Response of leucine metabolism to hyperinsulinemia in hypothyroid patients before and after thyroxine replacement

Tipo
Artigo
Data de publicação
2000
Periódico
Journal of Clinical Endocrinology and Metabolism
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13
Autores
Rochon C.
Tauveron I.
Dejax C.
Benoit P.
Capitan P.
Bayle G.
Prugnaud J.
Fabricio A.
Berry C.
Champredon C.
Thieblot P.
Grizard J.
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Resumo
We have investigated the effect of hypothyroidism and insulin on protein metabolism in humans. Six hypothyroid patients were studied in a postabsorptive state before and after 5 months of regular treatment for hypothyroidism (153 ± 17 μg/day of L-T4). The effect of insulin was assessed under hyperinsulinemic euglycemic and eukalemic conditions. Insulin was infused for 140 min at 0.0063 ± 0.0002 nmol/kg·min. An amino acid infusion was used to blunt insulin-induced hypoaminoacidemia. Whole body protein turnover was measured using L-[1-3C] leucine. When compared to L-T4-induced subclinical thyrotoxic state, hypothyroidism induced a significant decrease (P < 0.05) in leucine endogenous appearance rate (a reflection of proteolysis; 0.89 ± 0.09 vs. 1.33 ± 0.05 μmol/kg·min), oxidation (0.19 ± 0.02 vs. 0.25 ± 0.03 μmol/kg·min), and nonoxidative disposal (a reflection of protein synthesis; 0.87 ± 0.11 vs. 1.30 ± 0.05 μmol/kg·min). Insulin lowered proteolysis during both the subclinical thyrotoxic and hypothyroid states. Hypothyroidism impaired the antiproteolytic effects of insulin. Thyroid hormones are, therefore, essential for the normal antiproteolytic action of insulin.
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