Early effects of hormone replacement therapy on bone.

Estrogen replacement is currently the preferred therapy for postmenopausal osteoporosis, although its mechanism of action remains poorly understood. Its primary action on bone is generally considered to be antiresorptive, but there is evidence in animals to suggest a stimulatory effect on bone formation. We have now attempted to detect a similar effect in humans by administering hormone replacement therapy (estradiol valerate 2 mg/day and dydrogesterone 5 mg/day given in a continuous, combined manner) to ten postmenopausal women. We carried out histomorphometric analyses of transiliac bone biopsies after quadruple tetracycline labeling, which was commenced before and continued during the first 4 weeks of hormone replacement therapy. Biochemical markers of bone turnover suggested that bone resorption decreased, but no significant effects on histomorphometric parameters of bone formation were detected. We conclude that hormone replacement therapy at the dose given does not stimulate bone formation in the iliac crest as assessed by histomorphometry.