DIURNAL-VARIATION IN TOTAL AND UNDERCARBOXYLATED OSTEOCALCIN - INFLUENCE OF INCREASED DIETARY PHYLLOQUINONE

A diurnal variation exists in blood levels of the vitamin K-dependent bone protein osteocalcin. However, it is not known whether the carboxy lated and undercarboxylated constituents of osteocalcin also vary. The refore, osteocalcin and undercarboxylated osteocalcin were measured in specimens collected every 4 hours over a 24-hour period in nine healt hy subjects (five males, four females) ages 20-33 years who were consu ming a mixed diet containing 100 mu g of phylloquinone. Osteocalcin an d undercarboxylated osteocalcin were measured by radioimmunoassay (RIA ) before and after treatment with barium sulfate. Although the percent undercarboxylated osteocalcin did not change, a diurnal variation was observed in total osteocalcin, carboxylated osteocalcin, and undercar boxylated osteocalcin, with peak concentrations at 4 a.m. and the lowe st concentrations between 12 p.m. and 4 p.m. The difference between th e total osteocalcin peak and trough concentrations averaged 28 +/-:7 ( SEM)%. There were no gender differences in these rhythms. The effect o f dietary phylloquinone as a modulator of these rhythms was evaluated in a randomized study by increasing phylloquinone intake to 420 mu g/d ay with fortified corn oil, split between the lunch and dinner meals. Total and carboxylated osteocalcin fluctuations and concentrations wer e not affected by the dietary treatment. The diurnal variation in unde rcarboxylated osteocalcin was abolished with supplementation and conce ntrations at 8 a.m. (14 hours following supplementation) (2.3 +/- 0.2 ng/ml) were significantly lower than the unsupplemented levels (2.7 +/ - 0.2 ng/mL, P = 0.006). The percentage of under carboxylated osteocal cin was similarly decreased after supplementation (19.7 +/- 1.3%) in r elation to the mixed diet cycle (24.2 +/- 1.6%, P = 0.006) at 8 a.m. o n the second day. Dietary supplementation induced a fluctuation in per centage undercarboxylated osteocalcin with a decline in levels startin g at approximately 12 a.m. Therefore, additional dietary phylloquinone does not appear to modulate the total osteocalcin diurnal rhythm, but can influence its undercarboxylated component.