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Biomedical subjects

M J Clarke

Publications and source records attributed to M J Clarke.

At least 73 records · Page 4Linked to original sources
PubMed1988

Comparison of peptide release from fetal rat hypothalamic neurones cultured in defined media and serum-containing media.

Primary cultures of rat hypothalamic neurones were maintained either in a serum-supplemented medium or in a serum-free chemically defined medium for up to 6 weeks. The release of the 41 amino acid-containing peptide, corticotrophin-releasing factor (CRF-41), vasopressin (AVP) and somatostatin (SRIF) were followed using immunoassays. In response to K+ (56 mmol/l) depolarization both the quantities of peptides released and the magnitude of responses were significantly greater from cultures maintained in the fully supplemented defined medium. As a consequence, release of CRF-41 and AVP could be measured directly, without requiring the concentration step necessary for cultures grown in serum. The response to K+ depolarization increased with the age of the culture, suggesting neuronal maturation. Responses to K+ depolarization were Ca2+-dependent, and the addition of corticosterone (100 nmol/l) to the defined medium caused a significant reduction in the response of neurones secreting CRF-41 and AVP, but not those secreting SRIF, to depolarization. This suggests the retention in vitro of the responsiveness of stress-associated neuropeptides to the negative feedback effects of corticosterone. Neurones producing CRF-41 and AVP responded significantly in a dose-dependent manner to acetylcholine stimulation, whereas those producing SRIF did not. As cultures matured, the CRF-41- and AVP-producing neurones became more sensitive to acetylcholine with the maximal response at 1 nmol acetylcholine/l. In conclusion, the culture of rat hypothalamic neurones is improved in terms of peptide output when the cultures are maintained in a defined medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Ruthenium ammine complexes as electron acceptors for growth stimulation by plasma membrane electron transport.

Ammineruthenium(III) complexes have been found to act as electron acceptors for the transplasmalemma electron transport system of animal cells. The active complexes hexaammineruthenium(III), pyridine pentammineruthenium(III), and chloropentaammineruthenium(III) range in redox potential (E'0) from 305 to -42 mV. These compounds also act as electron acceptors for the NADH dehydrogenase of isolated plasma membranes. Stimulation of HeLa cell growth, in the absence of calf serum, by these compounds provides evidence that growth stimulation by the transplasma membrane electron transport system is not entirely based on reduction and uptake of iron.

Aminopyridines↗
PubMed1987

Assessment of corticotropin-releasing factor, vasopressin and somatostatin secretion by fetal hypothalamic neurons in culture.

The concomitant release of corticotropin-releasing factor (CRF), vasopressin (AVP) and somatostatin (SRIF) has been followed from primary cultures of rat hypothalamic neurons. 18-day-old fetal rat hypothalami were dissociated enzymatically and mechanically, then plated and maintained in a serum-containing medium at a density of 2.5 x 10(6) cells per dish (equivalent to 3 hypothalami). Cultured neurons remained viable for up to 6 weeks, and peptide release was followed by immuno-assay between days 14 and 39 in culture. The incubation media were concentrated on C4 and C8 silica columns to facilitate detection of CRF and AVP. Peptide release was measured at various times up to 4 h, at which point it was still increasing. To optimise measurements, taking into account peptide degradation, a 1-hour incubation period was chosen for further studies. Release of CRF, AVP and SRIF by 56 mM K+ or 10 microM veratridine was statistically significantly greater than basal (p less than 0.01) and was Ca2-dependent. For CRF and AVP, stimulated release increased considerably with the age of culture, whereas SRIF release was steadier. Basal release for all 3 peptides did not fluctuate greatly over this period. Basal and stimulated release of the peptides continued over at least 5 successive 1-hour periods. At day 35 of culture, the peptide content was still increasing in a pattern which paralleled the increasing content in hypothalami freshly removed from age-matched rats. In conclusion, we have demonstrated a development of CRF, AVP and SRIF production by neurons over extended periods in culture as assessed by their peptide content and increasing responses to depolarizing stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Chemical and biological properties of pentaammineruthenium-bleomycin complexes.

The reaction of [(H2O)(NH3)5RuII]2+ with bleomycin forms at least two stable products following oxidation to the Ru(III) analog. Spectroscopic and electrochemical measurements indicate monodentate binding of [(NH3)5RuIII] to the imidazole and pyrimidine moieties, with coordination to the latter involving the exocyclic amine nitrogen. DNA cleavage studies show the complexes to be ineffective in DNA strand scission. In vitro biological studies reveal these adducts to be cytotoxic.

Animals↗
PubMed1985

Suicides by opium and its derivatives, in England and Wales, 1850-1950.

In the mid-nineteenth century opium and its derivatives, such as laudanum and morphine, were the most common poisons in suicides in England and Wales. With legislative restrictions on these 'dangerous drugs' such a use declined. This study attempts to show this trend and indicates the large variety of these opium-related suicides.

England↗
PubMed1980

Structural and electronic effects resulting from metal-flavin ligation.

The synthesis and physical properties of a model metalloflavin complex, [(10-methylisoalloxazine)-(NH3)4Ru](PF6)2 . 2H2O are reported. The structure of this stable, enantiomeric compound was elucidated by x-ray diffraction methods with a final unweighted R value of 0.054. Crystals belong to the triclinic space group P1 with unit cell dimensions: a = 9.631, b = 10.618, c = 13.216 A; alpha = 113.86, beta = 100.19, gamma = 94.12 degrees. Chelation of the metal ion to the flavin occurs at the N(5) and O(4) positions, with a short Ru-N(5) bond distance of 1.979 A. Steric and electronic factors induce a 9.9 degrees bend in the isoalloxazine ring system and a significant lengthening of the C(4a)-N(5) bond. The flavin absorption bands shift significantly toward lower energy on complexation and a new band occurs at 617 nm. These absorptions are pH-dependent and pK alpha values for the complex are 0.6 and 7.4. The spectra of this complex exhibit similarities to that of metallosemiquinone species and arguments are made that a significant amount of electron density is donated to the pi-system of the flavin. Proton NMR studies suggest enhanced electron density at the N(10) position, probably occurring through backbonding interactions. Cyclic voltametry studies are also consistent with substantial metal to ligand pi-electron donation, since it is significantly more difficult to reduce the coordinated flavin relative to the free ligand under the same conditions. Moreover, the complexed flavin accepts electrons in 1-electron rather than 2-electron steps. Spectroelectrochemical studies on the 1-electron reduced complex indicate a similarity with other M(II)-F1 species.

Chemical Phenomena↗
PubMed1980

Mutagenic and toxic effects of ruthenium.

Selected platinum and ruthenium complexes were tested for their ability to cause Salmonella typhimurium strains TA98 and TA100 to revert to histidine independence. The results indicate that ruthenium compounds are capable of reverting both strains while cis-Cl2(NH3)2Pt primarily causes reversions in strain TA100. In addition, cis-platinum is an order of magnitude more mutagenic and toxic than are the ruthenium complexes. Selected compounds were also tested for their ability to induce the bacterial SOS system in the Bacillus subtilis Comptest. In this system, cis-platinum similarly showed greater inducing ability than did the ruthenium complexes. These results also demonstrated that the nature of the sixth ligand in the ruthenium compounds has a significant effect on the mutagenic capacity of these agents.

Bacillus subtilis↗
PubMed1980

Reduction and subsequent binding of ruthenium ions catalyzed by subcellular components.

The reduction of Cl(NH3)5Ru(III) and subsequent binding of heterocyclic ligands by the resultant (H2O)(NH3)5Ru(II) ion is shown to be catalyzed by components of rat-liver cells. The presence of air significantly decreases the rate of heterocyclic ligand binding. In the case of microsome and soluble component catalysis, this is probably due to oxidation of the Ru(II) ion prior to complexation. Various inhibitors of electron-transfer proteins were employed in an effort to determine the preferred reducing species. These results lend support to the hypothesis that the antitumor activity of acido ruthenium(III) ammine complexes involves activation by reduction in vivo prior to metal coordination to nucleic acids. Anticancer drugs functioning by this mechanism may be preferentially toxic to or may localize in hypoxic areas of tumors.

Animals↗
PubMed1975

Questionnaire surveys of passenger comfort.

This paper discusses the quantitative assessment of data obtained from questionnaire surveys. Examples are adduced from surveys carried out from Swansea. After discussing the validity of information derived in this way, general methods of assessment are described. The paper continues with a detailed examination of questionnaire methods of the subjective assessment of environmental stimuli, and concludes with examples of the pitfalls which may be inherent in such assessment.

Journal Article↗
PubMed1975

Crystal structure of a compound featuring caffeine bound at C8 to ruthenium (III).

The structure of a novel ruthenium purine compound, trans-chloro-8-caffeinechlorotriamminruthenium(III) chloride monohydrate, has been determined using single-crystal x-ray techniques. This compound crystallizes in space group Pbca (D152h) with cell dimensions a equal to 11.341 (3)A, b equal to 11.606 (5) A, c equal to 26.673 (7) A, Z equals to 8. The observed and calculated densities are 1.79 plus or minus 0.01 and 1.781 g/cm3, respectively. The structure has been refined using full-matrix least-squares methods to R equal to 0.059 based on 1314 independent observed reflections. The coordination geometry at the ruthenium atom is distorted octahedral. The carbon-ruthenium bond length is 2.03 (1) A. The chloride-ruthenium bond lengths are 2.350 (4) A and 2.427 (3) A for the cis and trans forms respectively suggesting a strong trans-influence due to the caffeine.

Caffeine↗
PubMedDate not supplied

Microwave sensing of increased intracranial water content.

A new technique to monitor brain edema is described that uses microwave energy to detect increased intracranial water content. By recording the phase of a transmitted microwave signal, increases in intracranial water content on the order of 1% are detected in vivo. These findings suggest that the progression of brain edema on a long-term basis can be assessed by progression of brain edema on a long-term basis can be assessed by our technique. Furthermore, phase changes related to small intracranial pressure variations are observed, indicating that the detection of pathologic pressure variations such as Traube-Hering-Mayer waves and plateau waves is possible by a noninvasive microwave technique.

Animals↗
PubMedDate not supplied

The miracle of DICE therapy for acute stroke: fact or fictional product of subgroup analysis?

OBJECTIVE: To determine whether inappropriate subgroup analysis together with chance could change the conclusion of a systematic review of several randomised trials of an ineffective treatment. DESIGN: 44 randomised controlled trials of DICE therapy for stroke were performed (simulated by rolling different coloured dice; two trials per investigator). Each roll of the dice yielded the outcome (death or survival) for that "patient." Publication bias was also simulated. The results were combined in a systematic review. SETTING: Edinburgh. MAIN OUTCOME MEASURE: Mortality. RESULTS: The "hypothesis generating" trial suggested that DICE therapy provided complete protection against death from acute stroke. However, analysis of all the trials suggested a reduction of only 11% (SD 11) in the odds of death. A predefined subgroup analysis by colour of dice suggested that red dice therapy increased the odds by 9% (22). If the analysis excluded red dice trials and those of poor methodological quality the odds decreased by 22% (13, 2P = 0.09). Analysis of "published" trials showed a decrease of 23% (13, 2P = 0.07) while analysis of only those in which the trialist had become familiar with the intervention showed a decrease of 39% (17, 2P = 0.02). CONCLUSION: The early benefits of DICE therapy were not confirmed by subsequent trials. A plausible (but inappropriate) subset analysis of the effects of treatment led to the qualitatively different conclusion that DICE therapy reduced mortality, whereas in truth it was ineffective. Chance influences the outcome of clinical trials and systematic reviews of trials much more than many investigators realise, and its effects may lead to incorrect conclusions about the benefits of treatment.

Bias↗