Effect of electroacupuncture pre-conditioning on the expression rhythm of core clock gene Bmal1 in uterine tissue of controlled hyperstimulation rats.

Objectives: To observe the effect of electroacupuncture (EA) pre-conditioning on the expression rhythm of clock gene Bmal1 in the uterine tissue of rats with controlled ovarian hyperstimulation(COH), so as to explore its mechanisms underlying improvement of the endometrial receptivity of ovarian superovulation during implantation.

Methods: Seventy-two female SD rats with typical estrous cycles were randomly divided into normal control, model and EA pre-conditioning (pre-EA) groups, with 24 rats in each group. The COH model was established by giving the rats with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (HCG) by intraperitoneal injection. The rats of the pre-EA group received EA stimulation (1 Hz/5 Hz, a tolerable strength) of "Guanyuan"(CV4) and "Sanyinjiao"(SP6) for 15 min each time, once daily (at 21：00 every day). After successive EA intervention during the first two estrous cycles, the modeling began in the third estrus cycle and the EA intervention was continued till the end of modeling, followed by raising the rats with superovulation induction and male rats undergoing vasoligation in one cage (1∶1). The rats during the estrum in the normal control group or those of the model group at the end of modeling were raised together with the male rats undergoing vasoligation in one cage. On the 5 day (04：00 AM) after raising in one cage, the rats in the three groups were sacrificed in six batches every 4 hours, with 4 rats in each group in each batch. The H.E. staining was used for revealing alterations of the endometrial thickness, number of glands and blood vessels and tissue histology, and ELISA employed to ascertain the contents of estradiol (E2) and progesterone (Pg) in serum. The expression rhythm of core clock gene Bmal1 ［In the present study, Zeitgeber time (ZT) is an artificially set laboratory time, i.e., ZT7 (07：00) is light on and ZT19 (19：00) is light off.］ and the expression of endometrial HoxA10 and leukemia inhibitory factor (LIF) mRNAs were detected by quantitative real-time PCR. The Western blot was employed to detect the expression levels of HoxA10 and LIF proteins.

Results: Findings of the clock gene Bmal1 level showed that the expression peak was at ZT12 and the valley value at ZT20 in the normal control group, and that of the peak value was at ZT20 and valley value at ZT12 in the model group, while in the pre-EA group, the peak value was at ZT8, and the valley value at ZT4. The difference of Bmal1 levels among the three groups was most significant at ZT12 (12：00), therefore, the tissue samples were taken at ZT12 in this study for comparison of the levels of different indexes among the 3 groups. Compared with the control group, the endometrial thickness, number of glands and blood vessels, HoxA10 and LIF mRNAs and proteins were significantly down-regulated (<0.01, <0.05), and contents of serum E2 and Pg were considerably up-regulated in the model group (<0.01, <0.05). Relevant to the model group, the pre-EA group had an apparent increase in the endometrial thickness, number of glands and blood vessels, and expression levels of HoxA10 and LIF mRNAs and proteins (<0.05, <0.01), and a marked decrease in the serum Pg (<0.05). At the ZT12 (12：00 noon), compared with the normal control group, the mRNA level of Bmal1 was significantly decreased in the model group (<0.01)；and compared with the model group, the level of Bmal1 mRNA was significantly increased in the pre-EA group (<0.05). In addition, at the node of ZT16, the mRNA level of Bmal1 was significantly decreased in the model group in comparison with the normal control group (<0.01).

Conclusions: EA preconditioning can improve the endometrial receptivity during the implantation window period in rats with COH, which may be related to its functions in regulating the expression of clock gene Bmal1 in the uterine tissue and in correcting the disturbance of clock gene rhythm.