To investigate the effects and mechanism of Polygonum orientale flower (POR) extract on exercise arrhythmia (EA) in rats after exhaustive exercise.

The EA rat model was induced by 8 weeks of exhaustive weight-bearing swimming exercise and was randomly divided into model group and experimental -L, -M, -H groups, with 12 rats per group. Twelve normal rats were selected as the normal group. On the modeling day, normal and model groups were given pure water by intragastric administration. Experimental -L, -M, -H groups were given 50, 100 and 200 mg·kg^-1 POR extract solution by intragastric administration, respectively. Five groups were administrated with once a day for 8 weeks. The latent time and duration of arrhythmia in rats were detected by electrocardiograph. The contents of adenosine triphosphate (ATP), the activities of Na⁺/K⁺ATP and the contents of superoxide dismutase (SOD) in myocardial tissue were measured by corresponding kit. The transcriptional levels of calmodulin (CaM) and calmodulin dependent protein kinase Ⅱ (CaMK Ⅱ) in rat myocardium were measured by real-time fluorescence quantitative polymerase chain reaction.

The latent time of arrhythmia in experimental -M, -H groups and model group were (9.77±1.48), (10.61±1.61) and (7.44±2.12) min; the duration were (33.25±6.39), (20.01±3.89) and (71.44±13.68) min. The ATP contents in experimental -M, -H groups, model group and normal group were (26.45±2.96), (29.44±1.89), (10.38±1.22) and (34.50±4.24) ng·g prot^-1; the Na⁺/K⁺ ATP activities were (17.27±0.92), (19.57±1.33), (5.14±0.80) and (20.00±2.11) U·g prot^-1; SOD contents were (89.22±9.07), (86.29±7.22), (73.62±7.36) and (89.43±8.85) U·mg prot^-1; the relative expression levels of CaM mRNA in myocardial tissue were 1.28±0.08, 1.06±0.08, 2.34±0.30 and 1.00±0.10; the relative expression levels of CaMK Ⅱ mRNA in myocardial tissue were 1.46±0.09, 1.15±0.09, 2.80±0.19 and 1.00±0.11, respectively. Compared with model group, the differences of above indexes in experimental -M, -H groups were statistically significant (all P<0.05).

POR extract can effectively treat the rats with EA, and the mechanism is related to the increase of ATP contents, Na⁺/K⁺ ATP and antioxidant activities, and inhibition of Ca²⁺/CaM/CaMK Ⅱ signaling pathway.