Electroacupuncture may improve endometrial receptivity in controlled ovarian hyperstimulation mice by activating AVP neurons

Background: Controlled ovarian hyperstimulation (COH) can lead to reduced endometrial receptivity during the window of implantation (WOI) and disrupted expression of endometrial clock genes. This study aimed to explore the potential mechanisms by which electroacupuncture (EA) improves endometrial receptivity in COH mice, focusing on the regulation of central and peripheral clock genes within the circadian system. Methods: Experiment 1 included three groups of mice: control (CTR), COH, and EA. Each group was further subdivided into six subgroups according to sampling time. Tissue samples were collected at ZT12-ZT8 on days 4-5 of pregnancy (D4-5). Uterine morphology was examined, and serum estradiol (E2) and progesterone (P4) levels, endometrial receptivity markers, and mRNA expression of circadian clock genes in the hypothalamic-pituitary-ovarian-uterine (HPOU) axis were assessed. In Experiment 2, mice were assigned to five groups: CTR, COH, EA, agonist (AG), and antagonists and EA (AT+EA). All mice were sacrificed at ZT4 on day 5 of pregnancy (D5). We measured arginine vasopressin (AVP) neuropeptide levels in the suprachiasmatic nucleus (SCN); serum E2 and P4 levels; mRNA expression of circadian clock genes in the HPOU axis; and both protein and mRNA levels of endometrial receptivity markers. Results: EA ameliorates uterine morphological abnormalities in COH mice during the WOI. Furthermore, EA upregulates the mRNA expression of the endometrial receptivity markers, decreases serum P4 levels, and restores the circadian rhythmicity of HPOU axis clock genes. The most significant intergroup differences regarding endometrial receptivity markers were observed at WOI-ZT4. At this time point, both EA and AG interventions increased AVP neuropeptide expression, suppressed serum P4 levels, modulated HPOU axis clock gene expression, and elevated the expression of endometrial receptivity markers at the protein and mRNA levels. Notably, the co-administration of AT with EA attenuated the therapeutic efficacy of EA at this stage. Conclusion: EA may enhance endometrial receptivity in COH mice at the WOI-ZT4 stage by activating AVP neurons in the SCN and restoring the circadian expression pattern of clock genes along the HPOU axis. These findings provide experimental evidence supporting a circadian mechanism by which EA may enhance endometrial function during assisted reproductive processes.