Alterations in glutamine synthetase activity in rat skeletal muscle are associated with advanced age.
OBJECTIVE
Glutamine synthetase (GS), a key enzyme in the production of glutamine, is preserved in skeletal muscle during early aging (<24 mo). Because the effects of advanced age on GS are unknown, we investigated the effect of advanced age (>24 mo) on GS activity in skeletal muscle. We hypothesized that advanced age would enhance muscle GS activity.


METHODS
Muscle GS activities were assessed in adult (8 mo), mature adult (15 mo), aged (20-22 mo), advanced age (25-27 mo), or very advanced age (29-32 mo) female Wistar rats. Male Wistar (6-27 mo) were used to investigate the effect of gender on this activity.


RESULTS
Glutamine synthetase activity remained low and unaltered in rats from 8 to 22 mo of age, as previously demonstrated. In contrast, GS activity was high ( approximately 75% of individual values were higher than the low value mean) in 25-mo to 27-mo-old rats. In very-old-aged rats (29-32 mo), approximately 55% of GS activity data points exhibited low values. Changes in GS protein content paralleled those in GS activities. In male rats, GS activity was also high ( approximately 80% of individual values were higher than the mean value of 6-mo to 19-mo-old rats) at the upper limit of life expectancy (27 mo).


CONCLUSIONS
There is enhanced GS activity in old female and male rats suggesting a greater need for glutamine. In some very old rats, low GS activity may be associated with longevity or reflect a limitation in glutamine production due to extremely advanced age per se.
Pinel
Carole
C
UMR INRA 1019, Unité de Nutrition Humaine, Human Nutrition Research Center, Clermont-Ferrand Theix, France.
Coxam
Véronique
V
Mignon
Michelle
M
Taillandier
Daniel
D
Cubizolles
Christine
C
Lebecque
Patrice
P
Darmaun
Dominique
D
Meynial-Denis
Dominique
D
D000255:Adenosine Triphosphate / Q000032:analysis; D000375:Aging / Q000378:metabolism*; D000818:Animals; D001823:Body Composition; D004734:Energy Metabolism; D005260:Female; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism*; D018698:Glutamic Acid / Q000032:analysis; D005973:Glutamine / Q000032:analysis; D019344:Lactic Acid / Q000032:analysis; D008297:Male; D018482:Muscle, Skeletal / Q000737:chemistry / Q000201:enzymology*; D010725:Phosphocreatine / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D012727:Sex Characteristics
D010725:Phosphocreatine; D005973:Glutamine; D019344:Lactic Acid; D018698:Glutamic Acid; D000255:Adenosine Triphosphate; D005974:Glutamate-Ammonia Ligase