Abstract: Objective To investigate whether the melatonin (melatonin, MLT) could protect SD rats' cardiac muscular tissues from chronic intermittent hypoxia damage in the atmospheric pressure. Methods The 24 male, SD rats(5 weeks) were randomly divided into three groups: the Control group, the experimental group A and the experimental group B. The control group rats were fed with normally reared in the air, and the experimental group A and B rats were living in the atmospheric pressure and chronic intermittent hypoxia boxes. The control group rats and the experimental group B rats were fed with normal saline solution(NS), and the experimental group A rats were fed with melatonin (MLT). After 8 weeks, the cTnT capacity and Ca²⁺- ATPase activity of each rat were detected, and the right ventricles were taken for pathological section. Results ①Comparison of the experimental group B and the experimental group A: The cTnT capacity of the experimental group B was increased (P<0.05), and the Ca²⁺- ATPase activity of the experimental group B was decreased (P<0.05). Individual myocardial cell nuclei disappeared. Myocardial cells were hypertrophy and there was a large amount of bleeding between myocardial. ②Comparison of the experimental group A and the control group: The above indicators had no obvious differences (P>0.05). There was a small amount of bleeding between myocardial. ③Comparison of the experimental group B and the control group: The cTnT capacity of the experimental group B was increased (P<0.05), and the Ca²⁺-ATPase activity of the experimental group B was decreased (P<0.05). Individual myocardial cell nuclei disappeared. Myocardial cells were hypertrophy, and there was a large amount of bleeding in myocardial. Conclusion MLT can protect rats' cardiac muscular tissue from injury of chronic intermittent hypoxia.

Key words: Chronic intermittent hypoxia, cTnT, Ca²⁺-ATPase, Melatonin