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Davison AP, Jones JA, Dixon RM. Separate quantification of doubly and singly 13C-labeled metabolites by HSQC-filtered J spectroscopy. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 1999; 137:448-450. [PMID: 10089181 DOI: 10.1006/jmre.1998.1698] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
NMR detection of multiply labeled compounds in biological samples is often used to follow metabolic pathways. Detection of protons bound to 13C atoms offers a more sensitive approach than direct 13C detection, but generally results in the loss of carbon-carbon coupling information. We have modified an HSQC sequence to refocus the carbon chemical shifts in order to obtain a proton-correlated 13C homonuclear J spectrum, which allows us to measure singly and doubly labeled compounds in the same spectrum.
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Dixon RM, Mooney CT. Evaluation of serum free thyroxine and thyrotropin concentrations in the diagnosis of canine hypothyroidism. J Small Anim Pract 1999; 40:72-8. [PMID: 10088086 DOI: 10.1111/j.1748-5827.1999.tb03040.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Canine thyroid-stimulating hormone (cTSH), total thyroxine (T4) and free T4 by equilibrium dialysis (fT4d) were measured in serum samples from 107 dogs with clinical signs suggestive of hypothyroidism in which the diagnosis was either confirmed (n = 30) or excluded (n = 77) by exogenous TSH response testing. Median serum total T4 and fT4d concentrations were significantly lower and cTSH significantly higher (P < 0.001) in hypothyroid compared with euthyroid dogs. Differential positive rate analysis determined optimal cut-off values of less than 14.9 nmol/litre (total T4), less than 5.42 pmol/litre (fT4d), greater than 0.68 ng/ml (cTSH), less than 17.3 (T4 to cTSH ratio), and less than 7.5 (fT4d to cTSH ratio) for hypothyroidism. These had a sensitivity and specificity of 100 and 75.3 per cent, 80 and 93.5 per cent, 86.7 and 81.8 per cent, 86.7 and 92.2 per cent, and 80 and 97.4 per cent, respectively, for diagnosing hypothyroidism. Corresponding areas under the receiver operating characteristic curves were 0.92, 0.93, 0.87, 0.93 and 0.93. Unexpectedly low cTSH values in hypothyroid dogs may have resulted from concurrent non-thyroidal illness. Unexpectedly high serum cTSH values in the euthyroid dogs might have resulted from recovery from illness or concurrent potentiated sulphonamide therapy. Measurement of endogenous cTSH concentration is a valuable diagnostic tool for canine hypothyroidism if used in association with assessment of T4. Estimation of fT4d added only limited additional information over total T4 measurement.
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Dixon RM, Stockdale CR. Associative effects between forages and grains: consequences for feed utilisation. ACTA ACUST UNITED AC 1999. [DOI: 10.1071/ar98165] [Citation(s) in RCA: 157] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Intake of metabolisable energy (ME) when forages and grains are fed together
to ruminants may, due to digestive and metabolic interactions, be lower or
higher than expected from feeding these components separately. These
interactions, or associative effects, are due primarily to changes in the
intake and/or the digestibility of the fibrous components of forage.
Effects on voluntary forage intake (substitution effects) are usually much
larger than on the digestibility of fibrous components, although the changes
in forage intake may be a consequence of changes in the rate of digestion of
the fibrous components. Positive associative effects, where grains increase
voluntary intake and/or digestion of forage, are usually due to the
provision of a limiting nutrient (eg. nitrogen, phosphorus) in the grain which
is deficient in the forage. Negative associative effects, where grains
decrease voluntary intake and/or digestion of forage, occur frequently and
can cause low efficiency of utilisation of grain.
Rate of substitution of grain for forage is related to forage intake, forage
digestibility, the proportion of grain in the diet, and the maturity of the
animal. Substitution rates are usually high in ruminants consuming high
intakes of forage of high digestibility, probably due to the metabolic
mechanisms which control voluntary intake reducing forage intake. Substitution
rates are often low when animals are consuming forage of low to medium
digestibility. Since voluntary intake of such forages is most likely
determined by the capacity of the rumen to accommodate and pass to the lower
gastrointestinal tract undigested forage residues, and of the rate of forage
fibre digestion in the rumen, substitution is likely to be determined by
changes in these processes. Reduced rate of fibre digestion in the rumen is
often due to low rumen pH and/or an insufficiency of essential substrates
for rumen microorganisms. Use of grains for lactating dairy cows involves an
additional constraint since dietary grain may severely reduce milk fat
content. Negative associative effects can be alleviated by ensuring supply of
essential microbial substrates, feeding management, and modification of grain
to minimise their adverse effects on fibre digestion, while ensuring
satisfactory digestion of the grain and efficient microbial protein
production.
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Dixon RM. Effects of addition of urea to a low nitrogen diet on the rumen digestion of a range of roughages. ACTA ACUST UNITED AC 1999. [DOI: 10.1071/ar98185] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Four steers were given 2 diets consisting of oat hay and molasses which
contained either no urea or 4% urea. Sixteen roughages (including
cottonwool, straws, alkali-treated straws, and grass and legumes hays) were
incubated in synthetic fibre bags in the rumen for 24 h, and the disappearance
from the bags of insoluble organic matter (OM) was determined. In steers given
molasses containing 4% urea, rumen ammonia concentrations exceeded 100
mg N/Lfor only about 5 h during the 24-h cycle and were <50 mg
N/L within about 4 h after feeding. In steers given molasses without urea,
rumen ammonia concentration averaged 7 mg N/L. The depression in OM
disappearance from synthetic fibre bags due to the low rumen ammonia
concentrations, expressed as a percentage of the disappearance at the higher
rumen ammonia concentration, ranged among the roughages from 24 to 87%,
and was inversely related to the N content of the roughage. In additional
experiments the differences in ammonia concentration between rumen fluid
sampled from the ventral sac of the rumen and fluid extracted from synthetic
fibre bags were small compared with the differences between diets. These
results indicated that the effect of low rumen ammonia concentrations on
microbial digestion in the rumen varied widely among roughages.
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Griffin JL, Rae C, Dixon RM, Radda GK, Matthews PM. Excitatory amino acid synthesis in hypoxic brain slices: does alanine act as a substrate for glutamate production in hypoxia? J Neurochem 1998; 71:2477-86. [PMID: 9832146 DOI: 10.1046/j.1471-4159.1998.71062477.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Excitatory amino acids are an important cause of cell death in the hypoxic and ischaemic brain. Neuronal glutamate stores are depleted rapidly in hypoxia, but alanine production rises under such conditions and has been suggested to be a potential precursor of glutamate. To test this hypothesis, we have investigated amino acid metabolism using 13C NMR with superfused guinea pig cortical slices subjected to varying degrees of hypoxia. During severe hypoxia, brain slices metabolising 5 mM [2-(13)C]pyruvate exported [2-(13)C]alanine into the superfusion fluid. The metabolic fate of alanine during normoxia and hypoxia was tested by superfusion of brain slices with 10 mM glucose and 2 mM [2-(13)C,15N]alanine. Metabolism of exogenous alanine leads to the release of aspartate into the superfusion fluid. The pattern of labelling of aspartate indicated that it was synthesised via the glial-specific enzyme pyruvate carboxylase. 13C-labelled glutamate was produced with both normoxia and hypoxia, but concentrations were 30-fold lower than for labelled aspartate. Thus, although substantial amounts of glutamate are not synthesised from alanine in hypoxia, there is significant production of aspartate, which also may have deleterious effects as an excitatory amino acid.
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Abstract
The detection of lymphomatous infiltration of the liver has implications for the staging and treatment of this disease. Our studies of patients with Hodgkin's disease and non-Hodgkin's lymphoma suggest that the involvement of the liver could be detected by 31P nuclear magnetic resonance (NMR) spectroscopy as an increase in the phosphomonoester/ATP and phosphomonoester/Pi ratios in the liver spectra in vivo. Studies of extracts of lymphomatous lymph nodes and of the lymphomatous mouse liver, showed that phosphoethanolamine was largely responsible for the increase in the phosphomonoester (PME) signal. This compound is involved in phospholipid metabolism, as a precursor and breakdown product of phosphatidylethanolamine. The kinetics of the synthesis of phosphatidylethanolamine from [13C2]ethanolamine were studied using 13C NMR spectroscopy. The increase in phosphoethanolamine in the lymphomatous liver was not found to be due to increased flux through the synthetic pathway to phosphatidylethanolamine, nor was it due to increased availability of ethanolamine.
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Rae C, Scott RB, Thompson CH, Dixon RM, Dumughn I, Kemp GJ, Male A, Pike M, Styles P, Radda GK. Brain biochemistry in Duchenne muscular dystrophy: a 1H magnetic resonance and neuropsychological study. J Neurol Sci 1998; 160:148-57. [PMID: 9849797 DOI: 10.1016/s0022-510x(98)00190-7] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Duchenne muscular dystrophy (DMD) is a progressive muscle disorder associated with an intellectual deficit which is non-progressive. We obtained localised 1H magnetic resonance spectra from the left frontal lobe and left cerebellum of 15 boys with DMD (mean age 106 months+/-32) and 15 similarly aged control boys (mean age 115 months+/-31); all boys underwent a battery of neuropsychological tests. We found a significant (P<0.01) increase in the ratio of choline-containing compounds to N-acetylaspartate (Cho/NA) in the left cerebellum in boys with DMD compared with control boys. There was no change in the creatine/NA ratio and a significant increase (P=0.03) in the Cho/creatine ratio, suggesting that the change in Cho/NA ratio was due to an increase in choline-containing compounds; this increase has been previously observed in the brain of the murine model of DMD, the mdx mouse. No significant changes were observed in spectra obtained from left frontal lobe in DMD compared to controls. We also observed a significant association between Cho/NA in the left cerebellum, and the performance of DMD boys on the Matrix Analogies Test (MAT). The MAT is a test of visuo-spatial ability and non-verbal reasoning which requires neither manual dexterity nor a verbal response for an adequate performance. A comparison of DMD boys whose cerebellar Cho/NA fell within 2 standard deviations of the control norm (0.56+/-0.24) with DMD boys whose cerebellar Cho/NA was outside this range (i.e. >0.80) revealed a significant difference in ability on the MAT (P<0.05). DMD boys whose Cho/NA ratio is more than two standard deviations higher than controls perform significantly better on the MAT than DMD boys whose Cho/NA ratio is within the normal range. This finding suggests that the observed elevation in Cho/NA and Cho/creatine is not associated with intellectual deficit (as sampled by the MAT), and may represent a compensatory mechanism. The possible interpretations of these metabolic changes are discussed.
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Rae C, Karmiloff-Smith A, Lee MA, Dixon RM, Grant J, Blamire AM, Thompson CH, Styles P, Radda GK. Brain biochemistry in Williams syndrome: evidence for a role of the cerebellum in cognition? Neurology 1998; 51:33-40. [PMID: 9674775 DOI: 10.1212/wnl.51.1.33] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE To determine what biochemical changes may occur in the brain in Williams syndrome (WS) and whether these changes may be related to the cognitive deficits. BACKGROUND WS is a rare, congenital disorder with a characteristic physical, linguistic, and behavioral phenotype with known cognitive deficits. METHODS We obtained 31P magnetic resonance spectra (MRS) from a region consisting of mostly frontal and parietal lobe of 14 patients with WS (age, 8 to 37 years) and 48 similarly-aged controls. 1H MRS (27 cm3) localized to the left cerebellum obtained from the WS cohort were compared with those from 16 chronological age- and sex-matched normal controls. A battery of cognitive tests were administered to all subjects undergoing 1H MRS. RESULTS WS brains exhibited significant biochemical abnormalities. All 31P MRS ratios containing the phosphomonoester (PME) peak were significantly altered in WS, suggesting that PME is significantly decreased. Ratios of choline-containing compounds and creatine-containing compounds to N-acetylaspartate (Cho/NA and Cre/NA) were significantly elevated in the cerebellum in WS cf. controls, whereas the ratio of Cho/Cre was not altered. This suggests a decrease in the neuronal marker N-acetylaspartate in the cerebellum. Significant correlations were found between the cerebellar ratios Cho/NA and Cre/NA and the ability of all subjects at various neuropsychological tests, including Verbal and Performance IQ, British Picture Vocabulary Scale, Ravens Progressive Matrices, and Inspection Time. CONCLUSIONS The correlations can be interpreted in two ways: 1) Our sampling of cerebellar biochemistry reflects a measure of "global" cerebral biochemistry and is unrelated to cerebellar function, or 2) The relations indicate that cerebellar neuronal integrity is a requirement (on a developmental time scale or in real-time) for ability on a variety of cognitive tests.
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Rae C, Lee MA, Dixon RM, Blamire AM, Thompson CH, Styles P, Talcott J, Richardson AJ, Stein JF. Metabolic abnormalities in developmental dyslexia detected by 1H magnetic resonance spectroscopy. Lancet 1998; 351:1849-52. [PMID: 9652669 DOI: 10.1016/s0140-6736(97)99001-2] [Citation(s) in RCA: 127] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
BACKGROUND Neurological and physiological deficits have been reported in the brain in developmental dyslexia. The temporoparietal cortex has been directly implicated in dyslexic dysfunction, and substantial indirect evidence suggests that the cerebellum is also implicated. We wanted to find out whether the neurological and physiological deficits manifested as biochemical changes in the brain. METHODS We obtained localised proton magnetic resonance spectra bilaterally from the temporo-parietal cortex and cerebellum of 14 well-defined dyslexic men and 15 control men of similar age. FINDINGS We found biochemical differences between dyslexic men and controls in the left temporo-parietal lobe (ratio of choline-containing compounds [Cho] to N-acetylaspartate [NA] p< or =0.01) and right cerebellum (Cho/NA, p< or = 0.01; creatine [Cre] to NA p< or =0.05; (not significant). We found lateral biochemical differences in dyslexic men in both these brain regions (Cho/NA in temporo-parietal lobe, left vs right, p< or =0.01; Cre/NA in cerebellum, left vs right, p< or =0.001). We found no such lateral differences in controls. There was no significant relation between the degree of contralateral chemical difference and handedness in dyslexic or control men. INTERPRETATION We suggest that the observed differences reflect changes in cell density in the temporo-parietal lobe in developmental dyslexia and that the altered cerebral structural symmetry in dyslexia is associated with abnormal development of cells or intracellular connections or both. The cerebellum is biochemically asymmetric in dyslexic men, indicating altered development of this organ. These differences provide direct evidence of the involvement of the cerebellum in dyslexic dysfunction.
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Peck RW, Seaber EJ, Dixon RM, Layton GR, Weatherley BC, Jackson SH, Rolan PE, Posner J. The pharmacodynamics and pharmacokinetics of the 5HT1B/1D-agonist zolmitriptan in healthy young and elderly men and women. Clin Pharmacol Ther 1998; 63:342-53. [PMID: 9542478 DOI: 10.1016/s0009-9236(98)90166-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
OBJECTIVE Zolmitriptan is a selective 5HT1B/1D-agonist for the treatment of migraine. In this study we investigated the cardiovascular and central nervous system effects and the pharmacokinetics of zolmitriptan in young and elderly adults. METHODS Twelve young adult and 12 elderly volunteers received single doses of 5, 10, and 15 mg zolmitriptan during a randomized, double-blind, placebo-controlled study. Blood pressure, heart rate, ECG, and central nervous system effects were monitored, and pharmacokinetic parameters of zolmitriptan and its metabolites calculated. RESULTS Zolmitriptan did not affect heart rate and had little effect on systolic blood pressure in the young adults. In the elderly, mean peak supine systolic blood pressure values were 9 to 16 mm Hg higher after zolmitriptan than after placebo. Mean peak diastolic pressure was 6 to 10 mm Hg higher in both age groups. These changes were transient. Postural changes in blood pressure were unaffected. There was a dose-related increase in sedation, but the magnitude of the effects was small. Mean observed peak plasma concentration (Cmax) and area under the plasma concentration-time profile [AUC(0-infinity)] for zolmitriptan and its active N-desmethyl metabolite were similar in both age groups but higher in young women than in young men. Metabolite/parent ratios probably the result of greater first-pass metabolism in young men. Zolmitriptan half-life was 2.8 to 3.6 hours in the elderly compared with 2.7 to 2.9 hours in young adults. Mean Cmax and AUC(0-infinity) for the inactive, N-oxide, and the indole acetic acid metabolites were higher in the elderly, associated with lower renal clearance. CONCLUSIONS Zolmitriptan was well tolerated, with an effect of age on its effects on blood pressure and the pharmacokinetics of its metabolites. The data suggest no need for dose adjustment for age. In young subjects, concentrations were higher in women than in men, but the differences were insufficient to justify dosage adjustment.
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Dixon RM, Meire HB, Evans DH, Watt H, On N, Posner J, Rolan PE. Peripheral vascular effects and pharmacokinetics of the antimigraine compound, zolmitriptan, in combination with oral ergotamine in healthy volunteers. Cephalalgia 1997; 17:639-46. [PMID: 9350383 DOI: 10.1046/j.1468-2982.1997.1706639.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Members of the new class of antimigraine compounds, 5HT1B/1D agonists, as well as ergotamine, may cause vasoconstriction through stimulation of 5HT receptors on peripheral vessels. The cardiovascular effects of 20 mg oral zolmitriptan (Zomig, formerly 311C90), 2 mg oral ergotamine and the combination were assessed in a randomized double-blind, placebo-controlled crossover study in 12 healthy subjects. Pharmacodynamic measures included oscillometric blood pressure, systolic blood pressure at the toe and arm using a strain gauge technique, stroke volume and cardiac output using bioimpedance cardiography, high-resolution ultrasound to measure brachial arterial diameter and a novel Doppler method to measure blood flow velocity. Both drugs produced small degrees of peripheral vasoconstriction, including increases in diastolic blood pressure and blood flow velocity and decreases in arterial diameter and toe-arm systolic pressure gradient. These effects were generally additive with the combination but of no clinical importance. There were no significant changes in cardiac output, stroke volume heart rate or ECG. Zolmitriptan, at eight times the likely therapeutic dose, was generally well tolerated both alone and in combination with ergotamine. Ergotamine had no clinically important effects on zolmitriptan pharmacokinetics.
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Dixon RM, Pasnak R. Perceptions of the risk of child abduction or loss and the utility of child electronic security devices. Child Care Health Dev 1997; 23:415-21. [PMID: 9339768 DOI: 10.1111/j.1365-2214.1997.tb00908.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Perceptions of the susceptibility of young children to becoming lost or being abducted, and of the potential usefulness of child electronic security devices, were examined via a questionnaire. Data were provided by 41 volunteers, most of them from a local government office centre. The questionnaire asked for demographic data, and then for the risk of a child being abducted or lost when under the supervision of different caregivers and in different situations. The probable effectiveness of three common abductor ploys was also addressed. The questionnaire concluded with 10 questions about child electronic security devices. Respondents viewed mothers, fathers, and grandparents as equally responsible caregivers and young adults/babysitters as the least responsible. These effects diminished as the age of the children increased. The garden at home was judged to be the most secure environment for children of all ages, while an amusement park was judged the least secure environment. Children were perceived to be more at risk of an abduction when a stranger asked for physical assistance or to take them to the hospital because their parents were hurt, than when asked for directions. Furthermore, the respondents expressed a moderately strong need for child electronic security devices, and viewed parents who use them as more responsible than those who do not.
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Marshall PW, Williams AJ, Dixon RM, Growcott JW, Warburton S, Armstrong J, Moores J. A comparison of the effects of aspirin on bleeding time measured using the Simplate method and closure time measured using the PFA-100, in healthy volunteers. Br J Clin Pharmacol 1997; 44:151-5. [PMID: 9278200 PMCID: PMC2042813 DOI: 10.1046/j.1365-2125.1997.00639.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
AIMS The aim of this study was to compare the effects of aspirin on platelet function as measured by the 'classical' template bleeding time with a new ex vivo method measuring closure times using the PFA-100 machine. Platelet aggregation in response to arachidonic acid was also measured ex vivo. METHODS The trial was a randomized, double-blind, placebo-controlled crossover design, with each volunteer taking 750 mg aspirin (BP) or placebo, three times a day for 5 days, with an 18 day wash-out period between treatments. Bleeding times and closure times were measured before the first dose on the first day and 0.5 h after the last dose on the fifth day of each treatment period. They were also measured 2 weeks after the last day of the trial. RESULTS Baseline bleeding times (pre-placebo) were 415 s using the Simplate, whilst baseline closure times were 115 s using the PFA-100. Aspirin treatment caused an increase of both the template bleeding time (61%) and the closure time of the PFA-100 (79%) when compared with the effects of placebo. The platelet aggregatory response to arachidonic acid was completely inhibited following aspirin treatment and was unaffected following placebo. Two weeks after the end of the trial, all values had returned to pre-treatment levels. The template bleeding time was unaltered in 1 of the 12 volunteers during aspirin treatment and was significantly prolonged in 3 of the 12 volunteers during placebo treatment. The PFA-100 closure time was unaltered in 1 of the 12 volunteers during aspirin treatment and was prolonged in 1 subject during placebo treatment. CONCLUSIONS The change in closure time using the PFA-100 is as sensitive and reproducible to the effects of aspirin on platelet function as is the template bleeding time test. However, the PFA-100 produced less variable effects with fewer false positive results.
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Sonnenberg GE, Garg DC, Weidler DJ, Dixon RM, Jaber LA, Bowen AJ, DeChemey GS, Mullican WS, Stonesifer LD. Short-term comparison of once- versus twice-daily administration of glimepiride in patients with non-insulin-dependent diabetes mellitus. Ann Pharmacother 1997; 31:671-6. [PMID: 9184703 DOI: 10.1177/106002809703100601] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
OBJECTIVE To investigate the metabolic effects and frequency of adverse events with 6 mg of glimepiride, a new oral sulfonylurea, given both in once- and twice-daily dosages to patients with non-insulin-dependent diabetes mellitus (NIDDM). RESEARCH DESIGN AND METHODS This 15-week study involved 161 subjects with NIDDM. Subjects were randomized into two groups. For 4 weeks, group 1 received glimepiride 3 mg twice daily, and group 2 received glimepiride 6 mg once daily. After a 3-week placebo-washout period, twice- and once-daily regimens were crossed over for a second 4-week treatment period. Subjects were hospitalized at the end of each placebo or active-treatment phase. Their glucose concentrations were recorded at 20 time points over a 24-hour period, and their insulin and C-peptide concentrations were recorded at 16 time points over the same period. Parameters that were calculated included fasting, 24-hour, and postprandial concentrations of glucose, insulin, and C-peptide. RESULTS One hundred six patients were randomized to receive treatment; 94 completed the entire study. Existing physiologic mechanisms of glucose control were apparently unimpaired by glimepiride treatment. Insulin concentrations increased more during the postprandial glucose peaks than when subjects were fasting. Both twice- and once-daily regimens proved equally effective in reducing concentrations of fasting, postbreakfast, postlunch, and postdinner plasma glucose. Twenty-four-hour mean glucose concentrations showed a slightly greater decrease from baseline for the twice-daily regimen; the difference between the regimens was statistically significant but not clinically meaningful. The incidence of adverse events with glimepiride approximated that obtained with placebo, with both groups reporting only one adverse event, headache, in more than 5% of the subjects. CONCLUSIONS Glimepiride is equally effective whether administered once or twice daily. Glimepiride seems to stimulate insulin production primarily after meals, when plasma glucose concentrations are highest, but controls blood glucose throughout the day.
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Seaber E, On N, Dixon RM, Gibbens M, Leavens WJ, Liptrot J, Chittick G, Posner J, Rolan PE, Pack RW. The absolute bioavailability and metabolic disposition of the novel antimigraine compound zolmitriptan (311C90). Br J Clin Pharmacol 1997; 43:579-87. [PMID: 9205817 PMCID: PMC2042784 DOI: 10.1046/j.1365-2125.1997.00614.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
AIMS Two open studies in healthy volunteers were conducted to determine the absolute bioavailability and metabolic disposition of zolmitriptan (311C90), a novel 5HT1D agonist for the acute treatment of migraine. METHODS After an initial test i.v. infusion, bioavailability was assessed by comparison of AUC after an i.v. infusion (3.5 mg) and an oral tablet (10 mg), in six men and six women using a randomised, crossover design. Disposition was studied by administration of a 25 mg capsule, labelled with 100 microCi [14C]-zolmitriptan, to five men and one woman on a single occasion. RESULTS Zolmitriptan was well tolerated by both i.v. and oral routes. Adverse events were mostly mild, consistent with earlier studies and characteristic of this class of drug. Reports were similar in nature and number after both oral and i.v. dosing. Mean +/- s.d. oral bioavailability was 0.49 +/- 0.24 (0.38 +/- 0.16 in men and 0.60 +/- 0.28 in women). After oral dosing, Cmax and AUC values in women were approximately double those in men. Relative to zolmitriptan concentrations, metabolite concentrations were higher after oral dosing than after i.v., and higher in men compared with women. Half-life was significantly longer after oral dosing (mean 22%, 95% CI 6-35%). Mean +/- s.d. values for CL, V2 and t1/2,z after i.v. dosing (all subjects) were 8.7 +/- 1.7 ml min-1 kg-1, 122 +/- 321 and 2.30 +/- 0.59 h respectively. Following administration of 25 mg [14C]-zolmitriptan, 91.5% of the dose was recovered in 7 days, 64.4 +/- 6.5% in urine and 27.1 +/- 6.0% in faeces. Less than 10% was recovered unchanged in urine, with 31.1 +/- 6.4% recovered as the inactive indole acetic acid metabolite. Most of the faecal material was unchanged zolmitriptan, representing unabsorbed drug. Plasma concentrations of [14C] were slightly higher than those of the summed concentrations of known analytes zolmitriptan, the active N-desmethyl metabolite (183C91), the inactive N-oxide (1652W92) and indole acetic acid (2161W92) metabolites, which accounted for 86% of total plasma radioactivity. No other significant metabolites were detected in plasma. Some minor additional metabolites were detected in urine, none of which contributed more than 5% of the dose. CONCLUSIONS The data suggest that zolmitriptan undergoes first-pass metabolism and this is more extensive in men than in women. Zolmitriptan has suitable bioavailability for an acute oral migraine treatment and there are no significant unidentified metabolites in man.
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Metcalfe AM, Phillips P, Dixon RM, Radda GK. Vasopressin synergistically stimulates DNA synthesis in normal and regenerating rat liver cell cultures in the presence of hepatocyte growth factor. J Mol Endocrinol 1997; 18:161-6. [PMID: 9134502 DOI: 10.1677/jme.0.0180161] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Liver regeneration is significantly impaired in rats with both alpha-adrenergic hepatic denervation and hereditary vasopressin deficiency. This may implicate a direct role for these agonists in the process of compensatory hyperplasia. The mitogenic capacities of norepinephrine, vasopressin and hepatocyte growth factor (HGF), either alone or in combination were investigated by [3H]thymidine incorporation into hepatocyte cultures prepared from normal and regenerating rat livers. The results show that normal hepatocytes incorporate less [3H]thymidine in response to HGF than do regenerating hepatocytes. In addition, physiological concentrations of vasopressin cause a synergistic stimulation of [3H]thymidine uptake in rat liver cells in the presence of HGF.
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Metcalfe AM, Dixon RM, Radda GK. Wild-type but not mutant p53 activates the hepatocyte growth factor/scatter factor promoter. Nucleic Acids Res 1997; 25:983-6. [PMID: 9023107 PMCID: PMC146535 DOI: 10.1093/nar/25.5.983] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
p53 transactivates the expression of a variety of genes by binding to specific DNA sequences within the promoter. We have investigated the ability of wild-type p53 and a non-DNA binding p53 mutant to activate the hepatocyte growth factor/scatter factor (HGF/SF) promoter using chloramphenicol acetyltransferase reporter constructs. We also used deletion sequences of the HGF/SF promoter to identify which regions, if any, were responsible for p53 binding. Our results show that wild-type but not mutant p53 activates the HGF/SF promoter when using -3000 and -755 bp upstream of the HGF/SF gene. This activation is lost when promoter sequences covering -365 and -239 bp are used. Analysis of the DNA sequence between -365 and -755 bp shows one putative p53 half-site with 80% homology to the consensus sequence and another half-site 3 bases downstream of this with 100% homology to the consensus sequence. In contrast to previously identified p53 binding DNA sequences, the downstream half-site is inverted. We propose that the HGF/SF promoter can be activated by wild-type p53 in vivo and that this could be as a result of a novel form of sequence-specific DNA binding.
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Dixon RM, Meire HB, Leigh C, Posner J, Rolan PE. Evaluation of non-invasive techniques to assess vasoconstriction in healthy volunteers using methoxamine as a probe drug. Cephalalgia 1996; 16:507-17. [PMID: 8933997 DOI: 10.1046/j.1468-2982.1996.1607507.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Non-invasive methods for assessment of the vascular effects of antimigraine drugs were evaluated with respect to their utility, variability and sensitivity in a double-blind, placebo-controlled, three-period crossover study in six healthy volunteers using an intravenous vasoconstrictor, methoxamine, as a probe drug. Changes in the internal diameter of the brachial and radial arteries were measured using ultrasound which had low between-day and within-day coefficients of variation. Peak systolic velocity (PSV), time-averaged velocity (TAV), total flow, resistance (RI) and pulsatility indices (PI) were measured by Doppler from one arterial wave form. Whilst PSV and TAV increased with methoxamine, because of bradycardia, changes in PI and RI were difficult to interpret. An automatic oscillometric cuff, a mercury-in-silastic strain gauge method and the "Finapres", finger arterial blood pressure monitor were used to follow changes in systolic blood pressure (SBP). The strain gauge technique underestimated arm SBP compared to the oscillometric method but clearly showed drug-related increases whilst the Finapres did not reflect changes in blood pressure detected by the other methods.
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Dixon RM, Mooney CT. Investigation of canine hypothyroidism. Vet Rec 1996; 139:400. [PMID: 8913019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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Thompson CH, Kemp GJ, Sanderson AL, Dixon RM, Styles P, Taylor DJ, Radda GK. Effect of creatine on aerobic and anaerobic metabolism in skeletal muscle in swimmers. Br J Sports Med 1996; 30:222-5. [PMID: 8889115 PMCID: PMC1332335 DOI: 10.1136/bjsm.30.3.222] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
OBJECTIVE To examine the effect of a relatively low dose of creatine on skeletal muscle metabolism and oxygen supply in a group of training athletes. METHODS 31P magnetic resonance and near-infrared spectroscopy were used to study calf muscle metabolism in a group of 10 female members of a university swimming team. Studies were performed before and after a six week period of training during which they took either 2 g creatine daily or placebo. Calf muscle metabolism and creatine/choline ratios were studied in resting muscle, during plantar flexion exercise (10-15 min), and during recovery from exercise. RESULTS There was no effect of creatine on metabolite ratios at rest or on metabolism during exercise and recovery from exercise. Muscle oxygen supply and exercise performance were not improved by creatine if compared to placebo treated subjects. CONCLUSIONS Oral creatine supplementation at 2 g daily has no effect on muscle creatine concentration, muscle oxygen supply or muscle aerobic or anaerobic metabolism during endurance exercise.
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Dixon RM, Graham PA, Mooney CT. Serum thyrotropin concentrations: a new diagnostic test for canine hypothyroidism. Vet Rec 1996; 138:594-5. [PMID: 8799987 DOI: 10.1136/vr.138.24.594] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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Dixon RM. Phosphatidylethanolamine synthesis in the normal and lymphomatous mouse liver; a 13C NMR study. Anticancer Res 1996; 16:1351-6. [PMID: 8694501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The lymphomatous liver contains high levels of phosphoethanolamine. This compound is a precursor of the phospholipid, phosphatidylethanolamine. The kinetics of phosphatidylethanolamine synthesis has been studied by 13C NMR spectroscopy of extracts of the lymphomatous mouse liver following the administration of (13C2)ethanolamine. The concentrations of (13C2)ethanolamine, (13C2)phosphoethanolamine, and (13C2)phosphatidylethanolamine were fitted to kinetic models and the maximal activities of the enzymes in the synthetic pathway were estimated. Phosphatidylethanolamine synthesis in the normal liver appears to be limited by the supply of ethanolamine. In the lymphomatous liver, both ethanolamine kinase and PE:CTP cytidylyltransferase had lower activities than in the normal liver, and there was evidence for a higher activity of ethanolamine base-exchange enzyme.
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Dixon RM, Cramer M, Shah AK, Whitmore J, Benedict CR, Hahne WF. Single-dose, placebo-controlled, phase I study of oral dolasetron. Pharmacotherapy 1996; 16:245-52. [PMID: 8820468] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
STUDY OBJECTIVES To evaluate the safety, tolerability, and pharmacokinetics of single, escalating doses of oral dolasetron mesylate, a new 5-HT3 receptor antagonist. DESIGN Double-blind, placebo-controlled, dose-escalating phase I study. SETTING A clinical research center. PATIENTS One hundred twenty healthy male volunteers. INTERVENTIONS Subjects received either placebo or oral dolasetron mesylate 50, 100, 150, 200, 250, 300, or 400 mg. MEASUREMENTS AND MAIN RESULTS Compared with placebo, subjects receiving dolasetron mesylate reported a greater frequency of headache, light-headedness, dizziness, increased appetite, and nausea. There were no clinically significant changes in mean laboratory values from before to after treatment. Adverse events were transient, mild or moderate, and similar to those after single intravenous doses of the drug. No clinically significant electrocardiographic changes occurred, but lengthening of the QRS complex duration and dose-dependent lengthening of PR and QTc intervals were observed 1-2 hours after dosing. These effects were asymptomatic and were mainly associated with higher doses (< or = 300 mg). CONCLUSION Dolasetron mesylate is well tolerated when administered in single oral doses up to 400 mg to healthy volunteers. Clinical trials are under way to evaluate the agent's efficacy in preventing chemotherapy-induced and postoperative nausea and vomiting with doses up to 200 mg.
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Marks SJ, Dixon RM, Styles P, Ryley NG, Hockaday TD. Problems associated with using in vivo proton (1H) magnetic resonance spectroscopy to quantify liver fat. Asia Pac J Clin Nutr 1995; 4:195-198. [PMID: 24394282] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In-vivo 1H magnetic resonance (MR) spectra of the liver were obtained in 8 patients admitted for liver biopsy. These patients had abnormal liver function and the presumptive diagnosis of fatty liver prior to biopsy. Two patients with NIDDM were also studied but liver biopsies were not performed as liver function was normal. The MR spectra, obtained on a 60 cm clear-bore 1.9 tesla superconducting magnet showed two 1H resonances, one from water and the other from repeating methylene protons - (CH2)n - in triglyceride. The lipid: water signal ratio was used to characterize tissues as subcutaneous fat (high lipid:water ratio), normal liver (low lipid: water ratio) and fatty liver (intermediate lipid: water ratio). The spectra obtained at the greatest depth from the probe surface ~4.5 cm) was used as it was most likely to represent liver tissue. Although all 8 patients were expected to have fatty liver only 2 had evidence of significant fatty changes on microscopy. This was assessed by counting the vacuoles of fat over the area of the biopsy specimen and quantitated as 'fat vacuoles per high power field' (f/hpf). In the 2 patients with NIDDM, unusual stack plots suggested technical difficulties with 1H MR spectroscopy for in-vivo assessment of fatty liver. The first patient, PT had a significant increase in lipid:water ratio on the spectra thought to represent liver (lipid:water ~ 65% cf levels <3% in norma liver and 12.6% + 26.5% in those patients subsequently found to have fat on biopsy). This was later found on MR imaging to represent omental fat lying between the liver and muscle layer. The second patient, OM had a large amount of subcutaneous fat overlying the area assessed. As seen on the stack plot, the probe depth was not great enough to pass through the subcutaneous fat and muscle layer to penetrate liver tissue. There was a significant correlation between the lipid:water signal ratio and visible fat on biopsy in those patients who underwent liver biopsy. Difficulties experienced with probe depth suggests imaging would be necessary prior to spectroscopy to ensure liver tissue is actually assessed.
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Packer HL, Harrison DM, Dixon RM, Armitage JP. The effect of pH on the growth and motility of Rhodobacter sphaeroides WS8 and the nature of the driving force of the flagellar motor. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1188:101-7. [PMID: 7947898 DOI: 10.1016/0005-2728(94)90027-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Rhodobacter sphaeroides WS8 grew, and swam vigorously, over the pH range 6 to 9. Sustained motility was, however, observed in populations of cells resuspended at pH values between 4.9 and 10.4, although the mean run speed was reduced at the extremes of pH. The ability of R. sphaeroides to swim in strong alkaline conditions prompted the question of whether motility at alkaline pH was powered by a sodium motive force, as has been found in the facultative alkalophilic Bacillus and Vibrio species, particularly as motility was found to be sensitive to the sodium channel inhibitor amiloride. The nature of the driving force of the flagellar motor was therefore investigated. It was found that R. sphaeroides was motile over the same pH range in the absence and presence of sodium ions. The protonophore CCCP was found to inhibit motility under all conditions, whereas monensin, an inhibitor of sodium pumps, had no effect upon motility in the presence or absence of sodium. It was concluded that the delta p is the driving force for the flagellar motor in R. sphaeroides at all values of pH. Amiloride, a specific inhibitor of the sodium-driven flagellar motor in alkalophilic Bacillus and Vibrio was shown to act non-specifically on the proton driven motor of R. sphaeroides, reducing the swimming speed of this organism in media with and without sodium to the same extent and over the complete pH range. Measurement of the delta p by using the electrochromic absorbance change of the carotenoid pigments to measure delta psi and 31P-NMR to measure delta pH showed that the maximum delta p was about -215 mV. At pH 10 the cells swam more slowly and the delta p was about -90 mV. These data suggest that the flagellar motor of R. sphaeroides is proton-driven under all conditions with a threshold for motor rotation below -90 mV and saturation at above -90 mV and below -215 mV.
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