Chronic effects of methylmercury on the urinary excretion of catecholamines and their responses to hypoglycemic stress

Abstract

Five male Wistar rats were treated with methylmercury chloride (MMC) and compared with five age-matched control rats. A dose of 10 mg/kg was given three times. The chronic effects of the MMC administration on the urinary output of catecholamines [norepinephrine (NE), epinephrine (E) and dopamine (DA)] were measured for 50 days. On the 69th day after MMC administration, the rats were examined for insulin-induced hypoglycemic stress. On the 90th day, the animals were decapitated and various organs were weighed and serum thyroid hormones [thyroid stimulating hormone (TSH) and total and free thyroxine (T4)] were measured. Decreases in DA excretion and DA response to stress were observed in the MMC-treated group. Inflammation of the kidney was also found, suggesting MMC-induced damage to the renal tubular region, the apparent site of renal DA synthesis. The MMC group and the control group showed differential NE and E response patterns. The lowered baseline excretion of NE appeared to continue even 70 days after MMC administration, while the difference in E excretion between the two groups disappeared 1 month after MMC administration. Both NE and E showed normal responsiveness to hypoglycemic stress induced by insulin. All serum TSH and total and free T4 baseline levels showed slight increases, and the thyroid gland weights in the MMC group were slightly heavier. These findings suggest a rather hyperthyroid state after the initial acute phase suppression, as suggested by the previous examinations. Thus, these findings suggest long-lasting effects of methylmercury administration, especially on renal DA synthesis. Baseline urinary excretion of NE and thyroid function could also be affected for a long time.