ESTRADIOL RELEASE FROM SELF-SETTING APATITIC BONE-CEMENT RESPONSIVE TO PLASMA-CALCIUM LEVEL IN OVARIECTOMIZED RATS AND ITS PHYSICOCHEMICAL MECHANISM

The effect of plasma calcium levels on the release of oestradiol from a self-setting apatite bone cement containing 0.5% oestradiol was inve stigated in ovariectomized rats. The profiles of in-vitro release from the cements in simulated body fluid containing 0, 5 or 10 mg calcium per 100 mt indicated that the rate of release of oestradiol decreased with increasing calcium concentration in the dissolution media. After subcutaneous implantation of oestradiol-loaded cement in healthy and v itamin D-deficient rats, oestradiol release in diseased rats with low plasma calcium levels was significantly higher than that in healthy ra ts. These results suggest that in-vitro release of oestradiol from apa tite bone cement was dependent on the calcium concentration in the buf fer and that the in-vivo release of oestradiol from apatite bone cemen t was dependent on plasma calcium levels.