The effects of lactose on the absorption and retention of dietary lead.

Intubated lactose has been shown to facilitate the absorption and retention of radiolabeled tracer lead in weanling rats. The conditions under which this effect may be observed are specified here. In acute radiotracer studies with fasted rats, absorption of intubated lead from the intestines and lead uptake into kidney, liver, blood and brain were increased by lactose (3-6 mg/g, per os) in rats 22 and 26 days of age postpartum. However, neither absorption nor uptake by kidney and liver were affected in the suckling rat (less than 21 days postpartum), nor beyond the first week after weaning. The facilitation by lactose of lead absorption and uptake was inhibited by carrier lead concentrations of 100 and 1000 ppm. Lactose at 80 mM (the concentration in rat's milk) had no effect on absorption and uptake of lead, nor on excretion of parenterally administered lead. Chronic feeding of 80 mM lactose and lead (0, 10, or 100 ppm in diet) reduced the retention of lead in kidneys and bones of weanling rats, fed both a normal (0.47%) and a calcium-deficient (0.02%) diet. It is concluded that intubations of high concentrations of lactose into fasted weanling rats can cause an increase in the absorption and uptake of lead. When fed to weanling rats at physiological concentrations, however, lactose actually reduces the retention of lead in bone and kidney.