The zoapatle XV. Activity of 16a-hydroxy-ent-kauran-19-oic acid isolated from montanoa hibiscifolia, and its methyl ester on rat and guinea pig uterus

16α-Hydroxy-ent-kauran-19-oic acid was isolated from Montanoa hibiscifolia. The effects of this acid and its methyl ester on the contractile activity of rat and guinea pig uterine horns were studied. Both inhibited spontaneous, oxytocin-induced and potassium-induced contractile activities. The inhibitory effect produced by the methyl ester was greater than that observed with the acid. The methyl ester was 2–5 times more potent than the acid upon spontaneous and potassium-induced contractions and 11–15 times more potent than the acid upon the contractile activity of uterine smooth muscle induced by oxytocin. Such effects were observed using bath concentrations of 6, 15, 30 and 60 μM of each compound.