THE IN VITRO EFFECT OF “PYQUITON”ON SCHISTOSOMA JAPONICUM

Pyquiton (Praziquantel, Embay 8440), has been found to possess a strong and direct action against Schistosoma japonicum. When bisexual worms were exposed to culture medium containing 0.005 μg/ml of pyquiton, a stimulation of the activity of the worm appeared within 30 seconds. At the concentration of 0.05 μg/ml for about 3 minutes, the worms became contracted after an initial stimulation. Worms exposed to a concentration over 0.2/μg/ml rapidly shrank and remained motionless after a short stimulation period, with the exception of the oral sucker of the male worms which exhibited very feeble motion for some time. The minimum effective concentrations of pyquiton against schistosomes in vitro were the same for culture medium with or without sheep serum. When maintained in a concentration of 0.3～10 μg/ml of pyquiton, the mean survival time of male and female worms was 1.6±0.6～2.6±0.5 and 3.4±0.3～4.4±0.5 days respectively, while that of control worms was 13.3±0.3 days, When worm pairs were exposed to pyquiton at a concentration of 10μg/ml for 1,274,8, 16 and 24 hours, and then transferred to a drug-free medium, most of the affected worms would not recover from their motionless state and some would eventually die in 6～7 days. The admini stration of pyquiton to infected mice at a single oral dose of 100 or 500 mg/kg resulted in hepatic shift of the worms which were contracted and motionless. When worms were perfused out from the liver, and cultivated in drug-free medium for 3 days a large proportion of worms from animals treated with smaller dosages could recover to their normal activity, while those with bigger dosages could not. Histochemical studies indicated that, either in vitro or in vivo, pyquiton exhibited no effect on the acetyicho-linesterase activity of the worms.