Elevated regional lipolysis in hyperthyroidism

Hyperthyroidism is characterized by increased levels of circulating free fatty acids (FFA) and increased lipid oxidation, but it is uncertain which regional fat depots contribute. The present study was designed to define the participation of femoral and abdominal fat stores in the overall stimulation of lipolysis in hyperthyroidism in the basal state and during insulin stimulation. We studied nine women with newly diagnosed hyperthyroidism (HT) and after (euthyroidism, ET) medical treatment with methimazol and compared with eight control subjects (CTR). All subjects were studied in the postabsorptive state and during a 3-h hyperinsulinemic euglycemic clamp with microdialysis catheters sc in the abdominal and femoral adipose tissue. Before treatment, patients had elevated circulating concentrations of triiodthyronine, FFA, and glycerol. Levels of interstitial glycerol (mol/liter) in abdominal adipose tissue [485 24 (HT), 226 20 (ET) (P < 0.001), 265 34 (CTR) (P < 0.001)] and in femoral adipose tissue [468 41(HT), 245 29 (ET) (P < 0.01), 278 31(CTR) (P < 0.005)] were elevated in the basal hyperthyroid state, and these differences prevailed during the glucose clamp [230 23 (HT), 113 13 (ET) (P < 0.01), 132 22(CTR) (P < 0.01) and 303 39 (HT), 122 15 (ET) (P < 0.01), 166 21(CTR) (P < 0.01)]. These results suggest that femoral and abdominal adipose tissue contribute equally to the excessive rate of lipolysis in hyperthyroidism and that both tissues are resistant to the actions of insulin. (J Clin Endocrinol Metab 87: 4747– 4753, 2002)