Abstract
The effects of some antioxidants on hepatic microsomal enzymes and certain other parameters were studied in rats from 21 to 455 days post natum and in neonatal rats from dams given dietary antioxidant from 3 weeks before commencement of pregnancy till weaning of the neonates. The antioxidants used were vitamin E, butylated hydroxyl-anisole, ethoxyquin, nordihydroguaiaretic acid and n-Propyl gallate. The parameters studied included organ weights, microsomal protein, cytochromes P-450 and b5, biphenyl 4-hydroxylase and ethylmorphine N-demethylase, and in certain cases glucose-6-phosphatase. In developing rats, the antioxidants differed in their effect on liver weight gain and induction of drug-metabolizing enzymes, and enzyme activities rose to peak levels at different rates. Both ethoxyquin and nordihydroguaiaretic acid caused dramatic increases in the levels of these enzymes, with ethoxyquin producing the greater effect. Short-term studies revealed that after the post-weaning peaks were reached, the activities of the drug-metabolizing enzymes quickly diminished, but the levels in rats treated with ethoxyquin or nor-hydroguaiaretic acid were significantly higher than in controls. Dietary ethoxyquin increased liver weight and drug-metabolizing enzyme activity whether it was given from the 21st, 40th or 365th day of age. The enzyme activities always fell after reaching the peak levels, but remained at elevated levels compared with controls. Similar results were also obtained in long-term studies when the ethoxyquin was administered in the diet. The hepatomegaly and enzyme induction caused by dietary ethoxyquin were found to be due to hypertrophy and hyperplasia of the hepatic cells with proliferation of smooth endoplasmic reticulum. These also caused a dilution of hepatic microsomal glucose-6-phosphatase activity. All these changes were reversible in 30 days after withdrawal of ethoxyquin. Ethoxyquin was demonstrated to be a potent competitive inhibitor of the activities of biphenyl 4-hydroxylase and ethylmorphine N-demethylase and it bound to type I site of cytochrome P-450 with a high affinity. Single oral doses of ethoxyquin prolonged hexobarbitone sleeping-time in adult rats, while repeated dosing in the diet reduced this sleeping-time. In neonatal rats receiving ethoxyquin through placental transfer before birth and through rat-milk after delivery, the antioxidant inhibited drug-metabolizing enzymes and induced them after post-natal exposure for about 12 days. This showed a biphasic response of these enzymes to ethoxyquin. Single oral doses or chronic feeding of ethoxyquin in the diet afforded protection against carbon tetrachloride hepatotoxicity. The antioxidant gave little protection when carbon tetrachloride was administered 2 or 3 days after treatment with ethoxyquin and the results indicated that the presence of ethoxyquin in the tissue was needed for protection. In long-term studies, ethoxyquin showed some nephrotoxicity, and litters from dams fed dietary ethoxyquin had significantly lower body weights than those from untreated mothers and postnatal development of body hair was delayed.