Thorium exerts hazardous effects on some neurotransmitters and thyroid hormones in adult male rats.

Assessment of the hazardous effects of thorium, a naturally radioactive element, on the nervous and endocrine systems, which are intimately involved in maintaining homeostasis, is important. In the present study, rats were divided into control and thorium groups and were decapitated after 2, 4, and 6 weeks. We observed that intraperitoneally injected thorium (6.3 mg/kg body weight) crossed the blood-brain barrier and was localized in the cerebellum, cerebral cortex, and hypothalamus of the rats in the given order. Thorium administration significantly decreased the GSH level and increased MDA, NO, and Fe3+ levels. Furthermore, thorium administration decreased NE and DA levels and induced fluctuations in 5-HT level. Thorium administration also increased serum TSH level, which in turn increased T4 and T3 levels. Together, these results indicate that thorium administration stimulates TSH secretion, which significantly increases T4 and T3 secretion from the thyroid gland. Moreover, these results indicate that thorium administration exerts hazardous effects on the neuroendocrine axis.