Abstract
Early embryo and sperm transport through the oviductal isthmus depends on the contraction and relaxation of the smooth muscle layers. Dysfunction of the oviduct transport is considered to be one of the causes of infertility. For human infertility, Chinese medicine is used in East Asia. Although there are many clinical reports regarding Tokishakuyakusan (TSS), there is little scientific evidence that it affects infertility. In this study, we investigated the effect of TSS on bovine oviductal contraction and relaxation via the G protein-coupled estrogen receptor 1 (GPER1). We collected bovine oviductal isthmic tissues at four stages of the estrous cycle, classified based on a macroscopic observation of the ovary. The Magnus method was used to monitor longitudinal contractility (frequency, contraction force, and tonus). The effects of TSS solution, GPER1 agonist (G-1), and antagonist (G-15) on oviductal contractility were examined. The protein expression level of GPER1 in the oviductal isthmic smooth muscle of each estrous stage was assessed by Western blotting. Although TSS did not affect frequency and contraction force, the tonus was significantly increased by TSS or G-1 at all stages (p < 0.05), and the effect was especially highest at days 1-4 after ovulation. The addition of G-15 significantly suppressed the TSS-induced increase of oviductal tonus at all stages (p < 0.05). There was no significant difference in GPER1 protein expression among the estrous stages. TSS affects oviductal contractility by increasing tonus via GPER1, and it may accelerate gamete and early embryo transport by contracting the oviducts longitudinally.