Early effects of ethinyloestradiol and norethisterone treatment in post-menopausal women on bone resorption and calcium regulating hormones

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Abstract
The early effect of sex steroid therapy was assessed in 28 normal post menopausal women, 18 treated with ethyinylestradiol and 10 with norethisterone. There was a reduction in the fasting urinary excretion of both Ca and hydroxyproline with both treatments, indicating reduced bone resorption. This was apparent after 1 wk of therapy but became more marked after 3 wk. These changes were not accompanied by any changes in plasma levels of calcitonin or parathyroid hormone. Patients receiving ethynylestradiol showed a marked increase in plasma 1,25-dihydroxyvitamin D (1,25-(OH)2D) concentration but this was explicable entirely in terms of increased plasma levels of vitamin D binding protein. There was no change in the free plasma level of 1,25(OH)2D. Patients treated with norethisterone showed no increase in plasma concentrations of 1,25(OH)2D. Ethyinylestradiol and norethisterone have a rapid and similar effect in reducing bone resorption. This is not mediated via the plasma levels of the Ca regulating hormones.