Serotonin-activated adenylate cyclase during early development of Schistosoma mansoni

Schistosoma mansoni infection is a major parasitic disease which afflicts 200 million people, mostly in developing countries. The parasite has a complex life cycle during which it is parasitic on a snail at the larval stage and on a mammalian host as an adult. In addition, there are two free-swimming stages: miracidia, which must penetrate the snail host, and cercariae, which leave the snail to find the correct mammalian host. On penetration into the mammalian host, the cercaria loses its tail and is referred to as a schistosomule. Adult stages of Fasciola hepatica (liver fluke) 1,2 and S. mansoni 3 have probably the highest adenylate cyclase activity reported, and in both parasite the enzyme can be activated by serotonin. Studies on Fasciola have shown that GTP is necessary for serotonin activation. One possible main function of high adenylate cyclase activity is the regulation by cyclic AMP of anaerobic glycolysis, which is the main source of energy in the adult stage of these parasites 5,6 . We have compared the activities of adenylate cyclase in different developmental stages of Schistosoma . We report here that the cercariae have low adenylate cyclase activity which responds only poorly to activation by serotonin and GTP. However, in schistosomules cultures in vitro 7 , we found that within the first 4 days the cyclase system changed from one showing low serotonin activation, similar to that of cercariae, to one of high activity similar to that found in the adults.