Homeostatic equilibria between free thyroid hormones and pituitary thyrotropin are modulated by various influences including age, body mass index and treatment. (7th July 2014)

• Record Type: Journal Article
• Authors: Hoermann, Rudolf; Midgley, John E.M.; Giacobino, Adrienne; Eckl, Walter A.; Wahl, Hans Günther; Dietrich, Johannes W.; Larisch, Rolf
• Is Part Of: Clinical endocrinology. Volume 81:Number 6(2014:Dec.)
• Page Start: 907
• Page End: 915
• Publication Date: 2014-07-07
• Subjects: Endocrinology -- Periodicals; 616.4005
• DOI: 10.1111/cen.12527
• Languages: English
• ISSNs: 0300-0664

Abstract

<abstract abstract-type="main" id="cen12527-abs-0001"> <title>Summary</title> <sec id="cen12527-sec-0001" sec-type="section"> <title>Objective</title> <p>We examined the interrelationships of pituitary thyrotropin (TSH) with circulating thyroid hormones to determine whether they were expressed either invariably or conditionally and distinctively related to influences such as levothyroxine (L‐T4) treatment.</p> </sec> <sec id="cen12527-sec-0002" sec-type="section"> <title>Design and methods</title> <p>This prospective study employing 1912 consecutive patients analyses the interacting equilibria of TSH and free triiodothyronine (FT3) and free thyroxine (FT4) in the circulation.</p> </sec> <sec id="cen12527-sec-0003" sec-type="section"> <title>Results</title> <p>The complex interrelations between FT3, FT4 and TSH were modulated by age, body mass, thyroid volume, antibody status and L‐T4 treatment. By group comparison and confirmation by more individual TSH‐related regression, FT3 levels were significantly lower in L‐T4‐treated <italic>vs</italic> untreated nonhypothyroid autoimmune thyroiditis (median 4·6 <italic>vs</italic> 4·9 p<sc>m</sc>, <italic> P</italic> < 0·001), despite lower TSH (1·49 <italic>vs</italic> 2·93 mU/l, <italic>P</italic> < 0·001) and higher FT4 levels (16·8 <italic>vs</italic> 13·8 p<sc>m</sc>, <italic> P</italic> < 0·001) in the treated group. Compared with disease‐free controls, the FT3‐TSH relationship was significantly displaced in treated patients with carcinoma, with median TSH of 0·21 <italic>vs</italic> 1·63 (<italic>P</italic> < 0·001) at a comparable FT3 of 5·0 p<sc>m</sc> in the groups. Disparities were reflected by calculated deiodinase activity and remained significant even after accounting for confounding influences in a multivariable model.</p> </sec> <sec id="cen12527-sec-0004" sec-type="section"> <title>Conclusions</title> <p>TSH, FT4 and FT3 each have their individual, but also interlocking roles to play in defining the overall patterns of thyroidal expression, regulation and metabolic activity. Equilibria typical of the healthy state are not invariant, but profoundly altered, for example, by L‐T4 treatment. Consequently, this suggests the revisitation of strategies for treatment optimization.</p> </sec> </abstract>