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Based on traditional reports, the aqueous and ethanol extracts of the leaves of N. laevis were tested on isolated uterine preparations of non-pregnant rats. The effects of increasing cumulative concentrations of the extracts on the amplitude and frequency of spontaneously contracting uterine tissues were tested. Direct effects of the extracts and acetylcholine on uterine smooth muscle were also tested in organ baths containing aerated physiological salt solution maintained at 37°. The EC50 and Emax were determined and analyzed using one way ANOVA with Dunnett's post hoc test. The extract significantly increased the frequency (P<0.05) of spontaneous contractions without significantly affecting the amplitude. The extracts and acetylcholine were observed to directly stimulate uterine contractions, however there were significant differences (P<0.05) in their EC50 and Emax. In conclusion, the leaves of N. laevis increase the frequency of spontaneously contracting tissues and directly stimulate uterine contractions which may account for the use of the leaf extract traditionally.

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Ethnopharmacological relevance: The leaves of Justicia flava are traditionally used in the South of Nigeria to prevent preterm births. Aim of the study: In this study, the activity of the methanol leaf extract of J. flava (JF) was investigated on uterine contractility in non-pregnant and pregnant isolated mouse tissues. Material and methods: The effects on spontaneous, oxytocin, and KCl-induced contractions were determined. The effects in calcium-free media were also determined. Possible mechanisms of activity were investigated using receptor and channel modulators. Mass spectrometric analysis was additionally performed on the leaf extract to identify secondary metabolites. Results: JF was observed to inhibit spontaneous, oxytocin and high KCl-induced uterine contractility. JF also inhibited contractions in Ca 2+free media. JF was found to exert its inhibitory effect via interaction with inositol triphosphate and ryanodine receptors and also through modulation of K +-channels. Lignans and alkaloids were identified with the lignans being the most abundant in JF. Conclusion: JF has been shown to potently inhibit uterine contractions in non-pregnant and pregnant isolated mouse uterus. The inhibitory activity of JF has been shown to occur via blockade of extracellular and intracellular calcium entry and these effects may be due to the lignans identified in the JF. JF has therefore been shown in this study to be a lead plant in the discovery of new drugs with uterine inhibitory activity.