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Biomedical subjects

J H Barker

Publications and source records attributed to J H Barker.

At least 91 records · Page 5Linked to original sources
PubMed1995

Differential expression of two barley SNF1-related protein kinase genes.

We have amplified and cloned DNA sequences derived from a gene encoding a SNF1 (sucrose-non-fermenting 1)-related protein kinase which differs from that previously reported from barley. Northern blot and polymerase chain reaction (PCR) analysis of RNA populations, using specific probes and oligonucleotide primers, indicated that the two SNF1-related genes are differentially regulated. One is expressed in all tissues, whereas the other is expressed at high levels in the seed endosperm and aleurone, but at levels undetectable by northern blot analysis in other tissues. Comparisons with other plant SNF1-related protein kinase genes suggest that the form which is expressed at greatly enhanced levels in the seed is less similar to the other plant homologues which have been reported and may be unique to cereals.

Amino Acid Sequence↗
PubMed1995

Induction of thrombosis in a mouse model by IgG, IgM and IgA immunoglobulins from patients with the antiphospholipid syndrome.

Antiphospholipid syndrome is a disorder of recurrent thrombosis and pregnancy losses associated with production of anticardiolipin antibodies and lupus anticoagulant positivity. Recently, we have adapted a mouse model of induced venous thrombosis to study the role of autoantibodies in thrombus formation. To determine whether immunoglobulins from patients with the antiphospholipid syndrome play a role in thrombosis, we injected groups of CDI mice either with immunoglobulins purified from seven patients with the antiphospholipid syndrome (nine preparations studied: four IgG, three IgM and two IgA) or with immunoglobulins of the same isotype from healthy controls. Seventy-two h after injection, a non-occlusive thrombus was induced in the femoral veins of experimental mice by a pinch injury; the thrombus areas as well as times of formation and disappearance of the thrombi were measured. Eight of the nine antiphospholipid syndrome immunoglobulin preparations caused a significant increase in mean thrombus area and a significant delay in mean thrombus disappearance time as compared with normal controls. To determine whether anticardiolipin antibodies might be involved, separate groups of mice were injected with affinity-purified IgG (n = 2) or IgM (n = 2) anticardiolipin antibodies or with normal immunoglobulins of the same isotype, and the effects on thrombus formation compared. Mean thrombus area and mean disappearance times were again significantly increased in all four groups injected with affinity-purified antibodies. This is the first study to show that anticardiolipin antibodies of IgG, IgM and IgA isotypes may play a role in thrombosis in vivo.

Animals↗
PubMed1994

Microcirculation research, angiogenesis, and microsurgery.

Angiogenesis, the formation of new blood vessels, is essential to a variety of normal and pathologic processes such as wound healing and tumor growth. In microsurgery the development of new vessels between the transferred tissue and the recipient bed is critical to the final outcome of the reconstruction. Several experimental models have been previously developed to study angiogenesis and the effect that new substances have on regulating this process, but they lack the ability to make quantitative measurements. Therefore, we have developed an animal model using the homozygous (hr/hr) hairless mouse ear; by using intravital microscopy and computer-assisted analysis, angiogenesis can be quantitatively measured. Using this model we showed that basic fibroblast growth factor and transforming growth factor beta significantly increased total vessel length by 32% and 63%, respectively, during 20 days following subcutaneous injection. In this paper the importance of angiogenesis research to reconstructive microsurgery is presented and discussed.

Animals↗
PubMed1994

Microcirculatory consequences of microvascular surgery.

Although free tissue transfer success has been greatly improved by developments in operating microscopes, microsutures, microinstruments, and technique, free flap and replant failure remain a significant problem under certain adverse circumstances. The nature of these failures is often multifactorial and remains poorly understood. A greater understanding of the processes involved would provide the potential for greater pharmacological control of any adverse conditions prevailing and would thus offer the prospect of more effective adjunctive therapy in the presence of such adverse conditions. Research endeavors in this area have been hindered by the absence of good research models. The isolated rat cremaster muscle model is a recently developed model that simulates the conditions of free tissue transfer. Using this model, both thrombus formation and numerous microcirculatory parameters can be measured. The microcirculatory parameters studied to date include the formation of thromboembolism, capillary perfusion, vessel diameters, red blood cell velocity, leukocyte-endothelium interaction, and microvascular leakage. The isolated rat cremaster muscle model addresses many of the shortcomings of earlier research models and offers the promise of answering at least some of the many unanswered questions relating to free flap and replant failure.

Animals↗
PubMed1994

Direct visualization and measurement of microsurgically induced thromboembolism.

A common cause of free flap and replant failure is thrombotic occlusion of the anastomosed pedicle vessel(s). Clinical observations and subsequent experimental studies showed that platelet emboli generated at the arterial anastomosis caused significant alterations in the downstream microcirculation. To study both the thrombogenic arterial (anastomosis) site and the downstream microcirculation, we developed an animal model (the isolated rat cremaster) in which we could directly view and quantitatively analyze thrombus formation and the appearance of emboli in the downstream microcirculation. Using this model we studied the effect that reducing blood flow across the arterial anastomotic site had on thrombus formation at the anastomotic site and the appearance of emboli in the downstream microcirculation. In 40 male Sprague-Dawley rats we found that reducing blood flow velocity to approximately half of normal during reperfusion nearly eliminated emboli appearing in the downstream microcirculation compared with controls, 43.9 +/- 31.5 vs. 259.5 +/- 117.8 emboli, respectively. We also found that the same low flow had no effect on thrombus size at the pedicle artery injury site yet significantly decreased the rate at which thrombus formation occurred (time to maximum thrombus size; low flow = 25.3 +/- 8 minutes, normal flow = 6.6 +/- 3 minutes). From these studies we conclude that reducing pedicle artery blood flow in our rat model during reperfusion can protect the down-stream microcirculation from platelet emboli-induced injury; however, the same reduction in flow does not affect thrombus formation in the pedicle artery. Further studies using direct observation/measurement techniques are needed for a better understanding of the mechanisms regulating free flap and replant failure.

Anastomosis, Surgical↗
PubMed1994

Opportunities for manipulating the seed protein composition of wheat and barley in order to improve quality.

Wheat and barley are the major temperate cereals, being used for food, feed and industrial raw material. However, in all cases the quality may be limited by the amount, composition and properties of the grain storage proteins. We describe how a combination of biochemical and molecular studies has led to an understanding of the molecular basis for breadmaking quality in wheat and feed quality in barley, and also provided genes encoding key proteins that determine quality. The control of expression of these genes has been studied in transgenic tobacco plants and by transient expression in cereal protoplasts, providing the basis for the production of transgenic cereals with improved quality characteristics.

Amino Acid Sequence↗
PubMed1994

Improvement of skin flap perfusion by subdermal injection of recombinant human basic fibroblast growth factor.

The effect of subcutaneously injected recombinant human basic fibroblast growth factor (bFGF) was studied in an arterial skin flap model on the ear of the hairless mouse. Fifty-three male, hairless mice were randomly assigned to 4 groups and pretreated in two different time intervals with different doses of human bFGF. Microvascular perfusion of the skin flaps was determined over a 5-day period by means of intravital microscopy after intravenous injection of the fluorescence marker fluorescein isothiocyanate-dextran (M(r) 150,000). Human bFGF (2,700 ng) injected 6 days before flap creation could not improve perfusion of the flap (n = 10) when compared with controls. However, when applied 18 days before flap creation (n = 13), the same dose resulted in a significant reduction of nonperfused tissue at day 5 after flap creation (12.3% vs 26.8%, p < 0.01). Eighteen-day pretreatment with 1,200 ng (n = 10) and 480 ng (n = 10) had no significant effect on skin flap perfusion. We conclude, therefore, that successful pretreatment with bFGF for prevention of skin flap necrosis is time and dose dependent.

Animals↗
PubMed1994

Visualization of nutritive perfusion following tourniquet ischemia in arterial pattern skin flaps: effect of vasoactive medication.

We present an experimental model that makes it possible to investigate the effects of global ischemia and reperfusion on microvascular perfusion and viability of ill-proportioned (poorly designed) arterial pattern skin flaps in hairless mice. Skin flaps were created on the ears of hairless mice by dissecting two of three nutritional vessel bundles at the ear base. Under these nonischemic conditions, 19 percent of the total flap area went on to necrose (as a result of poor flap design). Global ischemia was induced to the flap tissue for 6 hours with a tourniquet clamp directly after flap incision. The extension of perfused tissue area and flap viability were assessed at the microcirculatory level by intravital video microscopy at 1, 3, 6, and 18 hours and 7 days after reperfusion in animals treated with either normal saline (control) or the vasoactive drug buflomedil hydrochloride (3 mg/kg of body weight per day, i.v., starting 4 hours prior to flap creation and continued at daily intervals until the end of the experiments). In untreated animals (n = 18), 1 hour after clamp release we observed reperfusion of 39.55 percent (38.5/44.9) of total flap area. Reperfusion remained unchanged within the following 5 hours. Within the next 12 hours, reperfused flap area was dramatically reduced to 21.9 percent (15.1/58.4). Seven days thereafter, only 18.8 percent (10.9/42.2) of total flap area remained viable. In contrast, we found in buflomedil-treated animals (n = 18) that 57.3 percent (53.5/62.9) of the total flap tissue was reperfused within the first hour after clamp release (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Comparison of the effects of commonly used wound agents on epithelialization and neovascularization.

BACKGROUND: The primary effect sought with most topical wound therapy is antimicrobial. Topical wound agents are thought to promote normal healing by protecting the wound from infection. In this study, we examined the effect of six commonly used topical wound agents (bacitracin, sodium hypochlorite, silver nitrate, silver sulfadiazine, mafenide acetate, and povidone-iodine) on epithelialization and neovascularization in noninfected wounds. For this study, a new wound model was used in which direct visualization and quantification of wound epithelialization and neovascularization were carried out throughout the entire healing process. STUDY DESIGN: We measured the effect which 500 U per g of bacitracin, 0.25 percent of sodium hypochlorite, 0.5 percent silver nitrate, 1 percent silver sulfadiazine, 8.5 percent mafenide acetate, and 10 percent povodione-iodine had on the rate of wound epithelialization and neovascularization. The agents were applied topically to 99 circular full-thickness wounds (2.25 mm diameter, 0.125 mm depth) created on the dorsum of male hairless mouse ears. This model enabled us to visualize and measure directly wound epithelialization and neovascularization repeatedly throughout healing, using intravital video microscopy and computerized digitized planimetry. RESULTS: Control wounds and wounds treated with silver sulfadiazine (n = 18) and mafenide acetate (n = 14) epithelialized in 7.2 +/- 0.7, 7.1 +/- 0.3, and 7.3 +/- 0.3 days, respectively. This was significantly (p < 0.01) faster than the wounds treated with povidone-iodine (n = 10), sodium hypochlorite, (n = 8), and bacitracin (n = 13). Wounds treated with povidone-iodine epithelialized the slowest (11.8 +/- 0.55 days). Wound neovascularization was completed most rapidly in the groups treated with povidone-iodine and silver sulfadiazine (15.0 +/- 0.4 and 15.3 +/- 0.7 days, respectively). This was significantly (p < 0.05) faster than wounds treated with silver nitrate (n = 15), which neovascularized in 18.4 +/- 0.56 days. One-half of the wounds treated with sodium hypochlorite (eight of 16) did not epithelialize or neovascularize. CONCLUSIONS: The various antimicrobial agents studied in our in vivo model affect wound epithelialization and neovascularization differently. These effects on these two very important aspects of healing should be taken into consideration when indicating a specific agent for treatment of different types of wounds.

Animals↗
PubMed1994

Effect of human IgG antiphospholipid antibodies on an in vivo thrombosis model in mice.

High levels of IgG antiphospholipid antibodies (aPL) have been associated with clinical thrombosis. It is uncertain however whether these antibodies play a direct role in thrombosis or are merely epiphenomena. To investigate whether antiphospholipid antibodies might play a role in thrombosis, we utilized a novel mouse model in which the dynamics of in vivo thrombosis can be studied. CD1 mice (26-30 g) were passively immunized with 25 mg of human IgG from a patient with the Antiphospholipid Syndrome (IgG-APS) (n = 17), IgG from normal pooled sera (IgG-NHS) (n = 9), or saline solution (n = 12), followed by 40 mg of the same preparations at 48 h. At 72 h, levels of human aPL antibodies, detected using the anticardiolipin ELISA test (aCL ELISA test), in mice immunized with IgG-APS, were 50-100 GPL units. Each animal was anesthetized, femoral vein minimally mobilized and subjected to a standardized "pinch" injury to induce thrombosis. The vessel was transilluminated using acrylic optical fibers connected to a light source, and clot formation and dissolution were visualized by a standard surgical microscope equipped with a video camera, video recorder, and computer assisted analysis system. Results showed that average clot size was significantly larger in mice immunized with IgG-APS compared to those treated with saline (p < 0.037). In addition, the thrombus persisted longer in a significantly higher number of mice immunized with IgG-APS (10/17) compared to mice immunized with IgG-NHS (1/9) or saline (2/12) (p < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Basic fibroblast growth factor accelerates wound healing in chronically ischaemic tissue.

The influence of subcutaneously injected recombinant human basic fibroblast growth factor (bFGF) on wound healing in normal (n = 20) and ischaemic (n = 28) skin tissue was investigated. Standardized wounds (5 mm2) were created on the ears of hairless mice and treated for the first 3 days after wound creation with total doses of 720 ng (n = 24) and 4050 ng (n = 24) bFGF. The bFGF had no effect on wound healing in non-ischaemic tissue. In ischaemic skin, mean(s.d.) wound surface area after treatment with 720 ng bFGF was 1.6(0.9), 0.5(0.6) and 0.1(0.3) mm2 compared with 2.8(1.0), 1.4(1.0) and 0.8(0.7) mm2 for control wounds on days 7 (P < 0.04), 10 (P < 0.03) and 13 (P < 0.04) respectively. High-dose bFGF (4050 ng) reduced the mean(s.d.) wound surface area to 2.4(0.7) and 0.8(0.7) mm2 compared with 3.9(0.6) and 2.1(0.8) mm2 for control wounds on days 7 (P < 0.006) and 10 (P < 0.02) respectively. These results suggest that bFGF may be of use for the treatment of wounds in ischaemic tissue.

Animals↗
PubMed1993

Experimental study of the relationship between alterations in tissue perfusion and anastomotic patency.

It is generally believed that alterations in perfusion which endanger a free flap or replant are directly related to thrombus formation and obstruction of blood flow at the anastomotic site. Recent experimental work in our laboratory suggests that the presence of platelet emboli downstream in the microcirculation might be responsible at least in part for postoperative perturbations in perfusion. To determine whether changes in tissue perfusion can occur in the absence of corresponding changes in anastomotic patency we studied microvascular blood flow in the exposed rat cremaster flap model. We made continuous measurements of both anastomotic patency and downstream microcirculatory perfusion following small vessel repair. Using this approach we found that during one hour after clamp release and reperfusion in the 10 animals studied, pedicle artery blood pressure, which indicates pedicle patency in this model, was functionally normal 97% +/- 2 of the time while blood flow in the downstream tissue (cremaster) remained normal an average of only 65% +/- 7 of the time. In most cases these flow alterations were associated with the presence of visible platelet emboli in the microcirculation. From these studies we conclude that when flap perfusion failure temporarily occurs, a microsurgeon must consider not only the anastomosis but also the downstream microcirculation when searching for a possible cause.

Anastomosis, Surgical↗
PubMed1993

The effects of heparin and dietary fish oil on embolic events and the microcirculation downstream from a small-artery repair.

In recent studies we demonstrated that platelet emboli induced by arterial injury impair the microcirculation. The present study was performed to determine if heparin or dietary cod liver oil reduces the incidence of emboli following the same arterial injury and, in turn, whether these agents prevent the associated decrease in microcirculatory blood flow. The cremaster muscle of 29 male Sprague-Dawley rats was isolated on a single neurovascular bundle consisting of the iliac artery and vein and the genitofemoral nerve. Emboli were generated by a thrombogenic injury of the iliac artery, and their number and their subsequent effect on capillary perfusion in the downstream microcirculation were measured. Nine animals received heparin (10-unit IV bolus plus 10 units/hour IV infusion), 10 were fed cod liver oil (10 percent by weight of food) for 3 weeks prior to the experiment, and 9 animals receiving no treatment served as controls. The number of emboli was significantly reduced in the heparin group, but there was no accompanying improvement in capillary perfusion. In contrast, in the cod liver oil group, the number of emboli was not reduced, but there was significant improvement in capillary perfusion. These findings suggest that the harmful effect that platelet emboli have on the microcirculation is probably biochemical in nature (vasoconstriction) rather than related to simple mechanical obstruction to flow.

Anastomosis, Surgical↗
PubMed1992

Capillary blood perfusion during postischemic reperfusion in striated muscle.

Monitoring of nutritive blood flow in muscle is of particular importance to reconstructive surgeons, since ischemia/reperfusion in striated muscle is known to result in postischemic microvascular perfusion failure. Laser Doppler flowmetry has recently been introduced as an easy-to-use, noninvasive technique for continuous monitoring of microvascular tissue perfusion. Despite its popularity, there exists a great deal of controversy as to what actually generates the laser Doppler signal recorded from a given tissue. Intravital microscopy is a technique for direct visualization of the nutritional circulation in tissue. By using intravital microscopy, direct measurements of blood perfusion in individual segments of the nutritional microcirculation can be made. In 22 Syrian golden hamsters we performed laser Doppler flowmetry and intravital microscopy measurements in muscle tissue prior to and during reperfusion after 4 hours of tourniquet ischemia using the dorsal skinfold chamber model. Intravital microscopy (n = 10) revealed a heterogeneous capillary perfusion during the early reperfusion phase with a decrease (p less than 0.01) in functional capillary density to 49.4 +/- 17.0 percent of control. No recovery was observed after 24 hours of reperfusion. Laser Doppler flowmetry (n = 12) showed a parallel reduction of capillary red blood cell flux during the early perfusion phase to 43.9 +/- 22.6 percent of control values (p less than 0.01), and no recovery was observed after 24 hours of reperfusion. However, the laser Doppler flowmetry technique was not able to detect the capillary perfusion inhomogeneities shown by intravital microscopy. Postischemic reperfusion in striated muscle is characterized by a decrease in functional capillary density and a heterogeneous capillary perfusion. Laser Doppler flowmetry is a useful tool for monitoring microvascular tissue perfusion, although in striated muscle of the hamster it must be considered that accurate nutritional "capillary" flow readings can be grossly overestimated if larger vessels, such as arterioles and collecting venules, are contained in the measuring field of the laser Doppler probe.

Animals↗
PubMed1992

Thrombosis and antithrombotic therapy in microvascular surgery.

Thrombosis in microsurgery can either totally or partially reduce the perfusion to the free tissue transfer. Total occlusion normally occurs at or near the microvascular anastomosis, while microscopic vasospasm in the distal microcirculation can account for malperfusion and wound healing problems. The mechanisms of the anastomotic and microcirculatory responses to thrombosis are discussed. Drug therapy for each risk zone is identified, and a rationale for therapy is given.

Aspirin↗
PubMed1992

[Use of vasoactive substances in prevention of skin necroses].

The nutritional blood flow to the tissue is the principle factor determining the outcome of reconstructive procedures in plastic surgery. Beside vasoconstriction, thrombocytes aggregation, leukocytes activation, followed by production of oxygen free radicals and release of proteases, impaired fluidity of erythrocytes and swelling of the microvascular endothelium are responsible for impaired perfusion following ischemia/reperfusion. Therefore, vasoactive drugs known to improve nutritional blood flow are of particular interest in the prevention and therapy of skin flap necrosis. Several methods have been employed to quantify nutritional blood flow in skin flaps but none of them have elucidated the mechanisms underlying potential tissue protection by these drugs. We have developed two skin flap models in the hairless mouse, in which nutritional blood flow can be directly assessed at capillary level by means of intravital microscopy. In the arterial skin flap model, the efficacy of three vasoactive drugs (naftidrofuryl [4.5 mg/kg/day], pentoxifylline [17.0 mg/kg/day] and buflomedil [3.0 mg/kg/day]) to prevent and/or reduce tissue necrosis was investigated. Buflomedil provided the most efficient tissue protection, a phenomenon also verified in a random skin flap model. It was demonstrated that preoperative application of buflomedil preserves functional vascular density in the distal part of skin flaps more efficiently compared to postoperative application. However, there were no significant differences in amount of skin necrosis between the two groups. The tissue protection effect was also observed in random pattern flaps rendered ischemic for six hours after flap elevation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗