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Biomedical subjects

D J Newton

Publications and source records attributed to D J Newton.

At least 19 recordsLinked to original sources
PubMed2007

Mechanisms influencing the vasoactive effects of lidocaine in human skin.

The vasodilator properties of lidocaine are believed to be due mainly to the inhibition of action potentials via sodium channel blocking in vasoconstrictor sympathetic nerves. However, mechanisms involving the vascular endothelium may also play a role, and in this study we investigated the potential influences of nitric oxide release, the cyclo-oxygenase pathway and the beta-adrenoceptors of vascular smooth muscle. Laser Doppler imaging was used to measure microvascular blood flow responses to intradermal injection of lidocaine 2%, with or without the addition of preservatives, in eight healthy, male volunteers. Co-injection of the nitric-oxide-synthase inhibitor Nomega-nitro-L-arginine methyl ester caused a 60% reduction in the response after about 20 min, and this reduction was enhanced with the lidocaine solution containing the preservatives methylhydroxybenzoate and propylhydroxybenzoate. No reduction in response was seen after blocking the cyclo-oxygenase or beta-adrenoceptor pathways. Nitric oxide release contributes to the vasoactivity of lidocaine in human skin.

Adult↗
PubMed2006

Effects of poor glucose handling on arterial stiffness and left ventricular mass in normal children.

AIM: Cardiovascular risk factors can be present in children and young adults. We previously found abnormal microvascular function in children who had glucose intolerance and insulin resistance. The aim of the present study was to investigate whether they also have abnormalities in left ventricular mass (LVM) and arterial stiffness. METHODS: We measured heart dimensions and LVM using echocardiography, and arterial stiffness using pulse wave analysis in 23 children with good glucose handling (postfeeding glucose: 3.9 to 5 mmol/L) and 21 with poor glucose handling (7.7 to 11.4 mmol/L). RESULTS: The time to pulse reflection was slightly shorter in the poorer glucose handlers (mean+/-SD: 143+/-10 vs 153+/-20 ms, P=0.04), suggestive of increased arterial stiffness. Also in this group, there were significant relationships between intraventricular septal thickness, blood pressure and body mass index, but not in the normal glucose handlers. CONCLUSIONS: We have found that normal children who are in the lowest quintile of glucose tolerance in comparison with their peers are exhibiting the first signs of arterial stiffening. In addition, we have seen the beginnings of a relationship between blood pressure, body mass index and left ventricular enlargement in this group. While these changes may not yet be clinically significant, their emergence might be further evidence of early predisposition to cardiovascular disease.

Adolescent↗
PubMed2005

Vasoactive characteristics of bupivacaine and levobupivacaine with and without adjuvant epinephrine in peripheral human skin.

BACKGROUND: Epinephrine is added to local anaesthetic preparations to prolong their action and reduce their systemic absorption. Bupivacaine and levobupivacaine cause vasodilatation at clinical doses, but lower doses appear to cause vasoconstriction. The aim of this study was to characterize fully the vasoactive effects of these anaesthetics, using an objective measure of blood flow, and to assess the influence of adding epinephrine. METHODS: Laser Doppler imaging was used to measure the forearm skin blood flow responses to intradermal injection of eight doses of bupivacaine and levobupivacaine in 10 healthy male volunteers. The doses tested ranged from 0.008% to 0.75%, and the five highest doses were administered both with and without adjuvant epinephrine 2.5 microg ml(-1). RESULTS: The cumulative responses to the lower subclinical concentrations (0.008-0.0625%) of both anaesthetics were smaller than or similar to that produced by saline alone, indicating a net vasoconstrictive effect. Higher doses caused net vasodilatation, and the levobupivacaine responses were generally lower than the corresponding bupivacaine responses (P=0.022). Epinephrine 2.5 microg ml(-1) significantly reduced the responses to clinical doses of both drugs (P<0.001), producing net vasoconstriction. CONCLUSIONS: Bupivacaine and levobupivacaine have a biphasic vascular effect when injected intradermally, with subclinical doses causing net vasoconstriction. The addition of epinephrine 2.5 microg ml(-1) decreases these responses markedly.

Adjuvants, Anesthesia↗
PubMed2005

Endothelin-1 levels predict 3-year survival in patients who have amputation for critical leg ischaemia.

BACKGROUND: Most patients with critical leg ischaemia (CLI) have co-existing coronary heart disease, which is the main cause of their increased mortality rate. The aim of this study was to investigate whether any markers of endothelial function could predict death in these patients. METHODS: In a cohort of 39 patients with CLI who were scheduled for lower-limb amputation, blood levels of vascular endothelial growth factor, homocysteine, endothelin (ET) 1, von Willebrand factor and vascular cell adhesion molecule 1 were measured, as well as forearm vascular responses to the endothelium-dependent vasodilator acetylcholine. RESULTS: Levels of ET-1 were significantly higher in patients who subsequently died within 3 years than in those who were still alive (P = 0.002) and Cox proportional hazards regression analysis demonstrated that ET-1 was an independent predictor of all-cause mortality:hazard ratio 3.53 (95 per cent confidence interval (c.i.) 1.29 to 9.70; P = 0.007) and cardiovascular mortality:hazard ratio 4.15 (95 per cent c.i. 1.30 to 13.23); P = 0.014. CONCLUSION: ET-1 was an independent predictor of death in these patients with CLI.

Adult↗
PubMed2005

Pilot study of the effects of local pressure on microvascular function in the diabetic foot.

AIM: The aim of the study was to determine whether areas of the diabetic foot that experience high pressures during normal activity also demonstrate reductions in cutaneous microvascular flow and/or endothelial function. METHODS: Sixteen patients with diabetes mellitus and eight healthy, age-matched control subjects were recruited. Maps of dynamic pressure on the plantar aspect of both feet were recorded during a normal gait cycle, and the skin microvascular blood flow response to the endothelium-dependent vasodilator acetylcholine was assessed at the sites of highest and lowest plantar pressure over the metatarsal heads. RESULTS: Patients with diabetes had higher plantar pressures than control subjects (P = 0.002), but there were no significant differences in basal skin blood flow or acetylcholine response between the groups. In the patients, baseline flow was increased (P = 0.041) but the acetylcholine response reduced (P = 0.03) at the high-pressure compared with the low-pressure site; this was most apparent in those who were particularly at risk of ulceration due to high plantar pressures. CONCLUSIONS: Chronically raised plantar pressure in the diabetic foot is associated with increased basal skin blood flow, compared with lower pressure areas on the same foot. Further work is required to determine whether, and under what conditions, this additional hyperaemia is protective or maladaptive. In addition, high-pressure areas have a reduced responsiveness to an endothelium-dependent vasodilator, although the clinical significance of these changes is not clear.

Acetylcholine↗
PubMed2003

Mechanisms contributing to the vaso-active effects of prilocaine in human skin.

We investigated the roles of the endothelial nitric oxide and cyclo-oxygenase pathways in mediating the vasoactivity of prilocaine in the skin. We injected prilocaine 1% intradermally into forearm skin of 10 healthy, male subjects. Nitric oxide synthesis was inhibited at a second site by co-injecting prilocaine with l-NAME 1%. We then repeated the injections while blocking the cyclo-oxygenase pathway with aspirin (4 x 600 mg). We measured blood flow responses to the injections using laser Doppler imaging. We found that, after the traumatic effects of injection had subsided, l-NAME reduced the vascular response to prilocaine by a third (p = 0.012), indicating an influence specifically on the drug response. Aspirin had no effect on the response (p = 0.588). We conclude that the vasoactive effects of prilocaine in human skin are mediated partly through the release of endothelial nitric oxide and, although other mechanisms might also be involved, the cyclo-oxygenase pathway does not appear to play a role.

Adolescent↗
PubMed2002

Vascular endothelial growth factor in patients with critical limb ischemia before and after amputation.

BACKGROUND: It is known that levels of vascular endothelial growth factor (VEGF) in biological fluids increase with inflammation and vascular proliferation. Theraputic angiogenesis by injection of VEGF or genes encoding for it may be a promising strategy for treatment of critical limb ischemia. However growth factors are also implicated in the development of vascular disease by smooth muscle cell proliferation. METHODS: We have previously shown VEGF levels to be increased in juvenile diabetic subjects with no clinical evidence of vascular disease. We have measured serum VEGF using an enzyme linked immunosorbent assay and cellular VEGF expression using flow cytometry in patients with critical limb ischemia prior to and 6 months postamputation to determine whether removal of the ischemic limb leads to changes in systemic endothelial cell function. RESULTS: Baseline VEGF levels were significantly increased in the patient group compared to controls with levels returning to control levels at 6 months postsurgery. Monocyte and neutrophil VEGF expression was significantly reduced in the patient group. Platelet expression of VEGF was also reduced but this failed to reach statistical significance. CONCLUSIONS: The results suggest that it may be useful to determine the balance between VEGF production and cellular receptor expression prior to treatment.

Aged↗
PubMed2001

Assessment of microvascular endothelial function in human skin.

Endothelial dysfunction is an important factor in many cardiovascular diseases, and is commonly associated with impaired endothelium-mediated vasodilatation. Information about the mechanisms behind this dysfunction has come largely from animal studies or, in humans, through invasive techniques that are not specific to one vascular bed. We have developed protocols to assess endothelial function non-invasively in the cutaneous microcirculation by measuring blood flow responses to four receptor-specific vasoactive compounds. Cumulative doses of acetylcholine, methacholine, bradykinin and substance P were administered iontophoretically to the forearm skin of healthy volunteers on two to three occasions. Dose-dependent increases in skin microvascular blood flow in response to these drugs were measured with laser Doppler imaging. Vascular responses to acetylcholine and methacholine were reasonably consistent, with coefficients of variation of approx. 17%. The coefficients of variation for bradykinin and substance P were much poorer, as high as 70% for some doses. This might partly be a consequence of the more unpredictable effects of histamine release in the vasoactive behaviour of these two agonists. Although it might be advantageous to find other agonists with which to test the function of different receptor pathways, we have shown that just acetylcholine and methacholine can currently be used with iontophoresis to allow sensitive and reproducible assessment of endothelial function.

Acetylcholine↗
PubMed2000

Case 4: a patient with symptomatic bradycardia.

Both the clinical and electrocardiographic presentations of sick sinus syndrome are highly variable. As illustrated by this month's case of Interactive Grand Rounds, the initial challenge to the clinician is to establish the correct diagnosis in the patient who has symptomatic bradyarrhythmias.

Aged↗
PubMed2000

Human cytochrome P-450 3A4: in vitro drug-drug interaction patterns are substrate-dependent.

Testosterone, terfenadine, midazolam, and nifedipine, four commonly used substrates for human cytochrome P-450 3A4 (CYP3A4), were studied in pairs in human liver microsomes and in microsomes from cells containing recombinant human CYP3A4 and P-450 reductase, to investigate in vitro substrate-substrate interaction with CYP3A4. The interaction patterns between compounds with CYP3A4 were found to be substrate-dependent. Mutual inhibition, partial inhibition, and activation were observed in the testosterone-terfenadine, testosterone-midazolam, or terfenadine-midazolam interactions. However, the most unusual result was the interaction between testosterone and nifedipine. Although nifedipine inhibited testosterone 6beta-hydroxylation in a concentration-dependent manner, testosterone did not inhibit nifedipine oxidation. Furthermore, the effect of testosterone and 7,8-benzoflavone on midazolam 1'-hydroxylation and 4-hydroxylation demonstrated different regiospecificities. These results may be explained by a model in which multiple substrates or ligands can bind concurrently to the active site of a single CYP3A4 molecule. However, the contribution of separate allosteric sites and conformational heterogeneity to the atypical kinetics of CYP3A4 can not be ruled out in this model.

Cytochrome P-450 CYP3A↗
PubMed1999

Eotaxin and eotaxin receptor (CCR3) expression in Sephadex particle-induced rat lung inflammation.

The beta chemokine eotaxin is a potent eosinophil activator and chemoattractant. We examined immunohistochemically eotaxin protein expression in a range of normal rat tissues and in rat lung during Sephadex particle-induced pulmonary inflammation. The time course of eotaxin expression in lung at various time points after Sephadex administration was related to the appearance of eosinophils in the bronchoalveolar lavage fluid and tissue distribution of eotaxin receptor (CCR3) positive cells. Results showed that eotaxin protein was constitutively expressed by both lung airway epithelial cells and gut epithelial cells in normal tissues in the absence of inflammation. During Sephadex induced pulmonary inflammation, eotaxin expression increased in alveolar macrophages prior to the major increase in eosinophil numbers which reached a peak at 72 h. The pattern of eotaxin pulmonary expression and the location of CCR3 receptor positive cells suggest a chemoattractant gradient resulting in migration firstly into the tissue and subsequently through the airway epithelium into the airways. Treatment of rats with the glucocorticoid dexamethasone or the immunosuppressant cyclosporin A reduced eosinophil entry into lung tissue and airways but had no apparent effect on eotaxin expression in vivo, indicating that both these drugs inhibit eosinophil recruitment either by an eotaxin-independent mechanism, or by targetting factors that synergise with eotaxin, or an event post eotaxin expression.

Animals↗
PubMed1999

Disruption of skin perfusion following longitudinal groin incision for infrainguinal bypass surgery.

OBJECTIVE: The objective of our study was to investigate whether such an incision results in a reduction in blood flow, and therefore haemoglobin oxygen saturation, across the wound. DESIGN: Microvascular oxygenation was measured with lightguide spectrophotometry in 21 patients undergoing femoropopliteal or femorodistal bypass procedures. A series of measurements were made in the groin, medial and lateral to the surface marking of the femoral artery. The mean oxygen saturation on each side was calculated, and the contra-lateral groin was used as a control. The measurements were repeated at 2 and 7 days postop. RESULTS: Oxygen saturation in the skin of the operated groins was increased significantly from baseline at 2 days postop (f = 25.80, p < 0.001) and had begun to return to normal by day 7. The rise was more marked on the lateral side of the wound than on the medial (f = 12.32, p < 0.001). There was no such difference in the control groins. All wounds healed at 10 days. CONCLUSIONS: These results show a significant difference in skin oxygenation between the lateral and medial sides of the groin following longitudinal incision. This may contribute to the relatively high incidence of postoperative infection in these wounds.

Aged↗
PubMed1999

Human decidualized endometrial T lymphocytes do not substantially down-regulate CD3zeta.

PROBLEM: The T-cell antigen receptor (TCR) has been reported to be down-regulated on T-cells in the decidualized endometrium in early pregnancy. METHOD OF STUDY: The expression of CD3zeta, a component of the TCR complex, has been investigated in human first-trimester decidual T-cells using flow cytometric analysis of permeabilized cells. RESULTS: Levels of CD3zeta expression were significantly lower in decidual than in peripheral T-cells from non-pregnant women, as assessed by mean fluorescence intensity (4.2 vs. 5.5, logarithmic scale, P < 0.05). However, when decidual and peripheral T-cells from the same subjects were analyzed (n = 10), mean levels of CD3zeta were slightly, but not significantly, lower in decidual than in peripheral T-cells (P > 0.1). CD3zeta was not substantially down-regulated systemically as mean cytoplasmic CD3zeta levels did not differ significantly between peripheral blood T-cells from pregnant women and non-pregnant controls (P > 0.2). CD8+ cells outnumber CD4+ cells in decidua, but neither the proportions of these two T-cell subsets positive for cytoplasmic CD3zeta nor the mean levels of CD3zeta were significantly different. CONCLUSIONS: These results indicate that human decidual T-cells do not greatly down-regulate CD3zeta, but it is unclear if a small decrease in mean levels may be sufficient to compromise their capacity for activation.

CD3 Complex↗
PubMed1999

Inhibitory anti-CYP3A4 peptide antibody: mapping of inhibitory epitope and specificity toward other CYP3A isoforms.

An antipeptide antibody has been produced that recognizes CYP3A4 and exhibits greater than 90-95% inhibition on CYP3A4-mediated reactions [Wang RW and Lu AYH (1997) Drug Metab Dispos 25:762-767]. The inhibitory epitope of the 21-amino acid peptide, corresponding to residues 253 to 273 of CYP3A4, has been identified to reside in a 7-amino acid sequence (LEDTQKH: residues 261-267 of CYP3A4). This conclusion was based on the reversal of antibody inhibition of testosterone 6beta-hydroxylation when peptides with overlapping sequence in this region were preincubated with the antibody. In immunoblotting analysis, this antibody did not recognize CYP3A5 or CYP3A7 in microsomes prepared from baculovirus-infected cells containing these two expressed isoforms. In addition, the antipeptide antibody did not inhibit testosterone 6beta-hydroxylation or midazolam 1'- and 4-hydroxylation in microsomes containing expressed CYP3A5 and CYP3A7. Because the corresponding sequence in CYP3A5 (LNDKQKH) and CYP3A7 (LKETQKH) differs from CYP3A4 by only two amino acids, six peptides with either one or two amino acid changes were used to determine which amino acid is essential for antibody-antigen interaction. Our data indicate that Glu, Asp, and Thr in the 7-amino acid sequence of CYP3A4 are critical determinants of selectivity among CYP3A isoforms.

Amino Acid Sequence↗
PubMed1998

A novel isoform of human membrane cofactor protein (CD46) mRNA generated by intron retention.

The reverse transcription polymerase chain reaction (RT-PCR) with primers specific for each of the 14 exons of the human complement regulatory protein membrane cofactor protein (MCP;CD46) has been utilized to determine MCP mRNA transcript expression in peripheral blood mononuclear cells (PBMC). An additional transcript of a larger size than predicted was consistently detected in reactions with a sense primer for exon 7, that encodes the first alternatively spliced serine-threonine-rich region (ST-A), together with an antisense exon 12 primer, RT-PCR with primers for other exons both 5' and 3' of exon 7 further showed that these MCP transcripts contain additional sequences immediately both 5' and 3' to the exon 7-encoded sequence. Comparison of genomic DNA with cDNA by PCR, in combination with sequence analysis, demonstrated the presence of the complete invariant sequences of both introns adjacent to exon 7, i.e. intron 6 (411 bp) and intron 7 (127 bp). RT-PCR using primers specific for the intron 6 sequence, together with Southern and Northern blotting using an intron 6-specific probe, confirmed retention of this intron within a novel 4.8-kb mRNA transcript in human PBMC. Due to the presence of a stop codon within intron 6, translation would result in a novel truncated MCP isoform (MCPi) containing the four invariant short consensus repeat (SCR) regions and a unique C-terminal 39 amino acid transmembrane and cytoplasmic tail region that may promote endoplasmic reticulum retention.

Alternative Splicing↗