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Rat Serum Osteocalcin Concentration Is Decreased by Restriction of Energy Intake¹

Biram Ndiaye, Giulia Cournot^*, Marie-Agnès Pélissier, Odile Walrant Debray^* and Daniel Lemonnier²

INSERM-GERM, Faculté de Médecine Xavier Bichat, BP 416, 75870 Paris cédex 18, France ^* CNRS URA 583, Hôpital des Enfants Malades, 75015 Paris, France Laboratoire de Biologie du CNAM, 75003 Paris, France

We studied the effects of energy restriction on serum osteocalcin concentration and bone formation rate in rats. The experiment was designed to achieve energy restriction by reducing the carbohydrate intake while providing identical quantities of protein, fat, vitamins and minerals. Energy intakes of three groups of post-weaning male rats were restricted by 20, 40 and 60% for 4 wk. Serum calclum, phosphorus, transthyretin, triiodothyronine (T₃), thyroxine (T₄), 1,25-dihydroxycholecalciferol, 25-hydroxycholecalciferol and immunoreactive parathyroid hormone (iPTH) concentrations were determined. Energy restriction (20, 40 and 60%) produced a significant and gradual drop of serum osteocalcin concentrations, although the serum concentrations of its key regulators, i.e., 1,25-dihydroxycholecalciferol and iPTH, were not significantly affected. On the contrary, serum concentrations of calcium, phosphorus, transthyretin, T₃ and T₄ were significantly lower in the energy-restricted groups. However, our results do not support their implication in the regulation of serum osteocalcin synthesis by energy intake. Serum osteocalcin concentration was positively correlated with bone mineral apposition (r = 0.50, P < 0.05) and bone mineralization (r = 0.50, P < 0.05) rates suggesting that its decrease resulted from a reduction of bone formation, and not from abnormal mineralization, because osteoid seam thickness was not modified. Energy intake seems to be an important determinant of serum osteocalcin concentration and bone formation; however, the exact mechanism underlying this regulation remains to be determined.

KEY WORDS: • calclum-regulating hormones • osteocalcin • bone formation • energy restriction • rats

¹ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

² To whom correspondence should be addressed.

Manuscript received 17 May 1994. Revision accepted 4 November 1994.