DYNAMICS OF SERUM rT3 AND 3, 3‐T2 DURING rT3 INFUSION IN PATIENTS TREATED FOR THYROTOXICOSIS WITH PROPYLTHIOURACIL OR METHIMAZOLE

The thyroid hormone secretory response to TSH was studied in twenty-eight patients undergoing thyroid and parathyroid surgery. Eighteen patients received bovine or human exogenous TSH by injection into a thyroid artery, and 10 received TRH to stimulate endogenous TSH secretion. Thyroid secretion rates of T4, T3, and rT3 were determined directly from measurement of blood flow and the hormone gradient across the gland. A significant secretory response was seen for all three hormones following TSH increase. T3 secretion accelerated more rapidly than that of T4 and rT3, thus reducing the T4/T3 and rT3/T3 ratios. The T4/rT3 ratio fell during the first 30 min but then increased. The responses correlated with the area under the curve of the TSH serum concentration, and were similar after administration of bovine and human exogenous TSH, and TRH. Conclusions regarding preferential secretion ought to be made by comparing ratios of thyroid hormone secretion with those of the hormone content of the gland, but our results indicate that TSH induces preferential secretion of triiodothyronines in man.

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Three-compartmental analysis of effects of D-propranolol on thyroid hormone kinetics

Heijden

Krenning

Toor

et al. 1988

American Journal of Physiology-Endocrinology and Metabolism

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Tracer thyroxine (T4), 3.3',5-triiodothyronine (T3), and 3,3',5'-triiodothyronine (rT3) kinetic studies were performed in normal T4 substituted subjects before and during oral D-propranolol treatment to determine whether changes in thyroid hormone metabolism in a propranolol-induced low-T3 syndrome result from inhibition of 5'-deiodination or inhibition of transport of iodothyronines into tissues. Data were analyzed according to a three-compartmental model of distribution and metabolism. T4 plasma appearance rate decreased by 16% (P less than 0.01), reflecting a decreased intestinal absorption of orally administered T4 during propranolol. Serum T4 and free T4 levels increased significantly by 14%, whereas T4 metabolic clearance rate (MCR) was lowered by 26% (P less than 0.001). No changes were observed in size of the three T4 compartments or in fractional and mass transfer rates of T4 from plasma to the rapidly (REP) and slowly (SEP) equilibrating pools. Serum T3, free T3, T3 plasma pool, T3 mass transfer rate to REP and SEP, and the T3 pool masses were all significantly decreased during propranolol to a similar extent as the T3 plasma production rate (PR). T3 MCR decreased by 14% (P less than 0.05). Serum total and free rT3 increased, whereas the rT3 MCR was substantially lowered during propranolol (P less than 0.001). The rT3 plasma pool, rT3 REP and SEP, and the mass transfer rates to REP and SEP increased, whereas no alterations were observed in rT3 PR and fractional transfer rates of rT3 to REP and SEP.(ABSTRACT TRUNCATED AT 250 WORDS)

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DYNAMICS OF SERUM rT3 AND 3, 3‐T2 DURING rT3 INFUSION IN PATIENTS TREATED FOR THYROTOXICOSIS WITH PROPYLTHIOURACIL OR METHIMAZOLE

Cited by 4 publications

References 21 publications

Neonatal Thyroid Function after Propylthiouracil Therapy for Maternal Graves' Disease

Neonatal Thyroid Function after Propylthiouracil Therapy for Maternal Graves' Disease

Thyroid Hormone Secretion Rates: Response to Endogenous and Exogenous TSH in Man During Surgery*

Three-compartmental analysis of effects of D-propranolol on thyroid hormone kinetics

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