MODULATION OF GLUTATHIONE-S-TRANSFERASE ACTIVITY AND ISOZYME PATTERN IN LIVER AND SMALL-INTESTINE OF RATS FED GOITRIN-SUPPLEMENTED AND T-3-SUPPLEMENTED DIETS

Goitrin is a potent goitrogen that has been shown to induce glutathione S-transferase (GST) activity and to increase aflatoxin detoxification. In the present study with rats, dietary goitrin (200 mg/kg diet) produced a hypothyroid state and significantly increased levels of hepatic GSSG (1.4-fold), GST protein (1.4-fold) and GST activity against chlorodinitrobenzene (CDNB) (1.7-fold). Cotreatment with dietary triiodothyronine (T-3) reversed these effects in a dose-related manner. Intestinal GST activities against CDNB and epoxynitrophenoxypropane did not change with goitrin or T-3 treatment. HPLC analyses showed that, in the liver, goitrin treatment increased the levels of GST-1b and -7 by 3.5- and 5-fold, respectively, and decreased the level of GST-3 by 50%. Cotreatment with T-3 returned levels of GST-7 and -3 to control levels but only partially reduced the level of GST-1b. In the small intestine, goitrin increased the level of GST-1b by 28% and decreased the level of GST-7 by 34% compared with those of controls; thyroid hormone treatment produced no additional effect on GST in this organ. Selenium deficiency altered thyroid hormone status but significantly affected the level only of hepatic GST-3, which was reduced by 30% compared with;that of controls. These results indicate that a modified thyroid hormonal status plays an important role in the GST-inducing effects of goitrin. A possible mechanism of thyroid-dependent GST induction by goitrin is discussed.