Nitric oxide mediates 17beta-estradiol-stimulated human and rodent osteoblast proliferation and differentiation

Oestradiol can stimulate osteoblast activity. Osteoblast function is thought to be regulated by nitric oxide (NO). We hypothesised that the effect of 17beta-oestradiol (17beta-E(2)) on osteoblast activity is mediated by NO. This hypothesis was tested using osteoblasts isolated from human trabecular bone, calvariae of rats, endothelial NO synthase (eNOS) gene-deficient mice, and their wild-type counterparts. Our results show that 17beta-E(2) dose-dependently stimulated proliferation and differentiation of primary human, rat and wild-typeosteoblasts. The presence of N(G)-monomethyl-l-arginine (10(-3) M), an inhibitor of NOS activity, blocked the 17beta-E(2)-(10(-7) M)-induced increases in thymidine incorporation (P < 0.01), alkaline phosphatase activity (P < 0.01) and bone nodule formation (P < 0.01) of wild-type, human and rat osteoblasts, respectively. Moreover, 17beta-E(2) did not induce a response in eNOS gene-deficient osteoblasts. 17beta-E(2) also increased total eNOS enzyme expression in rat osteoblasts. These findings indicate 17beta-E(2) modulates osteoblast function by NO-dependent mechanisms mediated via the eNOS isoform.