Bone Abstracts

The exposition of shift workers to light at night supresses the melatonin (ME) production. ME supression may contribute to the development of osteoporosis, which can be prevented and treated by resistance exercise (RE). This study evaluated the effect of ME release supression by pineal gland (pinealectomy) and the RE on rats tibiae morphology, mineral quantification and mechanical parameters. The project was approved by the local ethics committee (protocol 2014-00939). Fourty male Wistar rats were distributed in control (CNS), exercised (CNEX), pinealectomized (PNX) and pinealectomized exercised (PNXEX) groups. RE was performed in stairs during 8 weeks and the overload used was equivalent to 60% of the maximal strenght test. The trabecular microarchitecture (micro-CT), mineral quantification (DEXA) and mechanical parameters (3-point bending test) were evaluated. Anova (two-way) with Bonferroni post-test (GraphPad Prism 6.0) were used. The pinealectomy had no effect on the parameters evaluated (P<0.05). On the other hand, the RE increased (P<0.05): maximal overload (29.5% CNEX vs CNS; 34.3% PNXEX vs PNX); bone volume over total volume (%) (30.4% CNEX vs CNS; 39.8% PNXEX vs PNX); trabecular bone number (mm⁻¹) (29.7% CNEX vs CNS; 31% PNXEX vs PNX); bone mineral content (g) (27.8% CNEX vs CNS); bone mineral density (g/cm²) (20.2% CNEX vs CNS); energy to fracture (mJ) (41.2% CNEX vs CNS); extrinsic stiffness (N/mm) (19.1% CNEX vs CNS; 32.7% PNXEX vs PNX); breaking strenght (N) (17.7% CNEX vs CNS; 13.5% PNXEX vs PNX). The RE decreased (P<0.05): trabecular bone pattern factor (mm⁻¹) (22.5% CNEX vs CNS); structure model index (13.6% CNEX vs CNS); trabecular bone separation (mm) 45.3% CNEX vs CNS; 41.3% PNXEX vs PNX). In conclusion, the pinealectomy had no influence on bone parameters while the RE showed to be an extremely effective non farmacological alternative to improve bone morphometry, mineral quantification and mechanical parameters in both groups.