Possible mechanism of the uterotonic activity of the ethanolic leaf extract of Newbouldia leavis (Bignoniaceae) I

The aqueous and ethanolic leaf extract of Newbouldia laevis has been shown in a previous study to stimulate and increase contractions in isolated uterine preparations of non – pregnant rats. This study was therefore carried out in sequel to identify the possible mechanism(s) by which the ethanolic leaf extract causes uterine contraction in vitro.

The extract (10^-6 mg/ml) was tested in the presence and absence of; muscarinic receptor blocker, atropine (0.5×10^-4 mg/ml), α₁-receptor blocker, phentolamine (0.13×10^-3 mg/ml), H₁-receptor blocker, diphenhydramine (0.13×10^-3 mg/ml) and L-type calcium channel blocker, verapamil (0.13×10^-6 mg/ml). Concentration – response curves were constructed. The EC₅₀ and E_max were determined and statistically analyzed using one way Anova and Dunnett post hoc test.

No significant difference was observed in the EC₅₀ and E_max of the extract in the presence of phentolamine and diphenhydramine. However, significant differences were observed in the EC₅₀ of the extract (p<0.01; p<0.01) in the presence of atropine and verapamil respectively. With regards to the E_max, no significant difference was observed in the presence of atropine but a significant difference of p<0.01 was observed in the presence of verapamil.

In conclusion, the leaf extract of N. laevis contracts the uterus probably by increasing the open state probability of voltage – gated calcium channels directly or indirectly and may also activate muscarinic receptors present in the uterus. It thus seems that this crude leaf extract acts by more than one mechanism and may contain more than one active uterotonic principles.

Acknowledgements: Dr. A. Bafor, O. Uwumarogie