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M Wilkinson

Publications and source records attributed to M Wilkinson.

At least 109 records · Page 6Linked to original sources
PubMed1996

Ventricular, but not atrial, M2-muscarinic receptors increase in the canine pacing-overdrive model of heart failure.

OBJECTIVE: To investigate the effects of heart failure induced by chronic rapid ventricular pacing (six weeks) on canine atrial and ventricular muscarinic receptors. DESIGN: Dogs (n = 4) were fitted with a bipolar pacing electrode connected to a Medtronic pacemaker set at 240 stimuli/min. Pacing was maintained for six weeks. Tissue samples obtained from the left atrium and ventral wall of the left ventricle were frozen at -70 degrees C. Control tissue was obtained from normal dogs (n = 6) following anesthesia and thoracotomy. M2-muscarinic receptors were characterized and quantified in tissue micropunches using the hydrophilic ligand [3H] N-methyl-scopolamine (NMS). MAIN RESULTS: Cardiac tissue bound [3H] NMS with the specificity of an M2 subtype. Tachycardia-induced heart failure did not affect atrial muscarinic receptors but signify left ventricular myocytes (control 160.0 +/- 10.0 fmol/mg protein versus heart failure 245.0 +/- 25.0 fmol/mg protein; P < 0.01). CONCLUSIONS: Canine ventricular muscarinic receptors display a specificity for the M2 subtype. In contrast to previous work, tachycardia-induced heart failure was accompanied by an increase (+ 53%) in ventricular, but not atrial, M2 receptors compared with normal dogs.

Animals↗
PubMed1995

Multiple origins of anaerobic ciliates with hydrogenosomes within the radiation of aerobic ciliates.

Some ciliates live anaerobically and lack mitochondria, but possess hydrogenosomes: organelles that contain hydrogenase and produce hydrogen. The origin of hydrogenosomes has been explained by two competing hypotheses: (i) they are biochemically modified mitochondria; or (ii) they are derived from endosymbiotic association(s) of ciliates and anaerobic eubacteria that possessed the hydrogenosome biochemistry. Phylogenetic analyses of representative aerobic, and anaerobic hydrogenosomal ciliates using host nuclear SSU rDNA sequences indicate a minimum of three, but more likely four, separate origins of hydrogenosomes. Whereas this does not refute either hypothesis, the implausibility of multiple convergent endosymbioses gives further support to the view that hydrogenosomes in ciliates derive from an existing organelle, which ultrastructural evidence suggests is the mitochondrion. Our results indicate a considerable potential for physiological-biochemical plasticity among a group of predominantly aerobic eucaryotes, and provide a phylogenetic framework to further refine and test hypotheses of the origins of the hydrogenosomal enzymes.

Aerobiosis↗
PubMed1995

Anti-gastrin antibodies raised by gastrimmune inhibit growth of the human colorectal tumour AP5.

The neutralising ability of rabbit anti-gastrin-17 (G17) antiserum raised by Gastrimmune, an immunogen constructed of the N-terminal portion of human G17 conjugated to diptheria toxoid (DT), was evaluated. The anti-serum (denoted anti-G17: DT) was shown to displace 125[I] G17 from the gastrin receptors on AR42J cells. The therapeutic effect of the rabbit anti-G17:DT anti-serum was evaluated on a freshly derived human colorectal cancer cell line, AP5, which was shown to express both gastrin receptors and gastrin immunoreactivity as assessed by immunocytochemistry. Rabbit anti-G17:DT anti-serum was shown to block basal in vitro growth of AP5 cells when used at an antigen binding capacity of 3.75 x 10(-9) M. The same dilution of anti-serum completely reversed growth stimulated by human G17 at concentrations of 1 x 10(-10) and 1 x 10(-9) M but did not inhibit growth at 1 x 10(-8) M G17. When AP5 was grown as a xenograft in nude mice, the sensitivity to the proliferative effect of human G17 was maintained. In addition, the basal growth of AP5 xenografts was significantly reduced by i.v. infusion of rabbit anti-G17:DT anti-serum when compared to treatment with rabbit anti:DT control anti-serum. Thus anti-G17:DT antibodies raised by Gastrimmune may be of clinical value in gastrin-sensitive tumours.

3T3 Cells↗
PubMed1995

Phylogenetic relationships among karyorelictids and heterotrichs inferred from small subunit rRNA sequences: resolution at the base of the ciliate tree.

Ciliate protozoa are among the most diverse and complex cells that have been described. Ciliates are characterized by nuclear dimorphism, possessing a macronucleus and a micronucleus which share the same cytoplasm. An understanding of the evolution of ciliate diversity depends upon knowledge of their phylogeny. In this study we attempted to resolve some of the relationships at the base of the ciliate tree by determining the phylogenetic position of a sample of heterotrich and hypothesized primitive karyorelictid ciliates. Karyorelictids are considered primitive because they possess a "simple" form of nuclear dualism whereby the macronucleus does not divide once it has differentiated from a micronucleus. We micromanipulated cells of two heterotrichs, Spirostomum ambiguum and Gruberia sp., and two karyorelictids, Loxodes magnus and Tracheloraphis sp., and amplified their small subunit (SSU) rDNA using PCR. The primary structure of the SSU rDNA was determined for each species and used to infer their positions in the ciliate phylogenetic tree. The results indicate, with strong support, that the aerobic heterotrichs and the karyorelictids sampled constitute a monophyletic group. The most parsimonious interpretation of the form of nuclear dimorphism in karyorelictids is that it is derived from the general condition as found in its sister group the aerobic heterotrichs. The two anaerobic heterotrichs, Metopus contortus and Metopus palaeformis, comprise a distinct clade, so that the subclass Heterotrichia, as currently conceived, is not a monophyletic group. The complex mouth architecture which characterizes all heterotrichs must be reassessed in light of this finding.

Animals↗
PubMed1995

Modulation of cardiac M2 muscarinic receptor binding by progesterone-related steroids.

We have previously shown that progesterone, but not estradiol or testosterone, can compete with [3H]N-methyl scopolamine (NMS) for the cardiac M2 muscarinic binding site. Experiments have been carried out to investigate the inhibitory effects of a large variety of progesterone-like steroids on the M2 muscarinic receptor. These studies were performed with the aid of a new binding assay which uses intact tissue in the form of ventricular micropunches. Our data show that synthetic, clinically-used progestins such as Provera, norgesterel and cyproterone are largely ineffective at the M2 binding site whereas the naturally occurring progesterone derivatives 17 alpha hydroxy progesterone and Reichstein's Substance S are highly active. (Ki values 5 x 10(-6)M and 1 x 10(-6)M, respectively). Minor structural modifications such as acetylation of the 17 alpha hydroxy group abolishes activity. Steroids known to exert cell membrane effects, such as alfaxalone and pregnenolone sulfate, had no influence on [3H] NMS binding. The progesterone antagonist RU-486 did not block the inhibitory effect of progesterone. Moreover, this putative receptor may be located in the cardiomyocyte membrane since 17 alpha hydroxy progesterone induces rapid dissociation of [3H] NMS from its binding site (30% reduction in 5 min). We attempted to further localize the inhibitory locus to the M2 receptor itself by means of the irreversible antagonist propylbenzilylcholine mustard (PrBCM). Ninety percent of the M2 receptor could be blocked by PrBCM (10(-6) M), an effect reversible by the specific muscarinic antagonist scopolamine methyl bromide but not by progesterone. These results suggested that progesterone does not interact directly with the [3H] NMS labelled M2 binding site.(ABSTRACT TRUNCATED AT 250 WORDS)

Allosteric Site↗
PubMed1995

Reactions to other corticosteroids in patients with positive patch test reactions to budesonide.

BACKGROUND: Corticosteroid cross-reactions have been classified into four well-defined groups. A previous study of patch test reactions to other corticosteroids in patients allergic to hydrocortisone failed to conform to these groups. It was suggested that substitution at the C6 and C9 positions of the corticosteroid was the most important determinant of a further reaction. OBJECTIVE: Our aim was to analyze multiple positive patch tests to corticosteroids in patients sensitized to budesonide to confirm our earlier findings. METHODS: Forty-six patients with positive patch tests to budesonide were patch-tested to 17 other topical corticosteroids. The results were examined by a generalized linear model and a chi-square test. RESULTS: Substitution of the corticosteroid at the C6 and C9 positions significantly reduced the number of reactions. A different substitution at the C16 and C17 positions was less important, and that at the C21 position was of no significance. CONCLUSIONS: Patients sensitized to budesonide are most likely to react to other non-C6 and non-C9 substituted corticosteroids.

Adrenal Cortex Hormones↗
PubMed1995

Evidence for a weak angiogenic response to human colorectal cancers.

Many previous qualitative studies have shown that tumours are less vascular in the centre, and that host tissues become more vascular in close proximity to tumours. However, quantitative findings presented here for human colorectal cancer reveal some significant differences. Sections from 20 colorectal carcinomas (ten moderately and ten poorly differentiated) were immunostained with the QB/end/10 monoclonal to demonstrate blood vessels. These were measured by interactive morphometry and vascular volume density, surface density (Sv) and length density were recorded. In poorly differentiated carcinomas, the tumour centre was significantly less vascular than the periphery for all three parameters (P = 0.008 for Sv). However, no significant difference was seen for moderately differentiated tumours, which constitute the majority of colorectal cancers. Surrounding host tissues did not show a general increase in vascular density close to tumours. Furthermore, when total viable tissue was considered, the vascular density of carcinomas was not markedly different from normal mucosa. In the centre of moderately differentiated carcinomas for example, the mean value for Sv was only 1.4 times higher than the mean value for normal mucosa. These findings suggest that colorectal cancers may elicit a relatively weak angiogenic response, consistent with their exceptionally slow growth rate.

Animals↗
PubMed1995

Migraine and cluster headache--their management with sumatriptan: a critical review of the current clinical experience.

Sumatriptan is a potent and selective agonist at the vascular 5HT1 receptor which mediates constriction of certain large cranial blood vessels and/or inhibits the release of vasoactive neuropeptides from perivascular trigeminal axons in the dura mater following activation of the trigeminovascular system. The mode of action of this drug in migraine and cluster headache is discussed. On the basis of a detailed review of all published trials and available data from post-marketing studies, the efficacy, safety, tolerability and the place of oral and subcutaneous sumatriptan in the treatment of both conditions are assessed. A number of double-blind clinical trials have demonstrated that sumatriptan 100 mg administered orally is clearly superior to placebo in the acute treatment of migraine headache and achieves significantly greater response rates than ergotamine or aspirin. In other studies, 70 to 80% of patients receiving sumatriptan 6 mg sc experienced relief of migraine headaches by 1 or 2 h after administration, and patients consistently required less rescue medication for unresolved symptoms. Sumatriptan was also effective in relieving associated migraine symptoms like nausea and vomiting. Sumatriptan was equally effective regardless of migraine type or duration of migraine symptoms. Overall, approximately 40% of patients who initially responded to oral or subcutaneous sumatriptan experienced recurrence of their headache usually within 24 h, effectively treated by a further dose of this drug. In 75% of patients with cluster headache treated with sumatriptan 6 mg sc, relief was achieved within 15 min. Based on pooled study data, sumatriptan is generally well tolerated and most adverse events are transient. Adverse events following oral administration include nausea, vomiting, malaise, fatigue and dizziness. With the subcutaneous injection, injection site reactions occur in approximately 30%. Chest syumptoms are reported in 3 to 5% but have been associated with myocardial ischaemia only in rare isolated cases. The recommended dosage of sumatriptan at the onset of migraine symptoms is 100 mg orally or 6 mg subcutaneously. The recommended dosage for cluster headache is 6 mg sumatriptan sc. Sumatriptan must not be given together with vasoconstrictive substances, e.g., ergotamines, or with migraine prophylactics with similar properties, e.g., methysergide. Sumatriptan should not be given during the migraine aura. It is contraindicated in patients with ischaemic heart disease, previous myocardial infarction, Prinzmetal (variant) angina and uncontrolled hypertension.

Clinical Trials as Topic↗
PubMed1995

Recovery and phylogenetic analysis of novel archaeal rRNA sequences from a deep-sea deposit feeder.

In 1992, two independent reports based on small-subunit rRNA gene (SSU rDNA) cloning revealed the presence of novel Archaea among marine bacterioplankton. Here, we report the presence of further novel Archaea SSU rDNA sequences recovered from the midgut contents of a deep-sea marine holothurian. Phylogenetic analyses show that these abyssal Archaea are a paraphyletic component of a highly divergent clade that also includes some planktonic sequences. Our data confirm that this clade is a deep-branching lineage in the tree of life.

Animals↗
PubMed1994

Beta-adrenoreceptors in the trout (Oncorhynchus mykiss) heart: characterization, quantification, and effects of repeated catecholamine exposure.

Specific binding of the hydrophilic radioligand [3H]CGP-12177 to cell surface (functional) beta-adrenoreceptors was quantified in ventricular micropunches (2 mm diameter, 350 microns thickness) from seawater-acclimated rainbow trout held at 7-9 degrees. Binding was stereospecific, saturable, of high affinity, and displaceable by appropriate agonists and antagonists. Phentolamine failed to displace [3H]CGP at concentrations up to 10(-4) M, indicating an absence of [3H]CGP binding to alpha-adrenergic receptors. Trout ventricular beta-adrenoreceptors are exclusively of the beta 2 type. This conclusion is based on (1) the IC50 value for the beta 2-antagonist ICI 118551 (2.9 x 10(-6) M); (2) the inability of the beta 1-antagonist atenolol to displace [3H]CGP from beta-adrenoreceptors; and (3) the order of agonist-binding affinity (isoproterenol > epinephrine >> norepinephrine). The Bmax and Kd values for [3H]CGP binding to myocardial tissue were approximately 0.04 fmol micrograms protein-1 and 0.25 nM, respectively. The Bmax value indicates that the density of cell surface (functional) beta-adreno-receptors in the ventricle was 12,000 sites per cell or 3.38 sites per microns 2 of sarcolemma. The Kd and Bmax values for [3H]CGP binding to ventricular beta-adrenoreceptors were unaffected by the in vivo administration of five bolus catecholamine injections (4.0 micrograms kg-1 epinephrine, 2.0 micrograms kg-1 norepinephrine). This suggests that stress-induced increases in plasma catecholamines are unlikely to cause the down-regulation of heart beta-adrenoreceptors in fish. The method described here represents a simple but powerful technique for the quantification and characterization of adrenergic receptors in the fish heart.

Adrenergic beta-Antagonists↗
PubMed1994

Reduction of ventricular M2 muscarinic receptors in cardiomyopathic hamster (CHF 147) at the necrotic stage of the myopathy.

We have previously demonstrated that isolated ventricular myocytes from cardiomyopathic hamsters (CHF 147) during the necrotic stage (70-100 days) exhibit an attenuated contractile response to muscarinic stimulation. In the present study we have investigated whether this dysfunction may be related to a change in the density (or affinity) of cardiac muscarinic receptors. Thus, we have characterized and quantified the binding of the muscarinic antagonist [3H]-N-methyl scopolamine (NMS) to M2 muscarinic receptors in cardiac micropunches and in suspensions of isolated intact cardiomyocytes obtained from cardiomyopathic (CHF 147) and Golden Syrian hamsters. The hamsters were either 70-100 days old, when the cardiomyopathy had reached the cytolytic and necrotic stage or 30 days old, i.e. before the onset of the cardiomyopathy. In both preparations (micropunches and dissociated cardiomyocytes) the specific binding of [3H]-NMS was stereospecific, reversible, saturable, of high affinity and linearly dependent upon increasing amounts of tissue and cells. The binding site also possessed the drug specificity typical of an M2 muscarinic receptor. Saturation binding analysis revealed that the hearts of the older CHF 147 hamsters contain significantly fewer M2 muscarinic receptors than the control Golden Syrian hamsters while the affinity (Kd) was not altered. This reduction of M2 receptor number was not observed in CHF 147 hamsters at 30 days. Further, we found no differences in beta-adrenergic or in alpha 1-adrenergic binding in the two strains of hamster at either age. Thus, our results indicate that the parasympathetic regulation of cardiac function in CHF 147 hamsters may be compromised by a decreased number of muscarinic receptors at the necrotic stage of the cardiomyopathy.

Aging↗