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Biomedical subjects

M A Randolph

Publications and source records attributed to M A Randolph.

At least 55 records · Page 3Linked to original sources
PubMed1991

Vascularized muscle allografts and the role of cyclosporine.

This study examined the fate of vascularized muscle allografts using a genetically defined rat model. Its purposes were (1) to analyze the histologic/immunologic responses, (2) to study the effect of cyclosporine on graft survival, and (3) to examine the possibility of inducing tolerance. In rats differing at a major histocompatibility locus, vascularized gastrocnemius muscle transplants were performed based on the sural branches of the femoral artery and vein. Forty-two animals studied were divided into three groups: Group 1, allografts, was treated without cyclosporine; Group 2, allografts, was administered continuous cyclosporine; and Group 3, allografts, was administered cyclosporine for 6 weeks only. Evaluation consisted of gross examination, H&E histology, and immunologic studies (MLC, CML, and complement-dependent 51Cr lysis assay). Lytic units (LU) were derived from the assays and served as the indicator of immune response. Group 1 animals had uniform rejection with intense cell-mediated response (LU 23 to 47) and low humoral response. Group 2 animals had viable allografts throughout with suppressed lytic unit values of 0 to 9 initially, which rose to 14 to 29 at 6 weeks despite continuous cyclosporine treatment. Group 3 animals showed rejection similar to the untreated animals. Autografts were performed as controls and survived indefinitely. Analysis of variance was significant at p less than 0.05. Using a reliable rat model for vascularized muscle allografts, we found that in transplantation across a major histocompatibility barrier, the initial immune response was primarily cell-mediated. Cyclosporine suppressed rejection only when given continuously, and short-term cyclosporine treatment did not induce a tolerant state. These data should be useful for future studies of vascularized muscle allografts.

Animals↗
PubMed1991

The healing of facial bone fractures by the process of secondary union.

The mechanism of healing of facial bone fractures was investigated in a rabbit model. Twelve New Zealand white rabbits underwent surgically induced fractures of the right infraorbital rim and fracture ostectomies (4 to 5 mm) of the left infraorbital rim. Animals were sacrificed 2, 4, and 8 weeks postfracture. Bone, including periosteum, obtained from each fracture or fracture osteoctomy site was divided longitudinally for hematoxylin and eosin staining, fluorescent microscopy, microangiography, and microradiography. Sequential fluorochrome labels of oxytetracycline (30 mg/kg), alizarin complexone (30 mg/kg), DCAF (20 mg/kg), and xylenol orange (90 mg/kg) were administered 24 hours preoperatively and at 1, 2, 4, and 8 weeks postfracture. All fracture and fracture ostectomy sites demonstrated vascular ingrowth, mineralization, and woven bone formation by 2 to 4 weeks postoperatively, beginning with a cartilage precursor. Subsequently, the woven bone was replaced with remodeled lamellar bone, resulting in complete bony healing by 8 weeks postoperatively. These steps were substantiated by microscopic, microradiographic, and radiologic examination of the specimens. This study demonstrates that fractures of the facial bones in a rabbit model heal by a process of new bone formation that resembles secondary union in endochondral bones.

Animals↗
PubMed1991

Immunologic and ultrastructural changes during early rejection of vascularized bone allografts.

This investigation evaluated ultrastructural changes during the earliest phase of immunologic rejection of vascularized bone allografts in a genetically defined rat model. These results were correlated with the cell-mediated and humoral immunologic responses during this time period. Employing a model for heterotopic allograft transplantation, 33 rats divided into four categories were evaluated. Group I consisted of ungrafted (naive) Lewis and Brown Norway rats; group II consisted of Lewis-to-Lewis vascularized bone isografts; group III consisted of Lewis-to-Brown Norway vascularized bone allografts; and group IV consisted of Lewis-to-Brown Norway vascularized bone allografts in rats receiving cyclosporine (10 mg/kg/day). Experimental animals were sacrificed at 3, 5, and 7 days. Immunologic analysis was performed using a cell-mediated lymphocytotoxicity assay and a complement-dependent cytotoxic antibody assay. The results of this study show that rejection of vascularized bone allografts appears as early as 3 days postoperatively, with osteocytes and vascular endothelium being the first elements affected. This early rejection is probably a manifestation of the humoral response. All changes secondary to rejection were arrested by cyclosporine.

Animals↗
PubMed1991

Vascularized bone allografts: in vitro assessment of cell-mediated and humoral responses.

The immunologic consequences of transplantation of vascularized bone allografts have not been previously characterized. In this study, knee allografts, both vascularized and nonvascularized, were transplanted from Lewis rats to Brown Norway rats across a strong histocompatibility barrier. A total of 66 transplants and 8 control animals were evaluated. The vascularized knee grafts consisted of 1 cm of proximal tibia and distal femur with a minimal muscular cuff isolated on the femoral vessels, and these were transplanted to a heterotopic, subcutaneous position on the abdominal wall of the recipient rat. Nonvascularized allografts (identical but without anastomoses) were transplanted for comparison. The cell-mediated response was measured by lymphocytotoxicity assay, and the humoral response was measured by cytotoxic antibody assay, both employing 51Cr-labeled target cells. The timing and intensity of the immune response differed according to the type of graft. The vascularized bone allografts generated significant cell-mediated and humoral responses as early as 5 days posttransplant. A significant humoral response in nonvascularized bone allografts was not apparent until day 14, while cell-mediated response in these grafts was variable. These findings were correlated with the histologic appearance of the grafted tissue. Cyclosporine, which was administered to one group of vascularized bone allografts, resulted in the suppression of both types of immune responses. The histologic appearance of this group resembled that of isografts transplanted as controls. The clinical application of vascularized bone allografts may offer significant advantages over nonvascularized allografts in the reconstruction of massive bone defects. Complications such as nonunion, fracture, and collapse of articular segments seen in nonvascularized allograft transplantation may be avoided by preservation of the blood supply to the graft. Characterization of the immune response to vascularized bone allografts may subsequently allow the manipulation of the host and/or graft tissue and promote graft incorporation.

Analysis of Variance↗
PubMed1990

Inability of donor total body irradiation to prolong survival of vascularized bone allografts: experimental study in the rat.

At the present time, the toxic side effects of recipient immunosuppression cannot be justified for human non-vital organ transplantation. Total body irradiation has proven effective in ablating various bone-marrow-derived and endothelial immunocompetent cellular populations, which are responsible for immune rejection against donor tissues. Irradiation at a dose of 10 Gy was given to donor rats six days prior to heterotopic transplantation of vascularized bone allografts to host animals. Another group of recipient rats also received a short-term (sixth to fourteenth day after grafting), low dose of cyclosporine. Total body irradiation was able merely to delay rejection of grafts across a strong histocompatibility barrier for one to two weeks, when compared to nonirradiated allografts. The combination of donor irradiation plus cyclosporine did not delay the immune response, and the rejection score was similar to that observed for control allografts. Consequently, allograft viability was quickly impaired, leading to irreversible bone damage. This study suggest that 10 Gy of donor total body irradiation delivered six days prior to grafting cannot circumvent the immune rejection in a vascularized allograft of bone across a strong histocompatibility barrier.

Animals↗
PubMed1990

Study of growth kinetics and morphology in limbs transplanted between animals of different ages.

The influence of age and maturity on longitudinal skeletal growth was studied using heterotopic limb transplantation with microvascular anastomoses between syngeneic male Lewis rats of different ages. Longitudinal growth of the tibia and growth plate morphology were compared after transplantation between isochronografts (juvenile-to-juvenile and adult-to-adult), heterochronografts (juvenile-to-adult), and unoperated limbs. Four animals comprised each experimental group, except for the juvenile-to-adult heterochronograft group, which had six animals. Limbs were measured at 2-week intervals until sacrifice at 7 weeks. All transplanted limbs demonstrated significant longitudinal growth with maintenance of growth plate morphology and columnar organization. Despite being subjected to an adult hormonal environment, the juvenile tibias transplanted into adult hosts grew 12.0 +/- 1 mm--not significantly different from the unoperated juvenile controls, which grew 12.2 +/- 1 mm. Adult isochronografts showed continued growth of 3.1 mm, which was not significantly different from the unoperated control. Juvenile isochronografts demonstrated decreased growth when compared to unoperated limbs. Maintenance of growth in juvenile limbs transplanted to adults suggests a permissive effect of the hormonal milieu and that ultimate skeletal length is primarily determined by factors inherent in each physis. The use of vascularized transplantation of limbs in syngeneic animals of different ages offers a unique method of altering the hormonal and maturational milieu of the growth plate.

Age Factors↗
PubMed1990

The effects of different schedules of total-body irradiation in heterotopic vascularized bone transplantation. An experimental study in the Lewis rat.

To evaluate the effects of irradiation on heterotopically placed vascularized knee isografts, a single dose of 10 Gy of total-body irradiation was given to Lewis donor rats. Irradiation was delivered either 2 or 6 days prior to harvesting or subsequent transplantation, and evaluated at 1, 2, and 4 weeks after grafting. Irradiation caused endothelial depopulation of the graft artery, although vascular pedicle patency was maintained throughout the study. Bone graft viability and mineralization were normal. Dramatic changes in the bone marrow were seen that included an increase of its fat content (P less than 0.001), and a concomitant decrease in bone marrow-derived immunocompetent cells. These changes were more prominent in recipients of grafts from day -6 irradiated donor rats. Total-body irradiation did not prejudice the use of vascularized bone grafts, and exhibited an associated immunosuppresant effect over the vascular endothelium and bone marrow. This may be a further rational conditioning procedure to avoid recipient manipulation in vascularized bone allotransplantation.

Animals↗
PubMed1989

Quantitative histologic study of the influence of spinal instrumentation on lumbar fusions: a canine model.

UNLABELLED: Histomorphometric and microradiographic studies were performed on 28 beagle hounds 1 year of age, followed up for 6 months after an L5-L6 anterior and posterior spinal destabilization procedure--Group I (n = 7), destabilized surgical controls; Group II (n = 7), posterolateral bone grafting after destabilization; Group III (n = 7), Harrington rod instrumentation and posterolateral bone grafting after destabilization; and Group IV (n = 7), Luque instrumentation, and bone grafting after destabilization. Six months postoperatively, device-related osteoporosis occurred in spines treated with spinal instrumentation. Within the L5 vertebral body the mean trabecular width was less for the two groups with instrumentation (Groups III and IV) compared with the two groups without instrumentation (Groups I and II) (p less than 0.001). The bone formation rate [mm3/(mm3 x year)] x 10(3), which is based on the mean distance between sequenced fluorochrome labels, for Group I (destabilized, nonfused, noninstrumented dogs) was more than twice that of the other three groups, which were all equivalent (p less than 0.05). CLINICAL RELEVANCE: Stress shielding, or more correctly, device-related osteoporosis, probably can occur within vertebrae in response to rigid spinal instrumentation. However, the overall mechanical properties of vertebrae underlying spinal instrumentation are probably not at increased risk of fracture because the increase in cross-sectional area of the vertebra and incorporated fusion mass more than compensate for the loss of volumetric bone density.

Animals↗
PubMed1989

Oxygen radical scavengers improve vascular patency and bone-muscle cell survival in an ischemic extremity replant model.

We examined the use of oxygen radical scavengers in preventing the no-reflow phenomenon and improving bone-muscle cell survival in an ischemic extremity replant model. A total of 70 Lewis rat modified hindlimb replants were performed after specific periods of cold ischemia and intraarterial perfusion with either superoxide dismutase and catalase, specific oxygen free-radical scavengers, or a control solution. Ischemic hindlimbs treated with superoxide dismutase and catalase showed a statistically significant (p less than 0.05) improvement in vascular patency after prolonged cold ischemia when compared to controls. Histologically, experimental extremities demonstrated greater osteoblast, osteocyte, and muscle cell survival in replanted hindlimbs with patent vascular anastomoses. The perfusion of severed limbs and digits and free vascularized tissue transfers with superoxide dismutase and catalase after a period of ischemia has already occurred may prolong the ischemic "time window" tolerated for successful tissue survival.

Animals↗
PubMed1988

Orthotopic knee grafts in rats: a model for growth plate transplantation.

A model for orthotopic whole knee transplantation in syngeneic Lewis rats is presented. The donor knee was isolated on the femoral vessels 1 cm superior and inferior to the knee joint. A minimal muscle cuff was left attached to ensure adequate circulation to the graft via the popliteal vessels. The graft was transplanted to the recipient animal and secured in an orthotopic position by two intramedullary Kirschner wires. The graft pedicle was anastomosed to the recipient's femoral vessels and the muscular elements sutured. Preliminary results are reported, and future implications on growth plate autograft transplantation are discussed.

Anastomosis, Surgical↗
PubMed1988

Preventing oxygen free-radical injury in ischemic revascularized bone grafts.

Superoxide radicals have been shown to play a role in the cellular injury of reperfused ischemic tissues. We examined the protective effect of superoxide dismutase (SOD), a superoxide radical scavenger, on the reperfusion injury of replanted vascularized bone grafts after 4- and 8-hour periods of ischemia in a rat model. Histologic, fluorochrome, and histomorphometric analyses showed no difference between 4-hour superoxide dismutase-treated and control grafts, with both groups appearing viable. Similar analyses of the 8-hour ischemic grafts revealed both a qualitative and statistically significant quantitative difference (p less than 0.001) between the superoxide dismutase-treated and control grafts in parameters related to viability. Our results indicated that the administration of superoxide dismutase to free vascularized grafts by means of intraarterial perfusion after prolonged periods of warm ischemia significantly enhances the survival of these grafts.

Animals↗
PubMed1987

Experimental vascularized bone allografting.

Presented here is a compendium of studies investigating the fate of vascularized bone allografts. The first set of experiments employ the posterior rib graft in two canine models. The rib-to-mandible model was used to evaluate the rejection phenomena of vascularized bone allografts in an outbred dog model. This ascertained the time course of rejection and histological characteristics of the grafts. Immunosuppression of the graft recipients was attempted with azathioprine and cyclosporine. The results demonstrated that azathioprine was not an effective immunosuppressant, whereas cyclosporine resulted in survival of cortical osteons. The use of the vascularized rib allograft, with and without azathioprine, to bridge the defect in the dog femur was met with failure. Further studies employed a genetically defined rat model to determine the effect of different histocompatibilities on the survival of vascularized knee allografts. Grafts were transplanted from Lewis rats to syngeneic Lewis rats as isografts and to Fischer-344 rats (F-344) and Brown-Norway rats (BN) as allografts. Grafts across a major histocompatibility barrier to BN were rejected by 7 days, whereas grafts across a weak histocompatibility barrier to F-344 were rejected more slowly. The use of cyclosporine in this model abrogated the rejection response when administered to both groups continuously. However, a short course of cyclosporine was effective in preventing rejection in the F-344 animals. Efforts to induce tolerance by blood transfusions, from the donor strain or from a third-party donor, were not effective in preventing rejection.

Animals↗
PubMed1987

Prolonging survival in vascularized bone allograft transplantation: developing specific immune unresponsiveness.

Vascularized bone allografts (VBAs) could be useful adjuncts to the clinical reconstructive surgeon's arsenal. These grafts are known experimentally to be subject to host rejection. One way to control the rejection problem would be to develop specific immune unresponsiveness via host conditioning. Using a proven reliable model in inbred rats for studying heterotopic VBA transplantation, recipient animals were conditioned preoperatively with third-party unrelated blood, donor-specific blood (DSB) alone and with cyclosporine, and ultraviolet irradiated donor-specific blood. The combination of DSB plus cyclosporine delayed rejection of grafts across a strong histocompatibility barrier for three to four weeks. However, rejection was delayed across a weak histocompatibility barrier for five to six weeks using this same host pretreatment. The implications are that specific immunosuppression, although possible, is difficult to achieve in VBA transplantation, and that such techniques will rely on tissue-matching to minimize the genetic disparity between graft and host.

Animals↗
PubMed1987

The role of cyclosporin in prolonging survival in vascularized bone allografts.

It is known that experimental vascularized bone allografts are subject to host rejection. To be useful clinically, this rejection response would need to be controlled. Cyclosporin is a potent immunosuppressant whose precise role in vascularized bone allograft transplantation has not been established. Using a proven reliable vascularized knee allograft model in inbred rats, cyclosporin was used postoperatively both continuously and short term (14 days after transplant) at 10 mg/kg per day as recipient treatment. Across a strong histocompatibility barrier, continuous cyclosporin was required for long-term graft survival. Short-term therapy delayed rejection for 4 to 6 weeks. However, across a weak histocompatibility barrier, short-term therapy was as effective as continuous therapy in achieving long-term graft survival. The implication is that a limited course of cyclosporin may be clinically successful in sustaining vascularized bone allograft survival, provided the genetic disparity between graft and host has been minimized by genetic matching techniques.

Animals↗
PubMed1987

Histological characteristics of acute rejection in vascularized allografts of bone.

Using a genetically defined rat model for the heterotopic transplantation of a vascularized knee in the rat, histological and histochemical studies of acute rejection in vascularized allografts of bone were carried out. The graft consisted of the knee joint with the distal end of the femur, the proximal part of the tibia, the cartilaginous growth plates, the articular cartilage, and a minimum cuff of muscle, which was transferred to a location under the abdominal skin. A total of 160 transplants, including vascularized and non-vascularized isografts, vascularized and non-vascularized allografts that were transplanted across a strong histocompatibility barrier, and vascularized allografts of bone that were transplanted across a weak histocompatibility barrier, were studied by light microscopy at intervals for as long as twelve weeks after transplantation. Vascularized allografts of bone that were transplanted across a strong histocompatibility barrier showed evidence of rapid rejection, similar to that after transplantation of allografts of visceral organs. This was manifested at one week by necrosis of osteocytes, cessation of microcirculatory flow, massive extravasation of red cells, and deposition of fibrin in the marrow. The large vessels demonstrated changes that were characteristic of vascular rejection. Allografts that were transplanted across a weak histocompatibility barrier showed a more gradual, less intense process of rejection that allowed observation of the evolution of the process. In these grafts, the osteoblasts and marrow in the primary spongiosa of the metaphysis were early targets of rejection, as indicated by necrosis of osteoblasts, extravasation of red blood cells, and deposition of fibrin in the marrow spaces. Loss of osteoblasts from the surfaces of osteoid as well as from bone on spicules of calcified cartilage resulted in the cessation of new-bone formation. Calcification of the longitudinal septa between the lowermost hypertrophic chondrocytes was decreased. However, the proliferation and maturation of chondrocytes in the zone of proliferating chondrocytes and in the upper hypertrophic zone continued and resulted in the formation of a thickened growth plate. The loss of osteocytes in other areas of the graft occurred later and only in the areas where the microcirculation had been lost. These data suggest that ischemic damage, which is probably secondary to an immune-related vascular compromise, is a significant factor in the failure of grafts. In the grafts that were transplanted across a weak histocompatibility barrier, the growth of new bone and revascularization by the host occurred by twelve weeks.

Animals↗
PubMed1986

Heterotopic microvascular growth plate transplantation of the proximal fibula: an experimental canine model.

The reconstructive potential of microvascular transplantation of skeletal growth plates was investigated through heterotopic transfers. The distal radius was resected in two series of puppies of a known large breed and substituted with a microsurgically revascularized transplant from the proximal fibula. Evaluation was conducted through serial roentgenograms, goniometric registration of joint mobility, volume measurements, histology, and fluorescent bone labeling. In the first series, development of neuropathic-like destruction of the weight-bearing graft ensued in the majority of the animals. In the second series, prolonged protection from weight bearing inhibited this destruction and resulted in hypertrophy of the revascularized epiphyseal end of the transplant but clearly reduced longitudinal growth, with only one transplant exhibiting longitudinal growth that exceeded 50 percent of the value for the control. This experiment demonstrates that skeletal growth plates possess a capacity for hypertrophy under the influence of increased loads. Whether this adaptability is sufficient to allow microvascular transplantation of growth plates to become a clinically useful procedure in children remains unclear. Further laboratory investigations are mandatory prior to clinical application of microvascular transfers of epiphyseal growth plates.

Animals↗
PubMed1985

Short-term response of a skeletal growth plate to heterotopic microvascular transfer.

The capacity of the epiphyseal growth cartilage from the dog fibula to retain its growth potential after heterotopic transfer to a distal radial defect was investigated and compared to orthotopically transferred controls. Autoradiographs of the physes cultured in 3H-thymidine indicated continued proliferation of the growth cartilage in all revascularized transfers at the time of death, six weeks postoperatively. However, the nonvascular orthotopic controls did not incorporate the radioactive label. Fluorescent bone labels were incorporated in parallel bands in the metaphyseal bone, demonstrating linear bone growth in the revascularized transfers. Additional evidence for the viability of the transferred growth cartilage was obtained with histologic sections stained with hematoxylin and eosin and safranin-O. Roentgenograms and volume measurements showed a tendency toward hypertrophy of the heterotopic transfers.

Animals↗