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Biomedical subjects

D A Morgan

Publications and source records attributed to D A Morgan.

At least 37 records · Page 2Linked to original sources
PubMed1999

Bacterial contamination rates during bone allograft retrieval.

A retrospective study of allograft bone retrieved from 401 donors between January 1987 and March 1996 was performed to determine the incidence of bacterial contamination. Contamination according to type of donor (live, multiorgan, cadaveric) was also determined. Live donors donating a femoral head demonstrated a contamination rate of 13%; multiorgan donors, 24%; and cadaveric donors, 35%. Donor contamination by type of bone (hemipelvis, femur, tibia) showed no significant difference in the multiorgan donors. In cadaveric donors, there was a significant increase in contamination of the hemipelves as compared to the femur and tibias. Recommendations for contamination control in allograft retrieval are given. Our findings are of great significance for musculoskeletal banks that do not secondarily irradiate and rely on screening of allograft bone for contamination alone.

Bacteria↗
PubMed1999

Contrasting blood pressure effects of obesity in leptin-deficient ob/ob mice and agouti yellow obese mice.

OBJECTIVE: Recent advances in understanding the neuroendocrine pathways regulating appetite, metabolism and body weight afford an opportunity to explore further the mechanisms by which obesity influences arterial pressure. ob/ob(Lep(ob)/Lep(ob)) mice have a mutation in the ob gene and are leptin-deficient. Leptin possesses pressor actions and has been shown to increase arterial pressure when infused chronically or over-expressed transgenically. In contrast, agouti yellow obese(Ay) mice have overexpression of an agouti peptide that blocks melanocortin receptors. Stimulation of melanocortin receptors by alpha-melanocyte-stimulating hormone decreases arterial pressure. DESIGN AND METHODS: This study measured arterial pressure in leptin-deficient ob/ob mice, agouti yellow obese mice and their lean controls to test the hypothesis that the effects of obesity on arterial pressure are importantly influenced by the genetic and neuroendocrine mechanisms causing the obesity. We measured arterial pressure directly in conscious ob/ob mice (n = 14), agouti yellow obese mice (n = 6) and the same number of lean littermates. RESULTS: Body weight was nearly twice as high in ob/ob mice as in their lean controls, but mean arterial pressure was significantly lower in ob/ob mice (92+/-3 mmHg) compared with their lean controls (106+/-2 mmHg; P = 0.00017). In contrast, mean arterial pressure was significantly higher in agouti yellow obese mice (124+/-3 mmHg) than in their lean controls (99+/-1 mmHg; P = 0.000002) despite the fact that the agouti mice had milder obesity. CONCLUSIONS: This study prompts three conclusions: (1) leptin-deficient ob/ob mice and agouti yellow obese mice have contrasting blood pressure responses to obesity, (2) obesity does not invariably increase arterial pressure in mice, and (3) the arterial pressure response to obesity may depend critically on the underlying genetic and neuroendocrine mechanisms.

Animals↗
PubMed1999

Sympathetic inhibition, leptin, and uncoupling protein subtype expression in normal fasting rats.

To further investigate neural effects on leptin and uncoupling proteins (UCPs), we studied in vivo perturbations intended to block adrenergic input to peripheral tissues. We examined plasma leptin, leptin mRNA, and adipose and muscle UCP subtype mRNA in rats treated with alpha-methyl-p-tyrosine methyl ester (AMPT-ME), which inhibits catecholamine synthesis and 6-hydroxydopamine (6HDA), which is toxic to catecholinergic nerve terminals but, unlike AMPT-ME, does not enter the central nervous system. Intraperitoneal AMPT-ME, 250 mg/kg, was administered at 1800 and 0700 the following day, and rats were killed at 1200-1400. All rats were fasted with free access to water during this time. Intraperitoneal AMPT-ME increased plasma leptin by 15-fold, increased interscapular brown adipose tissue (IBAT) and epididymal fat leptin mRNA by 2- to 2.5-fold, and also increased plasma insulin and glucose concentrations. Intraperitoneal AMPT-ME decreased IBAT UCP-3 mRNA to 40% of control, while it increased epididymal adipose UCP-3 mRNA approximately twofold. Intravenous AMPT-ME, 250 mg/kg, administered to conscious rats for 5 h decreased lumbar sympathetic nerve activity, increased plasma leptin (5.89 +/- 1.43 compared with 2.75 +/- 0.31 ng/ml in vehicle-treated rats, n = 7, P < 0.05), and decreased cardiac rate with no sustained change in blood pressure. Intraperitoneal 6HDA, 100 mg/kg, as a single dose at 1800, increased plasma leptin approximately twofold after 18-20 h, increased IBAT (but not epididymal fat) leptin mRNA by two- to threefold, and decreased IBAT UCP-3 mRNA to 30-40% of control. Neither AMPT-ME nor 6HDA significantly altered mRNA encoding gastrocnemius muscle UCP-3, IBAT UCP-1, or IBAT and epididymal UCP-2. In summary, AMPT-ME and 6HDA increased plasma leptin and upregulated leptin mRNA expression. AMPT-ME also resulted in complex tissue and subtype-specific modulation of adipose UCP mRNA. These data are consistent with interaction between leptin and sympathetic nerve activity (SNA) in regulation of fat cell energy utilization. However, the in vivo modulation of leptin and UCPs appears complex and, beyond a causal effect of SNA per se, may depend on concurrent changes in plasma insulin, glucose, and circulatory hemodynamics.

Adipose Tissue↗
PubMed1999

State-of-the-art-lecture: Obesity-induced hypertension: new concepts from the emerging biology of obesity.

offsity is associated with an increased risk of hypertension. In the past 5 years there have been dramatic advances into the genetic and neurobiological mechanisms of obesity with the discovery of leptin and novel neuropeptide pathways regulating appetite and metabolism. In this brief review, we argue that these mounting advances into the neurobiology of obesity have and will continue to provide new insights into the regulation of arterial pressure in obesity. We focus our comments on the sympathetic, vascular, and renal mechanisms of leptin and melanocortin receptor agonists and on the regulation of arterial pressure in rodent models of genetic obesity. We suggest 3 concepts. First, the effect of obesity on blood pressure may depend critically on the genetic-neurobiological mechanisms underlying the obesity. Second, obesity is not consistently associated with increased blood pressure, at least in rodent models. Third, the blood pressure response to obesity may be critically influenced by modifying alleles in the genetic background.

Animals↗
PubMed1999

Interactions between the melanocortin system and leptin in control of sympathetic nerve traffic.

Leptin plays an important role in regulation of body weight through regulation of food intake and sympathetically mediated thermogenesis. The hypothalamic melanocortin system, via activation of the melanocortin-4 receptor (MC4-R), decreases appetite and weight, but its effects on sympathetic nerve activity (SNA) are unknown. In addition, it is not known whether sympathoactivation to leptin is mediated by the melanocortin system. We tested the interactions between these systems in regulation of brown adipose tissue (BAT) and renal and lumbar SNA in anesthetized Sprague-Dawley rats. Intracerebroventricular administration of the MC4-R agonist MT-II (200 to 600 pmol) produced a dose-dependent sympathoexcitation affecting BAT and renal and lumbar beds. This response was completely blocked by the MC4-R antagonist SHU9119 (30 pmol ICV). Administration of leptin (1000 microg/kg IV) slowly increased BAT SNA (baseline, 41+/-6 spikes/s; 6 hours, 196+/-28 spikes/s; P=0.001) and renal SNA (baseline, 116+/-16 spikes/s; 6 hours, 169+/-26 spikes/s; P=0.014). Intracerebroventricular administration of SHU9119 did not inhibit leptin-induced BAT sympathoexcitation (baseline, 35+/-7 spikes/s; 6 hours, 158+/-34 spikes/s; P=0.71 versus leptin alone). However, renal sympathoexcitation to leptin was completely blocked by SHU9119 (baseline, 142+/-17 spikes/s; 6 hours, 146+/-25 spikes/s; P=0.007 versus leptin alone). This study demonstrates that the hypothalamic melanocortin system can act to increase sympathetic nerve traffic to thermogenic BAT and other tissues. Our data also suggest that leptin increases renal SNA through activation of hypothalamic melanocortin receptors. In contrast, sympathoactivation to thermogenic BAT by leptin appears to be independent of the melanocortin system.

Adipose Tissue, Brown↗
PubMed1998

A computer software application for managing occupational exposure data.

The Health Hazard Information Module is the U.S. Army's computer software application for managing occupational exposure data. The project mission is to utilize automated information systems technology to improve the overall effectiveness of industrial hygiene programs. Field industrial hygiene professionals document their survey methods, findings, conclusions, and recommendations with a portable, pen-based computer. Back at the office, the data are electronically transferred to a desktop workstation. Users can generate standard or customized reports in hard copy or electronic formats. Annually, users transfer their data to a corporate mainframe computer. The software incorporates appropriate information and represents an excellent template worth examining during the ongoing international effort to standardize occupational exposure data. Planned refinements include distributing the software to other Department of Defense agencies and making it commercially available for a nominal fee through the National Technical Information Service in the near future.

Computer Systems↗
PubMed1998

Cardiovascular consequences of obesity: role of leptin.

1. Several mechanisms have been implicated in the association between obesity and hypertension, including salt-sensitivity, insulin resistance and sympathetic activation. Obese animals and humans exhibit exaggerated blood pressure responses to increases in salt intake. 2. Although insulin resistance is common in obesity, it is clear that abnormal insulin action is not the sole or sufficient cause of hypertension in obesity. Obesity is associated with increased activity of the sympathetic nervous system. Sympathetic blockade has been reported to attenuate sodium retention and hypertension in experimental models of obesity. 3. The mediators responsible for salt sensitivity, insulin resistance and sympathetic activation in obesity remain unclear. 4. The novel protein hormone leptin is produced almost exclusively by adipose tissue and acts in the central nervous system through a specific receptor and multiple neuropeptide pathways to decrease appetite and increase energy expenditure. 5. Increasing evidence suggests that leptin may have wider actions influencing autonomic, cardiovascular, renal and endocrine function. We have shown that leptin increases sympathetic nerve activity to kidney, hindlimb and adrenal gland, in addition to brown adipose tissue. 6. Despite this sympathoexcitatory action, acute systemic administration of leptin does not acutely increase arterial pressure or heart rate in anaesthetized animals. This may reflect opposing antihypertensive actions of leptin. For example, leptin increases renal sodium and water excretion, apparently through a direct tubular action. In addition, leptin increases systemic insulin sensitivity, even in the absence of weight loss. 7. In conclusion, leptin may act as a mediator linking body adiposity with changes in insulin action, sympathetic neural outflow and renal sodium excretion. Alterations in leptin generation or action may, in part, underlie the sympathetic, endocrine and renal consequences of obesity.

Animals↗
PubMed1998

Fresh osteochondral allografts: a 6-10-year review.

BACKGROUND: In young patients with limited articular cartilage damage, osteochondral allografts may offer an alternative to total joint replacement. The survival of chondrocytes after transplantation and the correlation with clinical outcomes was studied. METHODS: Between March 1987 and September 1990, nine patients received fresh osteochondral allografts. Three patients received tibial plateau transplants, three received patellar transplants, two received proximal interphalangeal joints and the remaining patient received a segmental femoral head allograft. Patient ages ranged from 16-51 years (mean = 30). They have been followed in a prospective manner for up to 10 years with clinical, radiographic and histopathological review during the period. RESULTS: Early histological analyses demonstrated preservation of hyaline cartilage. Subsequent analyses from the periphery of some grafts demonstrated chondrocyte death and a change from hyaline cartilage to fibrocartilage, but one specimen taken from the centre of a tibial plateau graft, nine years after transplantation, demonstrated viable chondrocytes. The three tibial plateau recipients improved at a clinical level from an average pre-operative score of 73 (HSS 0-200) to a postoperative average of 174 points. Two of those patients receiving patellar allografts improved from 91 points to 181 points on average. The third patella allograft recipient underwent a total knee replacement 18 months post-transplantation. The patella was not resurfaced. The proximal interphalangeal joint transplants failed and the femoral head allograft has been lost to follow-up. CONCLUSIONS: The clinical success of the tibial plateau and patellar allografts, irrespective of the histological results, has resulted in the formation of a code of specific indications for this operation. Future enthusiasm, although buoyed by the possibility of long-term chondrocyte viability and good clinical results, must be tempered by the ever-present risk of disease transmission.

Arthroscopy↗
PubMed1998

The current state of bone and tissue banking in Australia.

The development of bone and tissue banking in Australia over the last decade is described and details of the administrative structure, donor and recipient testing protocols, allograft segment processing procedures, and internal audit safety arrangements are also provided. Demographic data concerning both the retrieval and dispersal of musculoskeletal allograft materials in Australia are also discussed. Current price schedules for a variety of allograft materials available in Australia are made available for international comparison.

Australia↗
PubMed1997

Receptor-mediated regional sympathetic nerve activation by leptin.

Leptin is a peptide hormone produced by adipose tissue which acts centrally to decrease appetite and increase energy expenditure. Although leptin increases norepinephrine turnover in thermogenic tissues, the effects of leptin on directly measured sympathetic nerve activity to thermogenic and other tissues are not known. We examined the effects of intravenous leptin and vehicle on sympathetic nerve activity to brown adipose tissue, kidney, hindlimb, and adrenal gland in anesthetized Sprague-Dawley rats. Intravenous infusion of mouse leptin over 3 h (total dose 10-1,000 microg/kg) increased plasma concentrations of immunoreactive murine leptin up to 50-fold. Leptin slowly increased sympathetic nerve activity to brown adipose tissue (+286+/-64% at 1,000 microg/kg; P = 0.002). Surprisingly, leptin infusion also produced gradual increases in renal sympathetic nerve activity (+228+/-63% at 1,000 microg/kg; P = 0.0008). The effect of leptin on sympathetic nerve activity was dose dependent, with a threshold dose of 100 microg/kg. Leptin also increased sympathetic nerve activity to the hindlimb (+287+/-60%) and adrenal gland (388+/-171%). Despite the increase in overall sympathetic nerve activity, leptin did not increase arterial pressure or heart rate. Leptin did not change plasma glucose and insulin concentrations. Infusion of vehicle did not alter sympathetic nerve activity. Obese Zucker rats, known to possess a mutation in the gene for the leptin receptor, were resistant to the sympathoexcitatory effects of leptin, despite higher achieved plasma leptin concentrations. These data demonstrate that leptin increases thermogenic sympathetic nerve activity and reveal an unexpected stimulatory effect of leptin on overall sympathetic nerve traffic.

Action Potentials↗
PubMed1997

Protective role of nerve growth factor against postischemic dysfunction of sympathetic coronary innervation.

BACKGROUND: Nerve growth factor (NGF) is produced rapidly in myocardium after brief myocardial ischemia. It contributes to the maintenance of neural integrity in several tissues. We examined the effect of exogenous and endogenous NGF on ischemia-induced dysfunction of cardiac sympathetic nerves. METHODS AND RESULTS: In anesthetized dogs, bilateral stellate stimulation was performed, measuring changes in coronary vascular resistance (% delta CVR) before and after release of either a 7- or 15-minute occlusion of the left anterior descending coronary artery (LAD). NGF (10 ng.kg-1.min-1, n = 5) or vehicle (n = 6) was infused into the LAD in dogs during a 15-minute LAD occlusion. In separate experiments, antibody to NGF (anti-NGF, 2 ng.kg-1.min-1, n = 5) or vehicle (n = 6) was infused into dogs during a 7-minute LAD occlusion. After release of a 15-minute LAD occlusion, attenuation of the coronary constriction to stellate stimulation was seen in the vehicle group (30 +/- 3% to 15 +/- 1% increase in CVR, P < .05); however, no such reduction was seen in the group receiving NGF. A 7-minute LAD occlusion with reperfusion did not alter % delta CVR in the vehicle group (36 +/- 6% versus 37 +/- 7%, P = NS) but attenuated % delta CVR in the anti-NGF group (39 +/- 8% to 17 +/- 2%, P < .05). CONCLUSIONS: We conclude that exogenously infused and endogenously released NGF protects against postischemic neural stunning of sympathetic cardiac innervation.

Animals↗
PubMed1997

Cytokine mRNA expression in human platelets and a megakaryocytic cell line and cytokine modulation of platelet function.

Platelet formation and function are regulated, in vivo, to varying degrees by cytokines in the micro-environment. While white blood cells are the major source of cytokines within the cardiovascular system, the question addressed in this study was whether platelets and the platelet precursor, the megakaryocyte, may also serve as a source of cytokines. Cytokines produced by or carried within platelets could be released at sites of vascular injury and participate in wound healing. Platelets and a human megakaryocyte-like cell line, HU3, were found to express message for interleukin 7 (IL-7), stem cell factor (SCF), transforming growth factor beta (TGF-beta), cMpl, the IgE receptor subunits Fc epsilon RI alpha gamma and the transcription factor, NF-E2. Other cytokines expressed in HU3 cells but not in platelets included IL-1 beta, IL-6, IL-10, IL-13, TNF-alpha and the FC epsilon RI beta subunit. The HU3 cell line seemed to be further along the maturation/differentiation pathway to platelet formation than a second blood derived bipotential cell line, MB02. The MB02 cell line did not express IL-6, IL-10, SCF, TNF-omega nor cMpl. Furthermore, culturing the HU3 cells in TPO appeared to repress expression of Fc epsilon RI beta directing the cell closer to the platelet phenotype. In light of the presence of cytokine expression in platelets/megakaryocytes, agonist-induced platelet aggregation was measured in the presence of added cytokines as a means to evaluate potential cytokine modulation of platelet function. Collagen-induced aggregations were significantly enhanced by IL-6, SCF and TPO. Other cytokines tested significantly stimulated the thrombin receptor activating peptide, SFLLRNP-, U46619- and ADP-induced platelet aggregations with TPO being the most consistent activator. It is possible that cytokines released from platelets act in concert with cytokines released from other cellular sources to modulate haemostasis and thrombosis differentially depending upon the site of injury.

Base Sequence↗
PubMed1997

A comparison of late cosmetic results following two different radiotherapy techniques for treating basal cell carcinoma.

Fractionated superficial X-ray therapy and gold grain brachytherapy Elastoplast mould (EPM) methods of treating basal cell carcinoma (BCC) on facial skin were compared for long term cosmesis. Thirty patients were traced who had been treated successfully for a BCC on the face more than ten years previously. Late skin and subcutaneous changes were graded. Fifteen had been treated with 116 kV X-rays (32.5 Gy in five fractions on 5 consecutive days, and the remaining 15 with radioactive gold EPMs, delivering a dose of 6000-6500 R with an application lasting 7 days). The late cosmetic result scores of the patients treated by X-rays gave a mean score of 2.13; only three of these patients had a score of less than 2. The mean score for the patients treated with EPMs was 1.47; none had a score greater than 2. The difference is statistically significant (P < 0.01, Wilcoxon rank sum test). The EPM gave much more acceptable late cosmetic results.

Brachytherapy↗
PubMed1997

Role of adenosine receptor subtypes in neural stunning of sympathetic coronary innervation.

Adenosine plays an important role in postischemic dysfunction of cardiac sympathetic nerves because exogenously infused adenosine produces and adenosine deaminase prevents "neural stunning." We examined whether adenosine acts via a specific receptor mechanism to produce neural stunning. Anesthetized dogs were treated with propranolol to attenuate increases in coronary flow due to adrenergic stimulation of myocardial metabolism. A 15-min occlusion of the left anterior descending coronary artery (LAD) attenuated subsequent LAD coronary vasoconstriction to bilateral sympathetic stimulation during reperfusion by 75% (P < 0.05). Coronary infusion of the adenosine-receptor antagonist 8-p-sulfophenyltheophylline (nonspecific), 8-cyclopentyl-1,3-dipropylxanthine (A1 specific), or 3,7-dimethyl-1-propagylxanthine (A2 specific) during LAD occlusion prevented the attenuation of sympathetic coronary constriction. In separate experiments, either the specific adenosine agonist N6-cyclopentyl-adenosine (A1 specific) or CGS-21680 (A2 specific) or a combination of both agonists was infused into the LAD for 15 min. Neither agonist alone attenuated subsequent sympathetic coronary constriction. In contrast, 15 min after the combined administration of both agonists, sympathetic vasoconstriction was reduced. We conclude that adenosine is capable of attenuating neurogenic coronary constriction through a receptor-mediated mechanism. Activation of more than one receptor subtype is necessary to produce neural stunning.

Adenosine↗
PubMed1997

Modulation of baroreflex sensitivity and spectral power of blood pressure by heat stress and aging.

To investigate the effects of hyperthermia and aging on baroreceptor-heart rate reflex sensitivity (BRS), cardiovascular parameters were recorded during a progressive rise in core temperature in conscious mature and senescent Fischer 344 rats. BRS was calculated from spontaneous changes in blood pressure and interbeat interval. Low- (LF, 0.01-0.20 Hz) and mid- (MF, 0.2-0.5 Hz) frequency blood pressure power were also determined. In both age groups, hyperthermia caused an increase in blood pressure, renal resistance, and LF but no changes in renal nerve activity, whereas a tachycardia was only observed in the older rats. Increases in BRS (0.80 +/- 0.14 vs. 1.72 +/- 0.34 ms/mmHg, P < 0.05) and MF (3.10 +/- 0.55 vs. 7.81 +/- 1.89 mmHg2, P < 0.05) and a positive correlation between BRS and MF (r = 0.50, P < 0.01) were observed with heating in mature but not senescent rats. These results indicate that LF, which increased with elevated core temperature, may be modulated by thermal stimuli. The augmented BRS in the mature group may contribute to the hemodynamic adjustments that occur with hyperthermia, whereas the lack of an increase in BRS during heat stress in the senescent group suggests that baroreceptor reflex modulation is impaired with aging. The positive correlation between BRS and MF in mature rats, together with the lack of an increase in renal sympathetic nerve activity, indicates that MF may reflect the modulating influence of the efferent sympathetic portion of the baroreceptor reflex loop on arterial blood pressure rather than merely the activity of the peripheral sympathetic nervous system.

Aging↗