Investigation of the transport of trace elements across barriers in humans: studies of placental and mammary transfer

The barrier function of the human mammary gland for selected trace elements was evaluated by analysing 27 maternal sera and corresponding colostrum samples for 14 trace elements. To investigate the impact of the human placenta at the end of gestation on the transfer of 17 trace elements from the mother to the baby, 29 maternal and corresponding umbilical cord sera (UCS) were studied. The uptake of trace elements from the UCS by the fetus was investigated in nine pairs of arterial and venous UCS. In colostrum, the concentration of Cu was 19%, of Se 47%, of Co 80%, of Mg 146%, of Ca 222%, of Sn 228%, of Mn 275%, of Mo 814%, and of Zn 1470% of that of the maternal sera. For Cd and Pb the corresponding values were 200% and 325%, respectively. These data show that the mammary gland can exert an activating as well as an inhibiting effect on the trace element transfer. A concentration gradient mode of action for the transfer of Li, Mo and Sr could be found. In UCS the concentration of Cu was 20%, of Se 55%, of Co 60%, of Sn 85%, of Mo 100%, of Mg 105%, of Ca 120%, of Zn 148%, and of Mn 150% of that of the maternal sera. The corresponding values for Cd were 66% and for Pb 50%. Conclusions: These findings indicate that the placenta can exhibit an activation or inhibition on transfer as well as a gradient mode of action as for Mo, Cs, Li and Sr. The uptake of essential trace elements from venous UCS by the unborn ranged from 2.5% for Ca to 16.7% for Mo. Both the placenta and the mammary gland can exert an activating, inhibiting or gradient mode of action for selected trace elements, the biological impact of which needs to be further elucidated.