Serum osteocalcin (Bone Gla-Protein), an index of bone growth in lambs. Comparison with age-related histomorphometric changes

Abstract

In 96 normal male sheep, we studied the variations with age of serum osteocalcin (bone Gla-protein), measured with an assay specific for ovine osteocalcin. We compared serum osteocalcin with the main histomorphometric parameters of bone growth measured on the metacarpus of 20 normal lambs from birth to 90 days of age. Serum osteocalcin significantly decreased with age ( r = −0.70, p < 0.001), particularly during the first 90 days of life ( r = −0.85, p < 0.001). During this growth period, serum osteocalcin was significantly correlated with the appositional rate ( r = + 0.73, p < 0.001), the rate of longitudinal bone growth ( r = + 0.68, p < 0.002), the rate of production of chondrocytes in the growth plate ( r = + 0.60, p < 0.007), and the thickness of the growth plate ( r = + 0.79, p < 0.001). In low birth weight male lambs (growth-retarded animals), serum osteocalcin was significantly lower at birth when compared to normal lambs (271 ± 156 vs. 535 ± 169 μg/l, p < 0.001), and was also significantly correlated with histomorphometric parameters. We conclude that serum osteocalcin, which is already known as a sensitive and specific marker of bone formation, is also a sensitive biochemical marker of skeletal growth in normal and growth-retarded lambs. In addition, sheep appears as a valid animal for experimental studies on bone growth.