Effects of prostaglandin-F2 alpha and a plant protein "Trichosanthin", on 10-day pregnant rabbits.

The effect of Trichosanthin (TCS), a protein obtained from the roots of Trichosanthis kirilowii, alone or in combination with prostaglandin-F2 alpha (PGF2 alpha; Tromethamine salt) on the termination of pregnancy in rabbits was investigated. Intraperitoneal injection of 1 or 2 mg TCS/10-day pregnant rabbits neither altered the serum progesterone (delta 4P) level nor interrupted pregnancy. Doses of 0.5 or 0.25 mg PGF2 alpha incorporated in a Silastic-PVP tube and inserted intravaginally, terminated pregnancy within 72 h of treatment in 75 and 16% of the treated does, respectively. By contrast, does treated on day-10 of pregnancy with a combination of a non-effective dose of TCS (1 mg) and a sub-effective dose of PGF2 alpha (0.25 mg) terminated pregnancy in all the treated animals as no live embryos were found within 3 days of treatment. Pregnancy interruption was associated with a significant reduction of serum delta 4P and delta 4P/20 alpha-dihydroprogesterone (20 alpha-DHP) ratio. The present study indicates that TCS and PGF2 alpha act synergistically, rendering the termination of 10-day pregnancy possible in the rabbit. It was also noted that pregnancy cannot be maintained when the serum delta 4 P level drops below 4 ng/ml and delta 4P/20 alpha-DHP falls lower than 0.6 in the 10-day pregnant rabbit.