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Biomedical subjects

M Ng

Publications and source records attributed to M Ng.

At least 109 records · Page 6Linked to original sources
PubMed1990

Evaluation of the semi-automated Autosperm semen analysis system. II. Comparison with conventional method, time-exposure photomicrography, and automated CellSoft system.

Semen analysis results obtained by a recently developed semi-automated Autosperm system (Amsaten N.V.S.A. Corp., De Pinte, Belgium) were compared with those obtained by the conventional, time-exposure photomicrographic, and automated CellSoft system (Cryo Resources Inc., New York, NY) analyses. The Autosperm system either over- or underestimated the sperm concentration in comparison with the conventional analysis and more often underestimated the sperm concentration in comparison with the automated CellSoft system analysis. Comparison of the results for percent sperm motility by the conventional and Autosperm analyses showed that the latter tended to underestimate the percentage of fast-swimming spermatozoa and overestimate the percentage of slow-swimming spermatozoa. There were considerable variations in the measurement of sperm movement characteristics between the Autosperm and time-exposure photomicrographic and automated CellSoft system analyses, respectively. These findings demonstrate that the performance of the Autosperm system does not agree well with those of the currently available methods employed in the present study. Part of the disagreement in measurements of sperm parameters could be because of the subjective elements inherent in the semi-automated Autosperm analysis.

Humans↗
PubMed1989

A fluorescent oligopeptide energy transfer assay with broad applications for neutral proteases.

A fluorescent peptide substrate to explore the protease specificity for the amino acid regions C- and N-terminal to the cleavage site has been designed. Intramolecular quenching of indole fluorescence by an N-terminal dansyl group separated by six amino acid residues forms the basis of this assay. For a particular enzyme, specificity can be designed into the peptide sequence by means of the number of residues that separate the two chromophores. In the present instance, the heptapeptide Dns-Gly-Lys-Tyr-Ala-Pro-Trp-Val is used to assay angiotensin converting enzyme (ACE), Astacus protease, carboxypeptidase A, alpha-chymotrypsin, and trypsin, all of which cleave the peptide in accord with their known specificity: Trypsin and Astacus protease hydrolyze only the Lys-Tyr and Tyr-Ala bonds, respectively. alpha-Chymotrypsin primarily cleaves the Tyr-Ala bond while ACE makes three successive dipeptidyl cleavages from the C-terminus. Carboxypeptidase rapidly hydrolyzes first the Trp-Val and then the Pro-Trp bond. For all of the enzymes, catalytic activity (kcat/Km) is in the range from 10(5) to 10(6) M-1 s-1. Hydrolysis causes a fluorescence increase in the 310 to 410 nm region of 8.6- to 13.6-fold depending on the enzyme that is assayed. Assays can be designed based on the increase in tryptophan fluorescence or by individual product analyses using thin-layer or high-performance liquid chromatography. The specificity and sensitivity of such internally quenched fluorescent oligopeptides would seem to be ideal for the assay of specific endoproteases.

Amino Acid Sequence↗
PubMed1989

Endoplasmic storage disease of liver: characterization of intracytoplasmic hyaline inclusions.

Two cases of endoplasmic storage disease of liver are described. The liver tissue in each case showed numerous intracytoplasmic hyaline inclusions of varying sizes with formation of ground-glass hepatocytes. These inclusions were pale eosinophilic in hematoxylin & eosin stained sections, and were periodic acid-Schiff and HBsAg negative. Immunoperoxidase studies revealed strong positivity for fibrinogen and complement components C3 and C4 in case 1 and exclusive positivity for fibrinogen in case 2. On electron microscopy, the inclusions appeared as granular or fibrillar material within dilated cisternae of rough endoplasmic reticulum.

Adult↗
PubMed1988

Multivariate discriminant analysis of the relationship between the hypo-osmotic swelling test and the in-vitro fertilizing capacity of human sperm.

Multivariate discriminant analysis was used to evaluate the usefulness of routine semen parameters and the hypo-osmotic swelling test (HOST) as predictors of the in-vitro fertilizing capacity of human sperm as assessed by the zona-free hamster egg penetration assay (HEPA). Eighty-eight semen samples from untreated patients attending an infertility clinic were analysed. Semen samples were classified into the following three groups before statistical analysis: group 1--positive sperm penetration (greater than or equal to 10%, n = 39); group 2--borderline penetration rates for HEPA (greater than 0% but less than 10%, n = 39) and group 3--negative sperm penetration (0%, n = 10). The percentage of sperm with normal morphology and sperm count were found to be significant in discriminating between semen samples exhibiting different in-vitro fertilizing capacity. These two discriminating variables in combination gave an overall correct classification rate of 45.5%. The multivariate discriminant analysis was also performed after excluding the data of group 2 semen samples (n = 39), which exhibited borderline sperm penetration rates. As a result, three discriminating variables including semen volume, sperm count and the percentage of sperm with normal morphology were selected. These three variables in combination could accurately predict whether a semen sample would exhibit positive sperm penetration (group 1) or negative sperm penetration (group 3) with an overall accuracy of 75.5%. The percentage of swollen sperm after hypo-osmotic treatment was not related to the HEPA result, as determined by linear correlation and multiple regression analyses, and did not give additional information about the in-vitro fertilizing capacity of sperm as evaluated by multivariate discriminant analysis.

Female↗
PubMed1986

Spinal cord compression in multiple myeloma: who gets it?

Of 97 Chinese patients with multiple myeloma seen over a 12-year period, 23.7% were found to have cauda equina or spinal cord compression (SCC). Predictive features for SCC include paraprotein type, hemoglobin level, and the extent of bone lesion at initial hematological diagnosis. A discriminant function derived from this analysis can be used to predict the likelihood of SCC with 79% accuracy. It is postulated that when the cortex is more involved than the medulla in a vertebra, it will predispose to SCC while hemopoiesis is relatively preserved. Our patients presented late with advanced neurological deficit so that treatment was unsatisfactory. It is emphasised that early recognition of back pain and neurological symptoms is essential, as any delay would jeopardize the chance of neurological recovery.

Adult↗
PubMed1986

Structural domains of the avian erythroblastosis virus erbB protein required for fibroblast transformation: dissection by in-frame insertional mutagenesis.

Avian erythroblastosis virus (AEV) induces erythroblastosis and fibrosarcomas. The viral erbB protein is required for AEV-mediated oncogenesis. To explore the structural aspects of the v-erbB polypeptide necessary for its oncogenic function, we created a series of small in-frame insertions in different domains of the v-erbB oncogene. AEV genomes bearing lesions within the v-erbB kinase domain demonstrated a drastically decreased ability to transform avian fibroblasts, establishing a functional role for this structurally conserved oncogene domain. In contrast, mutations in the extracellular domain, between the transmembrane region and the kinase domain, or at the extreme C terminus of the v-erbB protein had no effect on AEV-mediated fibroblast transformation. One lesion within the v-erbB kinase domain, a 10-amino acid insertion, produced a temperature-sensitive mutant capable of fibroblast transformation at 36 degrees C but not at 41 degrees C, suggesting that small in-frame insertions have general utility for the in vitro creation of conditional mutants.

Alpharetrovirus↗
PubMed1985

Cross-sectional study of semen parameters in a large group of normal Chinese men.

Testicular size, semen characteristics and serum reproductive hormone levels were studied in 1239 normal Chinese men. The mean testicular size of 17 ml in this group of subjects was similar to other reports in Orientals but was smaller than that reported in Caucasians. Semen volume, and the sperm count, motility and morphology were comparable to those described for Caucasian subjects. The cervical mucus penetration test (Kremer's test) and the zona-free hamster egg penetration test were also studied in some of the subjects. Age showed a positive correlation with the serum levels of FSH and LH, which were highly correlated with each other. Sperm concentration and the total sperm count were positively correlated with testicular volume, the length of abstinence, the % of sperm with an oval head, and the zona-free hamster egg penetration test, but were negatively correlated with serum FSH. Sperm motility was negatively correlated with the duration of abstinence but was positively correlated with the % normal sperm. The results constitute a normal data base from Chinese men for comparison with studies in male infertility and fertility regulation.

Adult↗
PubMed1985

Herbal tea induced hepatic veno-occlusive disease: quantification of toxic alkaloid exposure in adults.

Four young Chinese women took daily doses of an unidentified 'Indian' herbal tea as treatment for psoriasis. Three (one of whom died), developed ascites, hepatomegaly and biochemical abnormalities within 19-45 days. The fourth patient discontinued herbal tea after 21 days when she developed a skin rash. Two patients had portal hypertension, while all had liver histology showing features of veno-occlusive disease. Pyrrolizidine alkaloids were identified spectrophotometrically in the brewed tea, and in the chopped leaves of the herbal mixture; the mean dose in the tea prepared for consumption being 12 mg/day of alkaloid base and 18 mg/day of N-oxide. The mean cumulative dose of alkaloids (base + N-oxide) before onset of symptoms (three patients), was estimated to be 18 mg/kg. In the asymptomatic patient with histological liver disease only, the corresponding dose was 15 mg/kg. These cases thus provide some measure of pyrrolizidine alkaloid toxicity in adults.

Adult↗
PubMed1985

Duodenal ulcer healing by separate reduction of postprandial and nocturnal acid secretions have different pathophysiology.

The endoscopic healing rates and factors related to healing of two cimetidine regimens designed to reduce respectively postprandial and nocturnal acid secretions were studied in a randomised trial of cimetidine 200 mg tds with meals, vs 600 mg at bedtime, vs 200 mg tds with meals plus 400 mg at bedtime in 246 patients with duodenal ulcer. The respective healing rates were 62.3%, 63.1%, 77.5% at four weeks and 86.6%, 83.3%, 91.2% at eight weeks. The healing rates at four weeks of both meal time and bedtime regimens were inferior (p less than 0.05) to that of the standard regimen. Analysis of 45 prospectively obtained factors showed that (i) habitual cigarette smoking adversely affected healing with the meal time regimen but not with the others, indicating that its adverse effect disappeared once nocturnal acid secretion was reduced, (ii) habitual use of analgesics impaired and their abstinence favoured healing by both meal time and bedtime regimens but these effects were lost with the standard regimen, suggesting that if analgesics cannot be withdrawn during ulcer treatment, a reduction of both meal time and night time acid secretions should be ensured, (iii) responders with the meal time and bedtime regimens had respectively significantly higher postprandial serum gastrin and higher basal acid output than the corresponding non-responders suggesting that these responders had different pathophysiology, and (iv) high maximal acid output and large ulcers healed less well by any regimen.

Adult↗
PubMed1984

Surface antigens of brain synapses: identification of minor proteins using polyclonal antisera.

Antigenic proteins of brain synaptic plasma membranes (SPM) and postsynaptic densities (PSD) were characterized using antisera raised against SPM. Immunostaining of brain sections showed that the antigens were restricted to synapses, and electron microscopy revealed staining at both presynaptic terminals and PSDs. In primary brain cell cultures the antisera were also neuron-specific but the antigens were distributed throughout the entire neuronal plasma membrane, suggesting that some restrictive influence present in whole tissue is absent when neurons are grown dispersed. The antigenic proteins with which these antisera react were identified using SDS gel immunoblots. SPM and PSD differed from one another in their characteristic antigenic proteins. Comparison with amido-black stained gel blots showed that in both cases most of these did not correspond to known abundant proteins of SPM or PSDs revealed by conventional biochemical techniques. None of the antigens revealed by the polyclonal antisera were detected by any of a large series of monoclonal antibodies against SPM.

Animals↗
PubMed1984

Randomised crossover trial of tripotassium dicitrato bismuthate versus high dose cimetidine for duodenal ulcers resistant to standard dose of cimetidine.

Of 212 patients with duodenal ulcer treated with four weeks of one gram daily cimetidine, 25 had ulcers which underwent no reduction in size despite treatment. The effects of tripotassium dicitrato bismuthate (TDB) tablet four times a day or cimetidine 1.6 g daily on the healing of these cimetidine resistant ulcers were compared in a randomised crossover trial. Ten of 12 patients on tripotassium dicitrato bismuthate and five of 13 patients on high dose cimetidine had complete healing (p less than 0.02). On crossing over, seven of the eight ulcers not healed by high dose cimetidine completely healed with TDB in another four weeks, and one of the two ulcers not healed by TDB healed with high dose cimetidine. Overall, TDB healed 85% of cimetidine resistant ulcers, whereas high dose cimetidine healed 40% (p less than 0.006). Tripotassium dicitrato bismuthate is recommended for cimetidine resistant duodenal ulcers.

Adolescent↗