Influence of pregnancy and lactation on maternal deposition and perinatal uptake of 241Am in the rat.

To investigate the metabolism of 241Am as affected by pregnancy and lactation, female rats were injected with 5 muCi of 241Am intravenously while nulliparous, pregnant or lactating. The females and subsequent litters were killed at various times after injection to determine 241Am distribution and retention. The temporal relationship between injection and pregnancy influenced the tissue retention of 241Am in both dams and progeny. The half-time of 241Am in livers of pregnant or lactating rats was more than twice that of nulliparous rats, although the initial uptake was approximately 50% of the activity in all groups. Both spleen and femur accumulated more 241Am at 7-10 weeks after injection than at earlier times, but this increase could not be related to pregnancy. Approximately 10 times more 241Am was transferred to offspring from dams that were lactating when exposed than was transferred via the placenta when exposure occurred late in gestation. Furthermore, more 241Am was transmitted to the progeny via milk if exposure of the dam occurred during lactation rather than during pregnancy.