Short-term course of 1,25(OH)2D3 stimulates osteoblasts but not osteoclasts in osteoporosis and osteoarthritis

Summary We investigated the effect of short-term, 1,25-dihydroxyvitamin D₃ therapy (4 μg/day for 4 days) on calcium metabolism in 27 postmenopausal women (11 cases with osteoporosis and 16 cases with osteoarthritis). Bone mass at the axial and appendicular skeleton was higher in osteoarthritis than in osteoporosis. Initial values of calcium metabolism were similar. Osteoporotic and osteoarthritic patients responded with a similar significant increase in serum osteocalcin (+61% and +54%, respectively), fasting urinary calcium excretion (+178% and +124%, respectively) and 24 hour calcium excretion (+148% and +142%, respectively). Parathyroid hormone (PTH) levels decreased significantly in both groups (−30% and −18%, respectively). Osteoclastic bone resorption, evaluated by urinary hydroxyproline excretion, was not stimulated in either group. We conclude that in osteoporosis and also in osteoarthritis (1) 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) stimulation of osteoblast function is similar in production of osteocalcin; (2) the vitamin D target tissues react adequately to 1,25(OH)₂D₃ stimulation; (3) short-term high dose of 1,25(OH)₂D₃ does not stimulate bone resorption; and (4) the differences in bone mass between osteoarthritis and osteoporosis are not related to an alteration of the responsiveness to stimulation by 1,25 (OH)₂D₃.