The effects of orchidectomy and supraphysiological testosterone administration on trabecular bone structure and gene expression in rats

Objective: This study aimed to determine the effects of orchidectomy and supraphysiological testosterone replacement on trabecular structure and gene expression in the bone. Methods: Twenty-four 3-month old male rats were randomized into sham (SH), orchidectomized (ORX) and testosterone-treated (TE) groups. Orchidectomy was performed on the ORX and TE group. Weekly testosterone enanthate intramuscular injection at 7 mg/kg body weight was administered to the TE group for 8 weeks while the other groups received peanut oil as vehicle. Blood was collected before and after treatment for serum testosterone analysis. The femora and tibiae were harvested after the treatment period for trabecular structure and gene expression analysis. Results: The trabecular bone volume decreased significantly and the porosity increased significantly in the ORX group compared to the SH group (p<0.05). Testosterone treatment prevented all these changes (p<0.05). The expression of osteogenic genes decreased significantly in the ORX group compared to the SH group (p<0.05). Testosterone treatment decreased the expressions of RANKL and OPG genes significantly (p<0.05). Conclusion: Orchidectomy-induced degeneration in trabecular structure is caused by a decrease in the expressions of osteogenic genes. Supraphysiological testosterone replacement is able to prevent these degenerative changes in the bone despite the modest changes in gene expression.