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Biomedical subjects

X Shen

Publications and source records attributed to X Shen.

At least 217 records · Page 12Linked to original sources
PubMed1994

Alteration of lysophosphatidylcholine content in low density lipoprotein after oxidative modification: relationship to endothelium dependent relaxation.

OBJECTIVE: The aim was to examine the formation of lipid peroxidation products and the alteration in phospholipid content in low density lipoprotein (LDL) after oxidative modification by CuSO4, and subsequently, to determine the ability of the modified LDL to impair endothelium dependent relaxation in rat aortic rings. METHODS: Blood samples were obtained from normal human volunteers. LDL was prepared by sequential ultracentrifugation and it was oxidatively modified in the presence of 5 microM CuSO4. Lipid peroxidation products (thiobarbituric acid reactive substances, TBARS), and alterations in electrophoretic mobility and phospholipid content were determined in normal (native) and oxidised LDL. Endothelium dependent relaxation was produced by acetylcholine (10(-8)-10(-5) M) in phenylephrine precontracted rat aortic rings. RESULTS: LDL incubated for 24 h with 5 microM CuSO4 at 20 degrees C and 37 degrees C with constant agitation displayed higher amounts of TBARS than the respective native LDL. While the amounts of TBARS in LDL modified at 20 degrees C and 37 degrees C were similar, the former condition resulted in statistically smaller changes of phospholipid contents. LDL with higher lysophosphatidylcholine content showed greater impairment of endothelium dependent relaxation in rat aortic rings than LDL with lower lysophosphatidylcholine content. CONCLUSIONS: The raised lysophosphatidylcholine level in oxidatively modified LDL was related to the ability of the LDL to impair endothelium dependent relaxation. However, lipid peroxidation products assessed by TBARS did not relate to the phospholipid changes in LDL and therefore cannot be used to predict the vascular effects of LDL after oxidative modification.

Acetylcholine↗
PubMed1994

[Effect of hemorheological factors on coronary flow during myocardial ischemia].

Intracoronary infusion of some drugs may induce superimposed coronary vasodilation upon endogenous vasodilation during myocardial ischemia, which was suggested as coronary vasodilator reserve. For an investigation of this phenomenon, 8 pigs were anesthetized, chest-opened, LAD (left anterior descending coronary artery)-dissected and instrumented. The LAD pressure was reduced to 4.67 kPa (35mmHg), and then intracoronary infusion of adenosine, saline, or anisodamine (at the same rate of 2ml/min) was started and maintained for 9 minutes. The three solutions all produced a significant increase in the coronary flow, including the saline (compared with the control, P < 0.05). The hemorheological examination of the distal coronary blood revealed a reduced hematocrit, plasma viscosity and whole blood viscosity during the saline and anisodamine infusion periods (P < 0.05), but in the adenosine infusion, the statistical analysis on hemorheological data revealed no significance compared with the control (P > 0.05). The results showed that the coronary vasodilator reserve induced by intracoronary drugs during myocardial ischemia might be partly accounted by regional hemodilution in the LAD bed. The study suggested that a decrease in blood viscosity might play an important role in the improvement of the narrowed coronary circulation, even more important than vasodilator drugs.

Adenosine↗
PubMed1994

[Effect of nifedipine on T wave in ischemic myocardium].

Calcium antagonists are generally considered to have no substantial effect on repolarization of the myocardium, so they have no direct effect on T wave, either. But in a pig model of myocardial ischemia, intracoronary nifedipine was found to reverse the inverted T wave induced by ischemia to upright promptly. Ten pigs were anesthetized with the chest opened, anterior interrentricular branch of left coronary artery (LAD) was narrowed to 4.67 kPa of LAD pressure, and then adenosine or nifedipine was infused into the coronary respectively. During the 9-minute ischemia, intracoronary adenosine or intracoronary nifedipine got the similar HR, LVEDP, LVDP, CAP, CAQ, and the intracoronary adenosine even got higher CAQ than the intracoronary nifedipine did. However, the T wave was retained inverted during the adenosine infused, but during the intracoronary nifedipine, the inverted T wave was promptly turned upright. The relevant factors and mechanisms are discussed.

Adenosine↗
PubMed1994

[Effects of endotoxin on coronary circulation].

To investigate the effects of endotoxin (ETX) on coronary circulation, we infused endotoxin (4ng/ml) intravenously in a small dose (0.3ng/kg.min-1) which did not reduce the blood pressure, nor did it disturb the coronary autoregulation, and the flow kept constant during the ETX infusion. But when the left coronary artery descending branch (LAD) was narrowed and the LAD pressure was reduced to 4.67kPa, the ETX showed a vasodilator effect on the LAD (pre-ETX 65.2 +/- 29.2 ml/min, post-ETX 89.5 +/- 32.7 ml/min, P < 0.05). This effect suggested that the ETX in a small dose had a vasodilator effect on a narrowed coronary artery, even when it did not disturb the hemodynamics. The possible mechanisms were surveyed preliminarily.

Animals↗
PubMed1994

[Comparative study of ischemia-induced and reperfusion-induced ventricular fibrillation in pigs].

To have a better understanding of reperfusion-induced ventricular fibrillation (VF), we studied the relevant morbidity in pigs and compared it with that of the ischemia-induced VF. In 10 hearts of anesthetized chest-open pigs, a total of 127 cycles of various degrees and varied duration of ischemia and reperfusion were completed. VF occurred 13 times (10.2%). Of these, 11 were ischemia-induced VF, while only 2 were reperfusion-induced VF. In two cases of ischemia-induced VF, electric defibrillation failed before the reestablishment of left anterior interventricular branch of coronary artery flow, but after adequate reflowing, all VF turned out to be sinus-rhythm by electric defibrillation. The results suggest that ventricular fibrillation be mainly induced by ischemia but less induced by reperfusion.

Animals↗
PubMed1994

Experimental healing of distraction osteogenesis comparing metaphyseal with diaphyseal sites.

Distraction osteogenesis was performed on 32 adult dogs to compare bone healing at metaphyseal and diaphyseal sites. Sixteen dogs underwent proximal metaphyseal corticotomy and 16 dogs underwent middiaphyseal corticotomy of the left tibiae for gradual lengthening. Each major group was then divided into four subgroups of four dogs each on the basis of zero-, seven-, 14- and 21-day latency periods. The standard radiograph, quantitative computer tomography density, and bone-healing index were used to evaluate new bone formation and consolidation. A distraction rate of 1 mm per day for four weeks created an average elongation of 23.9 +/- 3.7 mm in the metaphyseal groups and 23.8 +/- 2.0 mm in the diaphyseal groups, excluding nine premature consolidations. In the 16 metaphyseal lengthenings, there were six premature consolidations (37.5%): four with a 21-day latency, two with a 14-day latency, and one nonunion (6.2%). In the 16 diaphyseal lengthenings, three fused prematurely (18.7%), two with a 21-day latency and one incomplete corticotomy with a seven-day latency. Three lengthenings of the diaphyseal group resulted in nonunion (18.7%). All animals, metaphyseal and diaphyseal, successfully bridged the distraction gap after a zero-day latency. The bone-healing index showed that new bone consolidation was best with a zero-day latency in metaphyseal (22 +/- 7.6 days/cm) and diaphyseal lengthening (26.5 +/- 6.5 days/cm). Comparing the minimum quantitative computer tomography density ratio of the experimental side with the contralateral side indicated a significant difference at the end of distraction (p = 0.001), at fixator removal (p = 0.001), and when the dogs were killed (p = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Identification and chromosomal mapping of a receptor tyrosine kinase with a putative phospholipid binding sequence in its ectodomain.

We have cloned a novel receptor tyrosine kinase that has an unusual ectodomain. The extracellular sequence consists of 416 amino acids and has none of the structural motifs that have been found in other receptor tyrosine kinases. The 150 amino acids in the amino terminus of the receptor is homologous to a putative phospholipid-binding sequence that is found also in other cell adhesion molecules such as the neuronal A5 antigen and coagulation factors V and VIII. The kinase domain has a short cytoplasmic tail and contains a short insert between subdomains I and II. The structure of this receptor kinase suggests that it belongs to a new family of receptors involved in cell-cell interactions. The cell adhesion kinase (Cak) is expressed at low levels in most adult tissues and expression is highest in the brain and lung. Using fluorescence in situ hybridization and interspecific backcross mapping, the Cak gene was localized to human chromosome 6 and mouse chromosome 17.

Amino Acid Sequence↗
PubMed1993

Reversal of cytochrome P-4501A1 and P-450-EF expression in MCA-C3H/10T1/2 cell-derived tumors as compared to cultured cells.

The 3-methylcholanthrene-transformed tumorigenic cell line, MCA-C3H/10T1/2 CL15 (MCA), expresses the novel benz(a)anthracene (BA)-inducible polycyclic aromatic hydrocarbon-metabolizing cytochrome P-450 (P-450-EF). The level of expression is comparable to that reported for the nontumorigenic C3H/10T1/2 CL8 (10T1/2) cells (Pottenger, L. H., Christou, M., and Jefcoate, C. R. Arch. Biochem. Biophys., 286: 488-497, 1991). Sarcomas (3-12 mm in diameter) generated in athymic "nude" mice by s.c. injection of MCA cells exhibited much lower 7,12-dimethylbenz(a)anthracene-metabolizing activities (5-15% of the levels in cultured cells), both constitutively and after in vivo treatment with BA. A sharp decrease in P-450-EF expression was observed both at the functional level (10- to 30-fold) (as determined by antibody inhibition studies) and at the apoprotein level (50- to > 100-fold) (as determined by Western immunoblots). However, in contrast to the BA-treated MCA cells in which P-450-EF comprises essentially the total spectrally detectable P-450 content (approximately 30 pmol/mg) with virtually undetectable cytochrome P-4501A1, tumors from these cells expressed substantial levels of P-4501A1 immunodetectable protein in response to BA treatment (approximately 0.5-3 pmol/mg). In these tumors, P-450-EF expression decreased to undetectable or barely detectable levels (< 0.2-0.5 pmol/mg). P-4501A1-expressing cells were localized in tumor sections immunocytochemically and were morphologically identical to other MCA cells, which formed the majority of the sarcoma. At the functional level, antibody inhibition studies and product ratios demonstrated that P-4501A1 accounted for only 40% of the total dimethylbenz(a)anthracene-metabolizing activity of BA-induced tumor microsomes, whereas the remaining activity was due to P-450-EF. This low catalytic activity for P-4501A1 (35-95 pmol/mg/h) indicated that the majority of BA-inducible P-4501A1 in the tumors (> 95%) was expressed as apoprotein. The contribution from P-450-EF was consistent with full expression of hemoprotein. Tumor size affected the total dimethylbenz(a)anthracene-metabolizing activities/mg microsomal protein (small tumors were 2- to 3-fold more active than large tumors) but had no effect on the ratio of activities dependent on, respectively, P-450-EF and P-4501A1 holoenzymes (1.5:1), thus suggesting controlled coexpression of these proteins. Reculturing of tumor-derived cells effected partial restoration of P-450-EF expression and eliminated the expression of P-4501A1, confirming a unique contribution from tumor environment to the regulation of these genes. Possible mechanisms for an environment-dependent concerted regulation of the P-4501A1 and P-450-EF genes are discussed.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1993

Chicken oocyte growth: receptor-mediated yolk deposition.

During the rapid final stage of growth, chicken oocytes take up massive amounts of plasma components and convert them to yolk. The oocyte expresses a receptor that binds both major yolk lipoprotein precursors, vitellogenin (VTG) and very low density lipoprotein (VLDL). In the present study, in vivo transport tracing methodology, isolation of coated vesicles, ligand- and immuno-blotting, and ultrastructural immunocytochemistry were used for the analysis of receptor-mediated yolk formation. The VTG/VLDL receptor was identified in coated profiles in the oocyte periphery, in isolated coated vesicles, and within vesicular compartments both outside and inside membrane-bounded yolk storage organelles (yolk spheres). VLDL particles colocalized with the receptor, as demonstrated by ultrastructural visualization of VLDL-gold following intravenous administration, as well as by immunocytochemical analysis with antibodies to VLDL. Lipoprotein particles were shown to reach the oocyte surface by passage across the basement membrane, which possibly plays an active and selective role in yolk precursor accessibility to the oocyte surface, and through gaps between the follicular granulosa cells. Following delivery of ligands from the plasma membrane into yolk spheres, proteolytic processing of VTG and VLDL by cathepsin D appears to correlate with segregation of receptors and ligands which enter disparate sub-compartments within the yolk spheres. In small, quiescent oocytes, the VTG/VLDL receptor was localized to the central portion of the cell. At onset of the rapid growth phase, it appears that this pre-existing pool of receptors redistributes to the peripheral region, thereby initiating yolk formation. Such a redistribution mechanism would obliterate the need for de novo synthesis of receptors when the oocyte's energy expenditure is to be utilized for plasma membrane synthesis, establishment and maintenance of intracellular topography and yolk formation, and preparation for ovulation.

Animals↗
PubMed1993

An observation on flash evoked cortical potentials and Qigong meditation.

The purpose of this study was to investigate the functional state of the cerebral cortex during Qigong meditation with flash visual evoked potentials (F-VEPs) recorded from the occipital scalp in four groups of adults. The first group included 14 subjects who had exercised in Neiyang Gong for 0.5-5.5 years. The second group was composed of 12 subjects who had practiced Neiyang Gong for only 0.5-3 months. Eleven subjects who had never practiced Qigong before made up the third group and served as control. Eleven Qigong practitioners constituted the fourth group. It was found that F-VEP amplitudes were increased in the first group and decreased in the fourth group with the exception of one subject during Qigong meditation. No significant changes were found in the second group and controls. The results were discussed and it is shown that Qigong mediation may have either facilitative or inhibitory effects on the visual cortex depending on the Qigong methods practiced by different individuals.

Adult↗
PubMed1993

The function of 3' noncoding sequences of hepatitis B surface antigen gene in a non-hepatic cell expression system.

A series of expression vectors containing the hepatitis B surface antigen (HBsAg) gene were constructed in which the promoter region of the HBsAg gene was replaced by the mouse metallothionein promoter. The HBsAg 3' noncoding sequences were modified by various deletions and/or additions of the heterogeneous genetic elements. The expression levels of the derivates were evaluated in a transient expression system using HeLa cells. We found that the enhancer I (EN-I) of hepatitis B virus (HBV) and the polyadenylation (poly A) signal are the most important elements for the expression of HBsAg gene in non-hepatic cells, in addition to the necessity to replace the original promoter of HBsAg gene. The heterogeneous poly A signal in combination with the simian virus (SV40) splicing signal could substitute for the poly A signal of the HBsAg gene, and, moreover, could increase the expression level of the HBsAg gene in HeLa cells. On the contrary, the enhancer II (EN-II) of HBV has no effect on the expression of the HBsAg gene in HeLa cells. These results imply another role of HBV EN-II on the stability of HBsAg transcripts in addition to the demonstrated function of activation the promoter.

DNA Mutational Analysis↗
PubMed1993

[The influences of acupuncture on the cortical evoked potentials in rabbits].

In this work the visual, auditory, somatosensory evoked cortical potentials as well as raw EEGs were observed in 31 rabbits either anesthetized with urethane or conscious. The effects of acupuncture on them were as follows: 1) The main components of the evoked potentials were significantly depressed; 2) The raw EEGs were desynchronized while the animals appeared to be slightly activated; 3) Both the integral values of raw EEGs and the powers of lower frequency waves (1-3.99 Hz) were decreased and positively correlated well with the amplitudes of the main components of the evoked potentials. Therefore, It could not be ruled out that the effects of acupuncture on the evoked potentials are secondary to the changes of EEGs, and it is suggested that the inhibition of evoked potentials during acupuncture does not necessarily mean that the cerebral cortex is in an inhibitory state.

Animals↗
PubMed1992

Formation of the excited ferryl species following Fenton reaction.

A concomitant chemiluminescence burst can be detected when hydrogen peroxide is injected into the solution containing either free or chelated ferrous iron. The duration of the burst is slightly longer than the time for the oxidation of Fe2+. The luminescence intensity is a quadratic function of the initial concentration of H2O2 and is dependent on Fe2+ concentration. The scavengers of hydroxyl radical effectively inhibit, while the previously added ferric ions enhance, the luminescence. It is proposed that the excited species responsible for the luminescence is created by the reaction of hydroxyl radical with ferric iron. The theoretical analysis based on such a mechanism can fairly well interpret the experimental observation. The present study suggests that an excited ferryl species may be formed in Fenton reaction.

Free Radical Scavengers↗
PubMed1991

The laying hen expresses two different low density lipoprotein receptor-related proteins.

We have identified, by a combination of ligand, 45Ca2+, and immunoblotting, two large membrane proteins akin to the mammalian so-called low density lipoprotein (LDL) receptor-related protein (LRP) in chicken tissues. LRP has thus far been demonstrated only in mammalian species where it is thought to act as a receptor for proteinase-alpha 2-macroglobulin complexes and/or chylomicron remnants, lipoproteins not produced in birds. One of the chicken LRPs was demonstrated in liver, and has the same apparent Mr and hallmark biochemical properties as rat liver LRP. The other chicken LRP is smaller (approximately 380 kDa) and is expressed in ovarian follicles, but is undetectable in liver. Immunological analysis demonstrated a lack of cross-reactivity between the two LRPs, as well as between them and the previously identified chicken oocyte-specific 95-kDa receptor for the yolk precursors, very low density lipoprotein, and vitellogenin (Stifani, S., Barber, D. L., Nimpf, J., and Schneider, W. J. (1989) Proc. Natl. Acad. Sci. U.S.A. 87, 1955-1959). As shown by ligand blotting, both chicken LRPs have the ability to interact with vitellogenin, a property they share not only with rat LRP, but also with mammalian LDL receptors. To obtain independent confirmation of the ligand blotting results, the smaller (follicular) LRP was purified and high-affinity binding of vitellogenin to it was demonstrated by a solid-phase filtration binding assay. Amino acid sequences of tryptic fragments of the smaller LRP were obtained, and its homology with human LRP demonstrated through unambiguous alignment of three fragments. Both chicken LRPs, the chicken oocyte 95-kDa receptor, as well as rat LRP, could be shown by ligand blotting to interact specifically with chicken serum alpha 2-macroglobulin. In addition, human apolipoprotein E, a ligand implicated in receptor-mediated metabolism of chylomicron remnants, also binds to the smaller chicken LRP, further emphasizing the similarities between LDL receptors and related proteins from a variety of species. In analogy to the known dichotomy of chicken LDL receptors, which is characterized by the production of the 95-kDa oocyte-specific receptor on one hand and a 130-kDa LDL receptor that is exclusively expressed in somatic cells (Hayashi, K., Nimpf, J., and Schneider, W. J. (1989) J. Biol. Chem. 264, 3131-3139), it appears that the smaller and larger chicken LRPs also may be restricted to the oocyte and somatic cells, respectively.

Amino Acid Sequence↗
PubMed1991

Induced rotary motion and ocular torsion.

When a large patterned annulus rotates around a stationary sectored disc the latter appears to rotate in the opposite direction. Such induced rotary motion was examined with central discs subtending 5, 20 and 40 deg at the eye, with the surround filling the remainder of the visual field. The annular surround or the central disc could be oscillated sinusoidally around the fixation point through 20 deg at 0.2 Hz. In each case, subjects estimated the angles through which the moving and stationary parts of the display appeared to rotate on one half-cycle. Subjects also estimated the angle of rotation of an oscillating display that filled the visual field. Induced rotation of the centre was around 100% of the inducing amplitude for all disc sizes, but there was no induced motion of the surround when the centre rotated. Ocular torsion was measured under the same conditions, using the scleral search-coil technique. The amplitude of ocular torsion was a function of the size of the stationary or rotating field. Thus, variations in stimulus conditions affected induced rotary motion and ocular torsion in different ways. The implications of the results for theories of induced motion in terms of underregistered eye movements are discussed.

Eye Movements↗