Seasonal variation in uterotonic activity of Rhoicissus tridentata extracts.

BACKGROUND Rhoicissus tridentata lignotubers are widely used in southern African traditional pregnancy-related remedies. OBJECTIVES To determine the seasonal variation in contractile activity of extracts from different parts of the plant. METHODS Isolated rat uterus tissue was used to compare the contractile activity of crude aqueous extracts of R. tridentata made from plant material harvested every 3 months over a period of 2 years. RESULTS AND CONCLUSIONS The activity of the plant extracts from plants harvested in summer and autumn were 4-5-fold higher than extracts from plants harvested in winter or spring. The tubers stimulated the greatest degree of contractions, followed by the stems, roots and leaves. These results highlight the need to standardise the timing of harvesting R. tridentata.