Biomedical subjects

H Y Chang

Publications and source records attributed to H Y Chang.

At least 91 records · Page 5Linked to original sources

PubMed1997

Role of KATP channels on modulating diaphragmatic microvascular flow during hemorrhagic hypotension.

The effects of glibenclamide (GLB), a specific blocker of ATP-sensitive potassium (KATP) channels, and tetraethylammonium (TEA) on modulating the regulation of diaphragmatic microcirculation were assessed in anesthetized mechanically ventilated rats. With bicarbonate-buffered Ringer solution continuously suffusing the left hemidiaphragm, microcirculatory blood flow was recorded by laser-Doppler flowmetry (QLDF). Hemorrhagic hypotension (HH) was induced via bleeding into a pressure reservoir. Five sets of experiments were performed. In set 1 (n = 6), the vasodilator effect of diazoxide (3 x 10(-4) M) was abolished after a 30-min suffusion with GLB, whereas the vasodilator effect of sodium nitroprusside (3 x 10(-6) M) remained the same. In set 2 (vehicle + HH; n = 23), a stepwise reduction in systemic arterial blood pressure (ABP) induced two distinct patterns of microvascular responses. Regulation of QLDF could be observed in pattern A animals in a range of ABP from 113 to 52 mmHg, whereas QLDF in pattern B animals rose progressively with declining ABP. In set 3 (GLB + HH; n = 17), baseline values of QLDF were not significantly affected after a 30-min suffusion of GLB (10(-5) M). During HH, two microvascular patterns similar to those in set 2 were observed. GLB significantly potentiated the reduction in QLDF in pattern A animals. In contrast, GLB had no effect on QLDF in pattern B animals. In set 4 (TEA + HH; n = 17), similar microvascular responses, compared with the vehicle group, were observed during HH after a 30-min suffusion of TEA (2 x 10(-3) M). In set 5 (n = 5), baseline values of QLDF were not significantly altered during sham hypotension. We conclude that 1) KATP channels are functional but not active in the resting diaphragmatic microcirculation and 2) KATP channels can modulate regulation of the microcirculation in the resting diaphragm during HH.

Adenosine Triphosphate↗

PubMed1997

Role of nitric oxide in vasodilator response induced by salbutamol in rat diaphragmatic microcirculation.

To determine the contribution of nitric oxide (NO) to the vasodilator response induced by salbutamol in diaphragmatic microcirculation, we studied a diaphragmatic preparation in anesthetized rats. With bicarbonate-buffered Ringer solution continuously suffusing the diaphragm, laser-Doppler flowmetry was used to record microvascular blood flow (QLDF). The drugs were applied to the surface of the diaphragm. Salbutamol (3.2 x 10(-7)-10(-4) M), isoproterenol (3.2 x 10(-8)-3.2 x 10(-6) M), and forskolin (3.2 x 10(-7)-10(-5) M) each elicited a concentration-dependent increase in QLDF. The vasodilator response induced by salbutamol (3.2 x 10(-7), 10(-6), and 3.2 x 10(-6) M) was attenuated by a 15-min suffusion of N omega-nitro-L-arginine (L-NNA, 10(-4) M), and pretreatment with L-arginine (10(-2) M) could restore salbutamol-induced vasodilator responses. Salbutamol-induced vasodilation was also abolished by propranolol (10(-5) M). Similarly, the vasodilator response elicited by isoproterenol (3.2 x 10(-8), 10(-7), and 3.2 x 10(-7) M) and forskolin (3.2 x 10(-7), 10(-6), and 3.2 x 10(-6) M) was inhibited by L-NNA (10(-4) M). In contrast, the vasodilator response induced by adenosine (10(-6), 10(-5), and 10(-4) M) was not affected by L-NNA (10(-4) M). These data indicate that in rat diaphragmatic microcirculation salbutamol-induced vasodilation may be partly mediated by beta-adrenoceptors on the endothelium. Moreover, these data suggest that an elevation of cyclic AMP in the endothelium may cause release of NO.

Adenosine↗

PubMed1997

Mite-induced allergic airway inflammation in guinea pigs.

BACKGROUND: Mites are the most common aeroallergen in human allergic asthma. However, no animal model of mite-induced allergic airway inflammation has been reported before. In this study, an animal model of mite-induced allergic airway inflammation in guinea pigs was developed. METHODS: Firstly, we found that two intraperitoneal injections of 100 micrograms crude mite extract (CME), but not multiple aerosol inhalations of 10 mg/ml CME, can cause sensitization in guinea pigs. The sensitization to mites was confirmed by the measurement of serum antimite antibody titer and the detection of anaphylactic bronchoconstriction after intravenous injection of CME solution. Then, single or multiple aerosol challenges with different concentrations (8, 4 or 1 mg/ml) of CME in these sensitized animals were performed. The total white cell and differential counts in the bronchoalveolar lavage (BAL) fluids were studied at different time intervals after challenge in different animals, and tracheal pathology was performed to detect the allergic airway inflammation. For comparison with the study in animals treated with CME, a BAL study in animals treated with ovalbumin was also performed. RESULTS: The inhalation challenge of CME aerosol in sensitized animals caused prolonged eosinophilia in BAL fluid which persisted for at least 7 days after single challenge. Neither inhalation challenge at higher concentrations of CME aerosol nor repeated inhalation challenges increased the degree of eosinophilia in BAL fluid compared to a single challenge. Using the same procedures, we also found that the mite model caused more eosinophilia in BAL fluid than did ovalbumin. CONCLUSION: This is the first report of an animal model of mite-induced allergic airway inflammation in guinea pigs which can provide us with a useful model to study airway inflammation of mite-induced asthma in humans.

Allergens↗

PubMed1997

Fatal acute pulmonary oedema after inhalation of fumes from polytetrafluoroethylene (PTFE).

The cases of three patients with acute pulmonary oedema caused by inhalation of fumes from heated polytetrafluoroethylene (PTFE) in a plastic factory are described. One patient died from profound hypoxaemia and shock shortly after admission, and the other two patients survived after medical treatment. This is the first report of fatal pulmonary oedema in a worker exposed to PTFE heated in a plastic extruding operation. From this observation, it appears that inhalation exposure to pyrolytic products from polytetrafluoroethylene can cause fatal respiratory complications. Special precautions are warranted in this kind of operation to prevent workers from being exposed to these substances.

Acute Disease↗

PubMed1997

Prevalence of antithyroid antibodies in mood disorders.

We examined the prevalence of antimicrosomal and antithyroglobulin antibodies in psychiatric inpatients with unipolar depression (N = 218), bipolar disorder manic (N = 51), bipolar disorder depressed (N = 19), and bipolar disorder mixed (N = 26) in comparison with two control groups: psychiatric inpatients with adjustment disorder (N = 80) and family medicine outpatients without current psychiatric illness (N = 144). A statistical analysis that controlled for age and sex revealed the frequency of positive antibody titers not to be increased in patients with a diagnosis of unipolar depression (6.9%) or bipolar disorder manic (3.9%), when compared with patients with adjustment disorder (2.5%) and non-psychiatric subjects (6.9%). There was a weak trend toward an increased prevalence of antithyroid antibodies in patients with bipolar disorder, mixed (19%) or depressed subtype (16%). The excess occurrence of antibodies in patients with either mixed or depressed bipolar disorder did not appear to be related to lithium exposure, which was similar in all bipolar subgroups. When the intervening influences of age and sex are taken into account, unipolar depression does not appear to be associated with an excessive rate of antithyroid antibodies; however thyroid autoimmunity may be weakly associated with subtypes of bipolar disorder in which depressive symptoms are prominent.

Adult↗

PubMed1997

Heart rate variability in patients with atrioventricular block.

BACKGROUND: Heart rate variability (HRV) analysis has been an established method for assessment of the activities of autonomic nervous system. Conventionally, the RR intervals from the surface electrocardiogram (ECG) are used for HRV analysis, however, analysis of the RR intervals may not be suitable in patients with atrioventricular (AV) node dysfunction, particularly in patients with certain degree of AV block. We used an esophageal electrode to detect PP intervals for HRV analysis in these patients. METHODS: Seven AV block patients and 13 subjects with normal AV conduction (control group) were enrolled in this study. The signals from esophageal lead, surface lead and intraatrial lead were recorded. Correlation coefficient of heart beat intervals from different leads was analyzed. Then we compared the HRV parameter recorded by esophageal lead between AV block patients and the control group. RESULTS: The AA intervals in intraatrial ECG and the PP intervals in surface ECG were poorly correlated (r = 0.489) in the AV block patients. However, intraatrial ECG was correlated well with esophageal ECG (r = 0.968). HRV with time domain decreased significantly in patients with AV block. The standard deviation of NN intervals (SDNN), pNN-50 and r-MSSD in the control group and the AV block patients were 0.035 +/- 0.006 vs. 0.021 +/- 0.016 seconds (p = 0.002), 3.210 +/- 3.120 vs. 0.050 +/- 0.040% (p = 0.027) and 0.577 +/- 0.181 vs. 0.318 +/- 0.084 seconds (p = 0.009), respectively. CONCLUSIONS: The esophageal lead recording is a non-invasive, easy and safe method to detect HRV of AV block patients whose vagal activity is abnormal.

Electrocardiography↗

PubMed1996

Alkylglycerophosphate acetyltransferase and lyso platelet activating factor acetyltransferase, two key enzymes in the synthesis of platelet activating factor, are found in neuronal nuclei isolated from cerebral cortex.

Neuronal nuclear fractions (N1) isolated from cerebral cortices of 15-day-old rabbits were enriched in two acetyltransferases involved in biosynthetic pathways leading to platelet activating factor (PAF). Alkylglycerophosphate (AGP) acetyltransferase of the de novo biosynthetic path had specific activities in fraction N1 which were 3-times those of the microsomal fraction (P3D) from cerebral cortex. Lyso PAF acetyltransferase of the remodelling path had specific activities in N1 which were 16-times those of P3D and 51-times those of the homogenate. The maximum specific activity observed for the N1 AGP acetyltransferase was 1.4-times the corresponding N1 lyso PAF acetyltransferase value. The pH optimum for the N1 AGP acetyltransferase was within the alkaline range (pH 8-9), while the N1 lyso PAF acetyltransferase showed a much broader pH optimal range which extended over the neutral and physiological pH values. Both acetyltransferases were inhibited by MgATP (0.125-1 mM) or oleoyl CoA (2-10 microM). However, the N1 AGP acetyltransferase could be distinguished from the N1 lyso PAF acetyltransferase by a greater sensitivity to MgATP inhibition. When NaF was not present in the assays, less of the product of N1 AGP acetyltransferase was recovered, likely indicating a hydrolysis of the acetylated AGP. When the AGP and lyso PAF substrates were combined in acetyltransferase assays, the two N1 acetylations appeared to proceed independently. The enrichment of the acetyltransferases, and particularly the lyso PAF acetyltransferase, within the neuronal nuclear fraction is of particular interest with respect to the intracellular effects of PAF which are considered to be involved in nuclear signalling mechanisms.

Acetyl Coenzyme A↗

PubMed1996

An improved assay for UDPglucose pyrophosphorylase and other enzymes that have nucleotide products.

UDPglucose pyrophosphorylase catalyses the interconversion UDPglucose plus pyrophosphate and glucose 1-phosphate plus UTP. Several assay methods for this enzyme have been described but the only one that can be used to investigate the specificity with respect to various UDPsugars is based on coupling to UTP formation. This assay employs phosphoglycerate kinase to catalyse the formation 1,3- bisphosphoglycerate which is then used to oxidise NADH in the presence of glyceraldehyde 3-phosphate dehydrogenase. We have found that the activity of phosphoglycerate kinase towards UTP is low which limits the usefulness of the assay to very low rates, in agreement with the published recommendation of Hansen et al. Here it is shown that the dynamic range of the assay is increased by more than five fold on addition of nucleoside diphosphate kinase and ADP, which convert UTP to the preferred phosphoglycerate kinase substrate, ATP. It is also shown that the improved assay is suitable for enzymes with other nucleotide triphosphate products.

Adenosine Diphosphate↗

PubMed1996

Rate-determining steps in the biosynthesis of glycogen in COS cells.

Consistent with previous results, overexpression of rabbit skeletal muscle glycogen synthase in COS cells did not lead to overaccumulation of glycogen unless activating Ser-->Ala mutations were present at key regulatory phosphorylation sites 2 (Ser7) and 3a (Ser644) in the enzyme. In addition, we found that expression of glycogenin, glycogen branching enzyme, or UDP-glucose pyrophosphorylase alone in COS cells had no effect on the glycogen level. However, coexpression of the hyperactive 2,3a glycogen synthase mutant with either glycogenin or UDP-glucose pyrophosphorylase led to higher glycogen accumulation than that obtained from the expression of glycogen synthase alone. Coexpression of glycogenin with the 2,3a mutant of glycogen synthase led to the appearance of glycogenin with a lower molecular weight suggestive of reduced glucosylation. Increased glycogen synthesis may lead to competition between glycogenin and glycogen synthase for their common substrate UDP-glucose. In summary, we conclude that (i) glycogen synthase is a primary rate-limiting enzyme of glycogen biosynthesis in COS cells, (ii) that phosphorylation of glycogen synthase is regulatory for glycogen accumulation, and (iii) once glycogen synthase is activated, the reaction mediated by UDP-glucose pyrophosphorylase can become rate-determining.

1,4-alpha-Glucan Branching Enzyme↗

PubMed1996

The importance of conserved residues in human liver UDPglucose pyrophosphorylase.

Comparison of the amino acid sequences of five eukaryotic UDPglucose pyrophosphorylases has identified a number of conserved residues that may be important for substrate binding or catalysis. Using the cloned cDNA for the human liver enzyme, we have investigated the role of several of these residues by site-directed mutagenesis. Changing the single conserved cysteine (residue 123) to serine resulted in an active enzyme, as did mutating the single concerned histidine (residue 266) to arginine. The two conserved tryptophans were each altered to serine; W218S is active while W333S is not. In the latter case, the enzyme does not appear to fold correctly, and a similar result was obtained by mutation to lysine at one (residue 391) of the four conserved arginines. The other three arginines are not essential, as judged by the observation that R389H, R422Q and R445H are all active. The kinetic properties of each active mutant were investigated and in most cases were found to be similar to those of wild-type. The most dramatic change is a sevenfold increase in the Km for magnesium pyrophosphate with C123S. Overall, none of these conserved residues appears to be essential for activity, although such a role cannot be ruled out for W333 and R391 where mutation resulted in defective folding.

Animals↗

PubMed1996

Sequence differences between human muscle and liver cDNAs for UDPglucose pyrophosphorylase and kinetic properties of the recombinant enzymes expressed in Escherichia coli.

UDP-Glc pyrophosphorylase (EC 2.7.7.9) catalyses the interconversion of MgUTP plus Glc1P and UDP-Glc plus MgPPi. Complementation of an Escherichia coli strain lacking this activity has allowed isolation of cDNA encoding this enzyme from a human muscle library. Two forms were identified and the nucleotide sequence of each was determined; they were found to differ only in the 5' region and we suggest that these arise from the use of a different first exon in the two transcripts. These nucleotide sequences are different from that of the cDNA which was isolated previously from a human liver library [Peng, H.-L. & Chang, H.-Y. (1993) FEBS Lett. 329, 153-158] and it is proposed that these liver and muscle forms are derived from different genes. The cDNA for muscle form I, muscle form II, the liver form, and the liver form fused to part of the lacZ gene were expressed in Escherichia coli and the kinetic properties of each enzyme were characterised. Muscle form I and the LacZ/liver fusion enzyme exhibit Michaelis-Menten kinetics towards all substrates while muscle form II has a sigmoidal dependence of rate upon the concentration of MgPPi. The liver form shows Michaelis-Menten kinetics towards MgUTP. For the remaining three substrates, complex kinetics were observed involving a combination of sigmoidicity at low substrate concentration and partial inhibition at high substrate concentration.

Amino Acid Sequence↗

PubMed1996

Virulence and outer membrane properties of a galU mutant of Klebsiella pneumoniae CG43.

Non-mucoid mutants of a Klebsiella pneumoniae wild type strain CG43 were generated by transposon mutagenesis. One of the mutants was incapable of fermenting galactose and was designated CG43-17. Alterations of the bacterial surface including capsule, lipopolysaccharides, and several species of outer membrane proteins were noted. The mutant was avirulent to mice and became highly sensitive to human serum. The defects could not be complemented by the gaIETK operon. Diminished activity of UDP-glucose pyrophosphorylase in CG43-17 suggested that it is a gaIU mutant. This possibility was confirmed because the parental phenotypes could be fully restored in the mutant by transforming it with a human liver cDNA encoding UDP-glucose pyrophosphorylase.

Animals↗

PubMed1996

Identification and characterization of the acoD gene encoding a dihydrolipoamide dehydrogenase of the Klebsiella pneumoniae acetoin dehydrogenase system.

The acoD gene, which encodes a dihydrolipoamide dehydrogenase component of the acetoin dehydrogenase enzyme system of Klebsiella pneumoniae was isolated and the nucleotide sequence determined. The gene is capable of encoding a protein of 465 amino acid residues with conserved binding domains for NAD and FAD, and two redox-active cysteine residues. The acoD gene product exhibited a Michaelis constant of 170 microM for NAD, while NADP can not be used as a substrate. The purified enzyme appeared to be a dimer of the acoD gene product. It did not associate tightly with the E1 and E2 components of either acetoin dehydrogenase or 2-oxoglutarate dehydrogenase to form an active multi-enzyme complex.

Acetoin Dehydrogenase↗

PubMed1996

Isoniazid-induced fever.

A rare case of isoniazid (INH)-induced fever is described. A 27-year-old woman diagnosed with miliary tuberculosis (TB) began to receive combined anti-TB treatment including INH, ethambutol, rifampicin and pyrazinamide on the second day of hospitalization. A spiked fever developed in the afternoon of the seventh hospital day. There was no evidence of a hypersensitivity reaction. All examinations including liver function tests, routine biochemistry tests, serum titer of antinuclear antibody and rheumatoid factor were within normal limits. The blood leukocyte count was also within normal range and no evidence of infection at other sites was found. Following the discontinuance of anti-TB agents, the patient's body temperature gradually returned to normal. When the patient was rechallenged with INH, the high fever recurred. The fever subsided again after the discontinuance of INH, and her recovery followed a smooth course thereafter, on combination therapy with rifampicin, ethambutol and pyrazinamide. This experience demonstrates the potential of INH to cause an isolated fever without other manifestations, which may be misdiagnosed as an infectious process. Though it is very rare, INH-induced fever must be considered when fever develops during anti-TB treatment.

Adult↗

PubMed1996

Increased IL-5 and IL-10 transcription in bronchial cells after Sauropus androgynus ingestion.

An outbreak of rapidly progressive obstructive lung disease in Taiwan was noted in some patients regularly ingesting the vegetable Sauropus androgynus because of its perceived weight reducing properties. Bronchoalveolar lavage (BAL) prior to administration of medication was performed in two women who had regularly ingested this vegetable and had developed obstructive ventilatory defects. Both patients showed a significant increase in neutrophils and, to a lesser extent, of eosinophils in the lavage fluid as compared to two unrelated controls. Interleukin (IL)-1 beta, IL-2, IL-5, IL-10, interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha in cells recovered from BAL fluid were analyzed by reverse transcription-polymerase chain reaction (RT-PCR). Augmented expression of the IL-10 gene was detected in only two patients who had regularly ingested S. androgynus. Our results suggest that altered cytokine expression and infiltration of eosinophils and neutrophils may be involved in the pathology of obstructive lung disease caused by regular ingestion of S. androgynus.

Adult↗

PubMed1995

Asymmetric retraction of growth cone filopodia following focal inactivation of calcineurin.

The neuronal growth cone is thought to be the site of decision making in nerve growth and guidance. One likely mechanism of how the growth cone translates various extracellular cues into directed motility involves rises in intracellular calcium. A variety of physiological cues, such as adhesion molecules and neurotransmitters, increases intracellular calcium, and artificial manipulations of growth cone calcium levels affect growth cone morphology and neurite outgrowth. The molecular events downstream of calcium fluxes are incompletely understood. Here we show that calcineurin, a protein phosphatase enriched in growth cones that is dependent on calcium ions and calmodulin, functions in neurite outgrowth and directed filopodial motility in cultured chick dorsal root ganglia neurons. Cyclosporin A and FK506, inhibitors of calcineurin, delayed neuritogenesis and inhibited neurite extension. Chromophore-assisted laser inactivation of calcineurin in regions of growth cones causes localized filopodial and lamellipodial retraction and influences the direction of subsequent outgrowth. We suggest that a spatial distribution of calcineurin activity within the growth cone can regulate motility and direct outgrowth.

Animals↗

PubMed1995

The pH-dependence of the equilibrium between the fast- and slow-folding forms of bovine prothrombin fragment 1: a role for pH-induced self-association?

Examination of the pH- and ionic strength (mu)-dependence of the equilibrium between fast- and slow-folding forms of bovine prothrombin fragment 1 reveals a sharp dependence of Keq ([% fast-folding form]/[% slow-folding form]) and % fluorescence quenching (%Q) on pH at low mu, and the absence of a pH-dependence of Keq at high mu (0.1 M NaCl) and much reduced pH-dependence of %Q, suggesting that the ionization process is coupled to other processes, such as self-association. The observed low mu pH effect on Keq amounts to a 10% increase in the % of the fast-folding form of prothrombin at low pH. We hypothesize the existence of a pH-dependent self-association of bovine prothrombin fragment 1. This process is associated with a conformation change involving an ionizing group with pKa in the neighborhood of 6.5 and a change in Keq from 0.27 to 0.45.

Animals↗

PubMed1995

Intramolecular domain-domain interactions and intermolecular self-association in bovine prothrombin. A potentiometric and laser light-scattering study.

The interaction of bovine prothrombin with Ca2+ and Mg2+ ions was investigated by following H+ release as a function of metal ion concentration at pH 6 and pH 7.4 at high and low ionic strength. Prothrombin Ca2+ and Mg2+ binding is characterized by high- and low-affinity sites. M2+ binding at these sites is associated with intramolecular conformational changes and also with intermolecular self-association. The pH dependence of H+ release by M2+ is bell shaped and consistent with controlling pKa values of 4.8 and 6.5. At pH 6 and low ionic strength, both Ca2+ and Mg2+ titrations following H+ release clearly show independent low- and high-affinity binding sites. Laser light scattering reveals that at pH 7.4 and low ionic strength, and at pH 6.0 and high ionic strength, the prothrombin molecular weight is between 73 and 98 kD. At pH 7.4 and high ionic strength, prothrombin is monomeric in the absence of metal ions, but appears to dimerize in the presence of M2+. At pH 6.0 and low ionic strength prothrombin exists as a dimer in the absence of metal ions and is tetrameric in the presence of Ca2+ and remains dimeric in the presence of Mg2+. These results and those for metal ion-dependent H+ release indicate that H+ release occurs concomitantly with association processes involving prothrombin.

Animals↗