Cadmium-selenium antagonism and detoxifying enzymes in insects

Activities of non-specific carboxylesterases (CarE) have been studied in adult males of hissing cockroach Gromphadorhina portentosa subjected to prolonged intoxication (7 weeks) with Cd and/or Se to investigate whether sublethal dose of cadmium (0.4 micromol. g(-1) dry weight feed) would influence the detoxifying capabilities of the omnivorous insect, and whether selenium (0.01 micromol. g(-1) dry weight feed) given concomitantly would act as Cd antagonist. Activities of CarE have been measured in crude homogenate, postmitochondrial supernatant and the pellet obtained from midgut, Malpighian tubules and fat body, using alpha-naphthyl acetate (alphaNA) and rho-nitrophenyl acetate (rhoNPA) as substrates. The highest rate of alphaNA hydrolysis occurred in midgut, whereas that of rhoNPA in both the gut and Malpighian tubules. CarE activities in the Cd-group have been the highest in all tissues examined and for both substrates. A simultaneous administration of Cd and Se decreased the effects of Cd alone, probably as a result of partial elimination of the biologically active Cd pool. Selenium alone caused only minor effects when compared with cadmium. These results suggest, that disturbances of CarE activities depend on the Cd concentration in feed, and hence in tissues, as well as on possible interactions of the elements.