The occurrence of schistosomin, an antagonist of female gonadotropic hormones, is a general phenomenon in haemolymph of schistosome-infected freshwater snails

Abstract

In haemolymph ofLymnaea stagnalis, parasitized with the digenetic trematode parasiteTrichobilharzia ocellata, a neuropeptide (schistosomin) occurs which antagonizes female gonadotropic hormones, e.g. calfluxin (CaFl). By means of an ultracytochemical hormone-assay, the CaFl assay, it was demonstrated that the occurrence of schistosomin is a general phenomenon in schistosome-infected freshwater snails. Haemolymph of the schistosomiasis-transmitting snail speciesBiomphalaria glabrataandB. pfeifferi, parasitized withSchistosoma mansoni, also appeared to contain an antagonizing factor, i.e. schistosomin. In contrast, in haemolymph ofL. stagnalisparasitized withDiplostomum spathaceum(Diplostomatidae) no schistosomin could be found. This suggests that schistosomin may only occur in snails infected with parasites belonging to the Schistosomatidae. The effect of schistosomin is rather specific. Haemolymph ofB. glabrataparasitized withS. mansonihad not the capacity to inhibit the response to CaFl in the target organs for CaFl, the albumen glands ofL. stagnalisandBulinus truncatus. The same holds true for haemolymph of infectedL. stagnalis: it did not inhibit the CaFl response in glands ofB. glabrataandB. truncatusand even not in those of a related species (L. ovata). Schistosomins in haemolymph of infectedB. glabrataandB. pfeifferi, on the other hand, seem more related. Both appeared to inhibit the hormone response in glands of the twoBiomphalariaspecies studied. The results indicate that schistosomin in haemolymph of schistosome-infected pulmonate snails, although functionally related, may differ structurally.