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Biomedical subjects

B Chan

Publications and source records attributed to B Chan.

At least 109 records · Page 6Linked to original sources
PubMed1985

Can potentially infectious specimens containing hepatitis B virus be identified on the basis of their biochemical profile?

The potential infectivity of 1129 randomly selected plasma specimens was directly assayed by hepatitis B virus (HBV) DNA dot-hybridization. Presence or absence of HBV was then correlated with a biochemical profile of 20 common analytes obtained on these same specimens. We found that potentially infectious specimens could not be identified on the basis of any combination of simple biochemical tests; indeed, the infectious specimens were more "normal" in some tests of liver function than were the non-infectious specimens.

Blood Specimen Collection↗
PubMed1984

Acoustic properties of polyvinyl chloride gelatin for use in ultrasonography.

Visualization of superficial structures with conventional rapid scanners has been difficult. A solid flexible polyvinyl chloride (PVC) gelatin slab used as a stand-off material can provide a constant scan distance and thus overcome the problem of poor near field resolution. PVC gelatin expands the capability of the 3-4 MHz transducer to delineate superficial structures. We report on the acoustic properties of the PCV gelatin, including the values of velocity and attenuation as a function of both frequency and temperature, and the comparison of data with published values of velocity and attenuation for water, soft tissue, and a phantom material.

Gelatin↗
PubMed1983

Partial purification of [3H]mianserin binding sites.

Frontal cortex membranes were solubilized with digitonin, prelabelled with 4 nM [3H]mianserin, and partially purified by isoelectric focussing. Bound [3H]mianserin separated from free [3H]mianserin as a single radioactive peak with a pI value of 5.03. A 14-fold purification was achieved. Focussing in the presence of 1 microM ketanserin (R 41468) or 1 microM chlorpyramine (a histamine H1-antagonist) or 10 microM spiperone (an S2-antagonist) completely abolished the peak of radioactivity at pH 5. Pharmacological characterization of the eluted radioactive peak revealed both histaminergic and serotonergic binding properties. The data suggest that the serotonergic and histaminergic components of [3H]mianserin binding to frontal cortex are not separable by solubilization, gel filtration or isoelectric focussing.

Animals↗
PubMed1983

Specific binding of vasoactive intestinal peptide to human circulating mononuclear cells.

The interaction of the neuropeptide vasoactive intestinal peptide with human circulating mononuclear cells has been studied. Mononuclear cells were able to bind radiolabelled vasoactive intestinal peptide; the binding was rapid, reversible, saturable, and specific for vasoactive intestinal peptide. A fragment of vasoactive intestinal peptide (10-28) was 25-fold less effective than intact peptide as a competitor for the binding of the tracer. Secretin was 100-fold less effective as a competitor and glucagon competed poorly even at concentrations 10 000 times greater than that of the tracer molecule. In tracer dilution studies, the binding suggested a single class of binding sites with an apparent dissociation constant (Kd) of 2.4 X 10(-10) M and a capacity of 2 000 sites per cell. In the presence of vasoactive intestinal peptide, there was a dose-dependent augmentation of cyclic AMP in the mononuclear cells. The concentration of vasoactive intestinal peptide which produced a half-maximal effect was the same as the Kd for the peptide binding. We conclude that mononuclear cells have specific high-affinity binding sites for vasoactive intestinal peptide. Interactions between mononuclear cells and vasoactive intestinal peptide may be an important mechanism modulating local immune responses within tissues innervated by vasoactive intestinal peptide containing neurons.

Binding, Competitive↗
PubMed1982

[3H]Mianserin binding to solubilized membranes of frontal cortex.

[3H]Mianserin binding sites were characterized in membranes of dog frontal cortex and solubilized with digitonin. The solubilized [3H]mianserin binding sites retained the binding characteristics of the membrane preparation. The dissociation constant (KD) for the soluble material was 2.2 nM which compared closely to that of the membrane-bound site (1.1 nM). Drug binding profiles indicated that the solubilized sites were both serotonergic and histaminergic in nature. Drugs active both H1- and S2-receptors potently displaced [3H]mianserin with Hill slopes close to 1. More selective serotonergic drugs such as LSD and spiperone competed for [3H]mianserin binding with shallow displacement curves. Of the neurotransmitters tested, serotonin was the most potent for both preparations. Because all the components of [3H]mianserin binding co-solubilize, the soluble material can be used to isolate individual sites.

Animals↗
PubMed1982

Ascorbate injury and EDTA (or manganese) protection of D2-dopamine receptors.

Ascorbic acid, EDTA, and Mn2+ modulated neuroleptic binding to membrane receptors but not to solubilized receptors. Preincubation with ascorbic acid at 22 degrees C produced a profound time-dependent decline in [3H]spiperone binding to membrane receptors (prepared in Tris-ascorbate buffer). Ascorbate had minimal effect if introduced simultaneously with [3H]spiperone in the incubation medium, and receptor binding was performed and assayed at 0 degrees C. Binding to the solubilized receptor was not ascorbate sensitive. Both EDTA and Mn2+ blocked the ascorbate effect on membrane receptors but were without effect on solubilized receptors. The preparation and incubation buffers used for [3H]spiperone binding studies should include EDTA if ascorbate is present in the buffer.

Animals↗
PubMed1981

Assay for soluble dopamine receptors by the precipitation method.

Receptors with high affinity for neuroleptics (D2-type dopamine receptors) were solubilized from dog striatum using 1% digitonin. Soluble receptors were labelled using [3H]spiperone, and the bound 3H-ligand was separated from the free [3H]spiperone by molecular sieving on the Sephadex G-50 columns. This paper presents a polyethylene glycol (PEG) precipitation method designed to replace this column method. IC50 values for both neuroleptics and dopamine agonists, as well as dissociation constants for [3H]spiperone were similar for both methods. The precipitation method yielded a receptor density of 64 fmol/mg protein whereas the molecular sieving technique yielded a value of 194 fmol/mg protein. The qualitative similarities between the methods validates using the rapid precipitation method for monitoring the receptor during various stages of its purification.

Animals↗
PubMed1980

Irradiation of choroidal melanoma with iodine 125 ophthalmic plaque.

Radioactive iodine 125 is a low-energy gamma isotope with physical characteristics suitable for irradiation of intraocular tumors. Metal ophthalmic applicators have been designed to shield vital ocular structures while allowing irradiation of the tumor. We compared the radiation effects of iodine 125 and cobalt 60. The Greene melanoma was transplanted into the suprachoroidal space of rabbits. The tumor then grew as an intraocular mass, was irradiated, and was followed up for two months before enucleation. Histopathologic examination defined the extent of the radiation damage to the tumor and other ocular structures from the iodine 125 and from the cobalt 60. The eye irradiated with iodine 125 suffered minimal radiation damage, whereas the tumor was sterilized. The eye irradiated with cobalt 60 showed substantial radiation damage, and the melanoma was incompletely treated. Our results support the use of iodine 125 in treating intraocular tumors. More research is needed as to optimum total dose and dose rate.

Animals↗
PubMed1977

Radiation therapy of choroidal melanoma.

During the past 8 years, 32 patients with melanoma of the choroid have been treated with cobalt-60 ophthalmic applicators. Excluding three patients lost to follow-up, 24 patients who have now been observed for at least 3 years after treatment form the subject of this study. Each application but two delivered 8,500 to 10,000 rads to the tumour apex. A second application was performed in large tumours showing a poor response to the initial plaque treatment. The factors affecting results include age of the patient, tumour size, total dose delivered, and dose rate. Three out of seventeen patients with tumour diameters greater than 12 mm died of their disease with pulmonary and/or liver metastasis. Three eyes required enucleation and no residual tumour was found in two specimens. Three patients, average age 76 years, died from causes other than melanoma. An 83 per cent relative survival, excluding the three patients lost to follow-up, compares favourably with enucleation. The low incidence of metastasis after radiotherapy suggests augmentation and/or continuation of the host's immune response. Low energy radiation using Iodine-125, with its unusual protective characteristics is ideal for treatment of choroidal melanoma.

Aged↗
PubMed1976

Effectiveness of lead lenses in reducing radiation exposure.

Optically ground prescription lenses of glass, leaded glass, and plastic were exposed to radiations that simulated routine angiography. Radiations transmitted through the lenses were measured. Plastic provided no protection, regular glass provided moderate protection, and high lead content glass reduced radiation transmission by approximately 70%. A brief review of the literature concerning the biological effects of radiations to the eye is included.

Animals↗
PubMedDate not supplied

Dissociation of authentic and artifactual effect of circulating heparin on drug protein binding.

The purpose of this study was to dissociate the authentic and artifactual effect of in vivo heparin on drug protein binding using protamine as an inhibitor of ex vivo lipolysis. A mixture of ethylenediamine tetra-acetic acid (EDTA, 5 mg ml-1) and protamine in the concentration range of 0 to 7.5 mg ml-1 was added to blood samples from 23 cardiac catheterized patients before (control) and 10 min after 3000 IU of intravenous heparin. In control samples, protamine does not interfere with the protein binding of lidocaine (L), quinidine (Q) or propranolol (P) when plasma pH is readjusted to 7.4. In the absence of protamine, heparin induced a significant increase in the free fraction by 40, 130, and 30 per cent for L, Q, and P, respectively (p less than 0.001), while free fatty acid (FFA) levels increased 2 to 6 fold. When protamine was present, the heparin-induced elevation in free fraction was significantly lower for L (16 per cent) and Q (77 per cent) but not for P; FFA levels were decreased at all protamine concentrations. Residual increases in free fraction and FFA levels compared to control values may represent the true in vivo effect of heparin at the peak activity of lipoprotein lipases. For L and Q, variations in free fraction were strongly associated with variations in FFA, but for P, no significant correlation was observed (r = 0.492). These results indicate that variations in free fraction of L and Q caused by heparin are, to a large extent, artifactual but may be prevented by use of protamine in collection tubes (5 to 7.5 mg ml-1). For P, the increase in free fraction was not mediated by variations of FFA indicating that another mechanism must be involved.

Adult↗
PubMedDate not supplied

A simple, rapid method for HPLC analysis of lycopene isomers.

A rapid method for the extraction, separation and quantification of the geometric isomers of lycopene and beta-carotene from tomato fruit is described. Carotenoids in tomato were separated and eluted using a reversed-phase HPLC with a C30 column and a mobile phase consisting of methyl-t-butyl ether, methanol and ethyl acetate. The system provided sharp resolution of cis- and trans-isomers of lycopene within approximately 23 min in contrast to the longer and more complex gradient procedures required by previously described methods. Experiments indicate that the stability of extracts of fresh tomato may be improved if stored at -20 degrees C, and that the presence of the antioxidant BHA has no apparent effect on stability.

Carotenoids↗