The effects of stable strontium on calcium metabolism.: II. Effects of 1α-hydroxyvitamin D3 in strontium-fed rats, and inhibitory effect of strontium on bone resorptionin vitro

Abstract

It has been postulated that the effect of strontium on bone metabolism due to the reduced plasma 1,25-dihydroxyvitamin D3 level following the inhibition of 1α-hydroxylation by strontium. The effects of strontium were examined on intestinal calcium absorption when rats were received synthetic 1α-hydroxyvitamin D3. Four groups of rats at the age of 36 days were fed a semi-synthetic vitamin D-deficient diet for 4 weeks containing 1% strontium and vitamin D3 (Sr-D group), 1% strontium and 1α-hydroxyvitamin D3 (Sr-α group), vitamin D3 (Co-D group), or 1α-hydroxyvitamin D3 (Co- α group), respectively. At the age of 60 days, calcium and strontium balance studies were conducted to determine intestinal calcium absorption over a 3-day period, and 1,25-dihydroxyvitamin D level was then measured. Serum 1,25-dihydroxyvitamin D in Sr-D group was undetectable, and intestinal calcium absorption significantly decreased. Replacement of vitamin D3 with 1α-hydroxyvitamin D3 recovered serum 1,25-dihydroxyvitamin D to the level in Co-D group. However, this substitution in Sr-α group failed to increase intestinal calcium absorption. We also examined the direct of strontium on bone resorption using45Ca pre-labeled mouse calvaria. Strontium was injected every day until sacrifice, and percent45Ca release from cultured calvariae was measured. Bone resorption was inhibited by strontium dose-dependently in groups which had and had not received parathyroid hormone in culture. These results suggest that strontium inhibits intestinal calcium absorption and has a direct inhibitory effect on bone resorption.