ORAL 1,25-DIHYDROXYVITAMIN-D ADMINISTRATION IN OSTEOPOROTIC WOMEN - EFFECTS OF ESTROGEN THERAPY

Estrogen has been shown to modify calcium and skeletal homeostasis. In this study, we tested the ability of estrogen to influence the effect s of short-term 1,25(OH)(2)D administration on biochemical indices of bone formation and resorption in a cross-sectional analysis of untreat ed (n = 10) and estrogen-treated (n = 14) osteoporotic women. Patients were given oral 1,25(OH)(2)D (Rocaltrol) 0.5 mu g twice a day for 5 d ays. Serum and urine were sampled at baseline and then 1 h after the f irst daily Rocaltrol dose for the 5 days of the study. 1,25(OH)(2)D le vels rose similarly in both groups with plateaus reached by the third day of the investigation. Serum PTH levels decreased by the first samp ling period (1 h after first Rocaltrol dose; p < 0.008 both groups) an d continued to fall gradually in both groups. There were no changes in serum calcium but serum phosphorus rose by the second day (p < 0.05 b oth groups) and remained elevated throughout the remainder of the prot ocol. Serum bone Gla protein increased approximately 40% (p < 0.05) wi th no group differences. In contrast, total alkaline phosphatase and c arboxy-terminal propeptide of type I collagen did not increase in eith er group. Furthermore, there were no significant increments in any bon e resorption indicators, including serum tartrate-resistant acid phosp hatase and cross-linked carboxy-terminal telopeptide of type I collage n, as well as urine hydroxyproline and pyridinoline. Serum IGF-1 level s also remained unchanged in both groups. We conclude that oral 1,25(O IH)(2)D administration decreased 1-84PTH levels, probably due to a sup pression of parathyroid production, and did not stimulate bone resorpt ion. Since only bone Gla protein increased, it is unclear whether or n ot bone formation was actually stimulated. Estrogen treatment did not modify the skeletal response to low levels of oral 1,25(OH)(2)D stimul ation in osteoporotic women.