Praziquantel impairs the ability of exogenous serotonin to stimulate carbohydrate metabolism in intact Schistosoma mansoni.

Praziquantel (PZQ) (Droncit, Biltricide) at 10 microM completely abolishes the stimulatory effect of serotonin on glucose uptake and lactate excretion of Schistosoma mansoni. Fluoxetine (FXT) exerts similar effects on the serotonin-induced stimulation of glucose uptake and lactate excretion, however, at 100-fold higher concentrations. In comparison with PZQ, which is inhibitory at 10 microM, FXT and other amphiphilic cationic drugs (amitriptyline, propranolol, imipramine, chlorpromazine) inhibit glucose uptake or lactate excretion in schistosomes at 1 mM; the strongest inhibitor is FXT. Glycogen breakdown is maximally stimulated by PZQ in the absence or presence of serotonin. There is an additive effect of 50 microM chlorpromazine or FXT and 0.01 to 0.1 microM PZQ on glycogen breakdown. The rate of sodium-sensitive or insensitive serotonin uptake in Schistosoma mansoni is reduced by 10 microM PZQ by about 40%, as is the sodium-sensitive excretion of serotonin. The results show that PZQ interferes with the ability of serotonin to stimulate carbohydrate metabolism. The possibility that PZQ may act through an effect on tegumental integrity is discussed.