Abstract: Objective To study in vitro the effect of 5-hydroxytryptamine （5-HT） on the motility and length of primary sporocysts of Schistosoma japonicum and select the optimal concentration and time of 5-HT. Methods Eggs of S. japonicum were harvested from livers of the infected mice 6-8 weeks after infection, which were then incubated with water. The miracidia were axenically cultured in 1/2 RPMI 1640 containing 10% calf serum and a moderate amount of antibiotics （100 U/ml penicillin G and 100 μg/ml streptomycin） for 48 hours. They became mother sporocysts and were divided into two groups. Parasites in the first group were treated by 5-HT under concentrations of 0，0.1，1，10，100 and 1 000 μmol/L for 48 hours， respectively. Those parasites in the second group were treated by 5-HT of 10 μmol/L for 0.16，6，24 and 48 hours，respectively. The motility，length and succinic dehydrogenase（SDH） activity of the parasites were measured under Olympus microscope. Results Along with the increase of 5-HT concentration，the motility and length of the mother sporocysts all increased gradually. With the 5-HT concentration of 10 μmol/L， both of them reached a maximum value, being （65.6±1.5）% and （131.4±9.2） μm respectively. Meanwhile, along with the prolongation of treat-ment time, the motility and length also increased gradually. The motility reached a maximal value at 24 hours post-treat-ment. So did the length and SDH activity of the parasites at 48 hours post-treatment. Conclusion 5-HT shows a sig-nificant effect on the motility and length of mother sporocysts of S. japonicum and its optimal concentration is 10 μmol/L un-der in vitro conditions.

Key words: Schistosoma japonicum, Mother sporocyst, In vitro, 5-Hydroxytryptamine, Motility, Length