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Biomedical subjects

A Holt

Publications and source records attributed to A Holt.

At least 19 recordsLinked to original sources
PubMed2000

Comparison of neurochemical effects of the monoamine oxidase inhibitors phenelzine, moclobemide and brofaromine in the rat after short- and long-term administration.

BACKGROUND: Chronic administration of several irreversible monoamine oxidase (MAO) inhibitors induces a down-regulation of tryptamine and 5-hydroxytryptamine(2) receptors in rat brain, but there is a paucity of information available on the effects of reversible MAO-A inhibitors on these receptors. METHODS: Acute and chronic experiments were conducted in rats and the effects of the irreversible monoamine oxidase inhibitor, phenelzine and the reversible MAO type-A inhibitors, moclobemide and brofaromine, on tryptamine and 5-hydroxytryptamine(2) receptors were analysed using radioligand binding techniques. In addition, activities of MAO-A and -B were determined radiochemically and brain and/or urine levels of tryptamine, 5-hydroxytryptamine, 3-methoxy-4-hydroxyphenylglycol (MHPG), beta-phenylethylamine, brofaromine and moclobemide were determined by chromatographic procedures. RESULTS: After 30 days of administration, moclobemide and brofaromine selectively inhibited brain MAO-A activity and phenelzine inhibited MAO-A and -B to equal extents. All three drugs caused a significant down-regulation of tryptamine receptors, whereas only phenelzine significantly down-regulated 5-hydroxytryptamine(2) receptors. In a comparison of phenelzine and brofaromine, both caused marked elevations of urinary tryptamine and decreases of urinary MHPG levels, while only phenelzine increased beta-phenylethylamine levels. After 14 days of administration, phenelzine, but not moclobemide or brofaromine, significantly increased levels of tryptamine in brain; all three drugs significantly increased 5-HT levels. LIMITATIONS: 24-h urine samples were not collected for moclobemide-treated animals and brain levels of tryptamine were not measured after 30-day administration. CONCLUSIONS: These studies revealed marked neurochemical differences among phenelzine, moclobemide and brofaromine which could contribute to their actions in the clinical setting.

Animals↗
PubMed2000

The hardness and modulus of elasticity of primary molar teeth: an ultra-micro-indentation study.

OBJECTIVE: Baseline information on the mechanical properties of and the effect of load upon dental hard tissue is important in the development of successful dental materials. Existing methods of measuring such properties of tissue are subject to significant experimental error. This study reports on the use of an Ultra-Micro-Indentation System (UMIS) to measure the hardness and elastic modulus of primary enamel and dentine. METHODS: Primary molar teeth were sectioned, set in resin and polished. Thirty indentations were made in enamel and dentine using a Berkovitch indentor, 15 of which were subject to a load of 50mN and 15 to a load of 150mN. An automated computerised system converted the force/penetration graph for each indentation in to a hardness vs depth graph from which values for the mean hardness and elastic modulus were calculated. RESULTS: Primary enamel had a mean hardness of 4.88+/-0.35GPa whilst the hardness of dentine was 0.92+/-0.11GPa The elastic modulus for enamel was 80.35+/-7.71GPa and that of dentine 19.89+/-1.92GPa. Using linear regression analysis a significant relationship could be shown between the hardness and the elastic modulus for both enamel and dentine when loaded to 150mN but only for dentine at 50mN (P<0.05). In general the elasticity of tooth structure increased as the hardness increased. CONCLUSION: The UMIS offers a simple and reproducible method of measuring basic mechanical properties of small samples of enamel and dentine.

Child, Preschool↗
PubMed2000

Antenatal home blood pressure monitoring: a pilot randomised controlled trial.

OBJECTIVE: To measure recruitment to, compliance with, and the acceptability of a trial designed to test whether a reduced schedule of antenatal visits combined with training in self-measurement of blood pressure at home may improve hypertension screening and save money. To test the specific hypothesis that even after taking into account extra unscheduled visits, the reduced schedule with ambulatory monitoring reduces total visits. DESIGN: A pilot randomised controlled trial. SETTING: Four urban and four rural general practices in Yorkshire and Lancashire. POPULATION: One hundred and five low risk women in the third trimester of pregnancy. Eighty women participated. INTERVENTION: Women were invited to participate at 24-28 weeks. Those who accepted were allocated either to a standard nine subsequent visit schedule (30, 32, 34, 36, 37, 38, 39, 40, 41 weeks) or to a reduced schedule (34, 38, 41 weeks). Those in the latter group measured their blood pressure weekly using a portable sphygmomanometer at home. MAIN OUTCOME MEASURES: Recruitment, total number of clinic visits, frequency of blood pressure measurement, schedule preference, and anxiety. RESULTS: Although there were more unscheduled visits in the home monitoring group, this did not outweigh the reduction in scheduled visits, (total visits reduced from 7 x 4 to 4 x 5, P < 0 x 001), and blood pressure was measured during more weeks (9 vs 7 weeks, P < 0 x 001) in the experimental group. Most women expressed a preference for the reduced schedule both when the idea was first suggested, and after they had experienced it, and there were no significant differences in anxiety. CONCLUSION: Replacement of antenatal screening visits with home blood pressure monitoring is acceptable to women. The reduction in clinic visits is not compensated by an increase in visits for other reasons and overall blood pressure measurement is omitted less often. Whether it reduces adverse outcomes or has any rare side effects will require a larger trial, but this pilot study indicates that it is likely to be safe, and that such a large trial would be feasible.

Adult↗
PubMed1999

A database designed for utilization management in diagnostic imaging.

The methods and tools of health services research have been applied to a diverse number of health care areas. Surprisingly, they have been adopted only recently in diagnostic imaging, by a small number of professionals, in response to the severe fiscal constraints and widespread structural changes in the health industry, as well as to a growing concern that the value of social and individual investment in high-cost imaging services could not be validated objectively. As a result of the need for accountability for the use of scarce resources, regulators and payers of health services increasingly demand that a reasoned and objective evaluative process be adopted. To undertake a statistically driven evaluative approach that stands up to objective assessment of methodological rigour, an organized data-collection system is needed. Without this fundamental cornerstone, evaluators are left with little more than anecdotal evidence and professional and personal opinion to guide decision-making. It then becomes difficult to learn from both the successes and failures that are routinely experienced during times of rapid and fundamental change. This article describes the efforts made to integrate health services research in radiology into the routine daily activities and supporting systems of a large academic health system, the Hamilton Health Sciences Corporation and McMaster University Department of Radiology, in an attempt to move in the direction of evidence-based decision-making. The authors hope this will allow others to learn and improve on this work. Radiologists may then move the vast data systems and infrastructure associated with all imaging services to an evidence-based model for managing and guiding the vast resources entrusted to our collective stewardship.

Academic Medical Centers↗
PubMed1998

Identification of the quinone cofactor in mammalian semicarbazide-sensitive amine oxidase.

Mammalian semicarbazide-sensitive amine oxidase (SSAO) enzymes have been classified as EC 1.4.3.6 [amine:oxygen oxidoreductase (deaminating)(copper-containing)]. However, both the identity of the quinone cofactor and the presence of copper remain unconfirmed, and SSAO has proved impossible to purify to homogeneity in sufficient yield to permit cofactor identification. To circumvent this problem, we have partially purified SSAO enzymes from bovine and porcine aortae and have established, with a redox-cycling assay, that no other quinoproteins were present in enzyme preparations. Enzymes were then derivatized with (p-nitrophenyl)hydrazine (p-NPH), which forms a covalent yellow complex with the quinone cofactor. Visible absorbance spectra of derivatized bovine and porcine enzymes (respective lambdamax values 456 and 476 nm at neutral pH, shifting to 580 and 584 nm in 2 M KOH) were consistent with the presence of (2,4,5-trihydroxyphenyl)alanine quinone (TPQ) as cofactor. Resonance Raman spectra were essentially identical to that for pea seedling amine oxidase, a known TPQ-containing enzyme. Extensive digestion of SSAO enzymes, and of porcine kidney diamine oxidase, with pronase E yielded species with identical chromophoric properties characteristic of the dipeptide, TPQ(p-NPH)-Asp. Thermolytic digestion of porcine SSAO gave two cofactor-containing peptides that contained a TPQ consensus sequence, Asn-X-Asp-Tyr-Tyr, where X is a blank cycle corresponding to TPQ. N-terminal sequencing of whole enzymes revealed a membrane-spanning region typical of an extracellular type II glycoprotein. These results confirm the presence of TPQ in mammalian membrane-bound SSAO ectoenzymes.

Amine Oxidase (Copper-Containing)↗
PubMed1997

Determination of p-trifluoromethylphenol, a metabolite of fluoxetine, in tissues and body fluids using an electron-capture gas chromatographic procedure.

An electron-capture gas chromatographic procedure was developed for the analysis of p-trifluoromethylphenol, an O-dealkylated metabolite of fluoxetine, in biological samples. A basic extraction of the biological sample was employed, followed by derivatization with pentafluorobenzenesulfonyl chloride. The internal standard, 2,4-dichlorophenol, was added to all samples used in the procedure to aid in quantitation. The practical limit of detection (signal-to-noise ratio>3) for p-trifluoromethylphenol was <5 ng/ml in human plasma samples, <10 ng/g of rat brain tissue, <25 ng/g of rat liver tissue and <25 ng/ml in human and rat urine samples. In the rat, the levels of free p-trifluoromethylphenol in the liver were 10-fold higher than those in the brain, and a substantial amount was excreted in the urine. Human urine samples contained levels of free p-trifluoromethylphenol approximately 30-fold higher than those found in human plasma samples. The procedure described is useful for the detection and quantitation of free p-trifluoromethylphenol in humans and rats treated with fluoxetine.

Animals↗
PubMed1997

A continuous spectrophotometric assay for monoamine oxidase and related enzymes in tissue homogenates.

A continuous, peroxidase-linked spectrophotometric assay is described which is suitable for measuring monoamine and diamine oxidase and semicarbazide-sensitive amine oxidase activities in tissue homogenates. In the assay, 4-aminoantipyrine is oxidized and then condenses with vanillic acid to give a red quinoneimine dye. The absorbance at 498 nm is proportional to the amount of hydrogen peroxide released in the amine oxidase reaction. The molar absorption coefficient of the dye at pH 7.6 was 4654 M-1 cm-1. The method is suitable for use with any amine oxidase substrate which has a higher oxidation-reduction potential than does 4-aminoantipyrine. Following preincubation of rat liver homogenates with selective monoamine oxidase (MAO)-A and -B inhibitors, kinetic constants were obtained for metabolism of the mixed substrate, p-tyramine. Inhibition of MAO in rat liver homogenates was also measured following administration of the antidepressant, phenelzine. This inexpensive assay which employs reagents with low toxicity can thus be used to determine the degree of inhibition of MAO elicited by potential antidepressant and anti-parkinsonian agents. Drugs, their metabolites, and environmental toxins can also be screened as possible amine oxidase substrates or inhibitors, and kinetic constants for turnover of novel substrates can be determined.

Absorption↗
PubMed1996

Inhibition of rat brain monoamine oxidase enzymes by fluoxetine and norfluoxetine.

Fluoxetine and its primary metabolite, norfluoxetine, are inhibitors of neuronal uptake of 5-hydroxytryptamine. While fluoxetine has also been reported to inhibit monoamine oxidase (MAO) in vitro at concentrations much lower than those measured in brain following chronic fluoxetine treatment, neurochemical profiles are not consistent with substantial MAO inhibition in vivo. In an attempt to explain this inconsistency, we have examined the interactions of fluoxetine and norfluoxetine with rat brain MAO-A and -B by a radiochemical assay method. Fluoxetine and norfluoxetine were competitive inhibitors of MAO-A in vitro, with Ki values of 76.3 microM and 90.5 microM, respectively. Both compounds were non-competitive or uncompetitive inhibitors of MAO-B in vitro. Inhibition of MAO-B was time-dependent and was very slowly reversible by dialysis. IC50 values versus metabolism of 50 microM beta-phenylethylamine were 17.8 microM (fluoxetine) and 18.5 microM (norfluoxetine). Analysis of the time-dependence of MAO-B inhibition by fluoxetine revealed that an initial competitive interaction between the enzyme and the inhibitor (Ki 245 microM) was followed by tight-binding enzyme inactivation (K(inact) 0.071 min-1). Following administration of fluoxetine (20 mg kg-1 day-1) for 7 days, the cortical concentration of fluoxetine + norfluoxetine was estimated by gas-liquid chromatography to be 700 microM. Such drug treatment reduced MAO-A activity by 23% in 1:8 (w/v) cortical homogenates, but not in 1:80 homogenates. Inhibition of MAO-B in 1:8 homogenates was modest (12%) and was not significantly reduced by homogenate dilution. The concentration of 5-hydroxyindole-3-acetic acid, measured by high pressure liquid chromatography, was reduced by 47% in cortices from drug-treated rats, while concentrations of 5-hydroxytryptamine, noradrenaline, dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid were unchanged. These results suggest that, following chronic drug administration leading to relatively high tissue concentrations of fluoxetine and norfluoxetine, inhibition of either form of MAO would be restricted by competition for the enzyme with intraneuronal amine substrates.

Animals↗
PubMed1995

Metabolism of agmatine (clonidine-displacing substance) by diamine oxidase and the possible implications for studies of imidazoline receptors.

Clonidine-displacing substance, thought to be the endogenous ligand for imidazoline receptors, has been identified recently as agmatine (1-amino-4-guanidinobutane). The similarity of this compound's structure to that of the diamine oxidase (DAO) inhibitor, aminoguanidine, led us to investigate the possibility that agmatine might be a substrate for this enzyme. The metabolism of agmatine by purified porcine kidney DAO was measured by a peroxidase-linked colorimetric assay. Agmatine was a substrate for this enzyme and, under the experimental conditions used here, was metabolised at a rate of 0.8 mumol agmatine h-1 (unit DAO activity)-1. In contrast, agmatine was a substrate neither for rat brain monoamine oxidase (MAO) -A or -B, nor for rat brown adipose tissue semicarbazide-sensitive amine oxidase (SSAO). The metabolism of agmatine by DAO was inhibited by aminoguanidine (IC50 14.9 nM) and by the antidepressant, phenelzine (IC50 1.95 microM). These results suggest that administration of DAO inhibitors may increase endogenous agmatine levels and thus alter imidazoline receptor densities. A review of the literature documenting ligand affinities for idazoxan-preferring (I2) imidazoline binding site subtypes and drug affinities for DAO enzymes indicates that some of the I2 sites described elsewhere may correspond to DAO and not to an imidazoline receptor.

Agmatine↗
PubMed1995

Further studies on the ex-vivo effects of procarbazine and monomethylhydrazine on rat semicarbazide-sensitive amine oxidase and monoamine oxidase activities.

Following administration of the anticancer agent, procarbazine, or one of its metabolites, monomethylhydrazine, to rats, activities of monoamine oxidases A and B (MAO A and MAO B) and of semicarbazide-sensitive amine oxidase (SSAO) were measured ex-vivo. Both compounds were found to be potent inhibitors of SSAO in tissue homogenates, exhibiting ID50 values in most tissues of approximately 8 mg kg-1 (procarbazine) and 0.08 mg kg-1 (monomethylhydrazine). Concurrent dose-dependent inhibition of MAO activities did not occur. However, in liver, potentiation of MAO B activity, to 140% of that in controls, was apparent following monomethyl-hydrazine and this effect was independent of the drug dose. Both compounds produced a dose-dependent potentiation of MAO A in brown adipose tissue, the elevation being more pronounced following monomethylhydrazine, with activity rising to 350% of that in control homogenates. In a parallel in-vitro study, monomethylhydrazine was without effect on MAO A in brown adipose tissue homogenates. By perfusing the SSAO substrate, benzylamine, through the isolated mesenteric arterial bed of the rat, it was found that pretreatment of animals with procarbazine or monomethylhydrazine reduced metabolism of this amine by a similar degree as had been determined ex-vivo in blood vessel homogenates. The results presented suggest that these compounds would be suitable for use as selective inhibitors in pharmacological examinations of SSAO function in isolated tissues and organs.

Amine Oxidase (Copper-Containing)↗
PubMed1994

Location of the active site of rat vascular semicarbazide-sensitive amine oxidase.

Semicarbazide-sensitive amine oxidase (SSAO) activity in rat vascular smooth muscle cells is associated extensively with the plasmalemma. To determine which side of the plasmalemma the active sites of these enzymes face, the non-permeating agent, diazotised sulphanilic acid (DSA; 4.4 mM) was perfused through the isolated mesenteric arterial bed of the rat, in an attempt to inactivate only those active sites facing extracellularly. DSA perfusion abolished the pressor responses to noradrenaline via inactivation of extracellular alpha 1 receptors but had no effect on cytosolic lactate dehydrogenase activity. SSAO activity, estimated by perfusing [14C] benzylamine, was reduced following DSA perfusion to 55.9 +/- 4.9% of that in control beds and to 52.4 +/- 6.0% in homogenates of these vessels. These results suggest that almost half of SSAO active sites in rat mesenteric arteries face outwards.

Amine Oxidase (Copper-Containing)↗