title: Interaction of thyroid hormone and functional overload on skeletal muscle isomyosin expression.
abstract: This study examined the interaction of exogenous thyroid hormone 3,5,3'-triiodothyronine (T3) and functional overload on skeletal muscle myosin heavy chain (MHC) expression, studied at both the protein and mRNA level of analysis. Animals were allocated to the following groups: 1) normal control, 2) overload control, 3) hyperthyroid control, and 4) hyperthyroid+overload. Overload of the rat plantaris was accomplished by surgical removal of its synergists (soleus and gastrocnemius), and the animals were made hyperthyroid by injections of T3 (350 micrograms/kg every other day). After overload of 8 wk, muscle enlargement occurred by 53% for both overload groups (P < 0.05). This was accompanied by a 330 and 82% increase in the relative content of type I and IIa MHC, respectively, and a corresponding decrease by 16 and 44% in type IIx and IIb MHC, respectively, in the overload control group (P < 0.05 vs. normal control). Changes in the relative and absolute content of mRNA for these MHCs paralleled the protein response. Exogenous T3 completely reversed the upregulation of type I MHC and the downregulation of type IIx associated with overload at both the protein and mRNA level (P < 0.05). However, T3 was only partially effective in blunting the downregulation of IIb MHC and the upregulation of IIa MHC (protein and mRNA) accompanying the overload.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology and Biophysics, College of Medicine, University of California, Irvine 92717.
authors.forename: S J
authors.initials: SJ
authors.lastname: Swoap
authors.forename: F
authors.initials: F
authors.lastname: Haddad
authors.forename: V J
authors.initials: VJ
authors.lastname: Caiozzo
authors.forename: R E
authors.initials: RE
authors.lastname: Herrick
authors.forename: S A
authors.initials: SA
authors.lastname: McCue
authors.forename: K M
authors.initials: KM
authors.lastname: Baldwin
mesh_terms: D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D005260:Female; D006980:Hyperthyroidism / Q000378:metabolism; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000378:metabolism*; D009210:Myofibrils / Q000378:metabolism; D015879:Myosin Subfragments / Q000378:metabolism; D009218:Myosins / Q000096:biosynthesis*; D012313:RNA / Q000302:isolation & purification; D051381:Rats; D017207:Rats, Sprague-Dawley; D013963:Thyroid Hormones / Q000502:physiology*; D013974:Thyroxine / Q000097:blood / Q000502:physiology; D014284:Triiodothyronine / Q000097:blood / Q000502:physiology
chemical_list: D015879:Myosin Subfragments; D013963:Thyroid Hormones; D014284:Triiodothyronine; D012313:RNA; D009218:Myosins; D013974:Thyroxine