The effects of arg-vasopressin on osteoblast-like cells in endothelial nitric oxide synthase-knockout mice and their wild type counterparts.

In the present study, we investigated whether nitric oxide (NO) could be involved in the effects of arg-vasopressin (AVP) on osteoblast-like cells. Cells derived from endothelial nitric oxide synthase (eNOS)-knockout mice and their wild type (WT) counterparts, and an osteosarcoma cell line (SaOS-2) were used. AVP (10-100 pmol/l) increased proliferation of osteoblast-like cells from WT mice. The effect was abolished by an AVP V1-receptor antagonist. AVP increased proliferation of cells from eNOSKO mice only when a NO donor, SNAP, was added. A nitric oxide synthase-inhibitor, L-NAME, antagonized the increase in cell proliferation in response to AVP in SaOS-2 cells. In conclusion, this study indicates that NO is involved in the effects of AVP on cell proliferation in osteoblast-like cells.

Inhibited anabolic effect of insulin-like growth factor-I on stromal bone marrow cells in endothelial nitric oxide synthase-knockout mice.

AIMS: Insulin-like growth factor-I (IGF-I), parathyroid hormone (PTH) and PTH-related protein (PTHrP) are hormones that have anabolic effects on bone formation. The aim of this study was to investigate whether production of nitric oxide (NO) is involved in the effect of IGF-I and PTH/PTHrP on osteoblast-like cells. METHODS: Bone marrow stromal cells from adult endothelial nitric oxide synthase (eNOS)-knockout (eNOSKO) mice and wild type (WT) counterparts were cultivated with osteogenic substances. The cells showed an osteoblastic phenotype measured as osteocalcin production and alkaline phosphatase activity. DNA synthesis was measured as [3H] thymidine incorporation in the bone marrow cells and in a human osteosarcoma cell-line (SaOS-2). RESULTS: The stimulatory effect of IGF-I on thymidine incorporation seen in WT animals was absent in eNOSKO mice. Addition of a NO donor to eNOSKO cells recovered the effect of IGF-I on thymidine incorporation. PTH/PTHrP stimulated cell proliferation in both WT and eNOSKO mice. In SaOS-2 cells, incubation with IGF-I together with a NOS inhibitor resulted in an inhibition of the anabolic effect of IGF-I on cell proliferation. CONCLUSIONS: The stimulatory effect of IGF-I on WT cell proliferation was abolished in eNOSKO cells, recovered by an NO donor and inhibited in osteosarcoma cells by a NOS inhibitor. The results indicate that the effect of IGF-I is dependent on NO production. The impaired IGF-I response may contribute to the bone defect formation seen in eNOSKO animals.