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Biomedical subjects

X Xu

Publications and source records attributed to X Xu.

At least 775 records · Page 43Linked to original sources
PubMed1996

B cell antigen receptor signaling links biochemical changes in the class II peptide-loading compartment to enhanced processing.

In B cells, processing of antigens in the context of MHC class II molecules is initiated by the binding of antigen to the B cell antigen receptor (BCR). BCR-mediated processing is highly efficient, as a consequence of the BCR's linked roles of delivering antigen to the class II peptide-loading compartment and of signaling for increased antigen-processing activity. Evidence is emerging that receptor signaling regulates intracellular transport through the activities of kinases. These in turn have been implicated in the regulation of small mol. wt GTPases which govern membrane transport. Therefore, we investigated the changes in the phosphoprotein and GTPase profiles associated with the class II peptide-loading compartment following BCR cross-linking. We first show that protein kinase inhibitors, known to block BCR signal transduction, inhibit BCR-enhanced antigen processing, demonstrating the critical dependence of enhanced processing on the signaling activity of the BCR. Consistent with this observation, the phosphoprotein profile of the class II peptide-loading compartment underwent rapid and transient changes following BCR cross-linking. We also observed a marked increase in the low mol. wt GTPases associated with the class II peptide-loading compartment within 5 min of BCR cross-linking. The observed changes in both the phosphoprotein and GTPase profiles associated with the peptide-loading compartment were blocked by kinase inhibitors and were not accompanied by overall gross changes in the protein composition of the subcellular compartments. Thus, signal cascades initiated by BCR cross-linking at the plasma membrane are translated into changes in specific subsets of regulatory proteins associated with the peptide-loading compartment.

Animals↗
PubMed1996

Milk growth factors enriched from cheese whey ameliorate intestinal damage by methotrexate when administered orally to rats.

Currently, there are no truly effective therapies for the treatment of chemotherapy-induced intestinal mucositis, a debilitating side effect with a pathophysiology common to many chemotherapy regimens. We tested the efficacy of a growth factor extract derived from cheese whey against experimental intestinal mucositis in rats. Rats were subcutaneously injected with the chemotherapeutic drug methotrexate on d 1, 2 and 3 to induce severe damage in the small bowel and bacterial translocation across the gut. Whey extract (15 to 514 mg/d) was given orally for 5-12 d, starting on d 1. Controls were fed an isonitrogenous diet. Histological indices of villus and crypt integrity were utilized to assess potential efficacy of the extract. Administration of the whey extract for 5 d increased the villus surface length indices in the jejunum and ileum by 52% and 56%, respectively (P< 0.001) compared with controls not receiving the whey extract. The crypt area index was 64% greater (P < 0.001) in the jejunum, but not significantly greater in the duodenum or ileum compared with controls not receiving whey extract. Similarly, sucrase activity was significantly higher in the ileum (P < 0.001) but not significantly elevated in the jejunum, whereas bacterial translocation (incidence and number of colonies) was significantly reduced compared with controls not receiving whey extract. We conclude that oral whey growth factor extract reduces methotrexate-induced damage in the small bowel, which suggests clinical applications for the treatment of intestinal mucositis.

Administration, Oral↗
PubMed1996

A diet high in wheat fiber decreases the bioavailability of soybean isoflavones in a single meal fed to women.

The absorption of some dietary components may be inhibited by dietary fiber. To study the effect of dietary fiber on the bioavailability of Isoflavones, seven healthy women were randomly assigned in a crossover design to a control diet containing 15 g dietary fiber or a wheat fiber-supplemented diet containing 40 g dietary fiber, both fed with a single dose of 0.9 mg isoflavones/kg body weight from tofu or texturized vegetable protein (TVP). The fiber-rich diet produced 55% lower plasma genistein at 24 h after soy dosing (P < 0.05) and reduced total urinary genistein by 20% (P < 0.03). Urinary daidzein was not significantly related to fiber intake. Highly insoluble, dietary wheat fiber reduced the absorption of genistein probably by its bulking effect and hydrophobic binding to this compound. Urinary genistein was greater by 23% after tofu than after TVP consumption (P < 0.02), but the percentage of ingested genistein recovered in urine was not affected by soy product intake. The higher urinary genistein after tofu consumption compared with TVP was apparently due to differences in amount of genistein between these soy foods, not the different forms of genistein present in these two soy food products.

Absorption↗
PubMed1996

A complete sequence of the mitochondrial genome of the western lowland gorilla.

The complete mitochondrial DNA (mtDNA) molecule of the gorilla was sequenced. The entire sequence, 16,412 nucleotides, was determined by analysis of natural (not polymerase chain reaction) restriction fragments covering the whole molecule. The sequence was established from one individual and thus nonchimeric. After comparison with the COII gene of gorilla specimens with known geographical origin, the sequence was identified as characteristic of the Western lowland gorilla, Gorilla gorilla gorilla. With the exception of the NADH2 gene, all genes have a methionine start codon. The inferred start codon of NADH2 is ATT (isoleucine). The COIII, NASDH4, and cytochrome b genes are not terminated by a stop codon triplet, and the COI gene is probably terminated by an AAA triplet rather than by a regular stop codon. The great majority of genic sequences (rRNAs, peptide-coding genes, tRNAs) of the complete mtDNAs of Gorilla, Pan, and Homo show a greater similarity between Pan and Homo than between either of these genera to Gorilla. The analysis of the peptide-coding genes suggest that relative to comparison between Homo and Pan a certain degree of transition saturation has taken place in codon position 3 in comparisons between Gorilla to either Homo or Pan.

Amino Acid Sequence↗
PubMed1996

The complete mitochondrial DNA sequence of the greater Indian rhinoceros, Rhinoceros unicornis, and the Phylogenetic relationship among Carnivora, Perissodactyla, and Artiodactyla (+ Cetacea).

The sequence (16,829 nt) of the complete mitochondrial genome of the greater Indian rhinoceros, Rhinoceros unicornis, was determined. Like other perissodactyls studied (horse and donkey) the rhinoceros demonstrates length variation (heteroplasmy) associated with different numbers of repetitive motifs in the control region. The 16,829-nt variety of the molecule includes 36 identical control region motifs. The evolution of individual peptide-coding genes was examined by comparison with a distantly related perissodactyl, the horse, and the relationships among the orders Carnivora, Perissodactyla, and Artiodactyla (+ Cetacea) were examined on the basis of concatenated sequences of 12 mitochondrial peptide-coding genes. The phylogenetic analyses grouped Carnivora, Perissodactyla, and Artiodactyla (+ Cetacea) into a superordinal clade and within this clade a sister group relationship was recognized between Carnivora and Perissodactyla to the exclusion of Artiodactyla (+ Cetacea) . On the basis of the molecular difference between the rhinoceros and the horse and by applying as a reference to Artiodactyl/Cetacean divergence set at 60 million years ago (MYA), the evolutionary divergence between the families Rhinocerotidae and Equidae was dated to approximately 50 MYA.

Animals↗
PubMed1996

Pain-related somatosensory evoked potentials can quantitatively evaluate hypalgesia in Wallenberg's syndrome.

In 6 patients with Wallenberg's syndrome who showed a dissociated loss of pain sense, we recorded pain-related somatosensory evoked potentials following CO2 laser stimulation of the hand dorsum (pain SEPs). Two components, N2 and P2, were recorded by stimulation of the unaffected hand, whereas on the affected side they were absent or decreased in proportion to the severity of hypalgesia which was evaluated by both needle test and CO2 laser stimulation. Latency of either component, if appeared, was longer in the affected hand stimulation than that in the unaffected one. In contrast, N20 of the conventional electrically-stimulated SEPs (electric SEPs) showed no difference between the two sides. It is concluded that, unlike other electrophysiological methods, pain SEPs following CO2 laser stimulation can quantitatively evaluate functional impairment of the spinothalamic tract in Wallenberg's syndrome.

Adult↗
PubMed1996

Dual effects of arachidonic acid on ATP-sensitive K+ current of coronary smooth muscle cells.

ATP-sensitive K-channels (K(ATP)) play a major role in controlling blood vessel tone, particularly in coronary vasculature. Arachidonic acid (AA) exhibits potent vasorelaxant effects on coronary arteries with unclear mechanisms. We examined the activity of AA on the K(ATP) channel of dog coronary artery smooth muscle cells using the whole cell voltage-clamp technique. AA was found to have dual effects or the K(ATP) current. In cells dialyzed with 1 mM ATP pipette solution, external application of AA activated the K(ATP) current with a bell-shaped concentration-response curve. K(ATP) current (-50 mV) increased from 1.0 +/- 1.1 to 4.6 +/- 3.0, 25 +/- 9, 43 +/- 13, 26 +/- 10, and 23 +/- 16 pA by 1, 2, 4, 8, and 16 microM AA, respectively. If K(ATP) current was activated by dialyzing the cell with ATP-free pipette solution, external application of AA (from 2 to 16 microM) inhibited the K(ATP) current (half-maximal inhibitory concentration = 3.8 microM). Pretreatment of cells with 10 microM indomethacin or 10 microM nordihydroguaiaretic acid, which respectively blocked the cyclooxygenase or lipoxygenase pathway of AA metabolism, did not prevent the dual effects of AA. Eicosatetraynoic acid (ETYA), the nonmetabolizable analogue of AA, also produced dual effects on the K(ATP) current. ETYA (4 microM) increased the K(ATP) current (-50 mV) from 2.9 +/- 1.2 to 37 +/- 7 pA in 1 mM intracellular ATP, whereas 8 microM ETYA inhibited the K(ATP) current in 0 mM intracellular ATP by 71 +/- 3%. These results suggest that the dual effects of AA on the K(ATP) current of dog coronary smooth muscle cells do not require AA metabolism. Activation of K(ATP) channels in smooth muscle cells may contribute to the AA-induced coronary vasodilation.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1996

Role of endothelium-derived nitric oxide in the modulation of canine myocardial mitochondrial respiration in vitro. Implications for the development of heart failure.

The mechanism responsible for the regulation of cardiac function by endogenous nitric oxide (NO) remains unclear. In this investigation, O2 consumption by freshly isolated myocardial muscle segments from the left ventricular free wall of canine hearts was quantified by a Clark-type O2 electrode at 37 degrees C. S-nitroso-N-acetylpenicillamine (SNAP, 9 +/- 3% to 50 +/- 8%), bradykinin (BK, 14 +/- 3% to 30 +/- 5%), or carbachol (CCh, 15 +/- 4% to 29 +/- 4%) significantly attenuated tissue O2 consumption at doses of 10(-7) to 10(-4) mol/L (mean +/- SE, P < .05). The effects of BK and CCh, but not SNAP, were blocked by 10(-4) mol/L NG-nitro-L-arginine, consistent with both BK and CCh stimulating NO biosynthesis and with SNAP decomposing to release NO, respectively. Similar doses of 8-Br-cGMP caused a respiratory inhibition, but to a lesser extent (9 +/- 2% to 14 +/- 6%). A mitochondrial uncoupler, 2,4-dinitrophenol (at 1 mmol/L), blocked the effects of 8-Br-cGMP, but not those of SNAP, BK, or CCh, suggesting that the major site of action of NO is on mitochondrial electron transport. Myocardial muscle from dogs with pacing-induced heart failure had a basal O2 consumption rate of 251 +/- 21 nmol.min-1.g-1, which was 54% higher than the rate seen in muscle from normal healthy canine hearts. The inhibitory effects of BK and CCh on O2 consumption were not observed in failing cardiac tissue, but SNAP showed an unaltered inhibitory effect. Therefore, our results indicate that NO released from microvascular endothelium by BK, stimulation of muscarinic receptors, and perhaps flow velocity may play an important physiological role in the control of cardiac mitochondrial respiration, and the loss of this regulatory function may contribute to the development of heart failure.

2,4-Dinitrophenol↗
PubMed1996

Function and production of nitric oxide in the coronary circulation of the conscious dog during exercise.

This study determined the changes in NO production from the coronary circulation of the conscious dog during exercise. The role of endogenous NO as it relates to coronary flow, myocardial work, and metabolism was also studied. Mongrel dogs were chronically instrumented for measurements of coronary blood flow (CBF), ventricular and aortic pressure, and ventricular diameter, with catheters in the aorta and coronary sinus. Acute exercise (5 minutes at 3.6, 5.9, and 9.1 mph) was performed, and hemodynamic measurements and blood samples were taken at each exercise level. Nitro-L-arginine (NLA, 35 mg/kg IV) was given to block NO synthesis, and the exercise was repeated. Blood samples were analyzed for oxygen, plasma nitrate/nitrite (an index of NO), lactate, glucose, and free fatty acid (FFA) levels. Acute exercise caused significant elevations in NO production by the coronary circulation (46 +/- 23, 129 +/- 44, and 63 +/- 32 nmol/min at each speed respectively, P < .05). After NLA, there was no measurable NO production at rest or during exercise. Blockade of NO synthesis resulted in elevations in myocardial oxygen consumption and reductions in myocardial FFA consumption for comparable levels of CBF and cardiac work. The metabolic changes after NLA occurred in the absence of alterations in myocardial lactate or glucose consumptions. NO production by the coronary circulation is increased with exercise and blocked by NLA. The absence of NO in the coronary circulation during exercise does not affect levels of CBF, because it shifts the relationship between cardiac work and myocardial oxygen consumption, suggesting that endogenous NO modulates myocardial metabolism.

Animals↗
PubMed1996

Occupational and Environmental Risk Factors for Asthma in Rural Communities in China.

Respiratory allergens such as dust, gases/fumes, and hay smoke, which are frequently present in agricultural settings, can cause or aggravate asthma. The purpose of this study was to examine the relationships between occupational and environmental exposures and asthma in Chinese rural communities. The study population consisted of 28,946 people 15 years old or older, living in rural areas of Anhui province, China. A modified Mandarin translation of the ATS-DLD questionnaire was administered by trained interviewers to request information about exposures to specific occupational/environmental agents and respiratory disorders. In Huaining, the prevalence of wheezing was 3.8% for men; 2.1% for women; the prevalence of asthma was 1.6% for men; 1.8% for women. In Zongyang, the prevalence of wheezing was 2.7% for men; 1.9% for women; the prevalence of asthma was 1.7% for men; 1.2% for women. With control for potential confounders such as gender, age, residential area, education level, and smoking status, the pooled adjusted odds ratios (ORs) of wheezing and asthma for the group exposed to wood/hay smoke were 1.36 (95% CI: 1.14-1.61) and 1.27 (95% CI: 1.02-1.58), respectively. For coal-stove users, the pooled adjusted ORs were 1.47 (95% CI: 1.09-1.98) for wheezing and 1.51 (95% CI: 1.05-2.17) for asthma. After stratification of the subjects by dust type, the estimated ORs for wheezing were 1.58 (95% CI: 1.02-2.44) among the group exposed to inorganic dust and 3.03 (95% CI: 1.25-7.33) among the group exposed to metal dust. Asthma was not shown to be significantly associated with any specific dust type. Findings of the present study are consistent with previously reported adverse respiratory health effects related to occupational/environmental exposures to wood/hay smoke and dust, and indicate the need for further occupational disease surveillance in rural communities.

Journal Article↗
PubMed1996

Current-source density analysis of the electroretinogram of the frog: methodological issues and origin of components.

The technique of current-source density (CSD) analysis for extracellular potentials is reviewed, along with some methodological features that are important for performing CSD analysis of the electroretinogram. In addition, three formulas for computing CSD's are examined on model circuits of resistors and current generators. Finally, CSD results from frog retina that bear on the origins of the b, d, and M waves, along with slow PIII, are presented. It is concluded that the b and d waves are generated primarily and directly by bipolar cells, whereas the M wave and the slow PIII are generated by Müller (glial) cells through the K+ spatial buffer mechanism.

Animals↗
PubMed1996

[The influence of masking agent on adhesion of composite resin]

In this study we used light cured resin,opaque resin and composite resin/masking agent to bond 24 teeth in vitro and then we tested their bonding stress.We also used these three materials to treat 240 tetracycline stained teeth in clinic.After half a year,one year,two years follow-up we found:in vitro study,the highest stress of composite resin is 144.3kG/cm(2).There is no significant difference in statistics among these three materials if we used the masking agent or opaque resin or not.In clinical follow-up,there is no significant difference in shed,partial shed,margin stain,gingival inflammation,and unsatisfied rate in three groups.The author believed the masking agent or opaque resin has no influence on the stress of resin restoration.So when we treated tetracycline stained teeth,we could choose it to increase aesthetic feeling.

Journal Article↗
PubMed1996

[Clinical significance of the abnormal radiographic manifestations of pulp cavity]

Six cases showing abnormal radiographic appearance of the pulp cavity are presented in this article.According to the etiology.they are approximately divided into four patterns as follows:The first one was caused by hereditary disease,represented by mainly opalescent dentin.In the early stage,enlargement of the pulp cavity is obvious in radiograph,but in the late stage extensive atresia is observed.The second one was caused by tooth dysplasia.Its common clinical features are the maxillary lateral incisor accompanied by a lingual gingival groove and the mandibular second molar a "c-shaped" root canal.In radiograms,the former looks like a second root canal,while the latter regular pictures as if a reamer has perforated the pulp floor.The third one was caused by root fracture,especially root vertical fracture.The root canal space can be seen widened.The abnormal images might be due to the change of X-ray projected angulation.It's important that a clinical doctor must know all these in order to make correct diagnosis and render proper treatment.

Journal Article↗