Light and electron microscopic studies on the effects of l-,d- and dl-praziquantel on Clonorchis sinensis

The effects of l-, d- and dl-praziquantel on the fine structures of Clonorchis sinensis were compared using light microscopy and scanning and transmission electron microscopy. For the in vivo study, adult worms were collected from the biliary system of infected rats that had been treated 36 h previously with each compound at a single dose of 300 mg/kg. For the in vitro study, the liver flukes recovered from the infected rats were incubated for 8-10 h at 37 。C in Tyrode's medium containing l- and d-praziquantel at 0.1 and l Ug/ml, respectively. The results showed that both l- and dl-praziquantel caused strong muscular contraction and rapid and intensive changes in the tegumental surface and the membrane structures of the worms, whereas d-praziquantel did not. It is concluded that there is a stereoselective effect between praziquantel enantiomers on C sinensis, and that the antbelmintic activity is mainly attributable to the l-isomer. Its mechanism is most likely related to a stereospecific receptor reaction with membrane structures.