Abstract
Whole-body retention of 54MnCl2 after a single oral administration in rats of various ages was investigated. In adult rats, 0.3% of the dose was retained at 14 days, whereas new-born and suckling rats had higher retention rates than adults; these rates decreased sharply after weaning.
54MnCl2 was administered through the tail veins of pregnant rats between the 13th and 20th days of gestation in order to study the relationship between age and 54Mn intake. The rat conceptus and individual portions (the placenta, fetal membrane, amniotic fluid and fetus) were sampled periodically from each group. Placental 54Mn concentrations were slightly less when administration was in the later stages of pregnancy, but concentrations in the fetal membrane and amniotic fluid were relatively low and did not seem to vary on the basis of stage of gestation. For example, the values for 15-day pregnant rats increased from 0.2% of the initial dose 2 days after administration to 0.4% of dose on the sixth day.
54MnCl2 was administered intravenously to 8-, 14- and 20-day pregnant rats. In order to study the 54Mn transferred through the placenta and mother's milk, the“foster mother method”was adopted using the following three groups: 1) Sucklings born of and nursed by contaminated mothers received 54Mn through both the placenta and milk. 2) Sucklings born of contaminated mothers but nursed by controle foster mothers received only transplacental 54Mn. 3) Sucklings which were born of control mothers but nursed by contaminated foster mothers received 54Mn only from milk. Transplacental 54Mn in 8-, 14- and 20-day pregnants was 0.3, 0.9 and 1.3% of initial dose, respectively. The result showed the effect of the gestation age at the dosing on the transplacental 54Mn. It was observed that 0.4-1.4% of initial dose of 54Mn were transferred to sucklings via milk. The amount of milk transfer 54Mn in sucklings was dependent on the gestation age at the time of dosing.
