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Biomedical subjects

M Wong

Publications and source records attributed to M Wong.

At least 181 records · Page 10Linked to original sources
PubMed1994

Posttranslational modification of glycine-extended substance P by an alpha-amidating enzyme in cultured sensory neurons of dorsal root ganglia.

The terminal step in the biosynthesis of substance P is the conversion of its glycine-extended precursor to the mature, amidated peptide by the alpha-amidating enzyme. This posttranslational modification was demonstrated in cultured, dissociated sensory neurons of dorsal root ganglia from neonatal rats. An assay was developed to quantitate both substance P and its precursor peptide in these cells. More than 90% of these two peptides was present as mature peptide in uncultured cells. In contrast, after 8 days in culture, about 85% of the peptides was the precursor, which increased 200-fold, whereas the level of substance P itself tripled during this culturing period. Since alpha-amidating enzyme requires ascorbate for activity, this reducing agent was added to the culture medium. Ascorbate induced a dose-dependent rise in the percentage of amidated peptide, with an apparent Km of 20 microM. After 5 days of culturing in the presence of 500 microM ascorbate, substance P increased 8-fold, constituting 70% of the total. The alpha-amidating enzyme also needs copper for activity. Even with 500 microM ascorbate in the culture medium, the copper chelator diethyldithiocarbamate dose-dependently reduced substance P synthesis by the sensory neurons, with a concomitant increase in its precursor peptide. These results suggest the presence of alpha-amidating enzyme in sensory neurons of dorsal root ganglia. It is likely that conversion of other glycine-extended precursors to their mature peptides in cell cultures would also require ascorbate and copper.

Animals↗
PubMed1994

Effect of intravenous atrial natriuretic peptide on gas exchange in humans.

The aim of this work was to establish whether a physiological increase in atrial natriuretic peptide (ANP) plasma levels affects pulmonary gas exchange in humans. Ten volunteers received an infusion of either ANP (4 pmol.kg-1.min-1) or physiological saline, for 60 min. Baseline measures of the alveolar-arterial PO2 difference and of the physiological dead space were within normal limits and remained stable during and after the infusion of ANP or saline, although plasma ANP and cGMP rose significantly (p < 0.01) (mean +/- SEM: ANP: 13.4 +/- 3.9 to 56.0 +/- 10.4 pmol/l; cyclic GMP: 3.8 +/- 0.3 to 17.0 +/- 3.8 nmol/l). We conclude that a physiological increase in plasma ANP does not affect pulmonary gas exchange significantly in humans.

Adult↗
PubMed1994

Bacterial endotoxin increases type II phospholipase A2 immunoreactive content and phospholipase A2 enzymatic activity in human choriodecidua.

The aim of this study was to establish the effect of bacterial endotoxin lipopolysaccharide (LPS) on type II phospholipase A2 (PLA2) content and in vitro net PLA2 enzymatic activity in human choriodecidua. More particularly, the objective was to ascertain whether an increase in type II PLA2 tissue content and PLA2 enzymatic activity is associated with the previously documented stimulatory effect of LPS on prostaglandin E2 (PGE2) release from choriodecidua. Choriodecidua explants were incubated in RPMI 1640 (control) or RPMI 1640 containing LPS (0.1 ng/ml to 10 micrograms/ml) for up to 24 h. Under the incubation conditions utilized, LPS (1 microgram/ml) stimulated the release of PGE2 3-fold (p < 0.001, n = 4 tissues), in a time-dependent manner (p < 0.005). Tissue immunoreactive (ir)-type II PLA2 content and PLA2 enzymatic activity were determined by monoclonal antibody sandwich ELISA and radiolabeled enzyme assay procedures, respectively. The tissue content of type II PLA2 immunoreactivity in choriodecidua obtained from women (n = 7) at term but not in labor averaged 155 +/- 24 ng/ml DNA. PLA2 enzymatic activity average 29.8 +/- 5.1 pmol phosphatidylethanolamine (PE)/mg DNA/h. LPS at a concentration of 1 microgram/ml increased immunoreactive type II PLA2 tissue content by 180% of the control value (p < 0.05, n = 7) within 1 h of exposure and remained significantly elevated for 18 h when compared to controls (174% of control, p < 0.01, n = 7).(ABSTRACT TRUNCATED AT 250 WORDS)

Chorion↗
PubMed1994

Patch-clamp analysis of direct steroidal modulation of glutamate receptor-channels.

Steroid hormones regulate the neuroendocrine and behavioral functions of the brain by using a number of diverse cellular mechanisms. Many steroids exert rapid electrophysiological effects on neurons, involving specific interactions with membrane components, such as neurotransmitter receptors. Previous studies suggest that the steroids, estrogen and pregnenolone sulfate (PS), might directly modulate glutamate receptors. The present experiments utilized patch-clamp recording of glutamate receptor-channels in excised membrane patches to test for direct modulation by these steroids. Characteristic single-channel activity from N-methyl-D-aspartate (NMDA) receptors could be elicited in both inside-out and outside-out patches excised from acutely dissociated hippocampal neurons. PS, but not 17 beta-estradiol, increased the open probability of NMDA channel activity in inside-out and outside-out patches. The PS-induced increase in open probability could be attributed to an increase in both frequency of opening and mean open time of the NMDA receptor, though the effect on frequency of opening was more prominent. The non-NMDA agonist, kainate, induced continuous shifts and increased noise in the baseline current of outside-out patches, but rarely activated clearly resolvable single-channel openings. 17 beta-estradiol and PS had no apparent effect on the kainate-induced currents. These findings suggest that some steroids can directly modulate glutamate receptors, but other steroids may utilize indirect mechanisms for regulating glutamatergic synaptic transmission.

Animals↗
PubMed1994

School performance, nutritional status and trichuriasis in Jamaican schoolchildren.

Severe infections by the geohelminth Trichuris trichiura detrimentally affect young children's growth and development. There is concern that mild to moderate infections may affect older children's school performance and nutritional status. We therefore examined the relationship between varying intensities of infection and school achievement, attendance and nutritional status in 616 schoolchildren. A total of 409 children with Trichuris infection of intensities greater than 1200 eggs per gram of stool (epg) were first identified, then for every 2 infected children in a class, an uninfected child was selected. After controlling for socioeconomic status, gender, age, school and the presence of Ascaris infections, the uninfected children had higher reading and arithmetic scores than children with infections of more than 4000 epg and were taller than those with intensities greater than 2000 epg. However, there were no significant differences in spelling, school attendance and body mass index. Although a treatment trial is needed to determine causation, these results indicate that moderate levels of infection are associated with poor school achievement and growth.

Case-Control Studies↗
PubMed1994

Effect of a fat- and calcium-rich breakfast on pharmacokinetics of fleroxacin administered in single and multiple doses.

The effect of a fat- and liquid-calcium-rich meal on the pharmacokinetics of single and multiple doses of fleroxacin in 20 healthy men and women was investigated in a randomized crossover fashion. Fleroxacin was administered as 400 mg daily for 3 days and as a single 400 mg dose. Concurrent administration of fleroxacin with food resulted in a statistically significant (P < or = 0.05) decrease in the area under the curve (13.9% for multiple-dose administration, 10% for single-dose administration) and in the peak concentration (25.9% for multiple-dose administration, 27% for single-dose administration) and a lengthening of the time to peak (more than doubled for single- and multiple-dose phases). In addition, by using an equivalence criteria of 80 to 125%, the two one-sided tests procedure indicated that the mean areas under the curves for fleroxacin administered in a fed and a fasted state were statistically bioequivalent (P < or = 0.05) for both the single- and multiple-dose regimens. Although a meal high in fat and containing liquid calcium reduces the peak concentration by approximately 25%, a minimal effect on bioavailability is seen with concomitant food administration. In addition, multiple-dose bioavailability studies appear to give similar information to single-dose studies while representing the clinical setting more closely.

Adult↗
PubMed1994

Comparison of serum osteocalcin with total and bone specific alkaline phosphatase and urinary hydroxyproline:creatinine ratio in patients with Paget's disease of bone.

Osteocalcin or bone Gla protein (BGP) is secreted by osteoblasts, and its serum concentration is elevated in a number of conditions with high bone turnover. A comparison of serum osteocalcin with total (TALP) and bone specific alkaline phosphatase (BALP) and urinary hydroxyproline/creatinine (OHP/Cr ratio) was performed in 13 patients with active Paget's disease of bone. BGP did not correlate significantly with either BALP or TALP, but did show a significant correlation with OHP/Cr ratio (r = 0.76; P < 0.01). BGP does not appear to be as sensitive a marker as BALP or TALP in Paget's disease.

Aged↗
PubMed1993

A simple assay for the measurement of conversion of big endothelin-1 to endothelin-1 by smooth muscle.

The conversion of exogenous big endothelin-1 to endothelin-1 by the smooth muscle of denuded porcine coronary arterial strips was measured by radioimmunoassay. Repeated incubations of a porcine coronary arterial strip with the same concentration of big endothelin-1 yielded similar rates of conversion over a 4 h period. This property allowed the determination of a control rate of endothelin-1 conversion by a coronary arterial strip followed by measurement of rates under various conditions. The assay described in this report can be used to investigate the biochemical properties and inhibitor profiles of the extracellular enzyme mediating the conversion of big endothelin-1 to endothelin-1. The Km and Vmax of the enzyme were 34 +/- 2 microM and 88 +/- 8 fmol/min, respectively. Conversion of big endothelin-1 to endothelin-1 was optimal at pH 7.0 and was inhibited by classic metalloprotease inhibitors.

Animals↗
PubMed1993

Purification and characterization of a paired basic residue-specific yeast aspartic protease encoded by the YAP3 gene. Similarity to the mammalian pro-opiomelanocortin-converting enzyme.

Yeast cells express an alternate enzyme encoded by the YAP3 gene which can process pro-alpha-mating factor when this pheromone is overexpressed in KEX2-deficient mutants. The YAP3 gene product is an aspartic protease (YAP3) that cleaves at paired basic residues (Egel-Mittani, M., Flygenring, H.P., and Hansen, M. T. (1990) Yeast 6, 127-137). In this study, the YAP3 gene was overexpressed in the BJ 3501 strain of Saccharomyces cerevisiae. YAP3 was purified to apparent homogeneity using concanavalin A and pepstatin A affinity chromatography. The enzyme was characterized as an M(r) 68,000 glycoprotein with a pH optimum of 4.0-4.5. It was inhibited by pepstatin A and activated by 5 mM Ca2+. YAP3 cleaved at paired basic residues of mouse pro-opiomelanocortin (POMC) to yield adrenocorticotropin (ACTH) and beta-lipotropin (LPH); human beta-LPH to yield beta-endorphin-(1-31), beta-endorphin-(1-29), beta-endorphin-(1-28), gamma-LPH, and beta-melanocyte-stimulating hormone; and bovine N-POMC1-77 to yield gamma 3-melanocyte-stimulating hormone. It also cleaved the tetrabasic residues of ACTH1-39 to yield primarily ACTH1-15 and Lys-Arg-corticotropin-like intermediate lobe peptide. The physical properties, pH optimum, and specificity of YAP3 indicate that it is a homologue of the mammalian POMC-converting enzyme (EC 3.4.23.17), a paired basic residue-specific aspartic protease from bovine pituitary intermediate lobe secretory granules (Loh, Y. P., Parish, D.C., and Tuteja, R. (1985) J. Biol. Chem. 260, 7194-7205).

Adrenocorticotropic Hormone↗
PubMed1993

Nuserum, a synthetic serum replacement, supports chondrogenesis of embryonic chick limb bud mesenchymal cells in micromass culture.

In an effort to establish a more chemically defined culture system to study the regulation of chondrogenic differentiation in vitro, two commercially available serum replacements, NuSerum and NuSerum IV, were tested on embryonic limb mesenchyme. Limb bud (LB) mesenchymal cells were isolated from Hamilton-Hamburger stage 23-24 chick embryos and plated at various densities (1, 5, 10, or 20 x 10(6) cells/ml) in micromass culture for 4 days in media supplemented with 10% fetal bovine serum (FBS), NuSerum or NuSerum IV. Cell growth was assessed by the incorporation of [3H]leucine and [3H]thymidine. Chondrogenesis was determined by the incorporation of [35S]sulfate and by the number of Alcian blue-staining cartilage nodules. In high density (20 x 10(6) cells/ml) cultures, which favored chondrogenic differentiation, both serum replacements supported protein synthesis and chondrogenesis equally well as FBS. In cultures plated at 5 x 10(6) cells/ml, a cell density in which was chondrogenesis-limiting, both NuSerum and NuSerum IV significantly enhanced incorporation of [35S]sulfate (2.6-fold), [3H]leucine (1.4-fold), and [3H]thymidine (1.9-fold), compared to FBS. Enhancement of chondrogenesis was also apparent by the increases in the number of Alcian blue-staining cartilage nodules and the ratio of sulfate: leucine incorporation in cultures plated at 5 x 10(6) cells/ml. Interestingly, the localization of cartilage nodules was extended out to the periphery of micromass cultures fed with NuSerum or NuSerum IV.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Excitatory and inhibitory synaptic processing in the accessory olfactory system of the female rat.

The accessory olfactory system constitutes a sensory system specifically involved in regulating neuroendocrine function and reproductive behavior. The chemosensitive structure of this system, the vomeronasal organ, exclusively innervates the accessory olfactory bulb, which in turn projects via mono- or disynaptic pathways to a limited number of regions implicated in endocrine and sexual function, including the amygdala and hypothalamus. The present study investigated synaptic processing between the different levels of this sensory system, with particular focus on the input from the accessory olfactory bulb to the medial amygdala and the reciprocal connections between the medial amygdala and the ventromedial hypothalamus. Extracellular single-unit recordings were obtained from medial amygdala neurons in anesthetized female rats to study the synaptic responses elicited by stimulation of the olfactory bulb and hypothalamus. Locally applied agonists and antagonists of amino acid neurotransmitters were tested for their ability to mimic and block these synaptic responses in an attempt to identify the neurotransmitters involved in the stimulated pathways. Electrical stimulation of the accessory olfactory bulb induced orthodromic responses in 88% of 288 medial amygdala neurons, with 67% showing orthodromic inhibition and 21% showing excitation as the shortest-latency response. Many cells displayed multiphasic responses with both orthodromic excitation and inhibition. In separate experiments, main olfactory bulb stimulation also produced excitatory (39%) or inhibitory (50%) orthodromic responses in medial amygdala neurons (n = 105), but the latency and distribution of responses were significantly different than with accessory olfactory bulb stimulation. Stimulation of the ventromedial hypothalamus also had prominent excitatory (29%) or inhibitory (59%) orthodromic actions on the majority of amygdala neurons. Out of 288 cells tested with both accessory olfactory bulb and ventromedial hypothalamus stimulation, 79% were orthodromically responsive to both areas, whereas only 3% responded to neither area. Fourteen (6%) medial amygdala neurons were antidromically activated from the ventromedial hypothalamus, and 11 of these 14 cells were simultaneously orthodromically responsive to accessory olfactory bulb stimulation, indicating that the accessory olfactory bulb can influence medial amygdala neurons that project directly to the hypothalamus. Iontophoretic application of drugs to the medial amygdala revealed that glutamate and GABA consistently mimicked the orthodromic excitatory and inhibitory responses, respectively, from both the accessory olfactory bulb and ventromedial hypothalamus. In some cases, ejection of bicuculline could block or reverse excitation of the orthodromic inhibitory responses, whereas kynurenic acid could eliminate the orthodromic excitation, indicating that excitatory and inhibitory amino acid transmitters are at least partially involved in these pathways.(ABSTRACT TRUNCATED AT 400 WORDS)

Amygdala↗
PubMed1993

Substance P levels in experimental ileitis in guinea pigs: effects of misoprostol.

Substance P, a neuropeptide mediator of inflammation, was quantified during the evolution of trinitrobenzene sulfonic acid (TNBS)-induced ileitis in guinea pigs. Ileitis was induced by a single intraluminal injection of TNBS (30 mg/kg in 50% ethanol). Misoprostol, a prostaglandin E1 analogue, was administered parenterally (30 mg/kg sc twice daily) in a group of TNBS-treated animals. Control guinea pigs received intraluminal saline (sham) or 50% ethanol (TNBS vehicle). Guinea pigs were evaluated at day 1, 3, 7, 14, or 30 after ileitis induction for substance P content (radioimmunoassay) and distribution (immunohistochemistry), morphology, myeloperoxidase (MPO) activity, and protein leak into the gut lumen. TNBS administration caused an increase in ileal MPO activity that peaked at day 7 and increased mucosal leak of protein. Misoprostol attenuated the granulocyte infiltration (MPO) response to TNBS but exacerbated the mucosal leak of protein. Substance P levels in whole ileal segments were unaltered from baseline on day 1 in all groups. On day 3 a marked decrease in ileal substance P content was evident in the TNBS and TNBS + misoprostol groups. As early as day 1, immunohistochemistry suggested that the decreased substance P content was confined to the mucosa and submucosa, because myenteric plexus staining was not reduced. Loss of staining in the perivascular nerves was particularly marked. Substance P content and distribution returned to baseline by day 30 post-TNBS, although MPO activity remained slightly elevated. We concluded that TNBS ileitis is associated with a marked reduction in mucosal and submucosal substance P content in parallel with the inflammatory response. Although misoprostol attenuated granulocyte infiltration in this model, it did not prevent the disturbances in enteric substance P or mucosal protein leak.

Animals↗
PubMed1993

Blood-tissue transport of exogenous albumin and immunoglobulin G in genetically analbuminemic rats.

Tracer uptake studies were carried out in adult female Nagase (NA) strain analbuminemic rats [derived from Sprague-Dawley (SD) stock] and in adult female SD controls to determine the extent to which capillary permeability to plasma proteins is altered in the absence of endogenous albumin. Accessory measurements (arterial pressure, central venous pressure, plasma and interstitial fluid protein concentrations and oncotic pressures, plasma volume, and interstitial fluid volume) confirm the report of Joles et al. [Am. J. Physiol. 257 (Renal Fluid Electrolyte Physiol. 26): F23-F28, 1989] that shows elevated plasma volumes, normal interstitial fluid volumes, nearly normal plasma oncotic pressures (due to elevated globulin concentrations), and lower interstitial fluid oncotic pressures. In skin, skeletal muscles, and heart muscle, clearances of exogenous heterologous (bovine) albumin were 20-40% higher in NA than in SD controls. In intestine, albumin clearances were 20-30% lower. In NA rats blood-to-tissue clearances of heterologous (bovine) immunoglobulin G in skin and heart were higher and in the intestine they were lower than in SD controls; however, clearances in skeletal muscles were not elevated. The differences between NA and SD are small compared with the large increases in macromolecular permeabilities reported by others for organs and single microvessels perfused with albumin-free fluids.(ABSTRACT TRUNCATED AT 250 WORDS)

Albumins↗
PubMed1993

Ultrasonic-pathological comparison of the human arterial wall. Verification of intima-media thickness.

Recent intravascular ultrasound experience challenges the accuracy of ultrasonic measurement of arterial wall thickness. We reevaluated the correlation between histological and sonographic measurements of intima-media thickness using standard transcutaneous vascular technology. Carotid and femoral arterial segments were imaged before and after fixation using a 7-MHz linear-array vascular transducer. Log compression and beam orientation were varied. Mean intima, media, and adventitia thicknesses were measured and compared with corresponding histological tunica. Tissue processing caused 2.5% shrinkage. Intraobserver reading error was 0.7% for histology and 5.4% for sonography. Ultrasound overestimated the thickness of the intima and adventitia and underestimated the thickness of the media. For combined intima-media thickness, the differences between histology and imaging were insignificant, averaging 4% for the carotid artery and 9% for the femoral artery in the far-wall projection. In the near-wall projection, sonographic intima-media thickness was 20% less than that determined histologically. We conclude that ultrasonography is limited mainly by axial resolution in quantifying the dimensions of individual arterial tunica but is capable of accurately measuring far-wall intima-media thickness.

Aged↗
PubMed1993

Doppler-derived aortic valve gradients: imaging versus non-imaging techniques.

BACKGROUND: Quantitative Doppler echocardiography has become an established method for estimating aortic valve area in aortic stenosis, replacing cardiac catheterization as the confirmatory study. The technique is time consuming, especially when measuring the transaortic velocity, which is performed by convention. This is accomplished by interrogating multiple windows with a non-imaging probe to record the maximal velocity. To determine how the examination could be expedited, we prospectively compared aortic valve gradients measured by Pedof and duplex transducers. METHODS: One hundred eighty-two consecutive patients with native aortic valve disease, mechanical or bioprosthetic aortic valves were studied. Two technicians measured maximal transaortic valve velocities from apical, subcostal, right parasternal and suprasternal notch windows with a 2 MHz Pedof probe and from the apical window with a 3-3.5 MHz duplex probe using color flow to orient the continuous wave beam. Angle-corrected and non-angle-corrected signals were recorded. There were 109 comparisons read by two observers; intra- and inter-reader variations were 0.4% and 2.0%, respectively. RESULTS: Duplex imaging velocity gradients were consistently smaller than Pedof non-imaging measurements with a mean +/- 1 standard deviation difference between peak velocities of 0.40 +/- 0.71 meters per second (m/s) for angle-corrected, and 0.76 +/- 0.68 for non-angle-corrected signals (both p < 0.001). Technician variability accounted for some of the difference (p < 0.02). CONCLUSION: Although non-imaging and imaging methods share the apical window, the Pedof probe scans unlimited planes to locate the maximal aortic valve gradient, whereas the duplex probe is confined to the plane providing the optimal two-dimensional image. Therefore, Doppler echocardiographic estimations of aortic valve areas still require careful, time-intensive non-imaging recordings of transaortic velocities.

Aortic Valve↗
PubMed1993

Clinical profile of stage D carcinoma of the prostate--a ten-year experience.

Carcinoma of the prostate has become one of the top ten malignancies in Singapore but to date, there has been little local clinical data available on the disease. This study aims to establish the clinical profile of Stage D carcinoma of the prostate in the local population. Forty-seven patients with Stage D disease treated by the department over a ten-year period, 1981-90, were studied. The majority (47.7%) fell in the age-group 66-75 years and the most common presenting symptom was bone pain (36.2%). Both acid and alkaline phosphatases were found to be poor diagnostic markers of the extent of the disease. Acid phosphatase was not elevated in 25.0% and alkaline phosphatase not elevated in 39.1% of our patients. Forty of these patients had orchidectomy and of these, ten were also treated with oral stilbesterol. Five-year survival for the orchidectomy group was 22.7% and that for the orchidectomy-plus-stilbesterol group was 23.0%. This compares well with other studies done in the West. Eight patients died within the first year of diagnosis but of those who survived, all remained symptom-free within this first year. The proportion of those who remained symptom-free fell to 25.0% of the survivors for subsequent years.

Acid Phosphatase↗