Evidence for thyroid hormone as a positive regulator of serum thyrotropin bioactivity

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Data
2007-08-01
Autores
Oliveira, Juliana Helena Abreu de [UNIFESP]
Barbosa, Erika Ribeiro [UNIFESP]
Kasamatsu, Teresa Sayoko [UNIFESP]
Abucham, Julio [UNIFESP]
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Context: the regulation of TSH bioactivity in humans is not completely understood.Objective: the aim of the study was to investigate the role of serum thyroid hormones in regulating the bioactivity of TSH.Design: We determined in vitro TSH bioactivity and glycosylation in nine patients (six females and three males, age 41.3 yr) with primary hypothyroidism before and after L-T(4) replacement, in 11 age- and sex-comparable controls (seven females and four males, age 37.6 yr), and in two thyroidectomized patients with TSH-secreting adenomas during and after L-T4 withdrawal.Methods: in vitro TSH bioactivity was measured by a sensitive and specific bioassay based on cAMP generation by Chinese hamster ovary cells transfected with human TSH receptor. TSH glycosylation was assessed by concanavalin A lectin and ricin column affinity chromatography.Results: in vitro TSH bioactivity in hypothyroid patients was low as compared with controls (0.48 +/- 0.1 vs. 1.1 +/- 0.2; P = 0.004) and increased during L-T(4) (0.48 +/- 0.1 vs. 0.8 +/- 0.1; P = 0.01). A strong significant correlation (r = + 0.80; P = 0.004, Spearman) was observed between the absolute increments of serum TSH bioactivity and T(3) during L-T(4) replacement. the degree of sialylation was elevated in hypothyroid patients before treatment (47 +/- 2.4% vs. 29 +/- 4.3%; P = 0.002) and decreased significantly after L-T4 (47 +/- 2.4% vs. 33 +/- 4.3%; P = 0.02). the mannose content of serum TSH in hypothyroid patients was similar to controls and did not change during L- T(4). in vitro TSH bioactivity also decreased in patients with TSH-secreting adenomas during L-T(4) withdrawal.Conclusion: These data indicate that serum thyroid hormone level is a positive regulator of TSH bioactivity.
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Journal of Clinical Endocrinology & Metabolism. Chevy Chase: Endocrine Soc, v. 92, n. 8, p. 3108-3113, 2007.