The effects of pomegranate seed extract and beta-sitosterol on rat uterine contractions

The aim of this study was to investigate the effects of pomegranate (Punica granatum L., Punicaceae) seed extract on uterine contractility. Pomegranate seeds were methanolic extracted and their constituents analyzed using gas chromatography and mass spectrometry. Isometric force was measured in strips of longitudinal rat myometrium and the effects of pomegranate seed extract studied. We found beta-sitosterol to be the main constituent of the extract (16%) and its effects were also investigated. Pomegranate seed extract and beta-sitosterol increased spontaneous contractions in a concentration-dependent manner with a maximum effect at 250 mg/100 mL and 1 mg/100 mL, respectively. The amplitude and frequency of the phasic contraction were significantly increased along with basal tension. The effects of pomegranate seed extract were very similar to those of beta-sitosterol. Force produced in the presence of pomegranate seed extract was abolished by the inhibition of L-type calcium channels or myosin light chain kinase (MLCK). Contractions were not potentiated by pomegranate extract following the inhibition of K channels or inhibition of the sarcoplasmic reticulum calcium ATPase (SERCA). The actions of beta-sitosterol and the extract were not blocked by the estrogen receptor blocker, fulvestrant. We conclude that pomegranate seed extract is a potent stimulator of phasic activity in rat uterus. Our data suggest that the uterotonic effect is due to nonestrogenic effects of beta-sitosterol acting to inhibit K channels and SERCA and thereby increasing contraction via calcium entry on L-type calcium channels and MLCK. We suggest that pomegranate extract and beta-sitosterol may be a useful uterine stimulant.