Distribution of manganese in development

Elimination of manganese is closely related to uptake in the normal adult and is believed to play a critical role in maintaining manganese homeostasis in the face of changing manganese intake. Data from immature rats, mice and cats have suggested that elimination of manganese undergoes a period of maturation with adult patterns of excretion developing at about the time of weaning. In addition, the uptake of manganese from the intestine appears to be more efficient in young animals than in adults. These two sets of findings raise the possibility that exposure to elevated manganese levels during the perinatal period might yield excessive concentrations of this metal in the developing organism. Such an outcome might lead to manganese accumulations in organ systems where subsequent mobilization might be difficult and might produce permanent toxic injury. This review evaluates the patterns of manganese uptake and distribution following prenatal and pre-weaning exposure using a variety of model systems. The data demonstrate that manganese does cross the placenta and enter fetal tissue although the extent of material crossing the placenta appears to be limited. The issue of neonatal manganese elimination following tracer and toxic exposure levels to manganese is addressed. The data show that that the neonatal rodent is significantly more effective in eliminating manganese than previously believed based upon tracer studies. Finally, data are presented on regional brain manganese distribution. These data highlight the lack of agreement on whether manganese is concentrated in specific brain areas.