Effects of 1,25-dihydroxyvitamin D3 and growth hormone therapy on serum osteocalcin levels in children with growth hormone deficiency

Summary In order to investigate the influence on bone metabolism of growth hormone (GH), we evaluated the response to an acute load of 1,25(OH) 2 D 3 (Rocaltrol ® ) (1.5 μg/day for 4 days) in 16 growth hormone-deficient prepubertal children (11 boys and 5 girls, aged from 6.2 to 9.6 years) both before and after 1 month of human GH (hGH) therapy (0.1 IU/kg/day, 6 times per week). Before and after the 1,25(OH) 2 D 3 load, serum IGF-I, osteocalcin, Ca, P, alkaline phosphatase (ALP) and urinary excretion of Ca and P were measured. The serum levels of osteocalcin rose significantly after the first 1,25(OH) 2 D 3 load, without an increase in IGF-I values and with a slight non-significant increase in serum Ca and P. Almost superimposable increases of osteocalcin, Ca and P were observed after 1 month of hGH therapy, with a significant increase of IGF-I, but they did not rise further after the second 1,25(OH) 2 D 3 load. On the basis of our results, 1,25(OH) 2 D 3 seems to have a stimulatory action on osteoblastic activity even in the absence of normal levels of GH. However, there is no apparent additional stimulatory activity after administration of hGH. Osteocalcin level behaviour during our study might suggest that GH and 1,25(OH) 2 D 3 have a common and easily saturable stimulatory pathway on osteoblastic function.