Schistosomin, an antagonist of calfluxin.

The percentage of Ca2+ positive mitochondria in the cells of the albumen gland of Lymnaea stagnalis was used as a measure for the effect of the gonadotropic hormone calfluxin (CaFl) and for the interaction between schistosomin, an agent present in the hemolymph of snails infected with the schistosome Trichobilharzia ocellata, and CaFl. From 3 weeks postexposure on glands of infected snails showed a lower response to CaFl than glands of noninfected snails. The response decreased with infection time. Apparently the glands are already affected at an early stage of parasitosis. Albumen glands of noninfected snails preincubated in serum of infected snails and subsequently incubated with CaFl gave a lower response to CaFl than control glands. The response of preincubated glands appeared to increase when the glands were rinsed in Ringer during increasing periods of time (up to 1 hr) before being incubated with CaFl. This indicates that schistosomin binds relatively tightly to albumen glands, probably to a receptor complex. Rinsing (1-2 hr) did not influence the (low) response to CaFl of glands of infected snails, whereas the response of glands of noninfected snails increased considerably after a 1- or 2-hr period of rinsing. The results probably indicate that only a low number of receptors for CaFl is still present in glands of infected snails. In glands exposed first to schistosomin and then to CaFl, the inhibition of the effect of CaFl was stronger than in glands exposed to schistosomin and CaFl at the same time. The response to CaFl appeared to increase when a higher concentration of CaFl was used. These data indicate that schistosomin and CaFl interact at the level of receptor complex(es) in the gland. It is argued that both substances not necessarily act at the level of one and the same receptor complex.