The role of adrenal hormones in the response of glutamine synthetase to fasting in adult and old rats.
OBJECTIVE
During fasting, skeletal muscle exports increased amounts of glutamine (Gln) while increasing the production of this amino acid by glutamine synthetase (GS) in order to maintain the intramuscular Gln pool. Glucocorticoid hormones are believed to be the principal mediators of GS induction during stress conditions. The aim of this study was to evaluate (1) the effect of fasting on GS activity and expression in skeletal muscle during aging and consequently, (2) the role of glucocorticoids in fasting-induced GS activity.


METHODS
Male Wistar rats (6-, 22-month old) were fasted for 5 days and both the activity and expression of GS were measured in tibialis anterior muscle. To better demonstrate the role of glucocorticoids in the response of GS to fasting, we suppressed their action by RU38486 administration (a potent glucocorticoid antagonist) and their production by adrenalectomy in fed and fasted rats.


RESULTS
An increase in fasting-induced GS activity was observed in skeletal muscles from both adult and aged rats. Adrenalectomy, but surprisingly not RU38486, suppressed the fasting-induced increase in GS activity and expression.


CONCLUSIONS
The data clearly show that the GS responsiveness to fasting was not modified by aging in skeletal muscle.
Mezzarobba
V
V
Human Nutrition Research Center of Clermont-Ferrand, Institut National de la Recherche Agronomique, Nutrition and Protein Metabolism Unit, Ceyrat, France
Torrent
A
A
Leydier
I
I
Alles
S
S
Brajon
B
B
Mignon
M
M
Attaix
D
D
Meynial-Denis
D
D
D000311:Adrenal Glands / Q000378:metabolism*; D000315:Adrenalectomy; D000367:Age Factors; D000375:Aging / Q000378:metabolism*; D000704:Analysis of Variance; D000818:Animals; D015152:Blotting, Northern; D005215:Fasting / Q000378:metabolism*; D005938:Glucocorticoids / Q000378:metabolism*; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism* / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006727:Hormone Antagonists / Q000494:pharmacology; D008297:Male; D015735:Mifepristone / Q000494:pharmacology; D018482:Muscle, Skeletal / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D005938:Glucocorticoids; D006727:Hormone Antagonists; D012333:RNA, Messenger; D005973:Glutamine; D015735:Mifepristone; D018698:Glutamic Acid; D005974:Glutamate-Ammonia Ligase