Vertebrate-type steroids in cercariae of the schistosomeTrichobilharzia ocellata

Abstract

Vertebrate-type steroids (e.g. androgens, progestagens, and estrogens) have been demonstrated in a wide range of invertebrate species (Lehoux and Sandor 1970; Rees 1984; de Loof and de Clerck/986; de Loof 1987). This has led to the hypothesis that steroids are common to many, if not all, invertebrate phyla (Karlson 1983). As far as the platylhelminths in general and trematode parasites in particular are concerned, little is known about regulatory substances present in these animals (Spindler 1988; Halton etal. 1990). It has been suggested that steroids might play a role in the sexual development of helminths, but direct evidence for a hormonal role of steroids in these parasites is lacking (Morrison et al. /986). Whole-animal homogenates of adult worms of Schistosoma mansoni can perform some steroid transformation (Briggs 1972), but the presence and/or de novo synthesis of vertebrate-type steroids in schistosomes has not yet been established (Rees 1984; Gupta and Basch 1989). In the present study the presence of vertebrate-type steroids in cercariae of the schistosome Trichobilharzia ocellata was studied using radioimmunoassay (RIA), high-performance liquid chromatography (HPLC) combined with RIA, and immunocytochemistry. Juvenile specimens of the snail Lymnaea stagnalis were infected with miracidia of T. ocelIata as described by Sluiters et al. (1980). Cercariae were obtained from snails 8-12 weeks postexposure. Cercariae (total wet weight, 15.6 g) were homogenized in an acetone/methanol solution (1 : 1, v/v) and, after centrifugation, the supernatant was collected. The hydrophilic ecdysteroids, which are present in cercariae of T. ocellata (Schallig et al. 1991 a), were separated from the lipophilic steroids by water/diethyl ether extraction. The biological extract was accompanied by a blank, which was put through each stage of the purification procedure and biochemical analysis. The steroid content of the cercariae was quantified by RIA using a testosterone, /7fi-estradiol, or progester-