Absorption of 233U, 238Pu, 241Am, and 244Cm from the gastrointestinal (GI) tract was measured in rats, fed ad libitum or fasted, that were gavaged with solutions containing ferric iron, ferrous iron, iron powder, quinhydrone or ascorbic acid. Absorption and retention of all of these actinides was increased substantially by fasting and by the addition of mild oxidizing agents, ferric iron and quinhydrone. In contrast, absorption and retention were decreased to below the fasted level by all the reducing agents except ascorbic acid, which caused diarrhea and an increase in absorption. Absorption of the lanthanide element 147Pm from the intestine of fasted rats was also increased by ferric iron. Some of these actinide elements are polyvalent and are, in some cases, known to be absorbed from the GI tract more readily in their higher oxidation states. This suggested an oxidation-reduction mechanism for the effect of fasting and the action of the chemical agents used. However, the improbability that either 241Am(III) 244Cm(III) or 147Pm is converted to a different oxidation state under these conditions makes that mechanism unlikely. Other explanations are suggested.

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Absorption of U, Np, Am and Cm was increased by factors of 3.4, 7.1, 2.7 and 1.7, respectively, when nitrate solutions of these actinides were gavaged to adult rats fed an iron-deficient diet. Retention increased proportionately in liver, kidney and carcass. The concentration of the actinides excreted also increased substantially (over that of controls) in the urine of iron-deficient rats gavaged with 233U and 237Np, but not in those with 241Am or 244Cm. Weanling rats on an iron-deficient diet, gavaged with ferric nitrate immediately before administration of 238Pu nitrate, retained between 4% and 12% of the 238Pu retained by litter mates that were not treated intragastrically with iron.

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.

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