PLACENTAL COPPER TRANSPORT IN RATS - EFFECTS OF ELEVATED DIETARY ZINCON FETAL COPPER, IRON AND METALLOTHIONEIN

We hypothesized that the competition between zinc (Zn) and copper (Cu) during fetal accretion of copper could be discriminated at either the dam-to-placenta or placenta-to-fetus stage. This premise was tested b y feeding dams a high Zn diet (1000 mg/kg, HZn) during the second half of gestation. One day before delivery, dams were anesthetized, fetuse s removed and both maternal and fetal tissues and plasma obtained and assayed. Other rats were fed a normal Zn concentration diet (32.4 mg/k g, ND) throughout pregnancy. There were significantly lower fetal live r Cu concentrations and greater plasma Fe concentrations, but not plas ma Cu concentrations or river Fe concentrations in the HZn group. Both dam and fetal Zn liver concentrations were greater in the HZn than in the ND group. Plasma Cu levels were lower in the HZn-fed than in the ND-fed darns. Placental tissue from the HZn fitters had a greater conc entration of Zn and Fe than did the ND group, whereas no effect was no ted for Cu concentration. Metallothionein (MT) levels were elevated in dam livers and placenta in the HZn group, but there were no differenc es in fetal liver MT. The dynamic assessment of placental transport wa s conducted by injecting 2.5 mg/kg Cu acetate intravenously into dams of both groups. Sequential samplings of dam and fetal blood and placen tas were taken from 0 to 60 min. After the Cu bolus, there was a consi stently higher plasma Cu concentration in the HZn than in the ND dams, but no alteration in the concentration of Cu in the placenta or fetal plasma. This study indicates that placental Cu uptake is not affected by a high Zn diet in the dam. In addition, the greater Zn concentrati on in the placenta of HZn than in ND litters results in abnormal fetal Cu, Fe and Zn concentrations, suggesting that an imbalanced maternal mineral consumption is deleterious to normal divalent metal accretion.