Abstract
Although the increasing industrial sources of lanthanum (La) pose potential environmental problems in recent years, the effects of La on humans and animals remain to be elucidated. This histochemical study was undertaken to elucidate whether La in drinking water is absorbed via the intestine in the rat. The experimental animals were treated with oral administrations of lanthanum chloride in drinking water (5 mg LaCl3/ml) for 1-28 weeks. Histological paraffin sections of the intestine were stained by the alizarin complexone (ALC) method for La. Macrophages showing an ALC-positive reaction were distributed in the lamina propria of the mucous membrane of the small intestine. Electron opaque deposits were observed at an electron microscopic level in the lysosomes of the macrophages in the lamina propria of the intestinal mucous membrane. L lines of La were detected from the electron opaque deposits in the lysosomes by an electron microprobe X-ray analyzer. Thus, localization of La in the ALC-positive macrophages was confirmed by an analytical electron microscope. The ALC-positive macrophages distributed similarly in the duodenum, jejunum and ileum, but not in the large intestine. The ALC-positive macrophages were found in the small intestine even after one week of oral administration of La in drinking water. Thus, La in a drinking water is easily absorbed via the small intestine. Environmental pollution of La may be placed under close surveillance.
