THE UTEROTONIC ACTION OF THE AQUEOUS EXTRACT OF BRIDELIA ATROVIRIDIS IN THE RAT

Summary— The effects of the aqueous extract of leaves of Bridelia atroviridis (Bridelia), a small African tree, on the mechanical activity of rat uterus were studied. The aqueous extract of leaves of B atroviridis administered in a concentration-dependent manner (5 times 10−6-1.2 times 10−3 g/ml) induced contractions that were antagonized by various calcium entry blockers (nifedipine, diltiazem, manganese chloride). In absence of external calcium ions, repeated applications of a supramaximal concentration of Bridelia (1.2 times 10−3 g/ml) evoked sustained and repeated contractions the amplitude of which was = 20% of those obtained in the physiological external calcium concentration. Bridelia-induced contractions in calcium-free medium were inhibited by isoprenaline (8 times 10−7 M), caffeine (15 times 10−3 M) and trifluoperazine (10−5 M). Contractile responses induced by Bridelia in both calcium-containing and calcium-free media were antagonized by prior incubation of uterus with phorbol 12, 13-dibutyrate (6 times 10−7 M), cholera toxin (6 times 10−8 M) or pertussis toxin (5 times 10−7 g/ml). These results show that Bridelia has a potent uterotonic action in the rat. The cellular basis of this action appears to be complex, and involves various mechanisms including calcium mobilization from both intra and extracellular compartments and activation of phospholipase C through a G-protein.