[PHASIC CHANGES OF BONE MASS, BONE TURNOVER MARKERS, AND ESTROGEN LEVELS AT DIFFERENT TIME POINTS AFTER GLUCOCORTICOID INTERVENTION AND THEIR CORRELATION IN RATS].

OBJECTIVE

To analyze the phasic changes of bone mass, bone turnover markers, and estrogen levels at different time points after glucocorticoid (GC) intervention in rat and their correlation.

METHODS

Thirty-four female 3-month-old Sprague Dawley rats were randomly divided into the following 3 groups: baseline group (n = 6), dexamethasone (DXM) group (n = 14), and control group (n = 14). Rats were injected with DXM at the dose of 0.75 mg/kg, twice a week for 12 weeks in DXM group, with salt solution lavage in control group, and no treatment was given in baseline group. The body mass, adrenal weight, and uterus weight were measured. Bone mineral density (BMD), bone mineral content (BMC), and bone area (BA) of lumbar vertebral and femurs were detected by dual energy X-ray absorptiometry. Meanwhile, the serum levels of N-terminal propeptide of type I procollagen (PINP), C-terminal cross-linking telopeptide of type I collagen (β-CTX), and estrogen levels were determined by ELISA before experiment in baseline group and at 4, 8, and 12 weeks after experiment in control and DXM groups. At last, the correlation was analyzed among body weight, BMD, PINP, β-CTX, estrogen levels, and GC intervention duration of DXM group.

RESULTS

The body mass, adrenal weight, and uterus weight in DXM group were signiflcantly lower than those in baseline group and control group at all the time points (P < 0.05). The levels of PINP and β-CTX elevated slowly in DXM group, significant difference was found at 12 weeks (P < 0.05), but no significant difference at the 4 and 8 weeks (P > 0.05) when compared with those in baseline group and control group. The estrogen level in DXM group was significantly lower than that in baseline group and control group at all the time points (P < 0.05). BMD, BMC, and BA of lumbar vertebral and femurs in DXM group were significantly lower than those in control group at all the time points after GC intervention (P < 0.05). Loss of bone mass of L2 and femoral trochanteric region in DXM group was the lowest of all ranges of interest (ROIs). BMC and BA of lumbar vertebrae and BA of femoral shaft in DXM group at 4 weeks were significantly lower than those in baseline group (P < 0.05). But there was no significant difference in BMD, BMC, and BA of other lumbar vertebrae and femurs' ROIs between DXM group and baseline group at all the time points (P > 0.05). After GC intervention, BMD of lumbar vertebrae and femurs had negative correlation with PINP and β-CTX (P < 0.05) and positive correlation with estrogen level (P < 0.05).

CONCLUSION

The bone mass decreases rapidly at the early stage after GC intervention and then maintains a low level with time, the levels of bone turnover markers show a progressive increase, and the estrogen levels show a decrease trend. In addition, body weight, the levels of bone turnover markers and estrogen are associated with the change of bone mass.