EDN1 and polycystic ovary syndrome: Stener-Victorin reported that repeated EA stimulation significantly promoted the release of β-endorphins in the hypothalamus of polycystic ovary (PCO) rats and reduced nerve growth factor (NGF), corticotropin-releasing factor (CRF), and endothelin-1 (ET-1) in the ovaries of PCO rats [95, 121–123].