title: Role of masseter muscle β₂-adrenergic signaling in regulation of muscle activity, myosin heavy chain transition, and hypertrophy.
abstract: Chronic administration of clenbuterol (CB), a lipophilic β₂-adrenoceptor (β₂-AR) agonist, induces skeletal muscle hypertrophy and slow-to-fast fiber-type transitions in mammalian species, but the mechanism and pathophysiological roles of these changes have not been explored. Here, we examined the effects of CB not only on masseter muscle mass, fiber diameter, and myosin heavy chain (MHC) composition, but also on daily muscle activity, a factor influencing muscle phenotype, by means of electromyogram analysis in rats. MHC transition towards faster isoforms was induced by 2-week CB treatment. In addition, daily duty time was increased at 1 day, 1 week, and 2 weeks after the start of CB treatment and its increase was greater at high activity level (6-fold) than at low activity level (2-fold). In order to examine whether these effects of CB were mediated through muscle or CNS β₂-AR stimulation, we compared these effects of CB with those of salbutamol (SB), a hydrophilic β₂-AR agonist. SB treatment induced masseter hypertrophy and MHC transition, like CB, but did not increase daily activity. These results suggest that CB-mediated slow-to-fast MHC transition with hypertrophy was induced through direct muscle β₂-AR stimulation, but the increase of daily duty time was mediated through the CNS.
authors.affiliation: Department of Physiology, Tsurumi University School of Dental Medicine, Japan.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Ohnuki
authors.forename: Daisuke
authors.initials: D
authors.lastname: Umeki
authors.forename: Wenqian
authors.initials: W
authors.lastname: Cai
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Kawai
authors.forename: Yasumasa
authors.initials: Y
authors.lastname: Mototani
authors.forename: Kouichi
authors.initials: K
authors.lastname: Shiozawa
authors.forename: Hui-Ling
authors.initials: HL
authors.lastname: Jin
authors.forename: Takayuki
authors.initials: T
authors.lastname: Fujita
authors.forename: Eiji
authors.initials: E
authors.lastname: Tanaka
authors.forename: Yasutake
authors.initials: Y
authors.lastname: Saeki
authors.forename: Satoshi
authors.initials: S
authors.lastname: Okumura
mesh_terms: D058666:Adrenergic beta-2 Receptor Agonists / Q000494:pharmacology*; D000420:Albuterol / Q000494:pharmacology; D000818:Animals; D002490:Central Nervous System / Q000187:drug effects / Q000502:physiology; D002976:Clenbuterol / Q000494:pharmacology*; D004576:Electromyography / Q000187:drug effects*; D006984:Hypertrophy; D008406:Masseter Muscle / Q000187:drug effects / Q000378:metabolism / Q000473:pathology* / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000378:metabolism*; D051381:Rats; D018343:Receptors, Adrenergic, beta-2 / Q000187:drug effects* / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology*
chemical_list: D058666:Adrenergic beta-2 Receptor Agonists; D018343:Receptors, Adrenergic, beta-2; D018995:Myosin Heavy Chains; D000420:Albuterol; D002976:Clenbuterol