Ferric nitrilotriacetate (Fe-NTA) induces renal proximal tubular necrosis, a consequence of lipid peroxidation, that finally leads to a high incidence of renal adenocarcinoma in rats and mice. Male animals are much more susceptible than female animals to both effects. Moreover, the distribution of the susceptible proximal tubules is different between male and female animals. The present study investigated the effects of castration and sex hormones on Fe-NTA-induced renal lipid peroxidation. Male and female ddY mice were either left untreated, castrated, and/or treated with testosterone or estriol. Histochemical (reactivity to cold Schiff's reagent) and biochemical (thiobarbituric acid-reactive substance) evaluations were performed 1 h after the i.p. injection of Fe-NTA (5 mg iron/kg).

Testosterone treatment and/or oophorectomy increased the Schiff positivity of the renal cortical proximal tubules and the amount of thiobarbituric acid-reactive substance (testosterone-treated female > intact female, P < 0.005; castrated female > intact female, P < 0.1; castrated and testosterone-treated female > intact female, P < 0.005). In contrast, estriol treatment and/or orchiectomy decreased the Schiff positivity of the renal cortical proximal tubules and the amount of thiobarbituric acid-reactive substance (estriol-treated male < intact male, P < 0.01; castrated male < intact male, P < 0.01; castrated and estriol-treated male < intact male, P < 0.005). Estradiol treatment produced similar results to estriol treatment (estradiol-treated male < intact male, P < 0.005). Castration and/or administration of the opposite sex hormone reversed the sex difference in the distribution of proximal tubules susceptible to lipid peroxidation. However, the i.v. injection to male mice, 5 min prior to the Fe-NTA treatment, of conjugated estrogen that is promptly excreted via the urine produced no significant effect. Thus, altered metabolic pathways rather than the direct scavenging activity of estrogens seem to be involved in the sex hormone-dependent difference of lipid peroxidation. Genetically determined sex hormone status appears to have influenced the incidence of Fe-NTA-induced renal adenocarcinoma in intact animals.

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This work was supported in part by a Grant-in-Aid from the Ministry of Health and Welfare, Japan.

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