A heterologous radioimmunoassay system for human osteocalcin. Applications in performance sports girls.

Taking into account the involvement of the measurement of osteocalcin, a protein-containing gamma-carboxyglutamic acid (Gla), in investigating the physiopathology of bone and calcium metabolism, a radioimmunoassay (RIA) method useful in human clinics was developed. The reagents for the RIA of human osteocalcin namely, the radioiodination preparation, the reference preparation and the antiserum were obtained starting from bovine bone on account of the structure similarities between bovine and human osteocalcin. The reagents were incubated at 4 degrees C for 48 h followed by the polyethylene-glycol (PEG) separation technique. The sensitivity of the osteocalcin RIA method is 2.0 ng/ml, the intraassay precision is 3-5% and the interassay precision, 8-12% (coeficient of variation). Osteocalcin was measured in the sera of 3 groups of performance sports girls under basal conditions and being of more or less similar ages: rowing girls (n = 10, mean age 16 yr 6 mos), gymnast girls (n = 13, mean age 14 yr 8 mos) and table tennis girls (n = 9, mean age 16 yr). The same samples were used for the measurement of myoglobin. Osteocalcin quantification showed similar levels in the rowing and the table tennis girls, i.e. 11.91 +/- 3.39 ng/ml (X +/- SD) and 9.50 +/- 4.15 ng/ml, respectively. By contrast, in the gymnast girls, the osteocalcin levels were about 4 times higher (44.31 +/- 7.27 ng/ml) than in the other two groups. Myoglobin measurements showed lower levels in the gymnast group, than in the rowing and the table tennis groups, the latter two having similar levels. The multiplicative increase of osteocalcin in the gymnast girls is interpreted and commented in relation to their age and sexual development.