Metabolic effects of brown fat in transitioning from hyperthyroidism to euthyroidism

OBJECTIVE

Brown adipose tissue (BAT) controls metabolic rate through thermogenesis. As its regulatory factors during the transition from hyperthyroidism to euthyroidism are not well established, our study investigated the relationships between supraclavicular brown adipose tissue (sBAT) activity and physiological/metabolic changes with changes in thyroid status.

DESIGN

Participants with newly diagnosed Graves' disease were recruited. A thionamide antithyroid drug (ATD) such as carbimazole (CMZ) or thiamazole (TMZ) was prescribed in every case. All underwent energy expenditure (EE) measurement and supraclavicular infrared thermography (IRT) within a chamber calorimeter, as well as 18F-fluorodeoxyglucose (18F-FDG) positron-emission tomography/magnetic resonance (PET/MR) imaging scanning, with clinical and biochemical parameters measured during hyperthyroidism and repeated in early euthyroidism. PET sBAT mean/maximum standardized uptake value (SUV mean/max), MR supraclavicular fat fraction (sFF) and mean temperature (Tscv) quantified sBAT activity.

RESULTS

Twenty-one (16 female/5 male) participants aged 39.5 ± 2.5 years completed the study. The average duration to attain euthyroidism was 28.6 ± 2.3 weeks. Eight participants were BAT-positive while 13 were BAT-negative. sFF increased with euthyroidism (72.3 ± 1.4% to 76.8 ± 1.4%; P < 0.01), but no changes were observed in PET SUV mean and Tscv. Significant changes in serum-free triiodothyronine (FT3) levels were related to BAT status (interaction P value = 0.04). FT3 concentration at hyperthyroid state was positively associated with sBAT PET SUV mean (r = 0.58, P = 0.01) and resting metabolic rate (RMR) (P < 0.01).

CONCLUSION

Hyperthyroidism does not consistently lead to a detectable increase in BAT activity. FT3 reduction during the transition to euthyroidism correlated with BAT activity.

Resistance Training Improves Muscle Function and Body Composition in Patients With Hyperthyroidism

OBJECTIVE

To evaluate the effect of resistance training on skeletal muscle performance and body composition in patients with medically treated hyperthyroidism.

DESIGN

Nonrandomized controlled trial.

SETTING

Large public tertiary hospital.

PARTICIPANTS

Sixteen sedentary patients with recent clinical diagnosis and laboratory confirmation of hyperthyroidism (7 men, 9 women; age, 38+/-11 y; weight, 58.4+/-2.6 kg; height, 1.6+/-0.3m) were assigned to the control group (medical therapy; n=9) or training group (medical therapy associated with resistance training; n=7). An age- and sex-matched healthy group served as controls (3 men, 5 women; age, 40+/-3 y; weight, 68.4+/-4.3 kg; height, 1.6+/-0.3m).

INTERVENTION

Resistance training twice a week for 16 weeks.

MAIN OUTCOME MEASURES

Peak muscular strength (by dynamometry and 1 repetition maximum method) and endurance (30% of peak force) for 7 movements and anthropometric measurements.

RESULTS

The hyperthyroid patients as a group had lower baseline overall strength values when compared with healthy subjects (200.3+/-16.0 kg vs 274.9+/-21.8 kg, respectively; P=.006). Overall absolute increases in strength (49 kg vs 91 kg, P<.05) and endurance (78.5x10(2)kg/s vs 176.9x10(2)kg/s, P<.05) were higher in the training group compared with the control group. Body weight increased in both groups, but the sum of muscular circumference increased only in the training group (training group, 92.6+/-3.3 cm vs 97.1+/-3.8 cm; control group, 94.6+/-2.2 cm vs 94.4+/-2.1cm; P<.05), with no change in the sum of skinfolds.

CONCLUSIONS

Resistance training accelerates the recovery of skeletal muscle function and promotes weight gain based on muscle mass improvement in patients with medically treated hyperthyroidism.

[Possibility of correction of the hormonal state of girls by hypoxic training]

Hormonal effects on the functional status and working capacity were found in girls with juvenile dysfunctional uterine hemorrhage who had been exposed to ionizing radiation in early childhood, in those with primary hyperthyroidism and healthy athletic girls in different phases of a menstrual cycle. Whether the hormonal status might be corrected by interval hypoxic training was examined. There was a relationship of respiratory functional changes to the phases of a menstrual cycle in healthy girls. Impaired external respiratory function, blood flow, and blood respiratory function, lower oxygen consumption were found in girls who had been victims of the Chernobyl accident and respiratory functional changes were detected in patients with hypothyroidism. It was ascertained that interval hypoxic training was an effective alternative to mountain training, that it promoted higher aerobic and anaerobic productivity and special working capacity in athletes. An interval hypoxic training course was found to substantially improve oxygen regimens in girls with secondary anemia, to elevate hemoglobin levels to normal values, to recover normal ovarian function. It also enhanced the production of thyroid hormones, normalized oxygen consumption, improved the patients' condition, increased physical and mental performance in patients with hypothyroidism.

[Functional reserves of the thyroid gland in thyrotoxicosis remission]

A test with intramuscular injection of 5 or 10 U of TTH was carried out in 47 patients suffering from diffuse toxic goiter, including 34 cases at the stage of thyrotoxicosis remission. Results of this test were evaluated by the changes of I131 absorption by the thyroid gland and of the blood protein-bound iodine level. The thyroid gland TTH sensitivity was found to be diminished in 16 patients with thyrotoxicosis remission. The reaction was absent most regularly in patients with ophthalmopathy. This denotes a latent form of thyroid insufficiency and suggest that the patients with the negative response to the exogenous TTH are in the "risk group" in respect to the development of manifest hypothyroidism.