A simple spectrophotometric assay for micromolar amounts of lanthanum in the presence of calcium and phosphate.

A sensitive spectrophotometric assay for micromolar amounts of lanthanum in the presence of calcium and phosphate (as hydroxyapatite) was developed utilizing the change in absorption (at 652 nm) when the dye arsenazo III was complexed with lanthanum. Arsenazo III was used at a level of 25 microM and the solution pH was maintained at 3.1 with 0.2 M sodium acetate. Lanthanum concentrations down to 0.5 microM could be reliably assayed. Calcium ion did not complex well with arsenazo III at pH 3.1. With calcium present at 100 microM and lanthanum at 10 microM, the assay was 115 times more sensitive for lanthanum. The assay is simple, rapid, reproducible and, unlike the assay using radioactive lanthanum, can be performed at any time.

Tissue uptake and intracellular distribution of 140-lanthanum after oral intake by the rat.

The ability of lanthanum to stabilize hydroxyapatite against acid dissolution is well known. It is possible to use lanthanum to experimentally alter hard tissues in vivo and in vitro. It was, therefore, of interest to determine the tissue distribution of lanthanum following oral ingestion of a LaCl3 solution. Oral intake of 140-lanthanum (as LaCl3 in drinking water) in adult rats over a 3-d period was voluntary and amounted to 0.27 mmol LaCl3 per animal per day. The teeth sowed increases in 140-lanthanum uptake with time. Distribution of 140-lanthanum within the incisors of animals drinking the LaCl3 solution showed that the highest specific activity of 140-lanthanum was associated with the outer layer of the tooth (that portion exposed to the oral environment). The soft tissues, such as lung, kidney, and liver, maintained a constant 140-lanthanum concentration after the first day of intake. The intracellular distribution of 140-lanthanum was measured in liver, with the soluble fraction showing the highest content. No histological changes were observed in the rat tissues after 3 d of oral intake (0.27 mmol/d) of lanthanum.

Incorporation of 140-lanthanum into bones, teeth and hydroxyapatite.

The incorporation of lanthanum in the form of 140-lanthanum onto the surface of teeth, bone and synthetic hydroxyapatite was investigated. A small amount of lanthanum was taken up by the surface of all of the materials studied regardless of their origin. The depth of penetration into bone and teeth was dependent upon lanthanum concentration and time of incubation and, in these experiments, ranged from an estimated 5 to 15 microns. An exchange of lanthanum for calcium in the apatite matrix may be responsible for increased resistance of the hard tissues to acid dissolution. The effects of pH, temperature, time and concentration of the lanthanum solutions on this incorporation were investigated. Possible clinical uses of this effect are discussed.