Uterotonic activity of an aqueous extract of leaves of Helichrysum mechowianum commonly used for vaginal tightening by native populations in south east Gabon

Abstract

The leaves of Helichrysum mechowianum (Helymext) are traditionally used by some native populations of Gabon for vaginal tightening following childbirth. In order to validate its use scientifically, the current work was undertaken to investigate the possible tonic activity of the plant in the vaginal smooth muscles. Phytochemical screening of the plant extracts was carried out and its pharmacological effects were studied on isolated uterine smooth muscles from pregnant rats using the isolated organ bath. Helymext (10-8 - 10-2 mg/ml) evoked a concentration-dependent enhancement of the uterine smooth muscle contractile activity (EC50: 1.34 × 10-4 ± 0.1 × 10-5 mg/ml) comparable to that induced by acetylcholine (ACh) (EC50: 9.41x10-7 ± 0.02 × 10-8 mg/ml) or by prostaglandin (PGE1) (EC50: 8.46 × 10-7 ± 1.21 × 10-9 mg/ml). Atropine (10-6 mg/ml) failed to inhibit Helymext-induced contractions (EC50: 4.4 × 10-4 ± 0.12 10-5 mg/ml, p > 0.05). Whereas, indomethacin (10-6 mg/ml) significantly reduced the contractile activity caused by the plant extract (EC50: 9.68.10 -5 ± 0.2 × 10-4 mg/ml, p < 0.05). In calcium-free medium with or without EDTA, Helymext still induced spontaneous and tonic contractions. In the same conditions, a tonic contraction was caused by the PGE1. These results suggest that Helichrysum mechowianum plant extract would contain uterotonic ingredients which could act through pathways involving prostaglandin synthesis. Helymext-induced calcium mobilization from extracellular medium and from internal stores, highlighting a great potential of enhancement of the smooth muscle tonic activity.