Abstract
Leonurus japonicus Houtt is an exceptional medicinal herb used to treat obstetrical and gynecological diseases in traditional Chinese medicine, and it has significant effects on the treatment of dysmenorrhea and postpartum hemorrhage. This study investigated the effects of coumarins with diverse substituent groups from L. japonicus on isolated uterine smooth muscle and the preliminary mechanism of the most effective compound. Eight coumarins isolated from L. japonicus were assessed for their effects on the isolated uterine smooth muscle of nonpregnant rats in vitro. Coumarins 1 and 2 significantly promoted the contraction of rat uterine smooth muscle strips, whereas coumarins 3-5 showed remarkable relaxing effects against oxytocin (OT)-induced rat uterine smooth muscle contraction. Further mechanism investigations revealed that bergapten (coumarin 1) significantly increased the level of Ca2+ in uterine tissues by promoting extracellular Ca2+ influx and intracellular Ca2+ release, which were related to the activation of L-type Ca2+ channels and α-receptors. By contrast, osthole (coumarin 5), an α receptor antagonist, inhibited OT-induced uterine smooth muscle contraction by decreasing the level of Ca2+ in uterine tissues via inhibition of extracellular Ca2+ influx and intracellular Ca2+ release. This study demonstrates that the coumarins from L. japonicus are effective substances for regulating uterine smooth muscle contraction, but different coumarins with diverse substituent groups have different, even opposite effects. It can be inferred that coumarins are closely related to the efficacy of L. japonicus in the treatment of dysmenorrhea and postpartum hemorrhage.