CHANGES IN INSULIN-LIKE GROWTH FACTOR-I AND GROWTH-HORMONE AND PREVENTION OF BONE LOSS DURING ESTROGEN REPLACEMENT THERAPY

14 postmenopausal women with climacteric complaints were treated continuously with oral oestradiolvalerate 2 mg and cyproteronacetate 2 mg daily over a period of 96 weeks. The purpose of the study was to investigate the preventive effect on postmenopausal bone loss, how women react on this therapy and how serum concentrations of insulin-like growth factor-I (IGF-I) and growth hormone (GH) would react over a period of 2 years. Biochemical parameters were measured at week 0, 4, 12, 24, 48 and 96. Bone mineral content was measured by DPA L2-4 before therapy, after 48 and 96 weeks. The therapy was well tolerated by the women and bone mineral content did not change. Serum osteocalcin concentration, urinary excretion of hydroxyproline and calcium/creatinine ratios decreased (p < 0.001, p < 0.01 and p < 0.05 resp.) indicating a decrease in bone formation and resorption. Serum IGF-I showed a stable decrease of 14-23% (p < 0.05) and GH concentration showed a stable increase of 140-209% (p < 0.05). Oral oestrogen replacement therapy causes a decrease in IGF-I production in the liver, resulting in an increase in pituitary GH production. The fall in plasma IGF-I concentration leads to inhibition of bone formation and bone resorption. It is supposed that GH stimulates osteoblastic recruitment selectively, without influencing bone resorption, or with a much stronger effect on osteoblasts than on osteoclasts. The net result is a positive effect on the balance between bone formation and resorption. The changes in plasma IGF-I and GH concentrations seems to contribute to the preventive effect of oral oestrogen replacement therapy on postmenopausal bone loss.