Endocrine Abstracts

Introduction: Osteotropic hormones demonstrate circadian rhythms which are integral to bone homeostasis. Sclerostin is a physiological inhibitor of bone formation. We have established that Sclerostin has a distinct circadian rhythm with a nocturnal peak. Analysis was performed to determine the relationship of Sclerostin levels to PTH, Calcium, Phosphate, βCTX and P1NP in healthy young men.

Methods: Six healthy young men with normal BMD were admitted to our research facility. Blood samples drawn hourly for 24 h from 1400 h were centrifuged immediately. The serum/plasma separated was frozen at −70 °C. PTH, Calcium, Phosphate, βCTX and P1NP were measured. An enzyme linked immunoassay (Biomedica, Austria) was used to measure Sclerostin.

Statistical Analysis: Cross-correlational analysis was performed to determine the relationships between the 24 h profiles for Sclerostin, PTH, Calcium, Phosphate, βCTX and P1NP. This determines the correlation between two time series of equal length that have been paired, data point by data point, then one of the time series is shifted by one or more time points (lag time) and the correlation process is repeated. Time series for the groups were derived by calculating the mean value at each time point for all subjects.

Results: Secretory patterns of sclerostin Vs. PTH and Calcium demonstrate no definite correlation during the 24 h period. A positive correlation was noted between sclerostin and phosphate, βCTX, P1NP with correlation co-efficients of 0.637, 0.627, 0.666 respectively. The changes in the sclerostin preceded βCTX by 1 h, but zero lags between sclerostin Vs phosphate and P1NP.

Conclusion: Our results indicate, despite the existence of a circadian rhythm for sclerostin it does not seem to either directly influence or be influenced by PTH secretion. However the strong correlation of sclerostin to bone markers and phosphate with a zero lag indicates a direct influence of yet another factor on sclerostin circadian rhythm and bone homeostasis.