Exercise inhibits glucocorticoid-induced glutamine synthetase expression in red skeletal muscles.
One purpose of this study was to determine whether the suppression of glucocorticoid-induced glutamine synthetase (GS) gene expression by exercise is localized to fiber types that are known to be primarily recruited during endurance running. A second purpose examined whether denervation, which is associated with a reduction in contractile activity, would upregulate GS expression. Exercise consisted of treadmill running at 31 m/min for 12-16 wk. Glucocorticoid treatment (100 mg/kg body wt hydrocortisone 21-acetate) was administered during the last 11 days of the exercise program. Basal GS expression was lowest (GS enzyme activity, 43 +/- 3 nmol.h-1.mg protein-1; GS mRNA, 1.0 arbitrary units) in the slow-twitch red soleus, a muscle type that is known to resist glucocorticoid-induced muscle wasting, intermediate (74 +/- 10 and 1.7 +/- 0.2) in fast-twitch red quadriceps, a muscle type susceptible to atrophy, and highest (106 +/- 16 and 5.4 +/- 1.3) in fast-twitch white quadriceps, a muscle type known to be most susceptible to atrophy. Hormone treatment increased GS enzyme activity and mRNA by two- to fourfold in all muscle types. Exercise diminished GS enzyme activity and mRNA in the fast-twitch red fibers to 35-70% of sedentary control values in both basal and glucocorticoid-stimulated muscles. The running also reduced GS enzyme activity in hormone-treated slow-twitch fibers but did not alter basal or glucocorticoid-induced GS expression in fast-twitch white fibers. These results indicate that glucocorticoids induce similar relative GS expression across all muscle types, but the low absolute levels of expression in slow-twitch muscles are not related to any atrophy.(ABSTRACT TRUNCATED AT 250 WORDS)
College of Kinesiology, University of Illinois, Chicago 60680.
M T
MT
Falduto
A P
AP
Young
R C
RC
Hickson
D000818:Animals; D004492:Edetic Acid / Q000494:pharmacology; D005260:Female; D005938:Glucocorticoids / Q000494:pharmacology*; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism*; D009132:Muscles / Q000033:anatomy & histology / Q000201:enzymology* / Q000378:metabolism; D009929:Organ Size; D010807:Physical Endurance; D005082:Physical Exertion; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012965:Sodium Chloride / Q000494:pharmacology
D005938:Glucocorticoids; D012333:RNA, Messenger; D012965:Sodium Chloride; D004492:Edetic Acid; D005974:Glutamate-Ammonia Ligase