Rat serum osteocalcin concentration is determined by food intake and not by inflammation

Osteocalcin, or bone gla protein, is the major noncollagenous protein in bone. Previous findings of decreased serum osteocalcin concentrations in children with Kwashiorkor led us to analyze the respective influence of nutritional status and inflammation on circulating osteocalcin in growing rats. Food deprivation for 72 h induced a significant 24% decrease in serum osteocalcin. Refeeding produced a rapid rise in serum osteocalcin, which reached control concentrations after 24 h of refeeding. Bone osteocalcin was not affected by these dietary manipulations. The changes in serum osteocalcin were not correlated with serum 1,25-dihydroxycholecalciferol, whereas they could be related to serum 25-hydroxycholecalciferol concentrations. Turpentine injection reduced serum osteocalcin concentration, but pair-feeding showed that this decrease was entirely attributable to spontaneous food restriction and not to inflammation. By contrast, the sensitive nutritional marker, serum transthyretin, was affected by both inflammation and food restriction. These results indicate that serum osteocalcin is closely related to food intake but not to inflammation, suggesting that the dramatic decrease in serum osteocalcin that we previously observed in children with Kwashiorkor is due to malnutrition per se.