A bstract:Stable strontium has been shown to inhibit the synthesis of l a,25-dihydroxyvitamin D3(1,25(OH)~D3). In the present study, the effects of stable strontium on calcium metabolism were studied in growing rats. The rats were divided into control, 0.5%-Sr and 1.0~ groups. After dietary treatment for 4 weeks, both intestinal calcium absorption (Vna) and the calcium absorption ratio (B) were suppressed dose-dependently by strontium. In contrast, while intestinal strontium absorption (sVna) was higher in the 1.0~-Sr group than that in the 0.5%-Sr group, there was no change in the strontium absorption ratio in the intestine (s•). Although bone formation (Vo+) and bone resorption (Vo-) were both decreased in the strontium groups, no change was observed in the serum calcitonin and parathyroid hormone concentrations in the 1.0~-Sr group. Furthermore, a large amount of strontium deposited in newly formed bone. These results suggest that 1) the decrease of intestinal calcium absorption is due to either the reduction of 1,25 (OH) 2D ~ synthesis or the competitive antagonistic action between calcium and strontium in the intestine, and 2) accumulation of a large amount of strontium in bone might directly inhibit bone formation and resorption.

A bstract: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 1 ahydroxylation by strontium. The effects of strontium were examined on intestinal calcium absorption when rats were received synthetic la-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~and vitamin D3 (Sr-D group), 1~ and la-hydroxyvitamin D3 (Sr-a group), vitamin D3 (Co-D group), or l a-hydroxyvitamin D3 (Co-a 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 1 a-hydroxyvitamin D3 recovered serum 1,25-dihydroxyvitamin D to the level in Co-D group. However, this substitution in Sr-a group failed to increase intestinal calcium absorption. We also examined the direct of strontium on bone resorption using 4~Ca pre-labeled mouse calvaria. Strontium was injected every day until sacrifice, and percent 4~Ca 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.