Bone Blood Flow Research Articles

Bone blood flow and metabolism in humans: Effect of muscular exercise and other physiological perturbations

Human bone blood flow and metabolism during physical exercise remains poorly characterized. In the present study we measured femoral bone blood flow and glucose uptake in young healthy subjects by positron emission tomography in three separate protocols. In 6 women, blood flow was measured in femoral bone at rest and during one-leg intermittent isometric exercise with increasing exercise intensities. In 9 men, blood flow in the femur was determined at rest and during dynamic one-leg exercise and two other physiological perturbations: moderate systemic hypoxia (14 O2 ) at rest and during exercise, and during intrafemoral infusion of high-dose adenosine. Bone glucose uptake was measured at rest and during dynamic one-leg exercise in 5 men. The results indicate that isometric exercise increased femoral bone blood flow from rest (1.8 ± 0.6 mL/100 g/min) to low intensity exercise (4.1 ± 1.5 mL/100 g/min, p = 0.01), but blood flow did not increase further with increasing intensity. Resting femoral bone blood flow in men was similar to that of women and dynamic one-leg exercise increased it to 4.2 ± 1.2 mL/100 g/min, p < 0.001. Breathing of hypoxic air did not change femoral bone blood flow at rest or during exercise, but intra-arterial infusion of adenosine during resting conditions increased bone blood flow to 5.7 ± 2.4 mL/100 g/min, to the level of moderate-intensity dynamic exercise. Dynamic one-leg exercise increased femoral bone glucose uptake 4.7-fold compared to resting contralateral leg. In conclusion, resting femoral bone blood flow increases by physical exercise, but appears to level off with increasing exercise intensities. Moreover, although moderate systemic hypoxia does not change bone blood flow at rest or during exercise, intra-arterially administered adenosine during resting conditions is capable of markedly enhancing bone blood flow in humans. Finally, bone glucose uptake also increases substantially in response to exercise.

Effect of rhBMP-2 and VEGF in a vascularized bone allotransplant experimental model based on surgical neoangiogenesis

We have demonstrated survival of living allogeneic bone without long-term immunosuppression using short-term immunosuppression and simultaneous creation of an autogenous neoagiogenic circulation. In this study, bone morphogenic protein-2 (rhBMP-2), and/or vascular endothelial growth factor (VEGF), were used to augment this process. Femoral diaphyseal bone was transplanted heterotopically from 46 Dark Agouti to 46 Lewis rats. Microvascular repair of the allotransplant nutrient pedicle was combined with intra-medullary implantation of an autogenous saphenous arteriovenous (AV) bundle and biodegradable microspheres containing buffer (control), rhBMP-2 or rhBMP-2 + VEGF. FK-506 given daily for 14 days maintained nutrient pedicle flow during angiogenesis. After an 18 weeks survival period, we measured angiogenesis (capillary density) from the AV bundle and cortical bone blood flow. Both measures were greater in the combined (rhBMP-2 + VEGF) group than rhBMP-2 and control groups (p < 0.05). Osteoblast counts were also higher in the rhBMP-2 + VEGF group (p < 0.05). A trend towards greater bone formation was seen in both rhBMP2 + VGF and rhBMP2 groups as compared to controls (p = 0.059). Local administration of VEGF and rhBMP-2 augments angiogenesis, osteoblastic activity and bone blood flow from implanted blood vessels of donor origin in vascularized bone allografts.

In vivo measurements of blood flow and bone metabolism in osteoarthritis

With increasing age, there may be a decrease in femoral blood flow. In some patients, this may result in local ischaemia, which subsequently may lead to local degenerative changes. Consequently, bone blood flow may play an important role in the aetiology of osteoarthritis of the hip. Little is known about bone blood flow in the femoral head of patients with advanced hip osteoarthritis. The purpose of this study was to evaluate bone blood flow and metabolism in vivo in patients with osteoarthritis of the hip. Ten patients with symptomatic osteoarthritis of the hip were enrolled prospectively. Femoral bone blood flow and metabolism were measured using positron emission tomography together with H₂(15)O and [(18)F]fluoride, respectively. Blood flow was 0.054 ± 0.032 mL cm(-3) min(-1) and 0.041 ± 0.012 mL cm(-3) min(-1) in symptomatic and contralateral femoral heads, respectively (p = 0.435). The net flux of fluoride from plasma to bone mineral (K i ) was significantly (p = 0.027) higher in the femoral head of the osteoarthritic hip (0.022 ± 0.012 mL cm(-3) min(-1)) than in that of the contralateral hip (0.007 ± 0.005 mL cm(-3) min(-1)). This study showed significant increase in bone metabolism in the proximal femur of patients with symptomatic osteoarthritis of the hip joint. There was no evidence of decreased blood flow.

Surgical revascularization induces angiogenesis in orthotopic bone allograft.

Remodeling of structural bone allografts relies on adequate revascularization, which can theoretically be induced by surgical revascularization. We developed a new orthotopic animal model to determine the technical feasibility of axial arteriovenous bundle implantation and resultant angiogenesis. We asked whether arteriovenous bundles implanted in segmental allografts would increase cortical blood flow and angiogenesis compared to nonrevascularized frozen bone allografts and contralateral femoral controls. We performed segmental femoral allotransplantation orthotopically from 10 Brown Norway rats to 20 Lewis rats. Ten rats each received either bone allograft reconstruction alone (Group I) or allograft combined with an intramedullary saphenous arteriovenous flap (Group II). At 16 weeks, we measured cortical blood flow with the hydrogen washout method. We then quantified angiogenesis using capillary density and micro-CT vessel volume measurements. All arteriovenous bundles were patent. Group II had higher mean blood flow (0.12 mL/minute/100 g versus 0.05 mL/minute/100 g), mean capillary density (23.6% versus 2.8%), and micro-CT vessel volume (0.37 mm(3) versus 0.07 mm(3)) than Group I. Revascularized allografts had higher capillary density than untreated contralateral femora, while vessel volume did not differ and blood flow was lower. Axial surgical revascularization in orthotopic allotransplants can achieve strong angiogenesis and increases cortical bone blood flow.

Differences in regional bone metabolism at the spine and hip: a quantitative study using 18F-fluoride positron emission tomography

This study showed that regional bone blood flow and (18)F-fluoride bone plasma clearance measured by positron emission tomography are three times lower at the hip than the lumbar spine. Measurements of effective bone plasma flow (K (1)), bone plasma clearance (K ( i )) and standardised uptake values (SUV) using (18)F-fluoride positron emission tomography ((18)F-PET) provide a useful means of studying regional bone metabolism at different sites in the skeleton. This study compares the regional (18)F-fluoride kinetics and SUV at the hip and lumbar spine (LS). Twelve healthy postmenopausal women with no history of metabolic bone disease apart from two with untreated osteoporosis were recruited. Each subject underwent 60-min dynamic (18)F-PET scans at the LS and proximal femur two weeks apart. K (1), K ( i ) and SUV were measured at the LS (mean of L(1)-L(4)), femoral neck (FN), total hip (TH) and femoral shaft (FS). Differences between sites were assessed using the nonparametric Kruskal-Wallis test with a Bonferroni correction for multiple comparisons. Values of K (1), K ( i ) and SUV at the FN, TH and FS were three times lower than at the LS (p = 0.003). Amongst the proximal femur sites, K ( i ) and SUV were lower at the FS compared with the FN and TH, and SUV was lower at the TH compared with the FN (all p < 0.05). The volume of distribution was lower at the TH and FS compared with the LS (p < 0.05). The lower values of K (1), K ( i ) and SUV at the hip suggest that lower bone blood flow in the proximal femur is an important factor explaining the principal reason for the differences in bone fluoride kinetics between the LS and hip sites.

Loss of sympathetic nerve fibers in vital intertrochanteric bone cylinders lateral to osteonecrosis of the femoral head

ObjectivesAlthough etiology in osteonecrosis of the femoral head mainly depends on alterations of bone blood flow, vasoregulatory nerve fibers of the sympathetic and sensory nervous system have never been investigated in bone of osteonecrosis patients. This study aimed to demonstrate density of sympathetic and sensory nerve fibers in femoral head and, for comparison, adjacent periosteum, and synovium of the hip joint in patients with osteonecrosis. MethodsImmunofluorescence staining techniques were applied using specific nerve fiber markers. A total of 10 patients with early femoral head osteonecrosis (ARCO I-II), 10 with late femoral head osteonecrosis (ARCO III-IV), and 10 patients with osteoarthritis of the hip were investigated. ResultsIn the bone of the femoral head, density of sympathetic nerve fibers was lower in early and late osteonecrosis compared to osteoarthritis. There was a marked preponderance of sympathetic over sensory nerve fibers in bone of osteoarthritis patients, which was opposite in early and late femoral head osteonecrosis. In periosteum, density of sympathetic nerve fibers was similar in all three groups but density of sensory nerve fibers and cellularity were higher in early osteonecrosis compared to the other two groups. Discussion/ConclusionsDue to the different affinity of norepinephrine for α-adrenoceptors (high affinity) and β-adrenoceptors (low affinity), the loss of sympathetic nerve fibers relative to sensory nerve fibers in femoral head osteonecrosis might change the femoral head blood flow (towards α-adrenergic vasoconstriction). Higher density of sensory nerve fibers and cellularity in periosteum might indicate an inflammatory response in early osteonecrosis.

Alpha‐adrenergic regulation of muscle, adipose tissue and bone blood flow at rest and during exercise in humans

Positron emission tomography allows for determination of muscle and tissue‐specific blood flow in humans. Since hamstrings remain inactive during one leg exercise performed by knee extensors, the technique and model provide an opportunity to elucidate the role of nervous control of blood flow in the exercising limb in humans. Here we measured muscle and tissue‐specific blood flow in nine healthy young men under the femoral arterial infusions of norepinephrine (NE) and phentolamine. At rest, NE reduced blood flow by ~40% similarly in all muscles and in bone and adipose tissue. During exercise, NE reduced exercising muscle blood flow by 16%, but did not affect inactive muscle blood flow. Bone blood flow was not affected by NE, but blood flow in adipose tissue was reduced similarly as at rest. Phentolamine elevated blood flow similarly in different muscles and tissues of the limb at rest (by 3.5–6‐fold), and during exercise, the ratio of active‐to‐inactive muscle blood flow reduced from 18.3 ± 10.7 at control to 5.3 ± 4.0 during phentolamine, since blood flow in inactive muscles increased 3.4‐fold, but blood flow in exercising muscle remained essentially comparable to control exercise. In conclusion, the major novel finding here is that the release of á‐adrenergic tone markedly disturbs the distribution of blood flow in exercising human limb by elevating flow especially around inactive muscle fibers.

Endurance exercise training enhances regional femoral and tibial bone blood flow during exercise

The principal nutrient artery to the femur demonstrates an increase in endothelium‐dependent, nitric oxide mediated vasodilation in rats after endurance exercise training. The present study sought to determine whether exercise training alters hindlimb bone blood flow distribution at rest and during exercise. Sprague‐Dawley rats were exercise trained (ET, 6–8 mo. old, n=10) with treadmill (TM) exercise at 15 m/min, 15° incline for 60 min/d over a 10–12 wk period. Sedentary (SED, n=10) control animals were acclimated to TM exercise for 5 min/d during the week preceding their blood flow measurements using the microsphere method. During exercise, ET rats demonstrated increases in blood flow to the femoral diaphysis (rest: 27 ± 8, TM: 56 ± 10 ml/min/100 g, p&lt;0.05), femoral diaphyseal marrow (rest: 92 ± 13, TM: 154 ± 29 ml/min/100 g, p&lt;0.05), distal tibial metaphysis (rest: 43 ± 13, TM: 108 ± 22 ml/min/100 g, p&lt;0.05), and tibial diaphysis (rest: 37 ± 14, TM: 68 ± 12 ml/min/100 g, p&lt;0.05). The tibial diaphyseal marrow was the only hindlimb bone region to elevate flow during exercise (rest: 92 ± 7, TM: 202 ± 21 ml/min/100 g, p&lt;0.05) in SED animals. The more generalized elevations in bone perfusion during exercise in ET rats may serve to augment medullary fluid pressures and bone interstitial fluid flow, thus benefiting bone integrity. Supported by NASA NNX09AP06G and NIH AG‐31317.

Neurotransmitter and neuropeptide control of the bone resistance vasculature

Adequate bone blood flow is requisite for bone growth and repair. Regulation of bone blood vessels via the nervous system may provide a mechanism for the control of bone perfusion. We assessed whether the femoral principal nutrient artery (PNA), the primary conduit for blood flow to long bones, is controlled by various neurotransmitters and neuropeptides. Femoral PNAs from male Wistar rats (4 mon) were dissected and cannulated to assess vasomotor properties to increasing concentrations of neuropeptide Y (NPY; 0.125–1.000 mg/ml), Adenosine triphosphate (ATP; 0.78–50.00 μM/ml), mATP (4.95×10−4 – 4.95×10−8 M), norepinephrine (NE; 10−9–10−4 M), phenylephrine (PE; 10−9–10−4 M), clonidine (CLO; 10−9–10−6 M), vasoactive intestinal peptide (VIP; 10−10–10−4 M), calcitonin gene related peptide (CGrP; 10−10– 10−4 M) and Substance P (Sub P; 10−10–10−4 M). Interestingly, the femoral PNAs vasoconstricted to NPY, ATP and mATP (range = 31–57%). Additionally, vasoconstriction to NE and PE was ~77%, while CLO elicited only 33% vasoconstriction. Peak vasodilatations between 33–54% were observed to VIP, CGrP and Sub P. Data from the current study illustrate a potential role for these neurotransmitters and neuropeptides in the regulation of the bone resistance vasculature. Thus, the nervous system may provide a means of controlling bone blood flow during bone growth and repair. Supported by UTA REP grant 10466.

Bad to Bone: Homocysteine

Children born with severe homocystinuria i.e. mutation of the cystathionine‐â‐synthase (CBS) gene resulting in an elevation in plasma homocysteine (Hcy) levels, known as hyperhomocysteinemia (HHcy), develop skeletal mal‐formation with weaker bones.. Therefore present study examined the mechanism of changes in bone structure/function during HHcy. There were four groups of mice: WT, CBS+/−, WT+ Folic Acid (FA), CBS+/− + FA (0.03gm/L in drinking water for 6 weeks). The tibial bone blood flow was measured by laser Doppler. The tibial bone density was assessed by dual energy X‐ray absorptiometry. The tibia bone homogenates were analyzed for total Hcy, SAHH, CBS and MTHFR levels. MMP‐9 activity was measured by zymography and RT‐PCR. The levels of TIMPs were measured by Western blots, reverse zymography, RT‐PCR and immunehistochemistry. The levels of osteoblast/osteoclast/osteocyte were detected by immunohistochemistry and TRAP staining. The results suggested that there was decrease in bone blood flow in CBS+/− mice. The bone density was also reduced in CBS+/− mice. There was an increase in SAHH, MMP‐9 protein as well as MMP‐9 activity in CBS+/− mice and decrease in MTHFR, TIMP‐1,‐2 protein as well as mRNA levels, in part by increasing total Hcy level in CBS+/− mice. Interestingly, these effects were ameliorated by FA and suggested therapeutic role of FA in genetically HHcy induced bone disease.

Induction of angiogenesis and osteogenesis in surgically revascularized frozen bone allografts by sustained delivery of FGF‐2 and VEGF

Large conventional bone allografts are susceptible to fracture and nonunion due to incomplete revascularization and insufficient bone remodeling. We aim to improve bone blood flow and bone remodeling using surgical angiogenesis combined with delivery of fibroblast growth factor (FGF-2) and vascular endothelial growth factor (VEGF). Frozen femoral allografts were heterotopically transplanted in a rat model. The saphenous arteriovenous bundle was implanted within the graft medullary canal. Simultaneously, biodegradable microspheres containing phosphate buffered saline (control), FGF-2, VEGF, or FGF-2 + VEGF were placed within the graft. Rats were sacrificed at 4 and 18 weeks. Angiogenesis was determined by quantifying bone capillary density and measuring cortical bone blood flow. Bone remodeling was assessed by histology, histomorphometry, and alkaline phosphatase activity. VEGF significantly increased angiogenesis and bone remodeling at 4 and 18 weeks. FGF-2 did not elicit a strong angiogenic or osteogenic response. No synergistic effect of FGF-2 + VEGF was observed. VEGF delivered in microspheres had superior long-term effect on angiogenesis and osteogenesis in surgically revascularized frozen bone structural allografts as compared to FGF-2 or FGF-2 + VEGF. Continuous and localized delivery of VEGF by microencapsulation has promising clinical potential by inducing a durable angiogenic and osteogenic response in frozen allografts.

Biomechanical characterisation of a degradable magnesium-based (MgCa0.8) screw

Magnesium alloys have been in the focus of research in recent years as degradable biomaterial. The purpose of this study was the biomechanical characterisation of MgCa0.8-screws. The maximum pull out force of screws was determined in a synthetic bone without corrosion and after fixed intervals of corrosion: 24, 48, 72 and 96 h. This in vitro study has been carried out with Hank's solution with a flow rate corresponding to the blood flow in natural bone. A maximum pull out force (F(max)) of 201.5 ± 9.3 N was measured without corrosion. The biomechanical parameter decreased by 30% after 96 h in corrosive medium compared to the non-corrosion group. A maximum load capacity of 28 ± 7.6 N/h was determined. Our biomechanical data suggests that this biodegradable screw provides a promising bone-screw-fixation and has great potential for medical application.

Bone turnover at the spine and hip measured using 18F-PET

Bone turnover at the spine and hip measured using 18F-PET

Vascularized Bone Grafting in a Canine Carpal Avascular Necrosis Model

Limited experimental research has been performed on the treatment of avascular necrosis (AVN) by vascularized bone grafting. A new model simulating carpal AVN was created to investigate surgical revascularization of necrotic bone. In seven mongrel dogs, AVN was induced by removal of the radial carpal bones bilaterally, deep-freezing, coating in cyanoacrylate, and reimplantation. A reverse-flow vascularized bone graft from the distal radius was implanted in the avascular radial carpal bone. The contralateral side served as an untreated ischemic control. Bone blood flow, bone volume, radiography, histomorphometry, histology, and MRI were analyzed at 4 weeks. Blood flow was substantially higher in grafted bones when compared with controls (14.68 ± 15.43 versus 0.27 ± 0.28 mL/minute/100 g). Blood flow correlated with increased osteoid formation and higher levels of bone turnover. T1 and T2 signals on MRI did not correlate with quantitative bone blood flow measurements. Necrotic bones with no blood flow had normal T1 and T2 signals, whereas revascularized bones had signal changes when compared with adjacent carpal bones. No major collapse occurred in any radiocarpal bone. In a canine experimental model, investigation of carpal AVN shows the ability of vascularized bone grafting to revascularize and remodel avascular bone. Surgical revascularization of necrotic bone induced by vascularized bone grafting results in increased bone perfusion and bone remodeling as compared with untreated necrotic bone. MRI T1 and T2 signals can be normal in necrotic avascular bone.

Homocysteine mediated decrease in bone blood flow and remodeling: Role of folic acid

Deficiencies in folate lead to increased serum concentrations of homocysteine (Hcy), which is known as hyperhomocysteinemia (HHcy), is associated with bone disorders. Although, Hcy accumulates collagen in bone and contribute to decrease in bone strength. The mechanism of Hcy induced bone loss and remodeling is unclear. Therefore, the present study was aimed to determine the role of folic acid (FA) in genetically HHcy-associated decrease in bone blood flow and remodeling. Wild type (WT) and cystathionine-β-synthase heterozygous (CBS+/-) mice were used in this study and supplemented with or without FA (300 mg/kg, Hcy reducing agent) in drinking water for 6 weeks. The tibial bone blood flow was measured by laser Doppler and ultrasonic flow probe method. The tibial bone density (BD) was assessed by dual energy X-ray absorptiometry. The bone homogenates were analyzed for oxidative stress, NOX-4 as oxidative marker and thioredoxin-1 (Trx-1) as anti-oxidant marker, bone remodeling (MMP-9) and bio-availability of nitric oxide (eNOS/iNOS/NO) by Western blot method. The results suggested that there was decrease in tibial blood flow in CBS+/- mice. The BD was also reduced in CBS+/- mice. There was an increase in NOX-4, iNOS, MMP-9 protein as well as MMP-9 activity in CBS+/- mice and decrease in Trx-1, eNOS protein levels, in part by decreasing NO bio-availability in CBS+/- mice. Interestingly, these effects were ameliorated by FA and suggested that FA supplementation may have therapeutic potential against genetically HHcy induced bone loss.

Revascularization and bone remodeling of frozen allografts stimulated by intramedullary sustained delivery of FGF‐2 and VEGF

Frozen bone allografts are susceptible to nonunion and fracture due to limited revascularization and incomplete bone remodeling. We aim to revascularize bone allografts by combining angiogenesis from implanted arteriovenous (AV) bundles with delivery of fibroblast growth factor (FGF-2) and/or vascular endothelial growth factor (VEGF) via biodegradable microspheres. Rat femoral diaphyseal allografts were frozen at -80°C, and heterotopically transplanted over a major histocompatibility mismatch. A saphenous AV bundle was inserted into the intramedullary canal. Growth factor was encapsulated into microspheres and inserted into the graft, providing localized and sustained drug release. Forty rats were included in four groups: (I) phosphate-buffered saline, (II) FGF-2, (III) VEGF, and (IV) FGF-2 + VEGF. At 4 weeks, angiogenesis was measured by the hydrogen washout method and microangiography. Bone remodeling was evaluated by quantitative histomorphometry and histology. Bone blood flow was significantly higher in groups III and IV compared to control (p < 0.05). Similarly, bone remodeling was higher in VEGF groups. FGF-2 had little effect on allograft revascularization. No synergistic effect was observed with use of both cytokines. Delivered in microspheres, VEGF proved to be a potent angiogenic cytokine, increasing cortical bone blood flow and new bone formation in frozen allografts revascularized with an implanted AV bundle.

Feasibility of Treating Irradiated Bone with Intramedullary Delivered Autologous Mesenchymal Stem Cells

Background. We aimed to explore (i) the short-term retention of intramedullary implanted mesenchymal stem cells BMSCs and (ii) their impact on the bone blood flow and metabolism in a rat model of hindlimb irradiation. Methods. Three months after 30 Gy irradiation, fourteen animals were referred into 2 groups: a sham-operated group (n = 6) and a treated group (n = 8) in which 111In-labelled BMSCs (2 × 106 cells) were injected in irradiated tibias. Bone blood flow and metabolism were assessed by serial 99mTc-HDP scintigraphy and 1-wk cell retention by recordings of 99mTc/111In activities. Results. The amount of intramedullary implanted BMSCs was of 70% at 2 H, 40% at 48 H, and 38% at 168 H. Bone blood flow and bone metabolism were significantly increased during the first week after cell transplantation, but these effects were found to reduce at 2-mo followup. Conclusion. Short-term cell retention produced concomitant enhancement in irradiated bone blood flow and metabolism.

Bone blood flow is influenced by muscle contractions

Forces acting on the skeleton could be divided into those originating from gravitational loading and those originating from muscle loading. Flat bones in a non-weight-baring segment of the skeleton probably experience forces mostly generated by muscle contractions. One purpose of muscle contractions is to generate blood flow within skeletal tissues. The present study aimed to investigate the pulsatile patellar bone blood flow after low and high intensity leg extension exercises. Forty-two healthy individuals volunteered for the study. Dynamic isotonic one leg extension/flexion exercises were performed in a leg extension machine. Randomly, the exercises were performed with the left or right leg with either 10 repetition maximum (10 RM) continuously without any resting periods (high intensity muscle work), or 20 RM with a 2 second rest between contractions (low intensity muscle work). The work load, expressed in kilograms totally lifted, was identical in both legs. The pulsatile patellar blood flow was recorded continuously using a photoplethysmographic technique. Blood pressure was measured continuously during muscle work by a non-invasive method (Finapress). The patellar pulsatile bone blood flow increased significantly more after high intensity muscle work (61%) compared to the same work load performed using a lower intensity (22%), p = 0.000073. Systolic blood pressure changed equally during and after both interventions. Post-exercise bone hyperaemia appears to be correlated to the intensity of muscle contractions in the muscle compartment attached to the bone.

Hyperhomocysteinemia decreases bone blood flow

Elevated plasma levels of homocysteine (Hcy), known as hyperhomocysteinemia (HHcy), are associated with osteoporosis. A decrease in bone blood flow is a potential cause of compromised bone mechanical properties. Therefore, we hypothesized that HHcy decreases bone blood flow and biomechanical properties. To test this hypothesis, male Sprague–Dawley rats were treated with Hcy (0.67 g/L) in drinking water for 8 weeks. Age-matched rats served as controls. At the end of the treatment period, the rats were anesthetized. Blood samples were collected from experimental or control rats. Biochemical turnover markers (body weight, Hcy, vitamin B12, and folate) were measured. Systolic blood pressure was measured from the right carotid artery. Tibia blood flow was measured by laser Doppler flow probe. The results indicated that Hcy levels were significantly higher in the Hcy-treated group than in control rats, whereas vitamin B12 levels were lower in the Hcy-treated group compared with control rats. There was no significant difference in folate concentration and blood pressure in Hcy-treated versus control rats. The tibial blood flow index of the control group was significantly higher (0.78 ± 0.09 flow unit) compared with the Hcy-treated group (0.51 ± 0.09). The tibial mass was 1.1 ± 0.1 g in the control group and 0.9 ± 0.1 in the Hcy-treated group. The tibia bone density was unchanged in Hcy-treated rats. These results suggest that Hcy causes a reduction in bone blood flow, which contributes to compromised bone biomechanical properties.

A modified vascularized whole knee joint allotransplantation model in the rat

Previous papers have shown surgical neoangiogenesis to allow long-term bone allotransplant survival without immunosuppression. Whole joint composite tissue allotransplants (CTA) might be treated similarly. A novel rat knee CTA model is described for further study of the roles of neoangiogensis in joint allotransplant survival and adjustment of immunosuppression. Microvascular knee CTA was performed in nine rats across a major histocompatibility barrier with both pedicle repair and implantation of host-derived arteriovenous ("a/v") bundles. In the control group (N = 3), the pedicle was ligated. Immunosuppression was given daily. Joint mobility, weight-bearing, pedicle patency, bone blood flow, and sprouting from a/v bundles were assessed at 3 weeks. All but the nonrevascularized control knees had full passive motion and full weight bearing. One nutrient pedicle thrombosed prematurely. Blood flow was measurable in transplants with patent nutrient pedicles. Implanted a/v bundles produced new vascular networks on angiography. This new rat microsurgical model permits further study of joint allotransplantation. Patency of both pedicles and implanted a/v bundles was maintained, laying a foundation for future studies.