Schistosoma mansoni: serotonin uptake and its drug inhibition

5-Hydroxytryptamine (serotonin) uptake by male and female Schistosoma mansoni was studied in vitro. Initial uptake was determined during the first 2 min of incubation with the indoleamine. There were two types of uptake: a saturable component that is apparent at low concentrations of serotonin, and a passive component that predominates at high concentrations. Female S. mansoni take up more 5-hydroxytryptamine per milligram protein than do the males. Studies on the distribution of 5-hydroxytryptamine taken up by the parasites show that a large proportion of the indoleamine is in the tegument. The female tegument had a greater proportion of the 5-hydroxytryptamine taken up than did the male tegument. The evidence indicated that 5-hydroxytryptamine associated with tegument represented the passive uptake while uptake in the main parasite body was both active and passive. Compounds that were shown to inhibit 5-hydroxytryptamine uptake include methylclonazepam, metergoline, imipramine, and ouabain. Maximal inhibition by these compounds ranged from 50 to 60%. Inhibition appeared to be confined to the saturable uptake component of the body fraction.