V. Two days later the following serial measurements were started: Serum protein‐bound labeled iodine (PB 125 PB 131 I), serum total thyroxine, and excretion of 125 I and 131 I in urine.–In the control period (no drugs) the secretion rate for thyroxine was 83 μg/day. Carbimazole (15 mg three times daily) for 6 days did not affect thyroxine secretion despite a complete block of iodine uptake by the thyroid. Non‐thyroxine iodine secretion was 59 μg/day in the control period and rose to 183 μg under carbimazole.–Non‐thyroxine iodine includes triiodothyronine and any non‐hormonal iodine, such as iodide derived from the deiodination of iodotyrosines, secreted by the gland. Based on recently published estimates it was assumed that the triiodothyronine contribution was not more than 24 μg. This left a considerable efflux of non‐hormonal iodine even in the control period. Most of the non‐hormonal iodine produced, however, was recycled into thyroglobulin without leaving the gland. After blocking reutilization by carbimazole large amounts of non‐hormonal iodine were secreted by the gland. High doses of iodide (30 mg three times daily) in combination with carbimazole led to a rapid 45% decline in thyroxine secretion. Since a complete block of hormone synthesis by carbimazole alone had no such effect, high iodide doses must act at a different site, presumably by slowing down the release of hormone from preformed thyroglobulin stores. The findings indicate that carbimazole enhances the sensitivity of the normal thyroid gland toward pharmacological doses of iodide.–High doses of iodide together with carbimazole reduced the secretion of non‐hormonal iodine (which can be taken as an index of thyroglobulin hydrolysis) by only 31%. Moreover some subjects showed no reduction at all, despite of concomitant fall in hormone secretion. The lack of correlation between the decreases of thyroxine and of non‐hormonal iodine secretion does not support the generally held view that high doses of iodide block hormone release by interfering with the hydrolysis of thyroglobulin.