Incorporation and distribution of strontium in bone

The distribution and incorporation of strontium into bone has been examined in rats, monkeys, and humans after oral administration of strontium (eithe r strontium chloride or strontium ranelate), After repeated administration for a sufficient period of time (at least 4 weeks in rats), strontium incor poration into bone reaches a plateau level, This plateau appears to be lowe r in females than in males due to a difference in the absorption process. S teady-state plasma strontium levels are reached more rapidly than in bones, and within 10 days in the rat. The strontium levels in bone vary according to the anatomical site. However, strontium Levels at different skeletal si tes are strongly correlated, and the strontium content of the lumbar verteb ra may be estimated from iliac crest bone biopsies in monkeys. The strontiu m levels in bone also vary according to the bone structure and higher amoun ts of strontium are found in cancellous bone than in cortical bone. Further more, at the crystal level, higher concentrations of strontium are observed in newly formed bone than in old bone. After withdrawal of treatment, the bone strontium content rapidly decreases in monkeys. The relatively high cl earance rate of strontium from bone can be explained by the mechanisms of i ts incorporation. Strontium is mainly incorporated by exchange onto the cry stal surface, In new bone, only a few strontium atoms may be incorporated i nto the crystal by ionic substitution of calcium. After treatment withdrawa l, strontium exchanged onto the crystal is rapidly eliminated, which leads to a rapid decrease in total bone strontium levels, In summary, incorporati on of strontium into bone, mainly by exchange onto the crystal surface, is dependent on the duration of treatment, dose, gender, and skeletal site. Ne vertheless, bone strontium content is highly correlated with plasma stronti um levels and, in bone, between the different skeletal sites. (Bone 28: 446 -453; 2001) (C) 2001 by Elsevier Science Inc. All rights reserved.