Abstract: In order to construct a model of drug screening and toxicity evaluation in the silkworm, Bombyx mori, the metabolisms related to antioxidation and detoxification in the midgut and fat body in the 3-day-old 5th instar larvae of the silkworm fed with isoniazid, an antituberculosis model drug, at a dose of 2 000 mg/kg were investigated. The results indicated that in the midgut of female silkworms, the contents of total glutathione (GSH+2GSSG), glutathione (GSH) and oxidized glutathione (GSSG) increased rapidly first and then decreased slowly. The glutathione Stransferase (GST) activity also increased to a higher level first and then dropped gradually to a steady level. The decline of the GSH/GSSG ratio in the midgut of female silkworms indicated the oxidative shift of redox status at 72 min after treatment. In the fat body of female silkworms, however, the contents of total glutathione, GSH and GSSG dropped rapidly first and then increased quickly, while the GST activity fell gradually and then increased to a peak. The increase of the GSH/GSSG ratio in the fat body revealed the reduced shift of redox status at 72 min after treatment. In both female and male silkworms the contents of total glutathione, GSH and GSSG, and the GST activity were higher in the fat body than in the midgut. The contents of total glutathione, GSH and GSSG were higher in females than in males, whereas the GST activity was higher in males than in females. The results suggest that the intake of isoniazid resulted in the change of the glutathione redox status and the related enzyme activities in larvae of the silkworm, and fat body plays a major role in the process of detoxification.

Key words: Bombyx mori, isoniazid, glutathione redox cycle, glutathione S-transferase, fat body, midgut