Oestradiol Release from Self-setting Apatitic Bone Cement Responsive to Plasma-calcium Level in Ovariectomized Rats, and its Physicochemical Mechanism

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Abstract
The effect of plasma calcium levels on the release of oestradiol from a self-setting apatite bone cement containing 0.5% oestradiol was investigated 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 mL 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 vitamin D-deficient rats, oestradiol release in diseased rats with low plasma calcium levels was significantly higher than that in healthy rats. These results suggest that in-vitro release of oestradiol from apatite bone cement was dependent on the calcium concentration in the buffer and that the in-vivo release of oestradiol from apatite bone cement was dependent on plasma calcium levels.