[Osteocalcin].

Among the vitamin K-dependent proteins, characterized by a high content of gamma-carboxyglutamic acid (Gla), one has been identified in bone tissue which has been referred to as osteocalcin (BGP): it has been found in fish, birds, mammalians, primates and in man without significant changes in structure. "In vitro" and "in vivo" studies in the experimental animal and in man have shown that BGP: 1) binds to hydroxyapatite crystals in bone tissue at the maturation of the mineral phase; 2) is probably synthesized by the osteoblasts; 3) circulates as a newly synthesized molecule before binding to bone; 4) shows a rapid turnover rate and is subjected to renal clearance. In conclusion osteocalcin seems to represent a very good index of osteoblast activity. BGP ca be measured in biological fluids by radioimmunoassay. Plasma levels in man range 4-7 ng/ml, they increase in malignant or metabolic disorders (Paget's disease of bone, bone metastases, hyperparathyroidism) and decrease in hypoparathyroidism. In this paper we report the results obtained using a new radioimmunoassay for osteocalcin; the plasma levels were measured in 72 normal adults aged 18-84 years (37 males, 35 females) and in three normal adolescents. The normal range (M +/- SD) was found to be 4,1-7,84 ng/ml. No significant differences were found between males and females, whereas adolescents showed significantly higher values than adults. A positive correlation was found between plasma BGP level and age of subjects in males as well as in females (r = 0,613, p less than 0,001). Fifteen patients with Paget's disease and two with primary hyperparathyroidism showed very high values which fell dramatically in the latter group after surgical removal of parathyroid adenoma. Six cases of secondary hyperparathyroidism were also found to have higher values than normal. The significance of the progressive increase in BGP with increasing age is still to be interpreted.