[Myocardial free radical metabolic changes in rats after repeated high +Gz exposure and protective effects of low-G preconditioning and tea polyphenols].

Aim: To determine whether repetitive exposure to high sustained +Gz acceleration induces persisting changes in the myocardial free radical metabolism and observe the protective effects of low-G training and antioxidant tea polyphenols (TP).

Methods: Thirty-two male Wistar rats were randomly divided into four groups (n=8 each): group A, restrained, was only submitted to +1 Gz for 5 min. Group B, centrifuged, was exposed to five plateaus of 30 s at +10 Gz for intermittent times, three times a week, for three weeks. Group C, low-G trained, was exposed to +2 Gz for 5 min about 1 h prior to +10 Gz stress, and group D was orally given TP at dose of 200 mg/kg about 1 h prior to +10 Gz stress. On the next day morning after last centrifuge run, the rats were decapitated and the hearts were quickly removed. Malondialdehyde (MDA) concentration and superoxide dismutase (SOD) activity were measured. Additionally, CuZn-SOD and inducible NO synthase (iNOS) enzymatic contents were examined by immunohistochemical staining and their mRNA were analyzed by semi-quantitative reverse transcription polymerase chain reaction(RT-PCR).

Results: Compared with group A, MDA concentration and iNOS enzymatic content in myocardial mitochondria were increased significantly (P < 0.05) in group B. Compared with group B, mitochondrial SOD activity was significantly increased in group C (P < 0.05). iNOS enzymatic content was significantly decreased in group C and D. There were no significant differences of CuZn-SOD content, CuZn-SOD and iNOS mRNA levels among the four groups.

Conclusion: Repeated high +Gz exposure can induce myocardial free radical metabolic disorder and mainly result in mitochondrial peroxidative injury. But low-G training and natural antioxidant TP have protective effects, and the former is better.