A Systematic Review of the Uterine Relaxant Effect of Herbal Sources

Background: Preterm birth is a worldwide tragedy with a high incidence. Several medications are used to inhibit acute preterm labor, but tocolysis by these medicines do not extend pregnancy beyond 1-2 days. Objectives: The purpose of this study was to discover new medications from plant extracts or their active compounds which inhibit the uterine contractions in order to treat preterm labor. Data Sources: PubMed, Google Scholar, Scopus and IranMedex databases were searched up to 1^st February 2012 with the most relevant keywords. Study selection: All studies in which plant extracts or their active compounds inhibited the uterine contractions both in vivo and in vitro were included. The Results: Of initial search, 259 records were reviewed and finally 72 were included among which only 31 studies isolated an active compound from the plants extract belonging mostly to classes of flavonoids and terpenes classes. Flavonoids have been known as a phosphodiesterase (PDE) and a protein kinase C (PKC) inhibitor. It seems that the uterolytic activity of reviewed flavonoids such as naringenin, kaempferol and quercetin, especially in a calcium free solution, was via these inhibitory pathways. Conclusion: Laboring uterus response to dissimilar tocolytics differs from that of non-laboring uterus. In order to find a treatment for preterm labor, future studies should focus on the laboring uterus and also determine the structure activity relationship of the different tocolytics. This systematic review was registered to the PROSPERO with code number CRD42015027551.