Samuels A, Perry M J, Gibson R L, Colley S, Tobias J H
Rheumatology Unit, University of Bristol Division of Medicine, Bristol, UK.
Bone. 2001 Jul;29(1):24-9. doi: 10.1016/s8756-3282(01)00471-9.
It is well recognized that high-dose estrogen induces a marked osteogenic response in long bones of female mice. In light of evidence which suggests that nitric oxide synthase (NOS) plays a role in regulation of osteoblast activity, we analyzed whether NOS is involved in mediating this response. Intact female mice were administered 17beta-estradiol (E(2)) either alone or in combination with N(G)-nitro-L-arginine methylester (L-NAME) or aminoguanidine (AG), over 24 days. The former inhibits both constitutive and inducible isoforms of NOS, whereas the latter is a selective inhibitor of inducible NOS. Bone mineral density (BMD) of the femur was subsequently measured by dual-energy X-ray absorptiometry (DXA), and histomorphometry performed at the proximal metaphysis on longitudinal tibial sections. As expected, E(2) given alone led to a marked accumulation of cancellous bone at the proximal tibial metaphysis, associated with a significant gain in femoral BMD, and an increase in cancellous mineralizing surfaces as assessed by histomorphometry. Neither L-NAME nor AG affected cancellous histomorphometric indices when given alone. However, when administered in combination with L-NAME, the magnitude of the skeletal response to E(2) was significantly reduced. The tendency for L-NAME to reduce estrogen-induced bone formation within the proximal tibial metaphysis was more marked distally compared with proximally. In contrast, AG showed no tendency to suppress the osteogenic response to E(2). Subsequently, we examined the effect of E(2) administration on expression within mouse femoral bone marrow of endothelial NOS (eNOS), which is the predominant constitutive isoform of NOS within bone. No change in eNOS mRNA levels was observed following E(2) administration, as assessed by reverse transcription-polymerase chain reaction (RT-PCR). Taken together, our results suggest that eNOS plays a role in mediating estrogen-induced bone formation in intact female mice, possibly as a consequence of posttranscriptional regulation of eNOS activity by estrogen.
众所周知，高剂量雌激素可在雌性小鼠的长骨中诱导显著的成骨反应。鉴于有证据表明一氧化氮合酶（NOS）在调节成骨细胞活性中起作用，我们分析了NOS是否参与介导这种反应。完整的雌性小鼠在24天内单独给予17β-雌二醇（E₂），或与N⁰-硝基-L-精氨酸甲酯（L-NAME）或氨基胍（AG）联合给药。前者抑制NOS的组成型和诱导型同工型，而后者是诱导型NOS的选择性抑制剂。随后通过双能X线吸收法（DXA）测量股骨的骨矿物质密度（BMD），并在胫骨近端干骺端的纵向切片上进行组织形态计量学分析。正如预期的那样，单独给予E₂导致胫骨近端干骺端松质骨显著堆积，伴有股骨BMD显著增加，并且通过组织形态计量学评估，松质骨矿化表面增加。单独给予L-NAME或AG时，均不影响松质骨组织形态计量学指标。然而，当与L-NAME联合给药时，骨骼对E₂的反应程度显著降低。与近端相比，L-NAME降低雌激素诱导的胫骨近端干骺端骨形成的趋势在远端更明显。相比之下，AG没有显示出抑制对E₂的成骨反应的趋势。随后，我们研究了给予E₂对小鼠股骨骨髓中内皮型NOS（eNOS）表达的影响，eNOS是骨中主要的组成型NOS同工型。通过逆转录-聚合酶链反应（RT-PCR）评估，给予E₂后未观察到eNOS mRNA水平的变化。综上所述，我们的结果表明，eNOS在介导完整雌性小鼠中雌激素诱导的骨形成中起作用，这可能是雌激素对eNOS活性进行转录后调节的结果。
