| Objective:The Purpose of this study is to observe the effects of glucocorticoid on bone biochemical indicators, bone microstructure and morphometry and evaluate whether different doses of nitric oxide donor Nitroglycerin (NG) can inhibit the bone loss associated with glucocorticoid treatment in growing rats.Methods:Forty female Wistar rats 3 months old weighing 150～180 g were randomized into control group (CON), dexamethasone group (DXM), DXM plus a low dose nitroglycerin group(NG-L), DXM plus a middle dose nitroglycerin group (NG-M )and DXM plus a high dose nitroglycerin group(NG-H).The rats in DXM group and NG group were injected dexamethasone with the dosage of 1mg/kg twice a week .Furthermore 2% NG ointment with the dosage of NG 0.2 mg/kg , 0.4 mg/kg and 1.0 mg/kg were administered by dermal application to the rats in three therapeutic groups once a day. All rats were weighed once a week. After 10 weeks of treatment, bone metabolism associated markers were measured.⑴Changes of body weights: Body weights of animals were recorded at the beginning and at weekly intervals throughout the experiment.⑵BMD: Rats were anesthetized with a dosage of 1% sodium pentobarbital (40 mg/kg), BMD in the lumbar spine and femur was measured using the XR-36 dual-energy X-ray absorptiometry (DXA) bone scanner.⑶Serum markers: The blood was withdrawal through abdominal aorta. Serum was collected to examine the concentration of ALP﹑TRAP,BGP,NO and NOS.⑷Bone microstructure and morphometry: Bis-hindlimb were cut and put into the 4% formaldehydum polymerisatum for 48 hours and then was decalcified by 10% EDTA for six weeks.The decalcified examples were dehydrated and embedded in paraffin, sectioned (5um) and stained with haematoxylin and eosin(HE). All values were expressed as means±SEM. The data were analyzed by analysis of variance (ANOVA), and intergroup comparisons were made using LSD test.Results:Ten weeks after intramuscular dexamethasone injection, compared with CON group, the rats BMD in DXM group decreased significantly (P<0.05, P<0.01), with lower serum BGP levels and lower NO levels (P<0.01, P<0.05), higher TRAP levels (P<0.01). The histological section of femur shaft showed the bone trabecula in DXM group thinned with poor integrity, distortion and breaks. However, the change of serum BGP, NO and TRAP was restored in NG-L and NG-M groups. Bone morphometry displayed the trabecula microstructure in NG-L group and NG-M group was similar to CON group. There were no significant differences in serum BGP, BMD and bone morphometry markers between NG-H group and DXM group, but NG-H group had higher serum NO and TRAP level compared with DXM group. The differences of serum ALP and NOS levels among five groups were not significant.Conclusions:1. Our studies showed that glucocorticoids could inhibit bone formation and improve bone resorption at the same time, as shown by the decrease in BGP, and increase in TRAP, which represent the pathophysiologic bases leading to bone loss.2. Endogenous NO may play an important role in pathophysiology of glucocorticoid-induced osteoporosis. A moderate dose of nitroglycerin can prevent dexamethasone-induced bone loss in growing rats and suggests supplement with an NO donor could be considered as a new treatment method for glucocorticoid-induced osteoporosis.
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