Could male reproductive system be the main target of subchronic exposure to manganese in adult animals?

Manganese (Mn) is one of the most common chemical elements on Earth and an essential micronutrient in animal organism. However, in supraphysiological levels and long-term exposures, it is a potential toxicant. Although nervous system is the most studied in relation to Mn toxicity, other tissues can have their function impaired by Mn in high doses. The present study investigated the possible adverse effects of subchronic exposure to supraphysiologic level of Mn (5 mg/kg or 15 mg/kg, intraperitoneally) on reproductive, neurobehavioral, renal and hepatic parameters of male rats. For the first time, the vulnerability of these parameters to Mn was concomitantly investigated. While our results demonstrate that Mn treatments were not sufficient to produce a marked effect of neurotoxic, hepatotoxic or renal toxicity in adult rats, we found typical indicators of reproductive toxicity such as histopathological changes (major in testes and epididymis) and impaired sperm concentration and quality. Mn, under these experimental conditions, seems to exert reproductive toxicity by different testicular mechanisms, i.e. direct and indirect action on germ cells. On the other hand, exposure to Mn did not change the pattern of cognitive and emotional behaviors and the histological organization of kidneys of experimental rats. The liver showed a weight increasement and hidropic degeneration, probable due to the detoxification overload. In summary, for the first time it was demonstrated that adult male reproductive system was more sensitive to Mn toxicity than nervous, hepatic and renal systems, although nervous system is known as the main target tissue of this metal.