Subacute toxicity of p,p′-DDT on rat thyroid: Hormonal and histopathological changes

Abstract

The purpose of this study is to assess the effect of p,p′-DDT on thyroid activity of male Wistar rats. Pesticide was administered intraperitoneally (i.p.) for 10 consecutive days at doses of 50 and 100 mg/kg/day. At the end of the treatment, the endpoints examined included serum total levels of triiodothyronine (T 3), total thyroxine (T 4), and thyroid stimulating hormone (TSH). Thyroid gland histopathology and tissue metabolism of thyroid hormone (T 4 UDP-glucuronyltransferase UDP-GT and 5′-deiodinases) were determined. DDT treatment altered thyroid function namely by increasing hepatic excretion of T 4 glucuronide. At the dose of 50 mg/kg it decreased T 4 circulating levels and increased thyroid 5′-deiodinase type I (5′-D-I) and brown adipose tissue (BAT) 5′-deiodinase type II (5′-D-II) activities but it did not affect liver 5′-D-I activity which might contribute to the maintenance of the serum T 3 level. Treatment with 100 mg DDT/kg decreased serum thyroid hormone concentration and tissue 5′-D-I activity without affecting BAT 5′-D-II activity. Gland histomorphological analysis showed hyperplasia and squamous metaplasia with abundant colloid. These observations associated to the elevated serum TSH levels and gland hypertrophy suggest that DDT exposure induced an hypothyroidism state with a colloid goiter in rats.