DISTRIBUTION OF LEAD IN LACTATING MICE AND SUCKLING OFFSPRING WITH SPECIAL EMPHASIS ON THE MAMMARY-GLAND

The distribution of lead in lactating mice and suckling offspring was studied with whole body autoradiography at 4 and 24 h after a single i ntravenous injection of Pb-203 (50 nmol Pb/kg) to the dams. In the lac tating mice on day 14 of lactation, the highest uptake of radioactivit y at 4 h after administration was recorded in renal cortex, skeleton a nd liver. A high uptake was also evident in the mammary gland. At 24 h after administration, the radioactivity had decreased in most organs except in the skeleton. In the suckling pups, exposed to lead only via dams' milk for 24 h, the highest level of radioactivity was present i n the intestinal mucosa and a much lower level of radioactivity was pr esent in the skeleton. The mammary glands from mice given three daily intravenous injections of 240 mu mol Pb/kg were examined with X-ray mi croanalysis. At 4 h after the last injection, lead was found associate d with casein micelles both inside the alveolar cell and in the milk l umen, indicating that lead is excreted into the milk, bound to casein, via the Golgi secretory system.