The effects of thyroid hormones on brown adipose tissue in humans: a PET-CT study.
BACKGROUND
Brown adipose tissue (BAT) is important for energy expenditure through thermogenesis, although its regulatory factors are not well known in humans. There is evidence suggesting that thyroid hormones affect BAT functions in some mammals, but the effects of thyroid hormones on BAT activity in humans are still unclear. The aim of this study was to investigate the effects of thyroid hormones on glucose metabolism of BAT and other organs in humans.


METHODS
Nine Graves' disease-caused hyperthyroid patients who were newly diagnosed and untreated were studied. Putative brown adipose tissue activity was determined by the integrated ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron-emission tomography and computed tomography (PET-CT). All hyperthyroid patients were treated with methimazole and had been monitored until their symptoms disappeared and thyroid hormone levels returned to normal. At the end, a second PET-CT scan was performed. The average follow-up period was 77 days. Meanwhile, compared with a group of seventy-five brown adipose tissue-negative controls, thyroid hormones of seventy-five BAT-positive healthy subjects were measured.


RESULTS
Active brown adipose tissue was not present in any of the hyperthyroid patients. However, one patient with normalized thyroid function showed active BAT after therapy. The free T3 levels and free T4 levels were significantly lower in the 75 BAT-positive subjects than in the BAT-negative subjects. All hyperthyroid patients showed symmetrically increased uptake of fluorodeoxyglucose in skeletal muscles before treatment, whereas, the standardized uptake value was substantially decreased after treatment.


CONCLUSIONS
Abnormally high circulating thyroid hormone levels may not increase brown adipose tissue activity, which may be limited by the increased obligatory thermogenesis of muscle in adult humans.
Division of Endocrinology and Metabolism, Huashan Hospital, Department of Internal Medicine, Shanghai Medical College, Fudan University, Shanghai, PR China.
Qiongyue
Q
Zhang
Qing
Q
Miao
Hongying
H
Ye
Zhaoyun
Z
Zhang
Chuantao
C
Zuo
Fengchun
F
Hua
Yihui
Y
Guan
Yiming
Y
Li
D002001:Adipose Tissue, Brown / Q000000981:diagnostic imaging / Q000187:drug effects / Q000378:metabolism*; D050154:Adiposity / Q000187:drug effects; D000328:Adult; D013956:Antithyroid Agents / Q000627:therapeutic use; D004734:Energy Metabolism / Q000187:drug effects; D005260:Female; D019788:Fluorodeoxyglucose F18; D005500:Follow-Up Studies; D005947:Glucose / Q000378:metabolism*; D006111:Graves Disease / Q000097:blood / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000378:metabolism; D006801:Humans; D008297:Male; D008713:Methimazole / Q000627:therapeutic use; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000187:drug effects / Q000378:metabolism; D049268:Positron-Emission Tomography; D013963:Thyroid Hormones / Q000097:blood / Q000378:metabolism*; D014057:Tomography, X-Ray Computed; D051598:Whole Body Imaging; D055815:Young Adult
D013956:Antithyroid Agents; D013963:Thyroid Hormones; D019788:Fluorodeoxyglucose F18; D008713:Methimazole; D005947:Glucose
Brown adipose tissue (BAT); glucose metabolism; hyperthyroidism; muscle; positron-emission tomography and computed tomography (PET-CT)