Studies on factors influencing the acute toxicity of malathion and malaoxon in rats.

Abstract

A study was undertaken to investigate the mechanisms responsible for the higher susceptibility of immature rats to the organophosphate insecticide malathion. In vitro measurements of the activity of malathionase in the tissues of rats, at various time intervals after birth, indicated that the livers of immature rats detoxify the insecticide at a much slower rate than do the livers of adult animals. Evidence was obtained which showed that prolonged administration of testosterone causes a significant increase of the enzymatic activity in the livers of castrated young male rats and adult female rats. On the other hand, castration interferes with the maintenance of normal levels of malathionase in adult males and partially prevents the development of the activity in weanlings. Estradiol decreases the enzymatic activity in adult males. It appears, therefore, that the age difference in the susceptibility of rats to malathion might be due, to a large extent, to a slower rate of inactivation of the insecticide by the livers of immature animals. The results obtained also indicate that the sex hormones play an important role in the development and maintenance of normal levels of the enzyme system involved in the degradation of malathion in the livers of rats.