Cardiovascular Toxicities Upon Manganese Exposure

By: y. Jiang and W. Zheng Some of the first recorded signs of manganese(Mn) toxicity were observations made by Kobert in the late 1800's, showing that Mn salts can decrease blood pressure certain animals models. Since, multiple studies have been done to examine Mn toxicity, both in human and animal models, producing a variety of inconclusive results. In animals models, chronic Mn has been correlated to decreases in myocardial action potential durability that leads to increased calcium free conditions in the myocardiocytes. As an effect of less calcium a decline in contractile force is seen. However, acute models were found to have no effects on dog ECG's. On the other hand, outside of the heart acute doses of Mn also has some effects on blood vessel tone. Specifically, following high doses of acute Mn (10mg/kg), perfused through the inferior vena cava, is vasodialation and significant decreases blood pressure. Even less studies have been done looking at human Mn toxicity. From limited current literature, cardiovascular toxicity in humans its been shown correlated to chronic exposure, most due from environmental contamination in factories and mines. Overall, women tend to be more susceptible then men, however both sex's have been showed increased vasodialation and decreased heart rates due to decreased parasympathetic sensitivity. Possible mechanisms for this include reduced levels of serotonin, which causes vasoconstriction, and reduced superoxide dismutase activity causing increased vasodialation. In conclusion, studies examining Mn cardiovascualar toxcicity are still much needed for animal and human models. It does seems that some cardiovascular toxicities in both models can occur with chronic exposure to Mn. To what extent and exactly what mechanism these effects are occurring are still unknown. ~JI