Cadmium‐109 metabolism in mice. IV. diet versus maternal stores as a source of cadmium transfer to mouse fetuses and pups during gestation and lactation

The transfer of 109Cd from dam to offspring during gestation and lactation was studied in uniparous mice. From 70 to 210 d of age and during the subsequent reproductive period, young adult female mice received drinking water containing tracer amounts of 109Cd (8 ppb total Cd) and nutrient‐sufficient or ‐deficient solid diet containing stable Cd (5 ppm Cd). The nutrient quality of the deficient diet was patterned after that consumed by lapanese women who contracted itai‐itai disease. To evaluate established maternal stores as a potential source of cadmium transfer to pups, some dams were switched to water with no 109Cd and diet with an environmental or control level of cadmium (0.25 ppm Cd) during the reproductive period. The resulting pups were analyzed for 109Cd at birth and at 7‐d intervals throughout the lactation period. Pup 109Cd content at birth, representative of the amount transferred via the placenta during gestation, accounted for less than 1% of the total 109Cd transferred during the full reproductive period. During lactation, 109Cd levels in pups from dams with current 109Cd exposure approximately tripled with each 7‐d interval; no significant differences occurred due to nutrient quality of the dams’ diet. For 21‐d‐old pups, 98% of the 109Cd burden came from the diet of the dam, while only 2% came from her tissue stores, primarily the hepatic one. Such fractions represented a transfer per pup of about 0.01% of the oral 109Cd dose ingested by the dam during the reproductive period and about 0.05% of the 109Cd in her tissue stores. Overall, transfer per litter amounted to about 7% of the dietary 109Cd dose absorbed and retained by the dam during that interval and about 0.2% of the 109Cd from tissue stores. On lactation d 21, 90% of the total 109Cd in pups was sequestered in the gastrointestinal tract. Cadmium transfer was additionally examined in multiparous mice that began a repetitive breeding program at 70 d of age at the time of introduction to the same diet/water regimens already described. Overall, females consuming nutrient‐sufficient diet experienced 5 consecutive 42‐d rounds of gestation/lactation, while their deficient diet counterparts experienced 3 nonconsecutive rounds during an equivalent period. Transfer was examined during their last gestation/ lactation experience. Throughout the lactation interval, 109Cd transfer to pups was about 30% increased for multiparous versus uniparous females; however, transfer again was not significantly affected by nutrient quality of the dams’ diet. About 0.02% of the 109Cd dose ingested by the dam during the last reproductive round was transferred to each 21‐d‐old pup, while about 0.08% was transferred per litter; approximately 94% of pup whole‐body 109Cd was sequestered in the gastrointestinal tract. These results suggest that the itai factors of multiparity and nutrient‐deficient diet did little to increase the small amount of cadmium transferred from Japanese mothers to young during gestation and lactation and that this route of administration was not a significant source of exposure.