Meynial-Denis D, Mignon M, Miri A, Imbert J, Aurousseau E, Taillandier D, Attaix D, Arnal M, Grizard J
Centre de Recherche en Nutrition Humaine de Clermont-Ferrand, Ceyrat, France.
Am J Physiol. 1996 Dec;271(6 Pt 1):E1061-6. doi: 10.1152/ajpendo.1996.271.6.E1061.
Glutamine synthetase (GS) is a glucocorticoid-inducible enzyme that has a key role for glutamine synthesis in muscle. We hypothesized that the glucocorticoid induction of GS could be altered in aged rats, because alterations in the responsiveness of some genes to glucocorticoids were reported in aging. We compared the glucocorticoid-induced GS in fast-twitch and slow-twitch skeletal muscles (tibialis anterior and soleus, respectively) and heart from adult (age 6-8 mo) and aged (age 22 mo) female rats. All animals received dexamethasone (Dex) in their drinking water (0.77 +/- 0.10 and 0.80 +/- 0.08 mg/day per adult and aged rat, respectively) for 5 days. Dex caused an increase in both GS activity and GS mRNA in fast-twitch and slow-twitch skeletal muscles from adult and aged rats. In contrast, Dex increased GS activity in heart of adult rats, without any concomitant change in GS mRNA levels. Furthermore, Dex did not affect GS activity in aged heart. Thus the responsiveness of GS to an excess of glucocorticoids is preserved in skeletal muscle but not in heart from aged animals.
谷氨酰胺合成酶（GS）是一种糖皮质激素诱导型酶，在肌肉谷氨酰胺合成中起关键作用。我们推测老年大鼠中GS的糖皮质激素诱导可能会发生改变，因为据报道衰老过程中一些基因对糖皮质激素的反应性会发生改变。我们比较了成年（6 - 8月龄）和老年（22月龄）雌性大鼠的快肌和慢肌（分别为胫骨前肌和比目鱼肌）以及心脏中糖皮质激素诱导的GS情况。所有动物饮用含地塞米松（Dex）的水（成年和老年大鼠分别为0.77±0.10和0.80±0.08毫克/天），持续5天。Dex使成年和老年大鼠的快肌和慢肌中的GS活性和GS mRNA均增加。相比之下，Dex增加了成年大鼠心脏中的GS活性，而GS mRNA水平没有相应变化。此外，Dex对老年大鼠心脏中的GS活性没有影响。因此，老年动物骨骼肌中GS对过量糖皮质激素的反应性得以保留，但心脏中则不然。
