Neuropeptide Y1 Receptor Antagonist but not Neuropeptide Y itself Increased Bone Mineral Density when Locally Injected with Hyaluronic Acid in Male Wistar Rats.

BACKGROUND/AIM The nervous system controls bone mass via both the central (CNS) and the peripheral (PNS) nervous systems. Intriguingly, Neuropeptide Y (NPY) signaling occurs in both. Less is known on how the PNS stimulated NPY signaling controls bone metabolism. The objective of this study was to evaluate whether NPY or NPY1 receptor antagonist changes local bone mineral density (BMD) when injected into a Wistar rat tibia. MATERIALS AND METHODS Tibial intramedullary area of 24 wild type male Wistar rats (average weight= 350 ± 50 g, average age= four ± 0.5 months) were injected with NPY (1x10-5 M and 1x10-6 M) and NPY1 receptor antagonist (1x10-4M) dissolved in hyaluronic acid (HA) separately and cavies were closed with bone wax. Tibiae were collected after one and two weeks. BMD was measured with dual-energy X-ray absorptiometry (DXA) and micro quantitative computer tomography (QCT). Histological changes were analyzed with light microscopy, Goldner's Masson trichrome (MT), and hematoxylin-eosin staining. RESULTS According to DXA, the mean BMD of NPY dose 1 (1x10-5 M) was significantly lower than that of the control (HA applied) group and not significantly but still lower than that of the NPY dose 2 and NPY1 antagonist applied groups. QCT results indicated the same pattern statistically insignificantly in the trabecular area but not in the cortex of the bones. Histologically, only NPY1 antagonist applied tibiae revealed young spongiosis bone trabeculae formed in the borderline of the cortical bones. HA was remarkably biocompatible and late degrading in the tissues. CONCLUSION Local administration of NPY and NPY1 antagonists may hold regulating potential of BMD and bone formation. NPY1 antagonist caused new bone formation in trabecular bone when applied locally. NPY dissolved in HA however can be used to suppress bone formation.