[Distribution of [3H] praziquantel in tissues of Schistosoma japonicum at different developmental stages].

When [~3H] praziquantel was given orally to mice infected with Schistosoma japonicum at different developmental stages, less radioactivity was detected in the tissues of do (3 h) schistosomula by autoradiography. Thereafter, the radioactivity in the tissues of schistosomules increased gradually and reached a higher level in d_(21) schistosomula which was similar to that of adult worms (d_(28) and d_(35)).In d_0 and d_3 schistosomula the radioactivity distributed primarily in parenchyma. Up to d_(11) schistosomula,some radioactivity appeared in tegument and increased gradually thereafter. In d_(21) schistosomula more radioactivity was observed in tegument. Since only d_0, d_(28), d_(35) and d_(42) worms can be killed by praziquantel, the susceptibility of schistosomes of different developmental stages to praziquantel may not depend on the amount of the drug entered into the worm body.