METABOLISM OF CALCIUM AND PHOSPHORUS IN RATS AFTER CONTINUOUS ORAL-ADMINISTRATION OF LANTHANUM

In the present study, we examined the effects of a rare earth element, lanthanum (La) on the excretion into the urine and feces as well as the distribution of calcium (Ca-45) and phosphorus (P-32) in the liver, pancreas, spleen, kidney, lung, heart, thymus, brain, bone and blood of male rats. The experiments were performed using 5 rats in each group. Lanthanum chloride (LaCl3) was administered orally at a dose of 100 mg/rat/d as La for 5 weeks (La-A group). Ca-45 and P-32 were administered orally or intravenously once, and following the administration, the urine and feces were collected daily for 8 consecutive days. As a result, the amount of oral Ca-45 and P-32 excreted into the feces in the La-A group increased remarkably compared with that of the control group (41 --> 91% and 26 --> 99%, respectively), whereas Ca-45 and P-32 excreted into the urine in the La-A group was reduced (9.5 --> 0.2% and 28 --> 0.3%, respectively). However, the excretion patterns in the urine and feces and the distribution of Ca-45 and P-32 in the body of rats given La, were similar to those of the control rats after the stop of the La administration (La-B group). The levels of Ca-45 and P-32 in the body for 8 d after their administration was highest in the control group, followed by the La-B group, and lowest in the La-A group. Moreover, in the La-A group, the levels of Ca-45 and P-32 in each organ decreased by 1/2 to 1/75 compared with those in the control rats, but there was no significant difference between the control group and the La-B group. However, the excretion patterns in the urine and feces and the distribution of Ca-45 and P-32 in the La-A group was similar to those of the control group when Ca-45 and P-32 were administered intravenously. These results suggest that La inhibits the uptake of Ca-45 and P-32 temporarily, and that the action is reversible.