Gastrointestinal tract manganese

Only a small (ca 3%) fraction of ingested or inhaled manganese is absorbed, which occurs primarily by the intestines (209). Once absorbed, manganese is regulated by the Hver, where it is excreted into the bile and passes back into the intestine, where some reabsorption may occur (210). Manganese is elirninated almost exclusively (>95%) by the bile in the gastrointestinal tract. 

Calcium has long been implicated as a dietary factor which inhibits the absorption of manganese. Since manganese is better absorbed in the oxidized (+2) than in the reduced state (+3 or +4), any factor which increases gastrointestinal tract pH (increases alkalinity) would be expected to inhibit manganese utilization. Calcium carbonate, a commonly used antacid by humans as well as a calcium nutrient supplement, has been found to have a greater adverse effect on apparent manganese absorption in humans than does milk. 

The trace elements iron, copper, zinc, and manganese, however, are excreted via the feces. Not only do the insoluble and unabsorbed dietary metals pass through the gastrointestinal tract, but also continual sloughing off of intestinal cells removes significant amounts of metal from the organism. 

Drs. Filer and Muller, at the University of Iowa, treated an 8 year old girl with total parenteral nutrition for three two-month periods because of a poorly mobile gastrointestinal tract. Each period of treatment was separated by 5 months of oral alimentation. Following the last period of total intravenous nutrition, the same solution was administered via jejunostomy for an additional month. At that time, plasma and hair measurements were made. Table 5 shows that zinc and copper concentrations were significantly low in both plasma and hair. The chromium and manganese concentrations, however, remained in the normal range. 

Manganese entering the portal blood from the gastrointestinal tract may remain free or become associated with oi-macroglobulin, which is subsequently taken up by the liver. A small fraction enters the systemic circulation, where it may become oxidized to Mn + and bound to transferrin. Studies in vivo suggest that the Mn " " complex forms very quickly in blood, in contrast to the slow oxidation of the Mn " "-transferrin complex in vitro. Manganese uptake by the liver has been reported to occur by a unidirectional, saturable process with the properties of passive mediated transport. After entering... 

The major routes of manganese absorption in animals and humans are via the gastrointestinal and respiratory tracts. Absorption through the skin is thought to be minimal for inorganic manganese compounds, but may be important for organomanganese compounds (WHO 1981). 

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