Ancylostoma caninum: reduced glutathione stimulates feeding by third-stage infective larvae

The resumption of feeding in vitro has been proposed as an indicator of the reactivation of development by arrested third-stage hookworm larvae. The tripeptide glutathione was tested for its ability to induce in vitro feeding by third-stage infective larvae of the canine hookworm Ancylostoma caninum. Reduced glutathione, but not oxidized glutathione, stimulated larval feeding in a specific, concentration-dependent manner. Feeding began at 5-10 mM, and reached a plateau at 25-50 mM. Incubation in reduced glutathione for 3 hr was sufficient to stimulate the maximum feeding response at 24 hr. Larvae began feeding within 6 hr of incubation with reduced glutathione, and feeding reached a maximum percentage by 24 hr. The reducing agents dithiothreitol and 2-mercaptoethanol failed to stimulate feeding, whereas S-alkyl derivatives of reduced glutathione were stimulatory. Reduced glutathione synergistically increased serum-stimulated feeding to greater than 90% of the sample population, and low concentrations of glutathione appeared to enhance feeding by sensitizing the larvae to a stimulatory component in serum and not by a chemical interaction with a serum component. The data suggest that reduced glutathione might participate in the transition from the free-living third-stage larva to the parasitic third-stage larva during infection.