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R Mitchell

Publications and source records attributed to R Mitchell.

At least 271 records · Page 15Linked to original sources
PubMed1988

Antinociceptive actions of descending dopaminergic tracts on cat and rat dorsal horn somatosensory neurones.

1. The actions of dopamine (DA) and DA receptor specific agonists and antagonist ionophoretically applied in the spinal dorsal horn, and of focal electrical stimulation in the region of the supraspinal DA cell groups (A9 and A11) were assessed on the somatosensory responses of dorsal horn neurones, in both the rat and cat. The neurones tested were multireceptive, giving reproducible responses to both noxious (using a mechanical pinch or radiant heat) and innocuous (using a motorized brush) cutaneous stimuli, as well as to ionophoretically applied DL-homocysteic acid (DLH, a direct excitant). In the cat, all neurones tested were identified as belonging to the spinocervical tract (SCT) and were located in the dorsal horn laminae III-V, whilst in the rat, spinothalamic tract (STT) and spinomesencephalic (SMT) neurones located in the region of lamina I and laminae III-V were tested. 2. Ionophoretically applied DA and RU24213, a D2 DA receptor agonist, caused a selective inhibition of the responses to noxious stimuli of SCT, STT and SMT neurones, whilst the responses to non-nociceptive stimuli, spontaneous activity and DLH-evoked activity were unaffected. This action was reversed in the presence of sulpiride, the highly selective D2 DA receptor antagonist. Neither sulpiride alone nor SKF38393, a D1 DA receptor agonist, altered evoked or spontaneous activity when ionophoretically applied. 3. Focal electrical stimulation in the region of the A11, but not the A9, DA cell group selectively suppressed nociceptive responses of spinal, multireceptive neurones in the rat. This stimulus-evoked effect was consistently and rapidly reversed by ionophoresis of sulpiride, in the vicinity of the dorsal horn neurone being tested. In contrast, naloxone and idazoxan (RX781094), an alpha 2-antagonist, were not effective. 4. This study presents data supporting a selective antinociceptive role for DA at the spinal level, where it has a widespread antinociceptive influence, on cells in both the superficial and deeper dorsal horn. The A11 DA cell group was shown to be a supraspinal site from which a selective antinociceptive action could be electrically evoked and which was mediated by DA at the level of the dorsal horn.

Action Potentials↗
PubMed1988

Presence of an unusual methanogenic bacterium in coal gasification waste.

Methanogenic bacteria growing on a pilot-scale, anaerobic filter processing coal gasification waste were enriched in a mineral salts medium containing hydrogen and acetate as potential energy sources. Transfer of the enrichments to methanol medium resulted in the initial growth of a strain of Methanosarcina barkeri, but eventually small cocci became dominant. The cocci growing on methanol produced methane and exhibited the typical fluorescence of methanogenic bacteria. They grew in the presence of the cell wall synthesis-inhibiting antibiotics d-cycloserine, fosfomycin, penicillin G, and vancomycin as well as in the presence of kanamycin, an inhibitor of protein synthesis in eubacteria. The optimal growth temperature was 37 degrees C, and the doubling time was 7.5 h. The strain lysed after reaching stationary phase. The bacterium grew poorly with hydrogen as the energy source and failed to grow on acetate. Morphologically, the coccus shared similarities with Methanosarcina sp. Cells were 1 mum wide, exhibited the typical thick cell wall and cross-wall formation, and formed tetrads. Packets and cysts were not formed.

Journal Article↗
PubMed1988

The role of protein kinase C in LHRH-induced LH and FSH release and LHRH self-priming in rat anterior pituitary glands in vitro.

We have investigated the role of protein kinase C (PKC) in LHRH-induced LH and FSH secretion and LHRH priming. Hemipituitary glands from prooestrous rats were incubated with agents known to affect PKC and with or without LHRH, during which time the secretion of gonadotrophins was measured. Phorbol esters and phospholipase C, activators of PKC, released LH and FSH in a concentration-dependent manner and potentiated the LHRH-induced secretion of gonadotrophins in parallel with their ability to release these hormones alone. Inhibitors of PKC had either no effect on LH release (1-(5-isoquinolinesulphonyl)-2-methylpiperazine hydrochloride) or they augmented LHRH-induced gonadotrophin release (polymyxin B and 8-(N,N-diethylamino) octyl-3,4,5-trimethoxybenzoate). Neither the activators nor the inhibitors of PKC, when present with LHRH, caused any change in LHRH priming, even though the activators alone produced a release of gonadotrophins that showed a temporal pattern similar to that produced by LHRH priming. The profiles of effects on LH and FSH secretion were always qualitatively similar. These results show that PKC may be involved in general regulation of gonadotrophin release but that it is not important in acute responses to LHRH nor in LHRH self-priming.

Animals↗
PubMed1988

Facilitated calcium mobilization and inositol phosphate production in the priming effect of LH-releasing hormone in the rat.

The ability of LHRH to induce Ca2+ mobilization and production of inositol phosphates in rat anterior pituitary tissue in vitro was investigated in relation to the self-priming effect of LHRH. Prior exposure to LHRH (which caused a characteristic potentiation of subsequent secretory responses) specifically enhanced LHRH-induced inositol phosphate production and mobilization of intracellular Ca2+ stores. LHRH-induced influx of Ca2+ through dihydropyridine-sensitive Ca2+ channels was unaltered, as was ligand binding to LHRH receptors. These data suggest that a novel facilitation of signalling may occur in the phospho-inositide-Ca2+ mobilization response mechanism during LHRH priming, and that this may represent an important means of regulating cellular responsiveness in gonadotrophs.

Animals↗
PubMed1988

Addition of growth hormone secretion signal to basic fibroblast growth factor results in cell transformation and secretion of aberrant forms of the protein.

Basic fibroblast growth factor (bFGF) is a potent mitogen for a wide variety of cell types. Unlike most growth factors, the primary translation product for bFGF appears to lack a secretory signal peptide. To explore the normal mode of bFGF release, as well as to investigate the growth factor's oncogenic potential, expression vectors were created for a bFGF cDNA and for a chimeric molecule in which the bFGF coding sequence was linked to the human growth hormone signal peptide sequence. Transfection of NIH3T3 cells with the bFGF cDNA vectors caused the synthesis of high levels of biologically active, cell-associated bFGF, but no evidence of transformation was detected. In contrast, the chimeric bFGF-signal peptide expression vector induced foci of transformation at a very high frequency. The transformed cells grew in soft agar and were tumorigenic in nude mice. The majority of the immunoreactive bFGF species made by the transformed cells was found in the conditioned medium and appeared to be posttranslationally modified, indicating that the chimeric bFGF-signal peptide molecule was processed through the secretory pathway. The secreted bFGF exhibited little mitogenic activity, suggesting that interaction of bFGF with its receptor likely occurs while the fusion protein is being processed along the secretory pathway.

Animals↗
PubMed1987

Protonmotive stoichiometry of rat liver cytochrome c oxidase: determination by a new rate/pulse method.

The stoichoimetry of vectorial H+ ejection coupled to electron flow through the cytochrome c oxidase (EC 1.9.3.1) of rat liver mitochondria was determined by a new rate/pulse method. This is a modification of the oxygen-pulse method. Electron flow through the oxidase is initiated by adding oxygen to suspensions of anaerobic mitochondria at a known and constant rate. Cytochrome c oxidase was examined directly or in combination with cytochrome c reductase (ubiquinol:ferricytochrome c oxidoreductase). In both cases the----H0+/2e- ratio was found to be constant during the time-course of oxygen reduction, and thus independent of delta pH. The stoichiometries observed were consistent with mechanistic stoichiometries of 2 and 6 for cytochrome c oxidase alone and cytochrome c oxidase together with cytochrome c reductase, respectively. The stoichiometry of cytochrome c reductase alone was also examined, by using ferricyanide in place of oxygen. The results obtained were consistent with the accepted mechanistic stoichiometry of 4 for this enzyme.

Animals↗
PubMed1987

Mechanisms leading to hypogonadism in men with burns injuries.

A profound and persistent depression of serum testosterone concentrations was found in 19 men with burns injuries. This could not be explained by changes in sex hormone binding globulin capacity, hyperprolactinaemia, classical primary testicular failure, or a hypogonadotrophic state. Pulsatile release of luteinising hormone was found in control subjects but was absent or diminished in burnt patients with low serum testosterone concentrations. In addition, these patients showed reduced biological activity of luteinising hormone as measured by bioassay even though normal concentrations of luteinising hormone were detected by radioimmunoassay. The temporary hypogonadism after burns injury and possibly in other clinical states may be related to hypothalamic dysfunction, which leads to abnormal generation of luteinising hormone releasing hormone and non-pulsatile secretion of luteinising hormone of reduced biological activity.

Adult↗
PubMed1987

Who may give blood?

Explore the source record for details and available documents.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Epithelial wound healing enhanced by transforming growth factor-alpha and vaccinia growth factor.

Epidermal regeneration following middermal injuries to skin requires both proliferation and migration of keratinocytes. Epidermal growth factor (EGF) stimulates the proliferation of keratinocytes in culture, and topical administration of EGF accelerates epidermal regeneration of partial thickness burns or split-thickness incisions in vivo. Transforming growth factor-alpha (TGF-alpha) and vaccinia growth factor (VGF) have substantial sequence homology with EGF, and all appear to bind to the same receptor protein. Whether TGF-alpha or VGF can affect epidermal wound healing in vivo is not known. The present studies show that topical administration of TGF-alpha or VGF in antibiotic cream to partial thickness burns (second degree) accelerated epidermal regeneration in comparison with untreated or vehicle-treated burns. Low levels of both TGF-alpha and VGF (0.1 microgram per milliliter) appeared to be more effective than EGF in stimulating epidermal regeneration. Regenerated epithelium from burns treated with TGF-alpha or VGF appeared normal histologically. This finding suggests that topical application of selected growth factors may be useful in accelerating healing of partial thickness injuries.

Animals↗
PubMed1987

Ethanol and leucine oxidation--III. Leucine oxidation by rat heart in vitro.

The activities of leucine aminotransferase (BCAT) and 2-oxoisocaproate dehydrogenase (OADH) were measured in rat heart in vitro. The effect upon these enzyme activities of both ethanol and acetaldehyde, administered either acutely or chronically, was determined. Enzyme activities were not significantly altered by either acetaldehyde or ethanol when given chronically. Ethanol administered acutely to rats decreased OADH activity but BCAT was unaffected. Acetaldehyde administered acutely did not alter significantly BCAT activity but significantly increased OADH activity.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1987

Pituitary follicular cells produce basic fibroblast growth factor.

Cultured monolayers of bovine pituitary follicular cells, which transport ions, contain high amounts of mitogenic activity for endothelial cells which, on the basis of gene expression analysis, heparin-Sepharose elution profile, bioassay, immunoblotting, radioimmunoassay, and radioreceptor assay, has been identified as basic fibroblast growth factor (bFGF). These data indicate that follicular cells may be a major source of bFGF in the pituitary gland. Considering that bFGF has been proposed to play a role in paracrine regulation of pituitary hormone secretion, the data also suggest that these cells may exert important local regulatory functions.

Animals↗
PubMed1987

Prognostic factors for continued or rebleeding and death from gastrointestinal haemorrhage in the elderly.

We analysed 103 episodes of upper gastrointestinal bleeding in 88 elderly patients (age 76 +/- 7.7 years) to determine which of a group of 52 clinical and laboratory variables, measured on admission, best predicted continued or rebleeding, and death in these patients. Variables which related directly to the size of the bleed (blood urea, haemoglobin, pulse rate, systolic blood pressure) were all strongly predictive of both outcomes (P less than 0.001). Of the variables unrelated to the size of the bleed, prolonged prothrombin time and elevated serum creatinine were most strongly predictive of a poor outcome, suggesting that haemostatic dysfunction may be a major contributor to death from upper gastrointestinal haemorrhage in elderly patients. Other variables with strong predictive potential were age (P less than 0.001), the presence of multiple disease states (P less than 0.01), therapy with multiple drugs (P less than 0.01) and acute stroke or obtundation on admission (P less than 0.01). In general terms the size of the bleed was as significant as the premorbid condition of the patient in predicting the outcome. This, together with the fact that half the patients died of hypovolaemia, suggests that death from upper gastrointestinal bleeding in the elderly is not inevitable and that further reduction in mortality from this cause is attainable.

Aged↗
PubMed1987

Serological characterisation of a mouse monoclonal anti-P-like antibody.

An IgM mouse monoclonal antibody, LM 147/328, raised against an Escherichia coli immunogen, was found to possess anti-P-like specificity. It is proposed that this antibody recognises an epitope on a Gal beta 1-3GalNAc disaccharide structure (GalNAc = N-acetyl-D-galactosamine). The haemagglutinating activity of this antibody was consistently strong with adult erythrocytes, but gave significantly weak reactions with about 7% of cord erythrocyte samples.

Animals↗