Potassium bromate (KBrO3) is a prooxidant and
carcinogen, inducing thyroid
tumors.
Melatonin and indole-3-propionic
acid (IPA) are effective
antioxidants. Some antioxidative effects of
propylthiouracil (PTU)--a thyrostatic
drug--have been found. The aim of the study was to compare protective effects of
melatonin, IPA, and PTU against lipid peroxidation in the thyroids, collected from rats treated with KBrO3, and in homogenates of porcine thyroids, incubated in the presence of KBrO3. Wistar rats were administered KBrO3 (110 mg/kg b.w., i.p., on the 10th day of the experiment) and/or
melatonin, or IPA (0.0645 mmol/kg b.w., i.p., twice daily, for 10 days), or PTU (0.025%
solution in
drinking water, for 10 days). Homogenates of porcine thyroids were incubated for 30 min in the presence of KBrO3 (5 mM) plus one of the
antioxidants:
melatonin (0.01, 0.1, 0.5, 1.0, 5.0, 7.5 mM), or IPA (0.01, 0.1, 0.5, 1.0, 5.0, 7.5, 10.0 mM), or PTU (0.01, 0.1, 0.5, 1.0, 5.0, 7.5, 10.0 mM). The level of lipid peroxidation products (MDA + 4-HDA) was measured spectrophotometrically in thyroid homogenates. In vivo pretreatment with either
melatonin or with IPA or with PTU decreased lipid peroxidation caused by KBrO3--injections in rat thyroid gland. Under in vitro conditions, PTU (5.0, 7.5, and 10.0 mM), but neither
melatonin nor IPA, reduced KBrO3-related lipid peroxidation in the homogenates of porcine thyroids. In conclusion,
melatonin and IPA may be of great value as
protective agents under conditions of exposure to KBrO3.