A novel approach for comparative study of periosteum, muscle, subcutis, and skin microcirculation by intravital fluorescence microscopy

P407 hydrogel loaded with nitric oxide microbubbles promotes angiogenesis and functional improvement in testicular transplantation

Prepubertal male patients with cancer have decreased fertility after treatment, but there are currently no suitable means for fertility rescue. Testicular transplantation seems to be a promising treatment. The short-term insufficiency of blood supply after transplantation is the key problem that needs to be solved. In this research, nitric oxide (NO), a gas and small molecule transmitter with the effect of promoting angiogenesis, acted at the site of testicular transplantation. Herein, poloxamer-407 (P407) and lipid microbubble materials served as transport carriers for NO and helped NO to function at the transplant site. P407 hydrogel loaded with NO microbubbles (PNO) slowly released NO in vitro. The three-dimensional space of the hydrogel provided a stable environment for NO microbubbles, which is conducive to the continuous release of NO. In this study, 25% PNO (w/v) was selected, and the gelling temperature was 19.47 °C. The gelling efficiency was relatively high at body temperature. Rheological experiments showed that PNO, at this concentration, had stable mechanical properties. The results from in vivo experiments demonstrated that testicular grafts in the PNO group exhibited a notably accelerated blood flow recovery compared to the other groups. Additionally, the PNO group displayed a significant improvement in reproductive function recovery. In conclusion, PNO exhibited slow release of NO, and a small amount of NO promoted angiogenesis in testicular grafts and restored reproductive function.

"Periosteum: An imaging review"

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The periosteum has different characteristics between genders and age groups, and may change with the use of medications.

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Conventional plain radiography can often determine the aggressiveness of periosteal reactions.

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Knowledge of the periosteum’s anatomy eases the understanding of its periosteal reactions.

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Systemic periosteal reactions are generally underdiagnosed, due to compartmentalized analysis.

Periosteum is a fibrous sheath, coating the external bone, except in the articular surfaces, tendon insertions and sesamoid bone surface¹. It changes its aspects and characteristics with aging, becoming progressively less elastic and more firm. It is composed of two different layers: outer fibrous (firm, collagen-filled) and inner proliferative (cambium, containing osteoprogenitor cells)^². Four vascular systems are responsible for the blood supply of the periosteum: the intrinsic periosteal system, located between fibrous and proliferative layer; the periosteocortical, the main nutritional arteries of the periosteum; the musculoperiosteal, responsible for the callus formation after fractures; the fascioperiosteal, specifically for each bone.³ It is crucial to bone formation and resorption, reacting to insults in the cortical bone, such as tumors, infections, traumas, medications and arthritic diseases. The aggressiveness of the reaction can be suggested by its radiological aspect and appearance⁴. The periosteum in children is looser compared to adults, resulting in earlier and more exuberant reactions. All these aspects will be detailed, so the essential information all radiologists need to know will be discussed.

Autologous grafting of cryopreserved prepubertal rhesus testis produces sperm and offspring

Testicular tissue cryopreservation is an experimental method to preserve the fertility of prepubertal patients before they initiate gonadotoxic therapies for cancer or other conditions. Here we provide the proof of principle that cryopreserved prepubertal testicular tissues can be autologously grafted under the back skin or scrotal skin of castrated pubertal rhesus macaques and matured to produce functional sperm. During the 8- to 12-month observation period, grafts grew and produced testosterone. Complete spermatogenesis was confirmed in all grafts at the time of recovery. Graft-derived sperm were competent to fertilize rhesus oocytes, leading to preimplantation embryo development, pregnancy, and the birth of a healthy female baby. Pending the demonstration that similar results are obtained in noncastrated recipients, testicular tissue grafting may be applied in the clinic.

A novel method for in vivo visualization of the microcirculation of the mandibular periosteum in rats

OBJECTIVE

The periosteum plays an important role in bone physiology, but observation of its microcirculation is greatly limited by methodological constraints at certain anatomical locations. This study was conducted to develop a microsurgical procedure which provides access to the mandibular periosteum in rats.

METHODS

Comparisons of the microcirculatory characteristics with those of the tibial periosteum were performed to confirm the functional integrity of the microvasculature. The mandibular periosteum was reached between the facial muscles and the anterior surface of the superficial masseter muscle at the external surface of the mandibular corpus; the tibial periosteum was prepared by dissecting the covering muscles at the anteromedial surface. Intravital fluorescence microscopy was used to assess the leukocyte-endothelial interactions and the RBCV in the tibial and mandibular periosteum. Both structures were also visualized through OPS and fluorescence CLSM.

RESULTS

The microcirculatory variables in the mandibular periosteum proved similar to those in the tibia, indicating that no microcirculatory failure resulted from the exposure technique.

CONCLUSION

This novel surgical approach provides simple access to the mandibular periosteum of the rat, offering an excellent opportunity for investigations of microcirculatory manifestations of dentoalveolar and maxillofacial diseases.

Effects of a new piezoelectric device on periosteal microcirculation after subperiosteal preparation

INTRODUCTION

Subperiosteal preparation using a periosteal elevator leads to disturbances of local periosteal microcirculation. Soft-tissue damage can usually be considerably reduced using piezoelectric technology. For this reason, we investigated the effects of a novel piezoelectric device on local periosteal microcirculation and compared this approach with the conventional preparation of the periosteum using a periosteal elevator.

MATERIAL AND METHODS

A total of 20 Lewis rats were randomly assigned to one of two groups. Subperiosteal preparation was performed using either a piezoelectric device or a periosteal elevator. Intravital microscopy was performed immediately after the procedure as well as three and eight days postoperatively. Statistical analysis of microcirculatory parameters was performed offline using analysis of variance (ANOVA) on ranks (p<0.05).

RESULTS

At all time points investigated, intravital microscopy demonstrated significantly higher levels of periosteal perfusion in the group of rats that underwent piezosurgery than in the group of rats that underwent treatment with a periosteal elevator.

CONCLUSION

The use of a piezoelectric device for subperiosteal preparation is associated with better periosteal microcirculation than the use of a conventional periosteal elevator. As a result, piezoelectric devices can be expected to have a positive effect on bone metabolism.

Periosteal microvascular reorganization after tibial reaming and intramedullary nailing in rats

BACKGROUND

Intramedullary reaming and nailing of long bones impairs the endosteal circulation, often causing necrosis of the inner region of the bone cortex. We hypothesized that compensatory hypertrophy of the periosteal microcirculation may develop in response to mechanical destruction of the endosteum, and that this may affect bone survival in these circumstances. In these studies, nailing was performed with materials that affect regeneration of the endosteum differently, and the effects on the tibial periosteal microvasculatory organization were examined.

METHODS

In male Wistar rats, the right tibia was reamed and implanted with an inert titanium nail or a less osseointegrative polyethylene nail; the contralateral tibial endosteum was destroyed by reaming. Reaming without nailing or sham operation was performed on both extremities in two other groups of rats. Twelve weeks later, the anteromedial and anterolateral surfaces of the tibias were exposed by a microsurgical technique. The structural characteristics of the periosteal microcirculation (vessel density and distribution of vessel diameters) were determined by intravital videomicroscopy and computer-assisted analysis. The stability of the implants was assessed on the basis of grades 0-2 on a qualitative scale.

RESULTS

Tibial reaming alone caused significant increases in overall blood vessel and capillary densities in the periosteum compared with those of the intact tibias. Implantation with a titanium nail resulted in firm embedding of the nail and caused changes in the periosteal vasculature similar to those after reaming alone. In contrast, implantation of a polyethylene nail was followed by the development of marked instability of the endomedullary implant and significant increases in the percentage of capillaries and the vessel density in the periosteum.

CONCLUSIONS

Destruction of the endosteal microcirculation per se brings about an increase in periosteal vascular density, which is further augmented if implantation is performed with a material which delays regeneration of the endosteal circulation.

Effects of extensive circumferential periosteal stripping on the microstructure and mechanical properties of the murine femoral cortex

Extensive periosteal stripping (PS) is a risk factor for post-radiation pathologic fracture following surgery for extremity soft tissue tumors. The purpose of this study was to determine the effects of PS on bone structure and mechanical properties. Thirty-one skeletally mature mice underwent PS, with circumferential removal of periosteum from an 8-mm segment of the mid-diaphysis of the left femur. Thirty-one control mice underwent sham surgery in which the femur was isolated without manipulation of the periosteum. At 2, 6, 12, or 26 weeks following surgery, the left femora were examined by micro-CT to quantify cortical thickness (CtTh), cross-sectional area (CSA), bone volume (BV), and polar moment of inertia (PMI). Three-point mechanical bend testing was performed and peak load, stiffness, and energy to failure were determined. PS resulted in significantly decreased CtTh, CSA, BV, and PMI at all time points. Peak load, stiffness, and energy to failure were significantly reduced at 2, 6, and 12 weeks. There were no significant differences in mechanical properties at 26 weeks. In this mouse model, extensive circumferential PS resulted in sustained changes in bone structure that were still evident after 6 months, accompanied by reductions in bone strength that persisted for at least 3 months.

New clinically relevant, orthotopic mouse models of human chondrosarcoma with spontaneous metastasis

Background

Chondrosarcoma responds poorly to adjuvant therapy and new, clinically relevant animal models are required to test targeted therapy.

Methods

Two human chondrosarcoma cell lines, JJ012 and FS090, were evaluated for proliferation, colony formation, invasion, angiogenesis and osteoclastogenesis. Cell lines were also investigated for VEGF, MMP-2, MMP-9, and RECK expression. JJ012 and FS090 were injected separately into the mouse tibia intramedullary canal or tibial periosteum. Animal limbs were measured, and x-rayed for evidence of tumour take and progression. Tibias and lungs were harvested to determine the presence of tumour and lung metastases.

Results

JJ012 demonstrated significantly higher proliferative capacity, invasion, and colony formation in collagen I gel. JJ012 conditioned medium stimulated endothelial tube formation and osteoclastogenesis with a greater potency than FS090 conditioned medium, perhaps related to the effects of VEGF and MMP-9. In vivo, tumours formed in intratibial and periosteal groups injected with JJ012, however no mice injected with FS090 developed tumours. JJ012 periosteal tumours grew to 3 times the non-injected limb size by 7 weeks, whereas intratibial injected limbs required 10 weeks to achieve a similar tumour size. Sectioned tumour tissue demonstrated features of grade III chondrosarcoma. All JJ012 periosteal tumours (5/5) resulted in lung micro-metastases, while only 2/4 JJ012 intratibial tumours demonstrated metastases.

Conclusions

The established JJ012 models replicate the site, morphology, and many behavioural characteristics of human chondrosarcoma. Local tumour invasion of bone and spontaneous lung metastasis offer valuable assessment tools to test the potential of novel agents for future chondrosarcoma therapy.

Ischemic limb preconditioning downregulates systemic inflammatory activation

We examined local and systemic antiinflammatory consequences of ischemic preconditioning (IPC) in a rat model of limb ischemia-reperfusion (I-R) by characterizing the leukocyte-endothelial interactions in the periosteum and the expression of adhesion molecules playing a role in leukocyte-mediated inflammatory processes. IPC induction (2 cycles of 10 min of complete limb ischemia and 10 min of reperfusion) was followed by 60 min of ischemia/180 min of reperfusion or sham-operation. Data were compared with those on animals subjected to I-R and sham-operation. Neutrophil leukocyte-endothelial cell interactions (intravital videomicroscopy), intravascular neutrophil activation (CD11b expression changes by flow cytometry), and soluble and tissue intercellular adhesion molecule-1 (ICAM-1; ELISA and immunohistochemistry, respectively) expressions were assessed. I-R induced enhanced leukocyte rolling and adherence in the periosteal postcapillary venules after 120 and 180 min of reperfusion. This was associated with a significantly enhanced CD11b expression (by approximately 80% and 72%, respectively) and moderately increased soluble and periosteal ICAM-1 expressions. IPC prevented the I-R-induced increases in leukocyte adherence and CD11b expression without influencing the soluble and tissue ICAM-1 levels. The results show that limb IPC exerts not only local, but distant antiinflammatory effects through significant modulation of neutrophil recruitment.

Beneficial effects of phosphatidylcholine during hindlimb reperfusion

BACKGROUND

Microcirculatory dysfunctions and mast cell (MC) reactions play important roles in hypoxic tissue injuries. The aims of this study were to characterize the effects of hindlimb ischemia-reperfusion (I-R) on the periosteal microcirculation and to define the consequences of systemic phosphatidylcholine (PC) therapy during this condition.

MATERIALS AND METHODS

Microcirculatory changes were visualized by means of fluorescence intravital videomicroscopy in anesthetized Wistar rats. There was 60 min of complete hindlimb ischemia followed by a 180-min reperfusion in the presence of PC treatment (50 mg/kg i.v.; in the second 10 min of reperfusion) or vehicle. Further two groups served as vehicle- or PC-treated sham-operated controls. The proportion of degranulated MCs and the leukocyte accumulation (myeloperoxidase, MPO assay) were determined in muscle biopsies.

RESULTS

I-R significantly increased the muscle MPO activity (from 14.94 to 63.45 mU/mg) and the proportion of degranulated MCs (to 82.5%). The periosteal capillary RBC velocity (RBCV) and the functional capillary density (FCD) had decreased, while the primary and secondary leukocyte-endothelial cell interactions had increased by the end of reperfusion (rolling from 20.8 to 40.0%, and firm adherence from 254 to 872 mm(-2)). PC treatment decreased the leukocyte rolling and sticking, preserved the FCD and improved the RBCV. The MC degranulation and MPO activity diminished significantly in the muscle layer.

CONCLUSIONS

PC administration improves I-R-induced periosteal microcirculatory dysfunctions and ameliorates secondary inflammatory reactions. Systemic PC treatment could offer a potential treatment modality during hypoperfusion or inflammatory conditions of the bones.

Local Heat Shock Priming Promotes Recanalization of Thromboembolized Microvasculature by Upregulation of Plasminogen Activators

OBJECTIVE

Thromboembolization and subsequent microvascular perfusion failure is implicated in the pathology of a variety of diseases, including transient ischemic attack (TIA), stroke, and myocardial infarction, and also for the complications after interventional and microsurgical procedures in coronary heart disease and peripheral arterial occlusive disease. In vitro heat shock priming has been suggested to induce plasminogen activators, which are the major upregulators of the fibrinolytic system. Herein, we determined whether local heat shock priming endogenously upregulates plasminogen activators also in vivo, and whether this promotes recanalization of thromboembolized microvasculature.

METHODS AND RESULTS

To induce thromboembolization, a suspension of preformed microthrombi (maximum diameter: 40 microm) was injected via the femoral artery into the left hindlimbs of anesthetized rats. Local heat shock priming (42.5 degrees C, 30 minutes) was performed 24 hours before embolization and resulted in a significant increase of endothelium-derived plasminogen activator expression. The study of the microcirculation by intravital microscopy revealed in all tissues analyzed (muscle, periosteum, subcutis, and skin) that heat shock priming significantly (P<0.05) accelerates recanalization of the thromboembolized microvasculature when compared with nonprimed and sham-primed controls. Importantly, the addition of plasminogen activator inhibitor-1 to the microthrombi suspension completely blunted the heat shock-induced acceleration of microvascular recanalization.

CONCLUSIONS

Heat shock induces endogenous hyperfibrinolysis by upregulation of plasminogen activators that promote recanalization of thromboembolized microvasculature.

Thrombus formation in vivo

To examine thrombus formation in a living mouse, new technologies involving intravital videomicroscopy have been applied to the analysis of vascular windows to directly visualize arterioles and venules. After vessel wall injury in the microcirculation, thrombus development can be imaged in real time. These systems have been used to explore the role of platelets, blood coagulation proteins, endothelium, and the vessel wall during thrombus formation. The study of biochemistry and cell biology in a living animal offers new understanding of physiology and pathology in complex biologic systems.

Dermal capillary clearance: physiology and modeling

Substances applied to the skin surface may permeate deeper tissue layers and pass into the body's systemic circulation by entering blood or lymphatic vessels in the dermis. The purpose of this review is an in-depth analysis of the dermal clearance/exchange process and its constituents: transport through the interstitium, permeability of the microvascular barrier and removal via the circulation. We adapt an 'engineering' viewpoint with emphasis on quantifying the dermal microcirculatory physiology, providing the theoretical framework for the physics of key transport processes and reviewing the available computational clearance models in a comparative manner. Selected experimental data which may serve as valuable input to modeling attempts are also reported.

Immediate microcirculatory derangements in skeletal muscle and periosteum after closed tibial fracture

BACKGROUND

Severe musculoskeletal soft tissue injury sustained after a closed fracture to the extremities significantly influences bone healing and determines the patient's prognosis. The present study was aimed at quantitatively assessing immediate microcirculatory changes in skeletal muscle and periosteum after standardized closed fracture.

METHODS

Standardized closed fracture of the left tibia in isoflurane-anesthetized Sprague-Dawley rats (n = 14) was induced using a modified weight-drop technique. The left extensor digitorum longus (EDL) muscle (n = 7) and tibial periosteum (n = 7) were surgically exposed for in vivo fluorescence microscopy 15 minutes after fracture. Nonfractured rats (n = 14) served as controls. EDL muscle edema was determined by the ratio of wet to dry weight (EDL water content).

RESULTS

Closed tibial fracture resulted in a significant reduction of functional capillary density, red blood cell velocity, and volumetric blood flow in both EDL muscle and periosteum. Microvascular diameter, leukocyte adherence, and macromolecular leakage were markedly increased, indicating trauma-induced inflammation and endothelial disintegration. EDL muscle edema was found increased significantly after fracture.

CONCLUSION

This model permits for the first time direct in vivo visualization and quantification of fracture-induced microhemodynamic changes and cellular interactions within the surrounding soft tissue. It demonstrates that even simple fractures lead to profound microcirculatory disturbances in skeletal muscle and periosteum, and also at sites remote from the diaphyseal fracture site. It provides a useful approach for the development of therapeutic strategies to counteract fracture-induced microvascular dysfunction.

New model for in vivo quantification of microvascular embolization, thrombus formation, and recanalization in composite flaps

BACKGROUND

Microthrombi are suggested to be involved in the pathogenesis of composite flap failure. Due to the lack of appropriate experimental models, however, the significance of microvascular thrombus formation and microthromboembolization in free flap failure remains poorly understood. The purpose of this study was therefore to develop a rat hindlimb model that allows tissue-confined in vivo analysis of thrombus formation, thromboembolization, and recanalization within the microcirculation of osteomyocutaneous flaps using intravital fluorescence microscopy.

MATERIALS AND METHODS

Thrombus formation was induced photochemically in individual arterioles and venules of muscle, subcutis, and periosteum. To study thromboembolization, autologous arterial thrombi (40 microm) were preformed in vitro and were injected into the femoral artery supplying the osteomyocutaneous flap.

RESULTS

First platelet deposition was found independent from microvascular red blood cell velocity, while the subsequent growth of thrombus correlated inversely with red blood cell flow measured in the respective microvessel. Time required for complete thrombotic arteriolar occlusion exceeded 700 s, whereas thrombus growth in venules was found to be significantly accelerated ( approximately 300 s) without differences between the individual tissues analyzed. The embolization resulted in a complete shutdown of capillary perfusion in muscle, subcutis, skin, and periosteum. During subsequent spontaneous recanalization, capillary perfusion increased in all tissues to approximately half of baseline, however, without further recovery during the 4-h postembolization period.

CONCLUSIONS

The model presented is suitable to quantitatively study the pathophysiology of microvascular thrombus formation, thromboembolization, and recanalization in composite flaps, and may thus be used to evaluate the effectiveness of novel therapeutic strategies to prevent flap failure.

Microcirculatory effects of experimental acute limb ischaemia-reperfusion

BACKGROUND

The object of this study was to develop an animal model in which changes in microvascular haemodynamics and leucocyte-vessel wall interactions due to acute limb ischaemia-reperfusion (I/R) can be measured in the skin. Furthermore, it was investigated whether these changes are related to local muscle injury.

METHODS

Male Lewis rats were subjected to unilateral limb ischaemia for 1 h (n = 8) or 2 h (n = 8) by cuff inflation, or to a sham protocol (n = 6). Intravital video microscopic measurements of leucocyte-vessel wall interactions, venular diameter, red blood cell velocity and reduced velocity (which is proportional to wall shear rate) were performed in skin venules before ischaemia and at 0.5, 1, 2, 3 and 4 h after the start of reperfusion. Oedema and leucocyte infiltration of ischaemic/reperfused skeletal muscle were quantified histologically.

RESULTS

In skin venules, both 1 and 2 h of ischaemia induced a significant increase in leucocyte rolling (six and five times baseline, respectively; P < 0.05) and adherence during reperfusion (eight and four times baseline; P < 0.05). No significant increase in muscular leucocyte infiltration was detected. After an initial hyperaemic response of 180 per cent of baseline values (P < 0.05), blood flow decreased to about 60 per cent after 4 h of reperfusion in skin venules of both experimental groups. I/R induced tibial muscle oedema, the severity of which depended on the ischaemic interval (wet to dry ratio: control, 4.0; 1 h, 4.5 (P not significant); 2 h, 5.8 (P < 0.05)).

CONCLUSION

A non-invasive animal model was developed that enables investigation of the consequences of acute limb I/R.

Reduction of inflammatory response in composite flap transfer by local stress conditioning-induced heat-shock protein 32

BACKGROUND

The failure of composite flaps despite anastomotic patency is thought to be mediated by the inflammatory response within the microvasculature, which results from unavoidable surgical trauma and transfer-related ischemia-reperfusion. Evidence suggests that stress conditioning may improve flap survival; however, the molecular mechanisms of protection are far from being clear. Therefore, we analyzed whether stress conditioning-induced heat-shock protein 32 is effective to prevent the inflammatory response in transferred osteomyocutaneous flaps.

METHODS

In a rat model, leukocyte-endothelial cell interaction and endothelial integrity disruption as early indicators of the inflammatory response were quantitatively analyzed in muscle, subcuticular tissue, and periosteum of microvascularly transferred osteomyocutaneous flaps by using intravital fluorescence microscopy. Twenty-four hours before flap transfer, stress conditioning was induced by local heating of the left hindlimb up to 42.5 degrees C for 30 minutes. In additional animals, stress conditioning-induced activity of heat-shock protein 32 was inhibited by tin protoporphyrin-IX. Unconditioned flaps served as controls.

RESULTS

In all tissues analyzed, control flaps showed significant leukocyte adherence in postcapillary venules, increased intercellular adhesion molecule-1 (ICAM-1) expression, and endothelial integrity disruption, but a lack of heat-shock protein 32. In contrast, stress conditioning induced marked heat-shock protein 32 expression, which was associated with a significant reduction (P <.05) of leukocyte adherence, ICAM-1 expression, and endothelial hyperpermeability. The inhibition of heat-shock protein 32 by tin protoporphyrin-IX completely abolished the stress conditioning-induced amelioration of the inflammatory response in all tissues analyzed.

CONCLUSIONS

Stress conditioning by local heat-shock priming reduces the inflammatory response in osteomyocutaneous flaps. The protective effect is predominantly mediated by the induction of heat-shock protein 32.

Local heat-shock priming-induced improvement in microvascular perfusion in osteomyocutaneous flaps is mediated by heat-shock protein 32

BACKGROUND

Stress conditioning is thought to improve microvascular free flap survival but the mechanisms of protection are not clear. The aim of this study was to determine whether local induction of heat-shock protein (HSP) 32 improves microvascular perfusion in transferred osteomyocutaneous flaps.

METHODS

The hindlimb harvest region of osteomyocutaneous flaps in Wistar rats was subjected to stress conditioning by local heating (30 min, 42.5 degrees C) 24 h before microvascular flap transfer. In a second group of animals, after heat-shock priming, the action of HSP-32 was inhibited by tin protoporphyrin IX. Animals with unconditioned flaps served as controls. After transfer, the microcirculation of the muscle, cutaneous, subcutaneous and periosteal tissue of the flap was analysed quantitatively for 6 h using intravital fluorescence microscopy.

RESULTS

Immunohistochemistry revealed that HSP-32 was detectable only after priming and not in unconditioned flaps. Priming did not alter functional capillary density or capillary red blood cell velocity compared with that in unconditioned flaps. However, heat-shock priming induced significant capillary dilatation (P < 0.05) and thus a substantial increase in capillary blood flow volume (P < 0.05) in all tissues of the transferred flaps. Inhibition of HSP-32 by tin protoporphyrin IX completely abolished the priming-induced improvement in capillary perfusion, as indicated by the lack of increased capillary diameters and volumetric blood flow.

CONCLUSION

The present study demonstrated that stress conditioning by local heat-shock priming improves nutritive perfusion in osteomyocutaneous flaps by capillary dilatation, probably mediated through the vasoactive action of HSP-32.

Vasomotion in critically perfused muscle protects adjacent tissues from capillary perfusion failure

We analyzed the incidence and interaction of arteriolar vasomotion and capillary flow motion during critical perfusion conditions in neighboring peripheral tissues using intravital fluorescence microscopy. The gracilis and semitendinosus muscles and adjacent periosteum, subcutis, and skin of the left hindlimb of Sprague-Dawley rats were isolated at the femoral vessels. Critical perfusion conditions, achieved by stepwise reduction of femoral artery blood flow, induced capillary flow motion in muscle, but not in the periosteum, subcutis, and skin. Strikingly, blood flow within individual capillaries was decreased (P < 0.05) in muscle but was not affected in the periosteum, subcutis, and skin. However, despite the flow motion-induced reduction of muscle capillary blood flow during the critical perfusion conditions, functional capillary density remained preserved in all tissues analyzed, including the skeletal muscle. Abrogation of vasomotion in the muscle arterioles by the calcium channel blocker felodipine resulted in a redistribution of blood flow within individual capillaries from cutaneous, subcutaneous, and periosteal tissues toward skeletal muscle. As a consequence, shutdown of perfusion of individual capillaries was observed that resulted in a significant reduction (P < 0.05) of capillary density not only in the neighboring tissues but also in the muscle itself. We conclude that during critical perfusion conditions, vasomotion and flow motion in skeletal muscle preserve nutritive perfusion (functional capillary density) not only in the muscle itself but also in the neighboring tissues, which are not capable of developing this protective regulatory mechanism by themselves.

In vivo analysis of the microcirculation of osteomyocutaneous flaps using fluorescence microscopy

Previous studies have indicated that freely transferred osteomyocutaneous flaps may fail despite anastomotic patency. While microvascular dysfunction is thought to be one of the major causes for this type of flap failure, little is known of its underlying mechanisms, probably due to the lack of adequate experimental models allowing detailed intravital microcirculatory analysis. Herein we report quantitative analysis of the microcirculation of periosteum, muscle, subcutis and skin by intravital fluorescence microscopy using an osteomyocutaneous free flap model in the hindlimb of rats. The microcirculation of the different tissues was studied after microanastomotic transfer (free flap), and was compared to that after solely elevating the tissue, mimicking a pedicled osteomyocutaneous flap. Transferred flaps, which were exposed to 1 h of ischaemia during the anastomotic procedure, showed a slight but significant decrease (P< 0.05) of functional capillary density in muscle, subcutis and skin when compared with the microcirculation of pedicled flaps, while capillary diameters, red blood cell velocity and blood flow of perfused capillaries remained almost unaffected. The decrease of functional capillary density was associated by a significant (P< 0.05) inflammatory response, as indicated by the increased number of leukocytes adherent to the endothelial lining of postcapillary venules. While the functional capillary density of periosteum was not affected by the free transfer procedure, the inflammatory response was found similar when compared with that observed in muscle and subcutis. Thus, our study indicates that even after a short 1-h ischaemic time period, capillary perfusion failure and leukocyte-endothelial cell interaction are the main events, characterising microvascular dysfunction after free transfer of osteomyocutaneous flaps. Using the model described herein, intravital microscopic analysis of the microcirculation proved an appropriate tool to study the individual microvascular response after free tissue transfer, and may thus be used to evaluate the effectiveness of novel therapeutic regimens which aim at counteracting microcirculatory dysfunction in free osteomyocutaneous flaps.