Comparison of early pregnancy-terminating effect and toxicity between pseudolaric acids A and B

Two novel diterpenoids, pseudolaric acids A and B. were first isolated in China from the root of Pseudolarix kaempferi Gorden. Chemically, A and B have the same main structure with different substituted groups at C-7. Our experimental results indicated that the ED60 0f A given by gavage daily in rats on d 7-9 after mating was 8.2 (5.9-11.1) mg/kg and that of B was 4.5 (3.3-6.1) mg/kg, while the single oral ED60 of A and B given on d 7 after mating in rats were 14.5 (11.7-17.7) and 9.3 (8.5-10.5) mg/kg. respectively. In rats the single oral LD50 of A was 219 (193-250) mg/kg and that of B was 130 (114-149) mg/kg. The therapeutic indices of A and B were 14.1 and 15.2 and the safety indices were 4.3 and 3.2, respectively. It is concluded that pseudolaric acids A and B possess significant early pregnantterminating activity in rats and hamsters. However, the antifertility activity are significantly larger than A.