title: Alteration of contractile force and mass in the senescent diaphragm with beta(2)-agonist treatment.
abstract: Aging is associated with a decrease in diaphragmatic maximal tetanic force production (P(o)) in senescent rats. Treatment with the beta(2)-agonist clenbuterol (CB) has been shown to increase skeletal muscle mass and P(o) in weak locomotor skeletal muscles from dystrophic rodents. It is unknown whether CB can increase diaphragmatic mass and P(o) in senescent rats. Therefore, we tested the hypothesis that CB treatment will increase specific P(o) (i.e., force per cross-sectional area) and mass in the diaphragm of old rats. Young (5 mo) and old (23 mo) male Fischer 344 rats were randomly assigned to one of the following groups (n = 10/group): 1) young CB treated; 2) young control; 3) old CB treated; and 4) old control. Animals were injected daily with either CB (2 mg/kg) or saline for 28 days. CB increased (P < 0.05) the mass of the costal diaphragm in both young and old animals. CB treatment increased diaphragmatic-specific P(o) in old animals (approximately 15%; P < 0.05) but did not alter (P > 0.05) diaphragmatic-specific P(o) in young animals. Biochemical analysis indicated that the improved maximal specific P(o) in the diaphragm of CB-treated old animals was not due to increased myofibrillar protein concentration. Analysis of the myosin heavy chain (MHC) content of the costal diaphragm revealed a CB-induced increase (P < 0.05) in type IIb MHC and a decrease in type I, IIa, and IIx MHC in both young and old animals. These data support the hypothesis that CB treatment can restore the age-associated decline in both diaphragmatic-specific P(o) and muscle mass.
authors.affiliation: Department of Exercise and Sport Sciences, University of Florida, Gainesville, Florida 32611, USA.
authors.forename: Wesley N
authors.initials: WN
authors.lastname: Smith
authors.forename: Amie
authors.initials: A
authors.lastname: Dirks
authors.forename: Takao
authors.initials: T
authors.lastname: Sugiura
authors.forename: Susan
authors.initials: S
authors.lastname: Muller
authors.forename: Phillip
authors.initials: P
authors.lastname: Scarpace
authors.forename: Scott K
authors.initials: SK
authors.lastname: Powers
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000375:Aging / Q000502:physiology*; D000818:Animals; D001834:Body Water / Q000378:metabolism; D002950:Citrate (si)-Synthase / Q000378:metabolism; D002976:Clenbuterol / Q000494:pharmacology*; D003964:Diaphragm / Q000033:anatomy & histology* / Q000201:enzymology / Q000502:physiology*; D004435:Eating / Q000187:drug effects; D005260:Female; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology*; D009124:Muscle Proteins / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D000318:Adrenergic beta-Agonists; D009124:Muscle Proteins; D002950:Citrate (si)-Synthase; D018995:Myosin Heavy Chains; D002976:Clenbuterol