Hypothyroidism in Male Rats of Different Ages Exposed to Nitrate Polluted Drinking Water

Abstract

The effect of nitrate pollution on the thyroid hormonal levels, body weight and other health indices was studied in male rats of different ages. The tested rats were divided into young (3 weeks old) and adult (12 weeks old) groups exposed to pollution via sodium nitrate (NaNO3) intake in drinking water in concentrations 100, 250, 550 mg/L daily for 4 months. The study revealed a dose dependent decrease in serum levels of thyroid hormones thyroxine (T4) and triiodothyronine (T3) accompanied by increased levels of thyroid stimulating hormone (TSH) in all nitrate exposed rats, indicating development of hypothyroidism. A significant reduction of the body weight gain was also recorded in the young animals at different nitrate doses, but only in the adults with the high dose. Meanwhile, a significantly elevated nitric oxide (NO) level in the serum and urine were noticed that confined to the young animals with medium (250 mg/ L) and high (550 mg/L) nitrate doses and the high dose adult animals. In addition, nitrate exposure resulted in a decreased serum concentrations of total proteins and protein fractions (albumin and globulin), accompanied by significant increases in the urea and creatinine levels in both serum and urine of the tested rats. This together with the above detected changes was found to exceed as the nitrate concentration increased and to be more pronounced in the young rats. Therefore, it can conclude that prolonged exposure to nitrate polluted drinking water is toxic to the thyroid hormonal activity and the other measured indices in both young and adult rats, but the young animals comprised the most age group susceptible to nitrate toxicity.