STRONTIUM “ RICKETS ” : BONE, CALCIUM AND STRONTIUM CHANGES

Summary When rats were fed increasing levels of strontium in the diet, inhibition of calcification was shown by increased width of epiphyseal cartilage, presence of uncalcified bone matrix and decreased ash weight of bone. When ash weight was used as an indicator of mineralization, inhibition of calcification became greater as the dietary strontium level increased. This inhibition became most obvious when the calcium‐strontium ratio in serum, expressed on a molar basis, became less than 10 : 1. In contrast to ash weight, the percentage ash in bone was a less sensitive indicator of rhachitic change, because both mineral and organic weight decreased proportionately, and consequently the percentage ash remained unchanged until high dietary levels of strontium were reached. The incorporation of strontium into bone varied, not with dietary strontium levels, but with the ratio of calcium to strontium. The two ions were treated similarly, for the decrease in calcium‐strontium ratio in the bone was almost directly proportional to that in diet for both young and old rats. In growing animals, addition of new bone crystals was probably the most important mechanism whereby strontium became incorporated into ash, while in slowly‐growing rats ion exchange assumed a more important role. At low dietary levels of strontium, bone matrix formation decreased roughly proportionately to inhibition of calcification, but at higher levels uncalcified bone matrix became prominent. These results may be of significance to the problem of osteoporosis, for they demonstrate that disorder of calcification can be associated with decreased growth of bone matrix. This suggests that “ osteomalacic ” and “ anti‐anabolic ” mechanisms are not mutually exclusive, but may be interrelated factors in the pathogenesis of osteoporosis.