The effect of osteogenic growth factors on bone growth into a ceramic filled defect around an implant.

Currently available synthetic bone substitutes perform poorly compared to autograft. It is hoped that by adding osteogenic growth factors to the materials, new bone formation could be increased and the clinical outcome improved. In this study, IGF-1, bFGF and TGFbeta1, alone and in combination, were absorbed onto a carrier of beta-tricalcium phosphate (betaTCP) and implanted into a defect around a hydroxyapatite-coated, stainless steel implant in the proximal tibia of rat in a model of revision arthroplasty. Animals were sacrificed at 6 and 26 weeks for routine histology and histomorphometry and mechanical push out tests. The results show that only bFGF had a significant effect on ceramic resorption. The groups that received bFGF and bFGF in combination with TGFbeta1 had smaller and fewer betaTCP particles remaining in the defect at 6 and 26 weeks. No growth factor combination significantly enhanced new bone formation or the mechanical strength of the implant. These results indicate that, of the growth factors tested, only bFGF had any beneficial effect on the host response to the implant, perhaps by delaying osteoblast differentiation and thereby prolonging osteoclast access to the ceramic.     

Comparative performance of three ceramic bone graft substitutes.

BACKGROUND CONTEXT: A number of different synthetic calcium-based bone graft substitutes (BGS) are currently available for clinical use. There is, however, a lack of comparative performance data regarding the relative efficacy of these materials when placed in an osseous defect site. PURPOSE: To compare the rate, quality, and extent of osseous healing in a standard rabbit defect model for three commercially available BGS materials by measuring early bone formation and completion of defect healing and to identify whether rapid scaffold resorption stimulated or impaired bone healing. STUDY DESIGN: Osteochondral defects, 4.8 mm in diameter and 6 to 7 mm deep, were made through the articular surface into the subchondral bone of the femoral condyle of New Zealand White rabbits and filled with cylindrical pellets of one of three commercially available BGS materials: dense calcium sulfate (DCaS), ultraporous tricalcium phosphate (beta-TCP), and porous silicated calcium phosphate (Si-CaP). The repair response was examined at 1, 3, 6, and 12 weeks after surgery (n=4 per BGS per time point). METHOD: Qualitative histological and quantitative histomorphometric (% new bone, % bone graft substitute, capillary index, and mineral apposition rates) analysis. RESULTS: Rapid resorption of D-CaS, primarily through dissolution, elicited a mild inflammatory response that left the defect site empty before significant quantities of new bone were formed. Both beta-TCP and Si-CaP scaffolds supported early bone apposition (<1 week). However, beta-TCP degradation products subsequently provoked an inflammatory response that impaired and reversed bone apposition within the defect site. The Si-CaP scaffolds appeared to be more stable and supported further bone apposition, with the development of an adaptive bone-scaffold composite; cell-mediated resorption of scaffold and new bone were observed in response to local load and contributed to the production of a functional repair within the defect site. CONCLUSIONS: Rapid BGS resorption impaired the regenerative ability of local bone via three pathways: 1) insufficient persistence of an osteoconductive scaffold to encourage bone apposition, 2) destabilization of early bony apposition through scaffold disintegration, and 3) stimulation of an inflammatory response by elevated levels of particulate degradation products. This had a significant impact on the ultimate rate of healing. D-CaS did not stimulate early bone apposition, but bone repair was more advanced in D-CaS-treated defects at 12 weeks as compared with those treated with beta-TCP, despite the beta-TCP supporting direct bone apposition at 1 week. Si-CaP appeared to provide a more stable osteoconductive scaffold, which supported faster angiogenesis and bone apposition throughout the defect site, with the development of a functionally adaptive trabecular structure through resorption/remodelling of both scaffold and new bone. There was rapid formation of mineralized tissue at week 1 within the center of the defect and complete infiltration with dense, predominantly mature bone by weeks 3 to 6. The progressive remodeling of bone ingrowth and scaffold to reflect the distribution of local host tissue, combined with histological evidence of targeted osteoclastic resorption of both scaffold and bone, suggest that bone adaptation within the scaffold could be in response to Wolff's law. Although this model may not directly translate to a spinal fusion model and the products may vary according to the environment, these results suggest that, in patients in whom bone regeneration may be compromised, the degradation observed with some resorbable bone grafts may contribute to the decoupling of bone regeneration and resorbtion within the graft site, which may ultimately lead to incomplete bone repair.     

Enhanced Bone Bonding of the Hydroxyapatite/β‐Tricalcium Phosphate Composite by Electrical Polarization in Rabbit Long Bone

A review of the osteogenic cell activity and new bone growth in the regions bordering negatively charged surfaces of polarized Hydroxyapatite/β‐tricalcium phosphate (HA/TCP) composites implanted in the long bone in rabbits was conducted. Polarized and non‐polarized HA/TCP specimens were implanted into the right and left femoral condyle, respectively (each n = 10). After 3 and 6 weeks, five rabbits were sacrificed in each group, and histological analysis was administered. Large cuboidal‐shaped osteoblastic cells were predominantly observed lining the newly formed bone on the negatively charged surface (N‐surface) in the polarized HA/TCP implants. The TRAP‐positive multinucleated cells were observed extensively in the newly formed bone on the N‐surfaces compared with the 0‐surface and adhered directly to the HA/TCP composite. The bone area (B.Ar) value, newly formed bone area contacting the implant, and contact length (C.Le) value, percentage length of newly formed bone directly attaching to the implant, on both the 0‐ and N‐surface increased significantly with time in each group. Both the B.Ar and C.Le value on the N‐surface were significantly greater than those on the 0‐surface after 3 and 6 weeks. The number of TRAP‐positive cells/total length value on the N‐surface was significantly greater than that on the 0‐surface after 3 and 6 weeks postoperatively. It is hypothesized that electrical charge acquired by electrical polarization treatment may modify the biochemical and biophysical processes of the osteogenic cells, resulting in enhanced new bone formation and direct bonding between the recipient bone and implants.     

丝素蛋白/羟基磷灰石组织工程化骨修复兔桡骨节段性骨缺损

目的 探讨丝素蛋白/羟基磷灰石(SF/HA)组织工程化骨的成骨作用,以期为临床治疗骨缺损提供新的人工骨材料.方法 将SF/HA与成骨诱导的兔骨髓基质干细胞(BMSCs)复合,构建组织工程化骨.取54只兔于左侧桡骨中上段制备15 mm节段性骨缺损.实验分3组(A、B组各24只,C组6只):A组:植入SF/HA组织工程化骨,B组:单纯植入SF/HA;C组:骨缺损区不植入任何材料.于术后4、8、12及16周摄X线片,并于16周行螺旋CT扫描重建,观察骨缺损修复及骨塑形情况,参照Lane-Sandhu X线评分标准对各组骨缺损的骨修复程度评分.骨痂标本行 HE染色组织学观察,按照Lane-Sandhu组织学评分法比较12周和16周时各组的骨修复情况. 结果 术后16周,X线片示A组髓腔通畅,新骨塑形好,骨皮质连续;B组缺损区有缩小,两断端不连接;C组缺损区无明显骨痂生长.16周时螺旋CT扫描重建显示:A组骨塑形明显,骨缺损完全修复;B组有部分皮质骨形成,缺损区不能完全修复;C组骨缺损基本无修复.每组术后4、8、12、16周不同时间点的放射学评分差异均有统计学意义(P＜0.05).术后12、16周时3组间Lane-Sandhu组织学评分差异均有统计学意义(P＜0.05). 结论 SF/HA组织工程化骨具有良好的节段性骨缺损修复能力,但SF/HA本身缺乏骨诱导作用,单独修复节段性骨缺损作用有限.     

Formation and structure of Ca-deficient hydroxyapatite

Summary When amorphous calcium phosphate (ACP) was transformed to crystalline hydroxyapatite (HA) in a series of aqueous slurry concentrations ranging from low to high, the higher slurry concentrations produced more Ca-deficient HA as measured by Ca/P ratio and heat-produced pyrophosphate. We feel that the excess solution phosphate produced in the higher slurry transformations results in lower Ca/P ratio HA. It has been suggested that an ACP is the precursor to bone apatite. Regulation of the in vivo ACP slurry concentration could then control the stoichiometry and, therefore, the metabolic activity of bone apatite. X-ray radial distribution function (RDF) analyses showed that CO ₃ ²⁻ substitution in HA creates far greater structural distortions than do Ca deficiencies. The latter, however, do produce small, but observable, structural distortions when compared to stoichiometric HA. It now seems clear that the RDF of bone apatite can be modeled by a synthetic, Ca-deficient, CO ₃ ²⁻ -containing HA.     

In vivo osteogenic durability of cultured bone in porous ceramics: a novel method for autogenous bone graft substitution

BACKGROUND: Bone marrow cells differentiate into bone-forming osteoblasts when cultured in medium supplemented with 15% fetal bovine serum, ascorbic acid, beta-glycerophosphate, and dexamethasone. METHODS: To investigate in vivo osteoblastic activity and bone matrix formation by cultured bone marrow cells, Fischer rat marrow cells were cultured for 2 weeks in porous hydroxyapatite (HA) and then subcutaneously implanted into 7-week-old male syngeneic rats. The implants were harvested after 8 and 52 weeks for biochemical and histological analyses. RESULTS: At both times, formation of lamellar bone accompanied by regeneration of marrow were seen in many of the HA pores. When a fluorochrome (calcein) was administered at 50 weeks after implantation, it was detected in the pores of implants harvested at 52 weeks. Osteoclastic resorption followed by new bone formation was seen in some pores at 52 weeks, indicating that bone remodeling was continuing. The alkaline phosphatase activity of implants harvested at 52 weeks was comparable to that at 8 weeks, whereas the osteocalcin content of the implants harvested at 52 weeks was about twice that at 8 weeks. CONCLUSION: These results demonstrated that there was persistent in vivo osteogenic and hematopoietic activity in the prefabricated bone/HA constructs, and indicated that normal bone tissue was regenerated after grafting of the constructs, which were brittle before implantation. Tissue engineering using HA and cultured marrow cells culture may provide an alternative method of bone transplantation for patients with skeletal disorders, although further in vivo and in vitro experiments are needed.     

Comparative in vivo study of six hydroxyapatite‐based bone graft substitutes

Improvement of synthetic bone graft substitutes as suitable alternatives to a patient's own bone graft remains a challenge in biomaterials research. Our goal was to answer the question of whether improved osteoinductivity of a material would also translate to better bone‐healing orthotopically. Three porous biphasic calcium phosphate (BCP) ceramics (BCPA, BCPB, and BCPC), consisting of hydroxyapatite and β‐tricalcium phosphate, a porous biphasic calcium phosphate ceramic reinforced with a bioresorbable polylactic acid to improve its mechanical properties (BCPC+), a pure hydroxyapatite ceramic (HA), and a carbonated apatite ceramic (CA) were implanted intramuscularly and orthotopically by using a transverse process model in 11 goats for 12 weeks. BCPA and BCPB had similar chemical composition but differed in their microstructure. BCPB was not osteoinductive at all, but BCPA induced ectopic bone formation in 9 of 11 animals. Orthotopically, BCPA performed better than BCPB in both the amount and rate of bone formation. BCPC, similar to BCPA structurally and physicochemically, showed comparable results ectopically and orthotopically. Addition of resorbable polymer to BCPC made the material less osteoinductive (4 of 11 animals) and delayed bone formation orthotopically. Neither HA nor CA were osteoinductive, and their orthotopic performance was inferior to the osteoinductive ceramics. The results of the present study showed that material‐derived osteoinduction significantly enhanced bone healing orthotopically, and that this material property appeared more sensitive for predicting orthotopic performance than physicochemical and structural characteristics. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1363–1370, 2008     

In Vivo Osteogenic Capability of Human Mesenchymal Cells Cultured on Hydroxyapatite and on β-Tricalcium Phosphate

The aim of the current study was to examine in vitro osteogenic capability and in vivo bone formation of mesenchymal stromal cells (MSCs) on two kinds of calcium phosphate ceramics. MSCs derived from human bone marrow were seeded on either hydroxyapatite (HA) ceramic or β-tricalcium phosphate (β-TCP) ceramic and then cultured in a medium supplemented with a donor's serum, vitamin C, β-glycerophosphate, and dexamethasone. The culture revealed the expression of alkaline phosphatase activity, indicating the osteogenic differentiation of the MSCs on the ceramics (fabrication of tissue-engineered construct). The constructs were then implanted subcutaneously into nude rats for 8 weeks. New bone formation was observed in both types of ceramics, and human-specific Alu sequence was detected by in situ hybridization analysis. Quantitative microcomputed tomography showed that the volume of the new bone in the HA ceramic was greater than that in the β-TCP ceramic in six of seven cases. These results suggest that human MSCs cultured on ceramics could retain their osteogenic capability even after ectopic implantation and provide a rationale for the use of tissue-engineered constructs derived from a patient's MSCs and calcium phosphate ceramics in bone tissue regeneration.     

Bone growth into a ceramic-filled defect around an implant. The response to transforming growth factor beta1

Synthetic bone substitutes provide an alternative to autograft but do not give equivalent clinical results. Their performance may be enhanced by adding osteogenic growth factors. In this study, TGFbeta1 was absorbed on to a carrier of beta tricalcium phosphate and Gelfoam and used to fill a defect around a tibial implant in a rat model of revision arthoplasty. We added 0.0, 0.02 microg, 0.1 microg or 1.0 microg of TGFbeta1 to the carrier and then implanted it around an hydroxyapatite-coated stainless-steel pin in the proximal tibia of rats. The tibiae were harvested at three, six or 26 weeks and the amount of bone formation and ceramic resorption were assessed. TGFbeta1 had no effect on the amount of bone in the defect, the amount of fluorescent label incorporated or the rate of mineral apposition. The growth factor did not significantly affect the amount of betaTCP remaining in the tissue at any of the time points.     

Bone tissue engineering in a critical size defect compared to ectopic implantations in the goat.

Since the application of the autologous bone graft, the need for an alternative has been recognized. Tissue engineering (TE) of bone by combining bone marrow stromal cells (BMSCs) with a porous scaffold, is considered a promising technique. In this study we investigated the potential of tissue engineered bone to heal a critical sized defect in the goat. Orthotopic bone formation was compared to ectopic bone formation in comparable constructs. TE constructs were prepared from goat BMSCs and porous biphasic calcium phosphate ceramic scaffolds. These constructs and scaffolds without cells were implanted paired in critical sized iliac wing defects. Comparable samples were implanted intramuscularly. After 9 (n=7) and 12 (n=8) weeks implantation, the samples were analyzed histomorphometrically. After 9-weeks implantation in the iliac wing defect, significantly more bone apposition was found in the TE condition. After 12 weeks, the defects were almost completely filled with bone, but no significant advantage of TE was determined anymore. This contrasted with the intramuscular samples where TE implants showed significantly more bone at both time points. In conclusion, bone TE is feasible in critical sized defects. However, when appropriate osteoconductive/inductive materials are applied the effect of cell seeding may be temporary.     

Effects of the systemic administration of alendronate on bone formation in a porous hydroxyapatite/collagen composite and resorption by osteoclasts in a bone defect model in rabbits

Several bisphosphonates are now available for the treatment of osteoporosis. Porous hydroxyapatite/collagen (HA/Col) composite is an osteoconductive bone substitute which is resorbed by osteoclasts. The effects of the bisphosphonate alendronate on the formation of bone in porous HA/Col and its resorption by osteoclasts were evaluated using a rabbit model. Porous HA/Col cylinders measuring 6 mm in diameter and 8 mm in length, with a pore size of 100 μm to 500 μm and 95% porosity, were inserted into a defect produced in the lateral femoral condyles of 72 rabbits. The rabbits were divided into four groups based on the protocol of alendronate administration: the control group did not receive any alendronate, the pre group had alendronate treatment for three weeks prior to the implantation of the HA/Col, the post group had alendronate treatment following implantation until euthanasia, and the pre+post group had continuous alendronate treatment from three weeks prior to surgery until euthanasia. All rabbits were injected intravenously with either saline or alendronate (7.5 μg/kg) once a week. Each group had 18 rabbits, six in each group being killed at three, six and 12 weeks post-operatively. Alendronate administration suppressed the resorption of the implants. Additionally, the mineral densities of newly formed bone in the alendronate-treated groups were lower than those in the control group at 12 weeks post-operatively. Interestingly, the number of osteoclasts attached to the implant correlated with the extent of bone formation at three weeks. In conclusion, the systemic administration of alendronate in our rabbit model at a dose-for-weight equivalent to the clinical dose used in the treatment of osteoporosis in Japan affected the mineral density and remodelling of bone tissue in implanted porous HA/Col composites.     

以珊瑚转化羟基磷灰石为支架材料构建组织工程骨的实验研究

目的 探讨以珊瑚转化羟基磷灰石（CHA）作为骨组织工程支架材料的可行性。寻找最佳支架材料,为组织工程研究开辟新的途径。方法 取4周龄兔骨髓,分离骨髓基质细胞,体外培养,诱导分化为成骨细胞,胰酶消化后离心收集细胞,接种至高温灭菌的CHA材料,无菌条件下植入8只裸鼠皮下组织中,对照组为同体单纯植入CHA,分别于6、8周取材,行大体观察、X线摄征及组织学染色,观察新骨形成情况。结果 实验组6周时大体标本浅红色,X线片有较高密度阻射影像,组织学检查可见有新骨形成,8周时大体标本呈红色,质硬,X线阻射影像密度更高,镜下可见大量新骨形成并相互连接成骨小梁样结构。骨细胞位于陷窝中,对照组8周大体标本均为白色,周围软组织包裹,X线片仅见CHA阻射影。组织学检查无新骨形成,为大量纤维组织长入CHA孔洞内。结论 CHA可作为骨组织工程的支架材料,具有广阔的应用前景。     

Hydroxyapatite-coated titanium for orthopedic implant applications

The interface mechanical characteristics and histology of commercially pure (CP) titanium- and hydroxyapatite- (HA) coated Ti-6Al-4V alloy were investigated. Interface shear strength was determined using a transcortical push-out model in dogs after periods of three, five, six, ten, and 32 weeks. Undecalcified histologic techniques with implants in situ were used to interpret differences in mechanical response. The HA-coated titanium alloy implants developed five to seven times the mean interface strength of the uncoated, beadblasted CP titanium implants. The mean values for interface shear strength increased up to 7.27 megaPascals (MPa) for the HA-coated implants after ten weeks of implantation, and the maximum mean value of interface shear strength for the uncoated CP titanium implants was 1.54 MPa. For both implant types there was a slight decrease in mean shear strength from the maximum value to that obtained after the longest implantation period (32 weeks). Histologic evaluations in all cases revealed mineralization of interface bone directly onto the HA-coated implant surface, with no fibrous tissue layer interposed between the bone and HA visible at the light microscopic level. The uncoated titanium implants had projections of bone to the implant surface with apparent direct bone-implant apposition observed in some locations. Measurements of the HA coating material made from histologic sections showed no evidence of significant HA resorption in vivo after periods of up to 32 weeks.     

Locally delivered rhBMP-2 enhances bone ingrowth and gap healing in a canine model.

The purpose of the present study was to determine if recombinant human bone morphogenetic protein-2 (rhBMP-2) enhances bone ingrowth into porous-coated implants and gap healing around the implants. In the presence of a 3-mm gap between the implant and host bone, porous-coated implants were placed bilaterally for four weeks in the proximal humeri of skeletally mature, adult male dogs. In three treatment groups, the test implant was treated with HA/TCP and rhBMP-2 in buffer at a dose of 100 microg/implant (n=5), 400 microg/implant (n=6), or 800 microg/implant (n=5) and placed in the left humerus. In these same animals, an internal control implant was treated only with HA/TCP and buffer and placed in the right humerus. These groups were compared with a previously reported external control group of seven animals in which no growth factor was delivered [J. Orthop. Res. 19 (2001) 85]. The BMP treated implants in the two lower dose groups had significantly more bone ingrowth than the external controls with the greatest effect in the 100 g/implant group (a 3.5-fold increase over the external control, p=0.008). All three dose groups had significantly more bone formation in the 3-mm gap surrounding the BMP treated implants than the external controls with the greatest effect in the 800 microg group (2.9-fold increase, p<0.001). Thus, application of rhBMP-2 to a porous-coated implant stimulated local bone ingrowth and gap healing. The enhancement of bone formation within the implant (bone ingrowth) was inversely related to dose.     

Formation and structure of Ca-deficient hydroxyapatite

When amorphous calcium phosphate (ACP) was transformed to crystalline hydroxyapatite (HA) in a series of aqueous slurry concentrations ranging from low to high, the higher slurry concentrations produced more Ca-deficient HA as measured by Ca/P ratio and heat-produced pyrophosphate. We feel that the excess solution phosphate produced in the higher slurry transformations results in lower Ca/P ratio HA. It has been suggested that an ACP is the precursor to bone apatite. Regulation of the in vivo ACP slurry concentration could then control the stoichiometry and, therefore, the metabolic activity of bone apatite. X-ray radial distribution function (RDF) analyses showed that CO3(2-) substitution in HA creates far greater structural distortions than do Ca deficiencies. The latter, however, do produce small, but observable, structural distortions when compared to stoichiometric HA. It now seems clear that the RDF of bone apatite can be modeled by a synthetic, Ca-deficient, CO3(2-)-containing HA.     

Normal bone particles are preferentially resorbed in the presence of osteocalcin-deficient bone particlesIn vivo

Summary In anin vivo model of osteoclastic bone resorption, we previously showed that osteocalcin-deficient bone particles (BPs), derived from warfarin-treated rats, were resorbed 50% as well as normal BPs and that they recruited fewer osteoclastic cells with decreased tartrate-resistant acid phosphatase (TRAP) activity. In order to determine the specificity of the resorption response, we evaluated the fate of implanted mixtures of normal and osteocalcin-deficient BPs. Normal and warfarin-treated donor rats were prelabeledin vivo with oxytetracycline to permit identification of BPs from either source. Normal, osteocalcin-deficient, and 50∶50 mixtures of BPs (either labeled or unlabeled) were implanted into normal rats and recovered 12 days later for enzymatic (TRAP) and nondecalcified histomorphometric analyses. The incorporated oxytetracycline had no signficant effect on resorption of bone particles. The recovered osteocalcin-deficient BPs were surrounded by fewer osteoclastic cells, were resorbed less, and contained less extractable TRAP activity than normal BPs. In mixed BP implants with normal and osteocalcin-deficient BPs, each type of bone particle elicited the same tissue response as when implanted separately. Remarkably, the different particles evoked dissimilar osteoclastic responses and were resorbed to different extents, even when adjacent within the same implant. These data suggest that osteocalcin may act as a substrate signal for resorption and that osteocalcin in the normal BPs does not influence the cellular response to adjacent osteocalcin-deficient BPs.     

Effects of hydroxyapatite tricalcium phosphate coating and intracancellous placement on bone ingrowth in titanium fibermetal implants

The purpose of this study was to compare the host—bone response to hydroxyapatite/tricalcium phosphate (HA/TCP)-coated and noncoated titanium fibermetal implants placed in a load-sharing cancellous bone environment of the distal femurs of rabbits. The influence of implantation site was also investigated by comparing these intracancellous implants with intramedullary implants evaluated in a previous study. Three parameters were measured: percentage implant perimeter surface length in contact with new bone, percentage internal fibermetal surface length in contact with ingrown bone, and percentage of available pore space filled with bone. The HA/TCP coating significantly accelerated and increased bone ongrowth, new bone formation on the perimeter and internal surface of the implants. This effect was evident as early as 2 weeks after implantation. In contrast, there was no difference between HA/TCP-coated and noncoated implants in the bone ingrowth parameter, percentage of available pore space filled with bone, or pull-out strength. Scanning electron microscopy in the backscatter mode demonstrated that new bone formed directly onto the HA/TCP-coated fibers and did not usually form directly on noncoated fibers. Analysis of fluorochrome labeling revealed that bone formation in weeks 1 through 4 was primarily woven and there-after lamellar. Compared with intramedullary placement, intracancellous placement significantly accelerated the apposition of bone to the perimeter and internal surface of HA/TCP-coated implants and both accelerated and increased bone ingrowth as a percentage of available pore volume. These data show that the host response to titanium fibermetal implants is influenced both by HA/TCP coating and by the implantation site.     

急性心梗后骨髓细胞心肌内移植促进心肌细胞再生的实验研究

目的 研究急性梗死心肌内移植骨髓细胞的促进心肌再生作用。方法 局部注射将骨髓细胞移植入大鼠急性心肌梗死模型的急性心肌梗死区域，1、2、4、8周后处死动物，取心肌标本行组织形态学检查和梗死面积测量。结果 梗死区心肌标本观察到带荧光的骨髓细胞，部分已分化成肌源性细胞，电镜观察到不同分化阶段的新生心肌细胞。与成熟心肌细胞以闰盘相联。骨髓细胞移植组梗死心肌面积明显小于对照组。结论 在梗死心肌内移植的骨髓细胞具有心肌再生能力，并能缩小梗死心肌面积。     

Short-Term effects of high dose estrogen on tibiae of growing male rats

The short-term effects of estrogen at a single high dose (4 mg/kg body weight/day for 14 days) were determined on tibiae in the normal (noncastrate) growing male rat. In cortical periosteal bone, at a middiaphyseal site devoid of resorbing activity, estrogen suppressed periosteal bone formation and apposition rates, resulting in a smaller cross-sectional area. In middiaphyseal endocortical bone, estrogen had no effect on apposition and formation rates and, because medullary area was unchanged, probably had no effect on endocortical bone resorption. In the proximal tibial metaphysis, estrogen greatly suppressed longitudinal growth rate. In a site within the metaphysis adjusted for the effects of growth, cancellous mineral apposition was greatly reduced by the hormone. Estrogen-treated rats retained more of a fluorochrome label deposited in cancellous bone at the beginning of the study than vehicle-treated animals, indicating a reduced net bone loss. As a result of the lowered resorption induced by estrogen, cancellous bone mass (area and perimeter) were both significantly higher in estrogen-treated rats. No evidence was found for an anabolic action of the hormone in the male rat; indeed, estrogen reduced indices of bone formation. Received: 31 December 1995 / Accepted: 3 May 1996