Nitric oxide (no), citrulline - no cycle enzymes, glutamine synthetase and oxidative stress in anoxia (hypobaric hypoxia) and reperfusion in rat brain

Abstract

Nitric oxide is postulated to be involved in the pathophysiology of neurological disorders due to hypoxia/ anoxia in brain due to increased release of glutamate and activation of N-methyl-D-aspartate receptors. Reactive oxygen species have been implicated in pathophysiology of many neurological disorders and in brain function. To understand their role in anoxia (hypobaric hypoxia) and reperfusion (reoxygenation), the nitric oxide synthase, argininosuccinate synthetase, argininosuccinate lyase, glutamine synthetase and arginase activities along with the concentration of nitrate /nitrite, thiobarbituric acid reactive substances and total antioxidant status were estimated in cerebral cortex, cerebellum and brain stem of rats subjected to anoxia and reperfusion. The results of this study clearly demonstrated the increased production of nitric oxide by increased activity of nitric oxide synthase. The increased activities of argininosuccinate synthetase and argininosuccinate lyase suggest the increased and effective recycling of citrulline to arginine in anoxia, making nitric oxide production more effective and contributing to its toxic effects. The decreased activity of glutamine synthetase may favor the prolonged availability of glutamic acid causing excitotoxicity leading to neuronal damage in anoxia. The increased formation of thiobarbituric acid reactive substances and decreased total antioxidant status indicate the presence of oxidative stress in anoxia and reperfusion. The increased arginase and sustained decrease of GS activity in reperfusion group likely to be protective.

Keywords: Anoxia; Citrulline - Nitric oxide cycle; Excitotoxicity; Glutamine synthetase; Hypobaric hypoxia; Nitric oxide; Reperfusion; Thiobarbituricacid reactive substances; Total antioxidant status.

Figure 1

Activity of NOS in different regions of rat brain in anoxia and reperfusion. Statistical analysis was done by one-way ANOVA followed by post hoc analysis using Bonferroni's test. Values are mean ± S.D. for six animals in each group; ^a p < 0.001, ^a1 p<0.01 and ^a2 p<0.05 versus control group; ^b p <0.001 versus anoxia group.

Figure 2

Activities of AS, AL and Arginase in different regions of rat brain in anoxia and reperfusion. Statistical analysis was done by one-way ANOVA followed by post hoc analysis using Bonferroni's test. Values are mean ± S.D. for six animals in each group; ^a p < 0.001, ^a1 p<0.01 and ^a2 p<0.05 versus control group; ^b p <0.001 versus anoxia group.

Figure 3

Activity of glutamine synthetase in different regions of rat brain in anoxia and reperfusion. Statistical analysis was done by one-way ANOVA followed by post hoc analysis using Bonferroni's test. Values are mean ± S.D. for six animals in each group; ^a p < 0.001 versus control group; ^b p <0.001, ^b1 p <0.01 versus anoxia group.

Figure 4

Concentration of NOx^x, TAS^y and TBARS^z in different regions of rat brain in anoxia and reperfusion. ^x Concentration expressed as nanomol of NOx /g wet weight of tissue. ^y Concentration expressed as nanomol of uric acid equivalent / g wet weight of tissue. ^z Concentration expressed as nanomoles of MDA equivalent / g wet weight of tissue. Statistical analysis was done by one-way ANOVA followed by post hoc analysis using Bonferroni's test. Values are mean ± S.D. for six animals in each group; ^a p < 0.001, ^a1 p<0.01 versus control group; ^b p <0.001, ^b1 p<0.01 versus anoxia group.