Nitric Oxide Involved In The Protection Of Intermittent Hypoxia Against Ischemia/reperfusion Injury And Its Potential Mechanisms

Objectives: Intermittent hypoxia (IH) has been shown to provide myocardialprotection against ischemia/reperfusion (I/R)-induced injury. Our aim was toinvestigate whether NO was involved in the cardiac protection of IH and its potentialmechanisms. Methods: Adult male Sprague-Dawley rats were exposed to hypoxiasimulated 5000 m in a hypobaric chamber for 6 h/day, lasting 42 days. Normoxiagroup rats were kept under normoxic conditions. Isolated perfused hearts from bothgroups were subjected to 30 min of global ischemia followed by 30 min reperfusion.Immunohistochemistry was used to demonstrate the expression of iNOS and eNOSprotein in IH and normoxia cardiac tissue. Biochemical assay was employed to detectthe nitrite/nitrate level. RT-PCR was used to evaluate iNOS and eNOS mRNA levels.Expressions of different proteins, including iNOS, eNOS, PKC-α, ε, and δ isozymes,NF-κBp65 and Fos were also detected by Western Blot. Results: (1) Both L-NNA (anon-selective inhibitor of NOS) and AG (a specific inhibitor of iNOS) could reversethe improved recovery of cardiac function after ischemia in IH group, but had noinfluence in normoxia group. SNP (a NO donor) could improve the recovery ofcardiac function after ischemia in normoxia group, but had no influence in IH group.(2) Compared to normoxia group rats, the basal expression of iNOS in heartsdetected by immunohistochemistry was increased and that of eNOS protein wasdecreased in IH group rats. The similar results were demonstrated by Western blot 4英文摘要test. After I/R, the iNOS protein expressions were increased in normoxic rat heartsand decreased in IH rat hearts compared to the corresponding of baseline expressionand the eNOS protein expressions in both groups were decreased evidenced byimmunohistochemistry and Western blot. (3) The baseline content of nitrite/nitrate inIH hearts was higher than that of normoxic hearts. The nitrite/nitrate level innormoxic hearts was increased and has no significant change in IH hearts after 30min ischemia. L-NNA diminished the content of nitrite/nitrate in IH and normoxichearts during ischemia or/and reperfusion period. (4) Compared with normoxia group,the baseline level of iNOS mRNA was significantly increased in IH group. Thebaseline level of iNOS and eNOS mRNA could be decreased and protein had nosignificant change in both groups with administration of L-NNA. The mRNA andprotein expressions of iNOS and eNOS were reduced during ischemia period in bothgroups, except for eNOS mRNA in normoxic group. L-NNA usually reduced themRNA and protein expression of iNOS and eNOS during ischemia or/andreperfusion period in IH hearts. The effect of L-NNA on the mRNA and proteinexpression of iNOS and eNOS in normoxic hearts during ischemia and reperfusionperiod was complicated. In general, L-NNA had stronger inhibitory effect on IHhearts than that of normoxic hearts. AG had the similar effect with L-NNA, but theinhibitory effect was lower than that of L-NNA. (5) IH upregulated the baselineprotein expression of particulate fraction, not cytosolic fraction, of PKC-α, ε, and δisozymes compared to that of normoxic hearts. During ischemia and reperfusionperiod, particulate fraction expressions of PKC-α and ε isozymes in IH and normoxichearts were decreased and the corresponding expression of PKC-δ was not changedcompared with those of baseline level, but the levels of them in IH group were stillhigher than those of normoxic group. L-NNA could decrease the levels of particulate 5NO 在间歇性低氧抗心肌缺血再灌损伤中的作用fraction of PKC-ε and δ during ischemia or/and reperfusion period in IH rat hearts,not in normoxic hearts. SNP could increase the particulate protein expression ofPKC-ε and δ during ischemia or/and reperfusion period in normoxic hearts, not in IHhearts. Howe...