title: Age-related alterations in thyroid hormone binding properties of porcine skeletal muscle cytosol.
abstract: Thyroid hormone binding properties were evaluated in cytosol prepared from semitendinosus muscle of 1-d, 3-wk and 5-mo-old Yorkshire-Duroc crossbred pigs. Optimum thyroxine (T4) binding was obtained with 35 ug cytosolic protein in a solution containing 50 mM Tris-HCl buffer, pH 7.4, and 25 mM KCl and 10 mM MgCl2. The half-time of maximum T4 binding was approximately 10 min. Protease digestion of cytosol eliminated specific T4 binding. Muscle cytosol preferentially bound T4 over triiodothyronine (T3). At equimolar concentrations the amount of T3 binding relative to T4 was .1, 50 and 10% at 1 d, 3 wk and 5 mo, respectively. Scatchard analysis of T4 binding revealed a similar high-affinity, low-capacity component in all age groups. However, at 3 wk of age the concentration of the low-affinity, high-capacity binding component for T4 was 12-fold greater than at either 1 d or 5 mo of age. The affinity of this high-capacity binding component did not change with age. The function of thyroid hormones in regulating skeletal muscle growth and metabolism have not been elucidated. These data demonstrate that thyroid hormone binding properties of skeletal muscle do change with age and further research is needed to investigate the possible relationship of these findings to growth regulatory mechanisms.
mesh_terms: D000367:Age Factors; D000818:Animals; D003600:Cytosol / Q000378:metabolism; D009132:Muscles / Q000378:metabolism*; D011485:Protein Binding; D013552:Swine / Q000378:metabolism*; D013974:Thyroxine / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism*
chemical_list: D014284:Triiodothyronine; D013974:Thyroxine