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Biomedical subjects

W H Chang

Publications and source records attributed to W H Chang.

At least 163 records · Page 9Linked to original sources
PubMed1987

Purification of heat-labile enterotoxin from an enterotoxin from an enterotoxigenic Escherichia coli of human origin by monoclonal immunoaffinity chromatography.

Heat-labile enterotoxin (LT) was purified from an enterotoxigenic Escherichia coli 015H11 of human origin. The purification steps included French pressure cell disruption of the bacteria, salting-out, DEAE-Sephacel on chromatography. Application of this procedure resulted in a 95.1-fold purification of LT with a yield of 19.9% as determined by rabbit ileal loop assay. The final LT preparation showed only one protein-staining band on polyacrylamide gel electrophoresis, indicating that the purified LT was homogeneous.

Animals↗
PubMed1986

Acute and chronic effects of haloperidol on plasma and brain homovanillic acid in the rat.

The effects of acute and chronic administration of haloperidol on homovanillic acid (HVA) in plasma and the brain were examined in the rat. Acute haloperidol treatment (1 mg/kg) resulted in highly significant elevations in HVA within 30 min and produced a maximal increase of HVA in 3-6 hr in both plasma and the whole brain. The response of brain HVA to increasing doses (0.05-30 mg/kg) of haloperidol showed an inverted U pattern. Plasma HVA showed a very flat response to lower doses (less than or equal to 5 mg/kg) of haloperidol and a dramatically elevated one to higher doses (greater than or equal to 10 mg/kg). Haloperidol produced a parallel increase in plasma and brain HVA at lower doses (less than or equal to 2 mg/kg) only. After chronic administration of haloperidol for up to 28 days, the response of HVA in plasma correlated mainly with, but tolerated later than, those in the whole brain and the olfactory tubercle.

Animals↗
PubMed1984

Differential effects of clorgyline on catecholamine and indoleamine metabolites in the cerebrospinal fluid of rhesus monkeys.

The effects of acute and chronic administration of clorgyline, an irreversible inhibitor of monoamine oxidase type A (MAO-A), on the deaminated metabolites of norepinephrine, dopamine and serotonin were examined in rhesus monkey cerebrospinal fluid (CSF). Acute clorgyline treatment resulted in highly significant, dose-dependent reductions in 3-methoxy-4-hydroxyphenylglycol (MHPG) of 50% (1 mg/kg) and 68% (2 mg/kg) compared to pretreatment values. Chronic clorgyline administration (0.25 to 0.5 mg/kg X 24 days) resulted in a 67% reduction in CSF MHPG. In contrast, the concentrations of 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) were less affected by acute clorgyline administration, being reduced significantly only after the 2 mg/kg dose, which lowered 5-HIAA 27% and HVA 48%. Chronic clorgyline treatment had no significant effect on the CSF concentrations of HVA and 5-HIAA. These data, which suggest that MAO-A inhibition by clorgyline in vivo is more closely associated with changes in the noradrenergic than the serotonergic or dopaminergic systems in nonhuman primates, are in general agreement with the effects of clorgyline on CSF and urinary biogenic amine metabolites in man. They differ from several in vitro studies which indicate a primary role of MAO-A in the metabolism of serotonin and of MAO-B in norepinephrine degradation in primate brain. The discrepancies may reflect modulating effects of synaptic feedback mechanisms on the actions of clorgyline in vivo or perhaps a failure of CSF metabolites to adequately reflect brain amine metabolism changes. The lack of change in platelet MAO-B activity during clorgyline treatment together with the minimal changes in HVA concentrations indicate that the selective inhibitory effects of clorgyline on MAO-A were maintained during chronic administration of low drug doses.

Animals↗
PubMed1984

Nipple reconstruction with a T flap.

It is probably impossible to reproduce with available means a nipple with normal texture, sensation, and erectile function. The practical prerequisites are symmetry in diameter and projection. A new method is presented that fulfills those requirements and allows more latitude in varying and predicting those parameters. It utilizes the available local skin and avoids invasion of the normal contralateral breast or other nipple donor sites.

Breast↗
PubMed1984

Desipramine pharmacokinetics in Chinese and Caucasian volunteers.

In order to better define the role of pharmacokinetic variation in reported cross-ethnic differences in dosing patterns of some psychoactive drugs, single dose kinetics of the tricyclic antidepressant desipramine (DMI) were studied in 14 Chinese and 16 Caucasian healthy volunteers. DMI and 2-OH-DMI concentrations were assayed with h.p.l.c. in serial plasma and 24 h urine samples over 5 days following an oral 100 mg dose of DMI. Mean total clearance of DMI ( CLDMI ) from plasma was significantly (P less than 0.05) higher in the Caucasians (123 +/- 57 l/h) than in the Chinese (73.5 +/- 38.8 l/h). There was no significant difference in the apparent clearance of DMI by hydroxylation, fraction of dose metabolized to the hydroxy metabolite, DMI t1/2 or plasma protein binding between the two groups. Trimodal distribution of CLDMI was found, with 4/14 (29%) Chinese demonstrating slow CL (less than 33 l/h) and 4/16 (25%) Caucasians rapid CL (greater than 195 l/h). Correcting CL values for the greater mean weight of the Caucasians did not alter the pattern of distribution. CLDMI did not correlate with body weight. Although environmental factors cannot be ruled out, these results are consistent with genetically based differences in hepatic metabolism, probably affecting pathways in addition to hydroxylation, and suggest that 30% of Orientals would be at risk for toxicity from routine doses of tricyclics or similarly metabolized drugs.

Adult↗
PubMed1983

Measurement of 3-methoxy-4-hydroxyphenylglycol in human plasma with high-performance liquid chromatography using electrochemical detection.

A new method utilizing high-performance liquid chromatography with electrochemical detection for the determination of unconjugated 3-methoxy-4-hydroxyphenylglycol, a major metabolite of norepinephrine, in human plasma is described. A novel internal standard, 3-ethoxy-4-hydroxyphenylglycol, was used to correct for variations in extraction efficiency and detector sensitivity. Separation of sample components was achieved isocratically in 20 min per sample in a reversed-phase system. Column temperature had to be carefully regulated. The sensitivity of the assay is suitable for clinical studies, with a limit of detection of 2 pmol/ml. Intra- and interassay precision was good, with observed coefficients of variation of 7.5 and 8.8%, respectively. Accuracy was tested by comparing the results of the present HPLC method to those found with a specific gas chromatographic-mass spectrometric assay. A satisfactory correlation of 0.96 was obtained, with no significant bias between the two methods.

Chromatography, High Pressure Liquid↗
PubMed1983

Reliability of norepinephrine and major monoamine metabolite measurements in CSF of schizophrenic patients.

Concentrations of norepinephrine, 3-methoxy-4-hydroxyphenylglycol, homovanillic acid, and 5-hydroxyindoleacetic acid (5-HIAA) were quantified in the CSF of 28 drug-free schizophrenic patients. Fifteen patients provided more than one drug-free sample on separate occasions. Considerable intraindividual variability over time was found in the concentrations of norepinephrine and these major monoamine metabolites in the repeated samples. This was not explained by assay errors or changes in the patient's global psychosis ratings. The variability in the present sample for CSF 5-HIAA concentrations was almost twice as wide as has been reported for patients with affective disorder. Variables that contribute much of the variability of norepinephrine and major monoamine metabolite concentrations in drug-free CSF samples from schizophrenic patients remain unknown and cannot be controlled.

Adult↗
PubMed1983

Simultaneous determination of 3-methoxy-4-hydroxyphenylglycol, 5-hydroxyindoleacetic acid, and homovanillic acid in cerebrospinal fluid with high-performance liquid chromatography using electrochemical detection.

An improved high-performance liquid chromatographic method with electrochemical detection (HPLC-EC) for the simultaneous determination of 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxyindoleacetic acid (5-HIAA), and homovanillic acid (HVA) in cerebrospinal fluid (CSF) of humans and nonhuman primates is described. Quantitation is based on the use of an internal standard, 5-fluoro-HVA. Sample preparation consists of mixing an aliquot of CSF with a solution of the internal standard followed by ultrafiltration. The precision of the method is high, with within-run and between-run coefficients of variation of 2-6% and less than 10%, respectively, in the concentration ranges of the metabolites encountered in human lumbar CSF. Accuracy was tested by comparing the present HPLC method with specific gas chromatographic-mass spectrometric (GS-MS) assays for MHPG and HVA and a GC-MS-validated HPLC assay for 5-HIAA: the correlations obtained were 0.968 for MHPG, 0.989 for 5-HIAA, and 0.999 for HVA, with no systematic bias between the methods. The use of ascorbate as a preserving agent for monoamine metabolites in CSF was not found to be necessary when proper care was exercised in sample handling and storage. The analysis of samples with up to 2% ascorbic acid was possible as well, but MHPG had to be assayed separately using an extraction procedure and an alternative internal standard, 3-ethoxy-4-hydroxyphenylglycol.

Animals↗
PubMed1983

Rapid and simple determination of homovanillic acid in plasma using high performance liquid chromatography with electrochemical detection.

A rapid, yet highly reliable, procedure for determination of homovanillic acid (HVA) in plasma is described. After precipitation of proteins with perchloric acid, separation of sample components is directly achieved with high performance liquid chromatography on a reversed-phase column (C8), followed by quantitation based on electrochemical detection. The sensitivity of this method is 0.5 pmol/injection. Detector response is linear from the limit of detection to at least 0.5 nmol/injection. The intra-assay coefficient of variation is 2.2% in the concentration range of 50-150 pmol/ml plasma. The inter-assay coefficient of variation is 6.3%, based on determinations on 30 working days. A comparison of the present method and a specific gas chromatographic-mass spectrometric assay showed good agreement between the two procedures. One chromatographic run requires less than 16 min. for plasma and 10 min. for a standard.

Chromatography, High Pressure Liquid↗
PubMed1983

Simultaneous determination of haloperidol and its reduced metabolite in serum and plasma by isocratic liquid chromatography with electrochemical detection.

We describe a liquid-chromatographic method for simultaneous quantification of haloperidol and its reduced metabolite in plasma and serum. Haloperidol and reduced haloperidol are concentrated from blood samples by liquid/liquid extraction into a hexane/isoamyl alcohol mixture, with chlorohaloperidol as the internal standard. For chromatographic separation we used a reversed-phase cyano-bonded column and a mobile phase of pH 6.8 phosphate buffer/acetonitrile (55/45 by vol). Haloperidol and its reduced metabolite are detected electrochemically at +0.90 V potential between the working and reference electrodes. As little as 0.5 ng per injection is detectable. Within- and between-day CVs for determinations of haloperidol and reduced haloperidol ranged from 4 to 7% each at a concentration of 10 micrograms/L. Haloperidol concentrations measured by this method correlated well with those by gas-chromatography with nitrogen-sensitive detector and by radioimmunoassay. The present method can be used to study the effects of haloperidol on the central nervous system. It is simple enough for use in clinical laboratories that are monitoring haloperidol concentrations in the blood of psychiatric patients.

Antiparkinson Agents↗
PubMed1982

Prostacyclin production by vein grafts in the arterial circulation: a study in rats.

The in vitro production of prostacyclin by vein grafts was measured using vascular rings followed by radioimmunoassay of the medium. The grafts were prepared by interposing a segment of epigastric vein in a gap in the ipsilateral femoral artery of the rat. Measurements made over a period of 1 to 42 days showed a progressive rise from venous levels (less than 0.2 ng/ml) to values close to the arterial controls (10.9 +/- 2.2 ng/ml). This deficiency of prostacyclin synthesis during the "arterialization" of the graft may account for some of the early failures which can occur in vein grafting and suggests the possibility of pharmacological intervention to improve the success rate.

Animals↗
PubMed1980

Platelets, prostaglandins, and patency in microvascular surgery.

In light of recent research dealing with the proaggregatory and antiaggregatory effects of prostaglandins on the primary hemostatic event of platelet aggregation, we suggest that patency in microvascular surgery be viewed from a new perspective. The sequence of events in platelet aggregation and the effects of the products of arachidonic acid metabolism on these events are reviewed. Drugs affecting platelet aggregation are classified according to their sites of action. In particular, heparin, dextran, and aspirin are discussed in relation to new information regarding their effects on arachidonic acid metabolism. Original early experimental work and clinical reports from the literature are discussed with a view toward future directions for research in improving patency in microvascular surgery.

Anticoagulants↗