We investigated the metabolism of three larval stages of Schistosoma mansoni: the developing cercaria infecting Biomphalaria glabrata, the freeliving cercaria, and the schistosomule collected after penetration through rat skin membrane. The metabolism of the developing cercaria was studied by exposing infected snails to 14C-glucose and thereafter determining the distribution of 14C in the emerging cercariae. In one experiment, the radioactivity in the cercariae increased to a high peak on day 6 after 14C exposure, declined rapidly to day 12, and less rapidly to day 30. In a second experiment, increase and decrease were more moderate and the peak was reached on day 13. Protein, nucleic acid, lipid, and glycogen fractions were labeled with 14C. Radioactivity was highest during the first few days after infection and declined rapidly thereafter in most fractions, but the nucleic acid fraction retained a relatively high level of radioactivity for 19 days. When 14C-labeled cercariae were maintained free-living overnight, most of the radioactivity of the glycogen fraction disappeared. Free-living cercariae metabolized exogenous glucose to a very slight degree shortly after emergence, but activity increased after 18 hours of free-living existence and deletion of endogenous glycogen. Pyruvate was utilized very rapidly under both conditions resulting in production of CO2 from all three carbons and incorporation of a small fraction of the pyruvate carbon into the principal macromolecules. α-Ketoglutarate and acetate, and, to a small extent, glutamate, glutamine, and some of the intermediates of the citric acid cycle were also catabolized. The metabolic activity of the schistosomule appeared to differ considerably from that of the cercaria-the most pronounced difference being a great reduction in the level of pyruvate catabolism. We concluded that the developing cercaria is primarily engaged in synthesis and storage of glycogen. The free-living cercaria is geared to the production of energy either from its stores of glycogen or from an exogenous substrate such as pyruvate. The schistosomule loses its adaptation to rapid production of energy and, presumably, is again primarily engaged in synthesis. © 1969.
