Biomedical subjects

J T Bronk

Publications and source records attributed to J T Bronk.

16 recordsLinked to original sources

PubMed1996

Ultrasound-mediated transfection of mammalian cells.

Mammalian cells were successfully transfected with plasmid DNA in vitro using ultrasound transmitted through the walls of cell culture flasks or plates. Primary rat fibroblasts or chondrocytes were exposed to ultrasound in the presence of plasmids containing lacZ or neo genes. The transfection efficiency was evaluated by counting the number of beta-galactosidase (beta-Gal) positive cells or neomycin-resistant colonies. Transfection efficiency was optimized by varying ultrasound conditions, ambient temperatures (room temperature or 37 degrees C), plasmid concentrations, and initial cell populations. Additional experiments were performed performed to elucidate the mechanism of the ultrasound-mediated transfection. Maximal gene transfection was seen with two ultrasound conditions: 1-MHz carrier frequency 411 +/- 189 kPascal continuous wave with 20 or 30 sec of exposure time, and 1 MHz carrier frequency 319 +/- 157 kPascal continuous wave with 40 or 60 sec of exposure time. Gene expression was negligible when transfection procedures were performed at room temperature. The average stable transfection rate was 0.34% of surviving cells with a plasmid concentration of 40 micrograms/ml in primary fibroblasts. The transient transfection rate was 2.4% of surviving cells for primary chondrocytes. Data suggest that increasing plasmid concentration will increase efficiency. Identical treatment with 3.5 MHz produced no transfection, implying that cavitation produced by the ultrasound pressure wave appeared to play a critical role in mediating transfection. Ultrasound-mediated transfection was effective for suspended cells as well as for plated cells. This transfection method is simple, easy to keep sterile, and convenient. Ultrasound-mediated transfection appears to be a promising method for gene transfer into mammalian cells.

Animals↗

PubMed1996

Insulin treatment of corticosteroid-associated hyperglycemia and its effect on outcome after forebrain ischemia in rats.

BACKGROUND: Recent studies have reported that dexamethasone worsens neuronal injury after brain ischemia. This effect is assumed to be secondary to drug-induced hyperglycemia. The current study used a rat model to test the hypotheses that insulin treatment of dexamethasone-induced hyperglycemia would result in a postischemic neurologic outcome that is: (1) better than that of hyperglycemic, dexamethasone-treated subjects; and (2) better than, or equal to, that of saline-treated control subjects. METHODS: Twenty-four halothane-anesthetized (1.0% inspired) rats were randomly assigned to one of three treatment groups (N = 8 in each group): (1) normoglycemic, placebo-treated rats (group P) received an intravenous saline infusion; (2) hyperglycemic, dexamethasone-treated rats (group D) received 2 mg/kg intraperitoneal dexamethasone at days, 1 day, and h before ischemia plus an intravenous saline infusion; and (3) normoglycemic, dexamethasone- and insulin-treated rats (group DI) received the same treatment as group D, plus an intravenous insulin infusion shortly before ischemia. Blood gases and acid-base status were maintained within normal physiologic ranges. Pericranial and rectal temperatures were maintained at normothermia. Forebrain ischemia of 10 min duration was produced using an established model. Neurologic function was assessed by a blinded observer at 24 and 48 h postischemia. Brain histopathology was assessed at the time of ischemia-related death or after the examination at 48 h. All 24 rats were included in the analysis of neurologic function; however, only 21 rats that survived for > or = 24h post-ischemia were included in the histologic analysis. RESULTS: Rats were well matched for systemic physiologic variables, with the exception of glucose concentrations. Plasma glucose concentration immediately before ischemia was as follows: group P = 129 +/- 8 mg/dl (mean +/- SD), group D= 344 +/- 29 mg/dl, and group DI = 123 +/- 17 mg/dl. At 48h postischemia, groups P and DI were minimally injured and had similar functional scores. In contrast, all group D rats died of cerebral ischemia. Histologic injury was significantly worse in group D than in either group P or DI, but did not differ significantly between groups P and DI. When all groups were combined, there was a significant correlation between neurologic function and total histopathology score ranks. CONCLUSIONS: In the current study, dexamethasone administration before brain ischemia resulted in a worsening of postischemic outcome that was relate to drug-induced hyperglycemia. Restoration of normoglycemia, using insulin, resulted in a functional outcome similar to that in group P, and an attenuation of dexamethasone-associated histologic injury.

Animals↗

PubMed1996

Inflatable brace-related streaming potentials in living canine tibias.

In a canine osteotomy model, application of a pressurized brace increased the density of periosteal bone and, at 12 weeks postfracture, yielded a stronger union compared with fractures treated by conventional cast, as determined by biomechanical testing. Pulsatile transcortical electric potentials were caused by the fluctuations in intramedullary pressure that result from active circulation. This report describes a collaborative effort designed to determine whether pressure fluctuations within an inflatable brace, placed over a canine calf, can affect endogenous transcortical electric potentials. Pressure within a brace placed over a canine hindlimb was observed to oscillate between 20 and 52 mm Hg during normal ambulation in 3 dogs. Manual pulsatile inflation of a similar brace, causing brace pressure fluctuations between 12 mm Hg and 130 mm Hg, produced fluctuating transcortical electric potentials ranging from 1.2 microvolts to 87 microvolts in anesthetized canines. These electric potentials were proportional to intramedullary pressures between 3.4 mm Hg and 59 mm Hg. Transcortical electric potentials resulting from the application of a pressurized brace, rather than conventional casting, may be part of the mechanism by which the changes in fracture healing are achieved.

Animals↗

PubMed1995

Reperfusion injury in vascularized bone allografts.

A vascularized allograft canine tibia was used to evaluate the preservation of the osseous microcirculation. Six pairs of adult tibiae were harvested, and a vascular washout was performed with mannitol solution. The bones then were perfused continuously (0.03 ml/min at 5 degrees C) for 20 hours with University of Wisconsin solution. Following storage, each pair of bones was transplanted, by microvascular anastomosis, to a recipient dog, and bone blood flow was estimated using the radiolabeled microsphere method. Adrenoreceptor control mechanisms were evaluated in one specimen, and endothelial function was evaluated in the contralateral specimen. Alpha 1-adrenoreceptor blockade produced a significant increase (89 +/- 80%) in bone blood flow (p < 0.05). A further increase (99 +/- 56%) was observed with the addition of alpha 2-blockade (p < 0.01). Acetylcholine produced a decrease (65 +/- 65%) in blood flow (p < 0.01). This effect was inhibited by L-NG-monomethyl-arginine, which resulted in an increase (53 +/- 47%) in bone blood flow (p < 0.05). The no-reflow phenomenon was observed in two vascularized allografts. These results demonstrate that smooth muscle adrenoreceptors were preserved successfully for 24 hours. In contrast, endothelial function was abnormal. There was no evidence that the endothelium was producing endothelium-derived relaxing factor, and the results suggest that an endothelium-derived constricting factor dependent on L-arginine was produced during reperfusion. It is concluded that University of Wisconsin solution does not preserve normal endothelial function in the microcirculation of bone.

Anastomosis, Surgical↗

PubMed1994

Experimental study of the effect of weight bearing on fracture healing in the canine tibia.

The authors compared the effects of decreased loading, increased loading, and baseline loading on the early (six weeks) and intermediate (12 weeks) healing of tibial fractures treated with an external fixator in adult dogs. The different loading conditions were verified by gait studies. Periosteal bone in the increased-loading fracture site was significantly increased compared with the decreased-loading site at both time intervals, and with the baseline-loading site at six weeks. The mechanical variables of energy absorption and angle of rotation at six weeks were significantly increased in the increased-loading fracture site compared with the decreased-loading site and baseline-loading site. Blood flow to the increased-loading fracture site was significantly higher than that to the decreased-loading fracture site at six weeks. Five dogs were studied at 12 weeks to compare the effects of decreased loading to increased loading. The increased-loading fracture showed significantly increased rotation, torque, and energy absorption to failure. Blood flow was not measured in the 12-week animals.

Animals↗

PubMed1993

The relationship of increased capillary filtration and bone formation.

The effect of functional activity on bone formation and interstitial fluid space in a standardized tibial defect was measured in 19 dogs with one hind limb elevated and the other weight bearing and in 15 dogs bearing weight on all four legs. The interstitial fluid space (V(isf)) of the woven bone of the weight-bearing defect was larger than that in the elevated legs at seven and 14 days. By 28 days, this difference disappeared. In a third group of six dogs, medullary canal pressure was measured in the immobilized and weight-bearing tibias. The pressures were higher in the weight-bearing tibiae at two, three, four, and five days. Because the increase in V(isf) in the weight-bearing defects coincided with the onset of woven bone formation in the defects and an increase in medullary canal pressure, an increase in venous pressure could increase capillary pressure and capillary filtration. Such an increase in filtration might cause the larger V(isf) in the weight-bearing defects and better capillary perfusion of precursor cells of the osteoblast. A hypothesis is that increased fluid flow from increased capillary filtration might produce streaming potentials, a possible signal for increased cellular activity.

Animals↗

PubMed1993

A new concept in fracture immobilization. The application of a pressurized brace.

Sixteen dogs and 14 anatomic tibiae were studied to determine the effect of a pressurized brace on a canine tibial fracture model. Bilateral tibial fractures were treated with an external fixator for 48 days. At 48 days, the pressurized brace was applied to one tibia, and a conventional cast was applied to the opposite tibia. The dogs were allowed unrestricted weight bearing until 88 days. Postmortem biomechanical studies indicated that tibiae were stronger on the side treated by the pressurized brace. This was reflected in torque values, energy, and degrees of rotation. The histomorphometry of the periosteal bone of the fracture sites disclosed a more dense periosteal callus on the side treated with a pressurized brace. In vitro mechanical studies in cadaveric tibias at 30 degrees rotation indicated that the pressurized brace provided significantly more stability.

Animals↗

PubMed1990

Effect of fracture fixation on cortical bone blood flow.

Because internal and external fixation devices alter blood flow, and thus the transport of nutrients to the cortical bone of a healing fracture, we studied the effects of a fluted intramedullary rod (IMR), a half-frame external fixator (EF), and a compression plate (PL) on the cortical bone directly adjacent to the fracture site at 4 and 48 h and 14 and 90 days after fixation. Three specific areas of cortical bone were studied: endosteal cortex, periosteal cortex, and subplate cortex (cortical bone under the compression plate). The fractures fixed with IMR had the lowest blood flow at all time periods studied. At 4 h, the difference between IMR and PL or EF was statistically significant in the endosteal cortex (p less than 0.01 or p less than 0.05, respectively); also, the difference between the IMR and EF in the subplate cortical bone region was significant (p less than 0.05). At 14 days, the blood flow to the endosteal cortex was still significantly lower with IMR than with EF (p less than 0.025). At 90 days, the blood flow to the subplate region of cortical bone was significantly (p less than 0.02) higher with PL than with IMR but there was no significant difference in bone remodeling with the different fixation devices.

Animals↗

PubMed1990

Venous pressure and bone formation.

We have studied the relationship of increased venous pressure to formation of periosteal new bone in growing dogs. The methods used were measurement of fluid spaces in bone by steady-state tracer techniques, measurement of venous pressure, and measurement of the rate of periosteal new bone formation by histomorphometry. The results of paired comparisons--test versus control tibia--show an increase in venous pressure, a decrease in vascular space, an increase in extracellular fluid space (sucrose space), and an increase in periosteal new bone formation on the side of increased venous pressure. The data support the hypothesis that an increase in venous pressure results in an increase in passage of fluid from capillary to bone matrix. Increased extravascular perfusion could be a factor in increasing periosteal bone formation. This flux of fluid may increase streaming potentials in bone and these act as a signal to bone cells to increase bone formation.

Animals↗

PubMed1990

Reaction of the circulatory system to injury and regeneration.

The anatomy of the bone blood supply is well known. Techniques to measure bone blood flow are available, but no accurate method is available for clinical use. Ion movement from the capillary to the matrix is by diffusion, and efflux appears to be controlled by a concentration-dependent binding mechanism in the extravascular space of bone. The resistance vessels of bone are regulated by local, neural, and humoral factors. Fractures of long bone provoke a decrease in blood flow followed by a large increase in blood flow driven by metabolic demand. Fractures heal by coordinated formation of new bone, which is a combination of interstitial and surface remodeling. Age affects bone remodeling. Fixation of an experimental fracture may modify blood flow as well as bone remodeling. Fluid fluxes in bone may produce streaming potentials that in turn stimulate the osteoblasts to form new bone.

Animals↗

PubMed1990

Effect of weight-bearing on healing of cortical defects in the canine tibia.

UNLABELLED: It has been generally accepted that mechanical stimulation is an important factor in the promotion of formation of bone. Fracture-healing consists of periosteal bridging of the fracture, which achieves stability, and proliferation of endosteal bone to fill the defects between the ends of the bone. To evaluate the effect of weight-bearing on bone-healing, an operatively created defect in the tibial cortex was chosen as an experimental model. In one set of dogs (Group 1), a bilateral defect in the tibial cortex was created and weight-bearing was permitted on one tibia but not on the opposite one. In Group 2, a bilateral defect in the tibial cortex was made and weight-bearing was allowed on both tibiae. A third group of dogs of similar age (Group 3) had no tibial defects. Quantitative histomorphometry was used to measure formation and porosity of bone. Weight-bearing was measured with both static and dynamic techniques. Significantly less woven bone formed in the defects in the non-weight-bearing tibiae than in the weight-bearing tibiae. This appeared to be due to a disuse response in the underloaded tibiae, in which less bone formed, rather than to the formation of more bone in the weight-bearing tibiae. The data suggest that weight-bearing is a permissive factor, not a stimulus, for formation of woven bone in a tibial defect. CLINICAL RELEVANCE: This animal model supports the concept that lack of weight-bearing decreases the amount of woven bone that is formed in a healing tibial defect. The results of this study indicate that weight-bearing increases the formation of bone in fracture-healing.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Canine bone blood flow estimated with microspheres.

Blood flow rate in the periosteal and endosteal cortices of the diaphysis of long bones was determined in eight anesthetized adult dogs using the radioactively labeled microsphere method. The flow rate in endosteal and periosteal cortices is not significantly different unless the endosteal cortex contains cancellous bone from the medullary cavity. The highest flow rate is in the ulna, with 6.50 ml/min/100 g for the endosteal cortex and 5.15 ml/min/100 g for the periosteal cortex. The lowest flow rate is in the femur, with 2.89 ml/min/100 g for the endosteal cortex and 2.29 ml/min/100 g for the periosteal cortex. The results of this study indicate that variation of blood flow does exist between bones of dogs. However, the flow rates of individual bone on the left and right sides in the same dog are not significantly different. This indicates that the data are reproducible and reliable, and differences are not an inaccuracy of the radioactively labeled microsphere method. The results also demonstrate that there are no significant differences in bone blood flow as measured with small numbers (fewer than 400 microspheres per sample) and large numbers (more than 400 microspheres per sample) of microspheres. The adequate number of microspheres in each bone sample is 150-250. Therefore, a dose of 0.5 x 10(6) spheres/kg body weight can be sufficient.

Animals↗

PubMed1988

Interstitial fluid flow in cortical bone.

After injection of ferritin into the tibial nutrient artery of adult dogs, ferritin was seen in the interstitial fluid compartment of the tibial cortex immediately and up to 25 min after injection. The pattern of movement was consistent with bulk interstitial fluid flow influenced by hydrostatic pressure. In osteons sectioned transversely, evidence was seen of centrifugal movement of ferritin in a halo pattern around the central capillary. Haloes in the superficial part of the cortex coalesced to form a ferritin front which moved toward the periosteal surface. Movement of ferritin was delayed by appositional bone of the periosteal surface. Ferritin was seen in channels in the matrix and perivascular spaces termed "matrix prelymphatics" and "perivascular prelymphatics," respectively, because they lacked an endothelial lining.

Animals↗

PubMed1988

Cortical and cancellous bone: age-related changes in morphologic features, fluid spaces, and calcium homeostasis in dogs.

The changes in cortical and cancellous bone that occur with aging were studied by measuring morphologic and physiologic variables for both types of bone in dogs. The percentage area of cortical and cancellous bone, rate of bone formation, vascular volume, bone water, and volume of distribution of calcium tracer all showed statistically significant changes at the time of bone maturity. Canine cortical bone cell volume progressively decreased with advancing age, and cancellous bone cell volume significantly decreased between adult and old dogs. The volume of distribution technique can be used to determine the relative contributions of cortical and cancellous bone to the total body exchangeable calcium ion pool.

Aging↗

PubMed1988

Parathyroid hormone effects on skeletal exchangeable calcium and bone blood flow.

The effects of alterations in serum calcium levels on the volume of distribution of a calcium tracer in bone and on bone blood flow were investigated in dogs by manipulation of parathyroid status. The volume of distribution increases with increasing serum calcium. This implies that there is a concentration-dependent binding mechanism in the extravascular space of bone, which is not saturated at the levels of serum calcium achieved in these experiments. The skeletal exchangeable calcium was increased in hypercalcemic dogs and decreased in hypocalcemic dogs. Cancellous bone contains proportionately more exchangeable calcium than cortical bone. Bone blood flow was decreased by 50% 15 min after injection of a bolus of parathyroid hormone (PTH) but returned to control values by 240 min. Fifty-two hours after the induction of hypercalcemia with repeated doses of PTH, there was no difference in blood flow over control animals.

Animals↗

PubMed1987

Permeability of cortical bone of canine tibiae.

Movement of interstitial fluid in cortical bone is considered one of the important mechanisms affecting bone remodeling and fracture healing. To better understand such interstitial fluid movement, the hydrostatic permeability of cortical bone of the canine tibia was measured in this study. It was found that age has significant influence on permeability. The cortical bone permeability of puppy tibiae is six times higher than that of adult tibiae. Adult tibial cortex is impermeable unless the superficial layer of the periosteal cortex is removed. The permeability differs between regions and locations of the tibia. The pathways for such extravascular interstitial fluid movement were also identified to be primarily the haversian and Volkmann's canals and secondarily the canalicular and lacunar spaces. The high permeability of their cortical bone may explain the increase in periosteal new bone formation seen in puppies when a venous tourniquet is applied.

Aging↗