The effect of organophosphorus compounds on respiration by rat liver mitochondria

Rat liver mitochondria from normal and chronically intoxicated rats were prepared by standard methods. Three organophosphorus compounds were assayed: Parathion, Malathion and Dimetoate. Oxygen uptake and respiratory control ratio were measured by a polarographic method. The addition of the pesticides at the reaction vessel (containing normal mitochondria) or pretreatment of the animals with these compounds, decreased state 3, state 4 and 2,4-dinitrophenol stimulated respiration with glutamate-malate as substrate in the presence of malonate. The mentioned states were not significantly altered when succinate was used as substrate. Respiratory control ratio decreased in the presence of the pesticides with both substrates. Mitochondrial respiration results obtained in vivo and in vitro suggest that the three mentioned organophosphorus compounds behave as inhibitors of the mitochondrial electron-transport system. The decrease of the respiratory control ratio may be related to a possible change in the permeability of the inner mitochondrial membrane.