EFFECT OF SHORT-COURSE OF 1,25-DIHYDROXYVITAMIN D-3, ON BIOCHEMICAL MARKERS OF BONE REMODELING IN POSTMENOPAUSAL WOMEN

This study was designed to test the hypothesis that a short treatment course of 1,25(OH)(2)D-3 elicits a stimulation of osteoblast activity without any action on the osteoclast. To test this, oral daily doses o f 0.5 mu g or 1 mu g of 1,25(OH)(2)D-3 were administered for 7 days to two groups (n=5 and n=7, respectively) of postmenopausal women with l ow bone mineral density. Markers of osteoblast activity, i.e. osteocal cin (BGP), total alkaline phosphatase activity (ALP) and bone alkaline phosphatase activity (BALP), and markers of osteoclast activity, i.e. hydroxylysyl-pyridinoline (Pyr), lysyl-pyridoline (D-Pyr), and galact osyl-hydroxylysine (GHyl) were measured in plasma and in fasting urina ry samples, respectively, at sequential times during and after 1,25(OH )(2)D-3 administration. It resulted that short term 1 mu g 1,25(OH)(2) D-3 oral administration induced a significant (P<0.05) rise of BGP ser um level without any associated increase of D-Pyr and GHyl, the latter also expressed as GHyl to GGHy1 ratio. Urinary Pyr increased signific antly after 1 mu g daily doses of 1,25(OH)(2)D-3. Thus, a short course of 1 mu g daily doses of 1,25(OH)(2)D-3 elicits a stimulation of oste oblast activity without any enhancement of D-Pyr, the most specific ma rker of osteoclast activity. The enhancement of Pyr after 1 mu g daily doses of 1,25(OH)(2)D-3 might be due to the activation of extraosseou s metabolic pathways rather than to the activation of osteoclast. (C) 1996 The Italian Pharmacological Society