ECE2015 Eposter Presentations Pituitary: clinical (121 abstracts)
Alterations in thyroid hormone levels following GH replacement exert complex biological effects
Nigel Glynn 1 , Helena Kenny 2 , Tarik Salim 1 , David J Halsall 3 , Gerard Boran 4 , Paul Cook 5 , Diarmuid Smith 1 , Tommy Tun 6 , John H McDermott 6 , William Tormey 1 , Chris J Thompson 1 , Brendan McAdam 1 , Donal O’Gorman 2 & Amar Agha 1
1Beaumont Hospital and RCSI Medical School, Dublin, Ireland; 2Dublin City University, Dublin, Ireland; 3Addenbrooke’s Hospital, Cambridge, UK; 4Adelaide and Meath Hospital, Dublin, Ireland; 5University Hospital Southampton, Southampton, UK; 6Connolly Memorial Hospital, Dublin, Ireland.
Introduction: Alterations in the hypothalamic–pituitary–thyroid axis have been reported following GH replacement, with a decline in circulating T4 concentration the most consistent finding. However, the clinical significance of GH-induced alterations in circulating levels of thyroid hormone is unclear.
Aim: To examine the relationship between changes in serum concentration of thyroid hormones and known biological markers of thyroid hormone action.
Methods: We performed a prospective study of 20 hypopituitary adult men before and after routine GH replacement. Serum TSH and thyroid hormone (free T4, total T4, free T3, total T3, and reverse T3) were measured before and after GH substitution. Changes in thyroid hormone concentrations were compared to alterations in serum biomarkers of thyroid hormone action. Resting energy expenditure (REE) and cardiac systolic time intervals were also evaluated as sensitive markers of thyroid hormone exposure.
Results: The mean daily dose of GH was 0.34±0.11 mg. Following GH replacement, free T4 levels declined as expected (−1.28±0.44 pmol/l, P=0.02). Reverse T3 levels also fell (−3.44±1.42; P=0.03) and free T3 levels increased significantly (+0.34±0.15; P=0.03). REE did not rise as expected with GH substitution. SHBG and CK levels were unchanged. However, ferritin, copper, and caeruloplasmin declined suggesting reduced hepatic exposure to thyroid hormone (−26.8±8.5; P=0.005); (−1.7±0.63; P=0.02); and (−0.02±0.01; P=0.04). Complex alterations in lipid profile, including a rise in large HDL particles (+1.75±0.69; P=0.02) and Lp (a) (+12.5±4.7; P=0.002) as well as a fall in intermediate density lipoprotein concentration were variably associated with changes in thyroid hormone and GH. Cardiac systolic time intervals were unchanged. Observed changes in thyroid hormone biomarkers were more pronounced in subjects with multiple pituitary hormone deficiencies.
Conclusion: Our study demonstrates that GH replacement does not improve the biological actions of thyroid hormone in adults.
Disclosure: This work was supported by an unrestricted educational grant from Merck Serono.
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Endocrine Abstracts
ISSN 1470-3947 (print) | ISSN 1479-6848 (online)
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