Osteocalcin metabolism in the pulmonary circulation

The aim of this study was to evaluate the role of the pulmonary vessel endo thelium in the removal of circulating osteocalcin, by measuring the osteoca lcin levels in serum from pulmonary and radial artery blood from 39 patient s undergoing aorto-coronary bypass. Because of the discrepancies between me thods of measurement, two methods were used. Significant differences were o bserved in group A (n = 18), tested with heterologous radioimmunoassay (2.8 5 +/- 0.67 mu g l(-1) in the pulmonary versus 2.69 +/- 0.67 mu g l(-1) in t he radial artery serum, P < 0.001) and in group B (n = 21), tested with a t wo-site immunoradiometric assay (5.22 +/- 1.46 versus 4.93 +/- 1.36 mu g l( -1), P < 0.01). The percentage differences were -5.54 +/- 4.76% (P < 0.001) in group A and -4.99 +/- 8.13% (P < 0.01) in group B; the comparison betwe en the percentage differences was not significant. These different osteocal cin concentrations between the two vascular compartments were considered a marker of osteocalcin degradation. Therefore, the study seems to demonstrat e that, as well as kidney, liver and bone, the lung is a relevant site of o steocalcin catabolism. The proteolytic activity of pulmonary vessel endothe lium seems to involve about 5% of the circulating peptide.