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Biomedical subjects

T Yang

Publications and source records attributed to T Yang.

At least 271 records · Page 15Linked to original sources
PubMed1991

Changes in the baroreceptor reflex at the start of muscle contraction in the decerebrate cat.

1. The action of muscle contraction on the sensitivity of the cardiac vagal component of the baroreceptor reflex was examined in decerebrate cats. 2. The sensitivity of the baroreceptor reflex was expressed as the difference between the maximum prolongation of the R-R interval in response to carotid sinus baroreceptor stimulation and the mean of ten R-R intervals immediately before carotid sinus pressure elevation. 3. Muscle contraction elicited by electrical stimulation of L7 ventral roots (50 Hz) significantly reduced the sensitivity of the baroreceptor reflex by reducing the prolongation of the R-R interval from 269 +/- 31 to 159 +/- 22 ms. 4. Inhibition of the cardiac vagal component of the baroreceptor reflex was seen just 1 s after the onset of contraction and with stimulation frequencies as low as 10 Hz. 5. These results show for the first time that changes in the sensitivity of the baroreceptor reflex during exercise result in part from afferent information originating in the contracting muscles.

Animals↗
PubMed1991

Inhibition of cardiac vagal component of baroreflex by group III and IV afferents.

The action of electrically evoked activity in somatic afferent fibers on the sensitivity of the baroreceptor reflex was examined in decerebrate cats. The sensitivity of the reflex was expressed as the difference between the maximum prolongation of R-R interval in response to carotid sinus pressure elevation and the mean of 10 R-R intervals immediately before pressure elevation. The control value of R-R interval prolongation was 192 +/- 50 ms. Stimulation (10 Hz) of group I and II fibers of the right peroneal nerve (evoked volleys recorded from the sciatic nerve) had no effect on R-R interval prolongation (171 +/- 45 ms). Recruitment of group III fibers (10 Hz) conducting at 23.6 +/- 0.65 m/s reduced the prolongation of R-R interval to 52 +/- 14 ms. Recruitment of group IV fibers (10 Hz) conducting less than 2.5 m/s further reduced the prolongation of R-R interval to 1.0 +/- 8.0 ms. It is concluded that the inhibition of the cardiac vagal component of the baroreceptor reflex produced by electrical stimulation of the peroneal nerve is mediated by afferent fibers of groups III and IV.

Animals↗
PubMed1991

[Clinical study of superoxide dismutase in recurrent aphthous ulceration].

Activity of superoxide dismutase (SOD) was determined in erythrocytes obtained from 74 patients with recurrent aphthous ulcerations (RAU) and 100 healthy individuals. The results showed that activity level of SOD in RAU was significantly lower as compared with that in the controls (P less than 0.01). The activity of SOD in 30 cases of RAU at interval period was elevated on reexamination, but it was still lower than that in the controls (P less than 0.01). There is evidence that damage of superoxide radicals (O.2) and decrease of activity of SOD may play important roles in the pathogenesis of RAU. A random double-blind, placebo-controlled, cross-over trial on membrane SOD was carried out in 40 patients with RAU. The results demonstrated that the effective rate of SOD was 90%, being markedly higher than that of placebo. It is suggested that membrane SOD, as a topical medicine, could increase the concentration of SOD on the ulcerous surfaces, prevent O.2-induced injury, decrease capillary permeability, relieve inflammation and improve cure of ulcer.

Administration, Topical↗
PubMed1990

Rate-dependent class III antiarrhythmic action, negative chronotropy, and positive inotropy of a novel Ik blocking drug, UK-68,798: potent in guinea pig but no effect in rat myocardium.

The electromechanical effects of UK-68,798 (UK), a novel class III antiarrhythmic drug, were studied in guinea pig and rat papillary muscles (PMs) and atria in vitro using conventional microelectrode technique. UK (10(-8)-10(-6) M) prolonged the action potential duration (APD) by 21-58% and effective refractory period in parallel, without affecting the resting potential or maximum rate of depolarization in guinea pig PM stimulated at 1 Hz. UK increased the contractile force without prolonging the time to peak force or relaxation. In comparison, 5 x 10(-5) M d-sotalol was needed to induce the same electrophysiological effects as 10(-8) M UK. UK prolonged the APD significantly less at 2 Hz than at 1 and 0.5 Hz. Early afterdepolarizations (EADs) developed in 2 of 11 preparations after 10(-6) M at 0.5 Hz. No reversal of drug effect was seen after up to 2 h washout. UK (10(-9)-10(-5) M) reduced the spontaneous heart rate and prolonged the sinus node recovery time of guinea pig right atria. No effects on rat PM or atria, even after 10(-5) M, indicate a selective action of UK on the delayed rectifying outward potassium current, Ik. These results indicate a potent and selective, rate-dependent class III antiarrhythmic action of UK-68,798 linked with positive inotropy. Increased APD, bradycardia, and induction of EADs, however, represent a potential arrhythmogenic combination.

Action Potentials↗
PubMed1990

Assessing symptom change in Southeast Asian refugee survivors of mass violence and torture.

The authors evaluated changes in symptoms and levels of perceived distress of 21 Cambodian, 13 Hmong/Laotian, and 18 Vietnamese patients before and after a 6-month treatment period. Most of the patients improved significantly. Cambodians had the greatest and Hmong/Laotians had the least reductions in depressive symptoms. Although psychological symptoms improved, many somatic symptoms worsened. The authors conclude that refugee survivors of multiple traumata and torture can be aided by psychiatric care. They recommend investigations with larger samples and suitable control groups to further clarify the relative contributions of trauma, diagnosis, and acculturation stress to treatment outcome.

Acculturation↗
PubMed1990

A simple method for estimating association constants between monoclonal antibodies and derivatized or native antigens.

We describe a simple method for estimating the association constant between an antibody and an antigen, based on a theoretical treatment of experimental dose-response data. We used this method to calculate the association constants of an anti-progesterone monoclonal antibody for native progesterone and for progesterone 11 alpha-hemisuccinate. These association constants provide a quantitative measure of the bridging-group recognition by the antibody.

Antibodies, Monoclonal↗
PubMed1989

The effect of crosslinking by bis(3,5-dibromosalicyl) fumarate on the autoxidation of hemoglobin.

Bis(3,5-dibromosalicyl) fumarate was used to crosslink hemoglobin both in the oxy and deoxy states. This double headed diaspirin was known to crosslink oxy Hb A selectively between Lys 82 beta 1 and Lys 82 beta 2 (Walder, J. A., et al. (1979) Biochemistry 18, 4265) and deoxy Hb A between Lys 99 alpha 1 and Lys 99 alpha 2 (Chatterjee R. Y., et al. (1986) J. Biol. Chem. 261, 9929). The autoxidation at 37 degrees C of oxy alpha 99 crosslinked hemoglobin was found to be 1.8 times as fast as that of Hb A while that of the oxy beta 82 crosslinked hemoglobin was only 1.2 times as fast. After 5 hours the formation of methemoglobin in the alpha crosslinked Hb A is 21.3% compared to 10.8% in beta crosslinked Hb A and 6.4% in Hb A. These results may effect the proposed use of alpha 99 crosslinked hemoglobin as a blood substitute by demonstrating the need for protection from autoxidation during storage.

Aspirin↗
PubMed1989

Thermal stability and cross-linking of Hb New York [beta 113(G15)Val----Glu].

Hb New York [beta 113(G15)Val----Glu] has been cross-linked with bis (3,5-dibromosalicyl) fumarate, a reagent known to cross-link Lys 82 beta 1 and Lys 82 beta 2. Thermal denaturations of met Hb New York and its derivative have been compared to those of the corresponding Hb A samples. The structural transitions, observed as absorbance changes at 418 nm, were at 40.2 degrees C for Hb New York, 42.2 degrees C for Hb A, 53.7 degrees C for cross-linked Hb New York, and 56.2 degrees C for cross-linked Hb A. Transitions observed at 280 nm were approximately 2 degrees C higher. Thus, a single inter-subunit cross-link can stabilize an abnormal hemoglobin. A model of Hb New York in which Glu beta 113 forms a salt bridge to His beta 117 can explain the small changes in both the stability and the electrophoretic mobility of this protein.

Aspirin↗
PubMed1989

[Ultracytochemical studies on glycosaminoglycans during early corneal development in Bufo raddei].

Glycosaminoglycans (GAGs) and their changes in early corneal development of Bufo raddei Strauch (from stage 16, neural tube, to stage 25, operculum completely closed) were studied with electron microscopic cytochemical method. Results show that synthesis of GAGs changes from non-sulfated to sulfated, and its content increased gradually with the development of cornea. Hyaluronic acid (HA) in each part of cornea begins to increase gradually from stage 16 to 21 (mouth open stage), with its peak at stage 20 (gill circulation stage) to 21, then decreases. In the mean time, contents of dermatam sulfate (DS), chondroitin sulfate (CS), heparan sulfate (HS) and heparin (Hep) increase gradually. It is considered that HA, HS and collagen may be related to the migration of mesenchymal cells, and HA promotes the expansion and hydration of corneal stroma; sulfated GAGs are correlated with dehydration of cornea, cell density and corneal transparency; DS, CS, HS and Hep deposited among collagen fibrils could adjust their arrangement. All these changes would enhance transparency of cornea.

Animals↗
PubMed1988

Effects of crosslinking on the thermal stability of hemoglobins. II. The stabilization of met-, cyanomet-, and carbonmonoxyhemoglobins A and S with bis(3,5-dibromosalicyl) fumarate.

Hemoglobins A and S were crosslinked between Lys 82 beta 1 and Lys 82 beta 2 using bis (3,5-dibromosalicyl) fumarate (J. A. Walder et al. (1979) Biochemistry 18, 4265). Thermal denaturation experiments were used to compare the stabilities of the met, cyanomet, and carbonmonoxy forms of these crosslinked hemoglobins to the corresponding uncrosslinked proteins. Uncrosslinked carbonmonoxy- and cyanomethemoglobins had transition temperatures about 11 degrees C higher than the corresponding met samples. The increase in denaturation temperature (Tm) due to crosslinking was 15 degrees C for the methemoglobins, 10 degrees C for the cyanomethemoglobins, and 4 degrees C for the carbonmonoxy ones. There was no significant difference in stability between the met and carbonmonoxy crosslinked proteins. In order of increasing stability the samples were: met Hb S less than met Hb A less than CO Hb S less than CO Hb A = CN-met Hb A less than met XL-Hb S = CO XL-Hb S less than met XL-Hb A = CO XL-Hb A less than CN-met XL-Hb A. The slight decrease in the stability of Hb S (beta 6 Glu----Val) compared to Hb A can be explained by the replacement of an external ionic group by a hydrophobic residue in Hb S. In mixtures of crosslinked and normal Hb A, the Tm of the uncrosslinked material was slightly increased by the presence of the more stable crosslinked hemoglobin. The effects of both crosslinking and cyanide or carbon monoxide binding can be explained by Le Chatelier's principle since both would favor the native form of the protein.

Aspirin↗
PubMed1987

Monoclonal antibodies used in solid-phase and liquid-phase assays, as exemplified by progesterone assay.

Two immunoglobulins secreted by hybridoma cell lines have been systematically investigated to determine if they could be used in solid-phase assays to give results comparable with those obtained by conventional liquid-phase radioimmunoassay (RIA). The antibodies, BQ.1 and BQ.2, bind with high specificity to the steroid hormone progesterone. The affinity constants, Ka, to 125I-labeled progesterone derivatives are 1.1 X 10(11) L/mol and 9.1 X 10(9) L/mol, respectively. Progesterone inhibited the binding of radioiodinated derivatives (amides of tyramine, histamine, and tyrosine methylester with 11 alpha-progesterone hemisuccinate) equally well. For solid-phase assays, we immobilized antibody BQ.1 via Protein A to different polystyrene surfaces (about 30 pg per tube at 50% inhibition of radiolabeled tracer). Under these conditions, the performance of this antibody for the quantification of progesterone was equivalent to that obtained in RIA. For the immobilized antibody BQ.2, only 1/10 of the amount used for optimal results in RIA was required in solid-phase assays. Binding of either antibody to the antigen was undiminished after several freezing-thawing cycles. When immobilized on solid matrices, both antibodies retained up to 95% of their binding properties for one year. Thus high-affinity, high-specificity monoclonal antibodies can be obtained for haptens and, when suitably immobilized, can be used in solid-phase assays with results equal to or better than those obtained with liquid RIA.

Antibodies, Monoclonal↗
PubMed1987

Surface modification with protein A for uniform binding of monoclonal antibodies.

We describe optimal conditions for immobilization of two monoclonal antibodies to progesterone for solid-phase assays. Polystyrene surfaces are refined with Protein A to achieve uniform, reproducible, stable, and sterically accessible immobilization of immunoglobulins (IgG). To this end, we optimized the amount of immobilized Protein A, the pH of the medium for immobilization, the concentration of antibody, and the polystyrene surface. We also investigated three carriers for solid-phase assays: 12 X 75 mm polystyrene test tubes, Macrowells (Skatron, Inc.; suitable for processing with multiple pipettors), and microwell strips (Immulon II, Dynatech Inc.). Immunoglobulin does not appreciably dissociate from any of these solid matrices, even if the assay procedure takes several hours. Therefore, we postulate that more than one molecule of immobilized Protein A binds to IgG, or that there is an additional interaction between the antibody and the polymer surface.

Animals↗
PubMed1986

The primary structure of apolipoprotein A-I from rabbit high-density lipoprotein.

The amino acid sequence of rabbit apolipoprotein A-I (apo A-I) has been determined by degradation and alignment of two overlapping sets of peptides obtained from tryptic and staphylococcal digestions. All of the peptides of rabbit apo A-I resulting from digestion by staphylococcal protease were isolated and sequenced except residues 33-37. A digestion with trypsin was employed to find overlapping and missing peptides. The N-terminus of rabbit apo A-I was confirmed by sequencing the intact protein up to 20 residues while the C-terminus was identified through its homology with human apo A-I. The protein contains 241 residues in its single chain. Its primary structure is highly homologous to the reported canine apo A-I (80%) and human apo A-I (78%), but exhibits less similarity with rat apo A-I (60%). Like human apo A-I, rabbit apo A-I contains very little histidine (2) and methionine (1); it does however have two residues of isoleucine. Based on a comparison of the hydrophobic-hydrophilic character of apo A-I residues with that of the two synthetic peptides that activated lecithin: cholesterol acyltransferase (Pownall et al. and Yokoyama et al.), we found that the five segments with the highest corresponding homologies on the protein are located within the N-terminal half. This suggests that the N-terminal half of apo A-I contains the major portion of regions activating lecithin: cholesterol acyltransferase.

Amino Acid Sequence↗
PubMed1986

Biochemical and biophysical properties of cytochrome o of Azotobacter vinelandii.

Cytochrome o, solubilized from the membrane of Azotobacter vinelandii, has been purified to homogeneity as judged by ultracentrifugation and polyacrylamide gel electrophoresis. The detergent-containing cytochrome o is composed of one polypeptide chain with a molecular weight of 28 000-29 000, associated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The enzyme exists as a dimer by gel filtration analysis. The amino analysis which reveals the majority of residues are of hydrophobic nature. The cytochrome o oxidase contains protoheme as its prosthetic group and about 20-40% of phospholipids. The phospholipids are identified as phosphatidylethanolamine and phosphatidylglycerol by radioautographic analysis using 2-dimensional thin-layer chromatography. No copper or nonheme iron can be detected in the purified oxidase preparation by atomic absorption and chemical analyses. Oxidation-reduction titration shows this membrane-bound cytochrome o to be a low-potential component, and Em was determined to be -18 mV in the purified form and -30 mV in the membrane-bound form. Both forms bind CO with a reduced absorption peak at 559 and 557-558 nm in the native and solubilized forms, respectively. A high-spin (g = 6.0) form is assigned to the oxidized cytochrome o by electron paramagnetic resonance analysis, and KCN abolishes this high-spin signal. CO titration of purified cytochrome o in the anaerobic conditions shows the enzyme binds one CO per four protohemes and a dissociation constant is estimated to be 3.2 microM for CO. Cyanide reacts with purified cytochrome o in both oxidized and CO-bound forms, identified by specific spectral compounds absorbed at the Soret region. Cytochrome c, often co-purified with cytochrome c from the membrane, cannot serve as a reductant for cytochrome o in vitro, due to the apparent potential difference of about 300 mV. Upon separation, both cytochrome o and cytochrome c4 show a great tendency of aggregation. Furthermore, the oxidase activity (measured by tetramethyl-p-phenylenediamine oxidation rate) decreases as the cytochrome c concentration is decreased by ammonium sulfate fractionation. All these suggest the structural and functional complex nature of cytochrome c4 and cytochrome o in the membrane of A. vinelandii.

Azotobacter↗
PubMed1986

The effect of space radiation of the nervous system.

The long-term effects of irradiation by accelerated heavy ions on the structure and function of the nervous system have not been studied extensively. Although the adult brain is relatively resistant to low LET radiation, cellular studies indicate that individual heavy ions can produce serious membrane lesions and multiple chromatin breaks. Capillary hemorrhages may follow high LET particle irradiation of the developing brain as high RBE effects. Evidence has been accumulating that the glial system and blood-brain barrier (BBB) are relatively sensitive to injury by ionizing radiation. While DNA repair is active in neural systems, it may be assumed that a significant portion of this molecular process is misrepair. Since the expression of cell lethality usually requires cell division, and nerve cells have an extremely low rate of division, it is possible that some of the characteristic changes of premature aging may represent a delayed effect of chromatin misrepair in brain. Altered microcirculation, decreased local metabolism, entanglement and reduction in synaptic density, premature loss of neurons, myelin degeneration, and glial proliferation are late signs of such injuries. HZE particles are very efficient in producing carcinogenic cell transformation, reaching a peak for iron particles. The promotion of viral transformation is also efficient up to an energy transfer of approximately 300 keV/micron. The RBE for carcinogenesis in nerve tissues remains unknown. On the basis of available information concerning HZE particle flux in interplanetary space, only general estimates of the magnitude of the effects of long-term spaceflight on some nervous system parameters may be constructed.

Abnormalities, Radiation-Induced↗