title: Corticosteroid effects on isotonic contractile properties of rat diaphragm muscle.
abstract: The effects of corticosteroids (CS) on diaphragm muscle (Diam) fiber morphology and contractile properties were evaluated in three groups of rats: controls (Ctl), surgical sham and weight-matched controls (Sham), and CS-treated (6 mg . kg-1 . day-1 prednisolone at 2.5 ml/h for 3 wk). In the CS-treated Diam, there was a selective atrophy of type IIx and IIb fibers, compared with a generalized atrophy of all fibers in the Sham group. Maximum isometric force was reduced by 20% in the CS group compared with both Ctl and Sham. Maximum shortening velocity in the CS Diam was slowed by approximately 20% compared with Ctl and Sham. Peak power output of the CS Diam was only 60% of Ctl and 70% of Sham. Endurance to repeated isotonic contractions improved in the CS-treated Diam compared with Ctl. We conclude that the atrophy of type IIx and IIb fibers in the Diam can only partially account for the CS-induced changes in isotonic contractile properties. Other factors such as reduced myofibrillar density or altered cross-bridge cycling kinetics are also likely to contribute to the effects of CS treatment.
authors.affiliation: Department of Pulmonary Diseases, University Hospital Nijmegen, Nijmegen 6500 HB, The Netherlands.
authors.forename: R H
authors.initials: RH
authors.lastname: Van Balkom
authors.forename: W Z
authors.initials: WZ
authors.lastname: Zhan
authors.forename: Y S
authors.initials: YS
authors.lastname: Prakash
authors.forename: P N
authors.initials: PN
authors.lastname: Dekhuijzen
authors.forename: G C
authors.initials: GC
authors.lastname: Sieck
mesh_terms: D000305:Adrenal Cortex Hormones / Q000494:pharmacology*; D000818:Animals; D003964:Diaphragm / Q000166:cytology / Q000187:drug effects*; D005938:Glucocorticoids / Q000494:pharmacology; D007551:Isotonic Contraction / Q000187:drug effects*; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D018995:Myosin Heavy Chains / Q000378:metabolism; D010807:Physical Endurance / Q000187:drug effects / Q000502:physiology; D011239:Prednisolone / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000305:Adrenal Cortex Hormones; D005938:Glucocorticoids; D011239:Prednisolone; D018995:Myosin Heavy Chains