Effect of excess Fe on Cd or Pb absorption by rats.

Absorption of cadmium and lead from the gastrointestinal (GI) tract of adult rats was measured after gavage with solutions of 109Cd or 210Pb. Before the radionuclide gavage, animals were either fed or fasted for 24 h, or fasted and given a supplemental gavage of ferric or ferrous iron. Fasting caused a slight increase in 109Cd absorption that was not statistically significant; ferrous iron caused a three-fold increase; and ferric iron increased absorption 14-fold. In contrast, fasting increased 210Pb absorption fivefold, and the oxidizing agents ferric iron and quinhydrone blocked the effect of fasting. Gavage of 8-d-old rats with 109Cd and either ferric or ferrous iron doubled the amount of cadmium retained in the carcass and substantially decreased the amount retained in the GI tract. Some of the large fraction (60-70%) of 109Cd stored in the mucosa of the intestine was absorbed into the body with time. An excess of ferric iron had an opposite effect on the retention of lead in the carcasses of 8-d-old rats, decreasing it from 53% of the gavaged dose to 3%; the effect on the amount retained in the intestine was similar, decreasing it from 16% to 8%. These results suggest that the mechanisms for transport of cadmium and iron across the intestine may be similar in the adult and neonatal rat, but that the oxidizing effect of ferric iron on cadmium absorption is much greater in the adult.