Changes in the activity levels of glutamine synthetase, glutaminase and glycogen synthetase in rats subjected to hypoxic stress

Exposure to high altitude causes loss of body mass and alterations in metab olic processes, especially carbohydrate and protein metabolism. The present study was conducted to elucidate the role of glutamine synthetase, glutami nase and glycogen synthetase under conditions of chronic intermittent hypox ia. Four groups, each consisting of 12 male albino rats (Wistar strain), we re exposed to a simulated altitude of 7620 m in a hypobaric chamber for 6 h per day for 1, 7, 13 and 21 days, respectively. Blood haemoglobin, blood g lucose, protein levels in the liver, muscle and plasma, glycogen content, a nd glutaminase, glutamine synthetase and glycogen synthetase activities in liver and muscle were determined in all groups of exposed and in a group of unexposed animals. Food intake and changes in body mass were also monitore d. There was a significant reduction in body mass (28-30%) in hypoxia-expos ed groups as compared to controls, with a corresponding decrease in food in take. There was rise in blood haemoglobin and plasma protein in response to acclimatisation. Over a three-fold increase in liver glycogen content was observed following 1 day of hypoxic exposure (4.76+/-0.78 mg.g(-1) wet tiss ue in normal unexposed rats; 15.82+/-2.30 mg.g(-1) wet tissue in rats expos ed to hypoxia for 1 day). This returned to normal in later stages of exposu re. However, there was no change in glycogen synthetase activity except for a decrease in the 21-days hypoxia-exposed group. There was a slight increa se in muscle glycogen content in the 1-day exposed group which declined sig nificantly by 56.5, 50.6 and 42% following 7, 14, and 21 days of exposure, respectively. Muscle glycogen synthetase activity was also decreased follow ing 21 days of exposure. There was an increase in glutaminase activity in t he liver and muscle in the 7-, 14- and 21-day exposed groups. Glutamine syn thetase activity was higher in the liver in 7- and 14-day exposed groups, t his returned to normal following 21 days of exposure. Glutamine synthetase activity in muscle was significantly higher in the 14-day exposed group (4. 32 mu mol gamma-glutamyl hydroxamate formed.g protein(-1).min(-1)) in compa rison to normal (1.53 mu mol gamma-glutamyl hydroxamate formed.g protein(-1 ).min(-1)); this parameter had decreased by 40% following 21 days of exposu re. These results suggest that since no dramatic changes in the levels of p rotein were observed in the muscle and liver, there is an alteration in glu taminase and glutamine synthetase activity in order to maintain nitrogen me tabolism in the initial phase of hypoxic exposure.