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Biomedical subjects

Z Liu

Publications and source records attributed to Z Liu.

At least 1,279 records · Page 71Linked to original sources
PubMed1992

Adverse effects of alkali and acid on the anticoagulant potency of heparin, evaluated with methyl 2-deoxy-2-sulfamino-alpha-D-glucopyranoside 3-sulfate as a model compound.

A variety of chemical modifications can induce a reduction in the anticoagulant activity of heparin. Among such modifications are the removal in alkaline solution of the 2-O-sulfonate group of alpha-L-idopyranosyluronic acid 2-sulfate residues (1) and, in a weakly acidic medium, of the N-sulfonate group of residues of 2-deoxy-2-sulfamino-alpha-D-glucopyranose 6-sulfate (2). This study examined the possibility that the losses in anticoagulant potency are related to a concomitant removal of the 3-O-sulfonate group of residues of 2-deoxy-2-sulfamino-alpha-D-glucopyranose 3,6-disulfate (6) in the AT-III binding site. It entailed a synthesis of methyl 2-deoxy-2-sulfamino-alpha-D-glucopyranoside 3-sulfate (7), as a model compound that was subjected to both the strongly alkaline and weakly acidic conditions appropriate for the modification of residues 1 and 2, respectively. The 3-sulfate group of 7 was found to be highly stable in both environments. This indicated that the adverse effects that these conditions have on the anticoagulant properties of heparin are not specifically associated with the 3-sulfate substituent of residues of 6 in the polymer.

Blood Coagulation↗
PubMed1992

MHC class II binding of peptides derived from HLA-DR 1.

The aim of these studies was to determine whether auto- and alloreactivity can arise from T cell recognition of MHC-peptides in context of syngeneic MHC. Four synthetic peptides derived from the first domain of the HLA-DR beta 1 * 0101 chain were used in limiting dilution analysis to prime T cells from HLA-DR1- and HLA-DR1+ responders. The frequency of T cells responding to these four peptides was similar in individuals with or without HLA-DR1. In both cases, the peptide corresponding to the nonpolymorphic sequence 43-62, was less immunogenic than peptides corresponding to the three hypervariable regions 1-20, 21-42, and 66-90, eliciting a lower number of reactive T cells. Experiments using a T cell line with specific reactivity to peptide 21-42 showed, however, that this response can be efficiently blocked by adding to the culture a nonpolymorphic sequence peptide. This suggests that alloreactivity can be blocked by use of monomorphic (self) peptides. The binding of both "monomorphic" and "polymorphic" synthetic DR1 peptides to affinity purified HLA-DR 1 and DR 11 molecules was measured using radiolabeled peptides and high performance size exclusion chromatography. The data showed that the polymorphic as well as monomorphic synthetic DR1 peptides bound to both DR1 and DR11 molecules. Competitive inhibition studies indicated that the monomorphic 43-62 peptide can block the binding of the polymorphic peptides, consistent with the results obtained in T cell cultures. Taken together these data suggest that anti-MHC autoreactive T cells are present in the periphery and that both auto and alloreactivity can be elicited by MHC peptides binding to MHC class II molecules.

Amino Acid Sequence↗
PubMed1992

Carbon monoxide does not inhibit glyceryl trinitrate biotransformation by or relaxation of aorta.

Carbon monoxide (CO) was employed to assess the role of ferrous hemoproteins in the vasodilation and biotransformation of glyceryl trinitrate (GTN) in rabbit aortic strips. These tissues were contracted submaximally with phenylephrine, exposed to CO for 5 min, and then incubated with 0.5 microM [1,3(14) C]GTN in the presence of CO for 2 min or 30 s. The [14C]GTN-induced relaxation of the strips was recorded, and [14C]GTN biotransformation to [14C]glyceryl dinitrate metabolites by the tissues was determined by thin-layer chromatographic-liquid scintillation spectrometric analysis. CO treatment inhibited neither GTN-induced relaxation nor GTN biotransformation to glycerol dinitrate metabolites. These results indicate that ferrous hemoproteins are probably not involved in the biotransformation of GTN that is associated with relaxation of the rabbit aortic strips.

Animals↗
PubMed1992

T cell recognition of allopeptides in context of syngeneic MHC.

We have analyzed the ability of T cells to recognize peptides corresponding in sequence to an allogeneic HLA-DR molecule, in context of syngeneic MHC. PBMC from a responder with the HLA-DR beta 1*1101/DR beta 1*1201 genotype were stimulated in vitro with a mixture of four synthetic peptides derived from the first domain of the DR beta 1*0101 chain (amino acid residue 1-20, 21-42, 43-62, and 66-90). An alloreactive T cell line, TCL-LS, which proliferates only in response to peptide 21-42 presented by HLA-DR beta 1*1101, was obtained. The blastogenic response of the line was inhibited by anti-HLA-DR and CD4 antibodies but was not affected by antibodies to HLA-DQ, HLA-DP, HLA-ABC, and CD8. In the presence of irradiated, autologous APC, TCL-LS displayed specific proliferative responses to stimulating cells obtained from individuals carrying the DR beta 1*0101 allele. In the absence of autologous APC, TCL-LS recognized HLA-DR1 on allogeneic cells only when expressed together with HLA-DR beta 1*1101, the restrictive element. This indicates that TCL-LS recognizes processed HLA-DR1 molecule presented as nominal Ag. Study of TCR-V beta gene repertoire expressed by TCL-LS showed that only two V beta genes were used (V beta 13.2 and V beta 12). Two T cell clones (TCC) derived from this line, TCC-A5 and B4, exhibited a similar pattern of reactivity and expressed V beta 13.2. These results indicate that T cells recognizing peptides, which are derived from the breakdown of allogeneic MHC class II proteins and are presented by self-HLA-DR molecules, participate in allorecognition.

Antigen-Presenting Cells↗
PubMed1992

Somatostatin concentrations in cerebrospinal fluid and brain tissue of patients with refractory epilepsy.

The somatostatin concentrations of cerebrospinal fluid (CSF) and brain tissue in 16 refractory epileptic patients were measured simultaneously by a radioimmunoassay (RIA) method. An increased level of somatostatin was found in the epileptic foci of cerebral cortex, determined by the cortical EEG. There were significant differences among the epileptic foci (75.58 +/- 6.58 pg/mg wet wt, +/- SEM), nonfocal tissues (37.04 +/- 6.55 pg/mg), and normal tissues of control patients (47.69 +/- 10.12 pg/mg), p < 0.001 and p < 0.05, respectively. The somatostatin concentrations of CSF in 11 epileptic patients were determined before (257.78 +/- 19.11 pg/mL) and after (178.36 +/- 8.78 pg/mL) the removal of epileptic focal area, and a dramatic decrease of the CSF somatostatin concentration after operation was detected (p < 0.01). We also found that the somatostatin level of cerebral scar induced by head injury in cases of posttraumatic epilepsy was highest (106.39 +/- 12.41 pg/mg). The results suggested that the surgical removal of the epileptic focal area in refractory epileptic patients may reduce the increased central somatostatin level, which could play an important part in the pathophysiological process of refractory epilepsy.

Adult↗
PubMed1992

Interneuronal interaction between members of quadrature phase and anti-phase pairs in the cat's visual cortex.

Interactions between adjacent simple cells recorded simultaneously from the same microelectrode placement were studied by correlational analysis. The receptive fields of pairs of such cells exhibit either 90 degrees (quadrature phase) or 180 degrees (anti-phase) phase relationships. We now show that the majority of quadrature phase pair members do not receive common input from the immediately precedent stage along the visual pathway, nor do these cells interact with each other. The anti-phase pairs show relatively strong mutual inhibition. These results suggest that each of the physically adjacent phase-related simple cells receives excitatory input from a distinct group of pre-cortical cells, and that mutual inhibitions between members of anti-phase pairs are used to construct the inhibitory subzones of these cells. We propose a model which incorporates these new results and provides a parsimonious explanation for the construction of both quadrature phase and anti-phase pairs.

Animals↗
PubMed1992

Involvement of intrathalamic GABAB neurotransmission in the control of absence seizures in the rat.

The role of intrathalamic GABAB neurotransmission in the control of absence seizures was investigated. In rats with genetic absence epilepsy, bilateral injections of R-baclofen (50, 100 and 200 ng/side), a selective GABAB receptor agonist, into the specific relay nuclei and the reticular nuclei of the thalamus increased spontaneous spike and wave discharges in a dose-dependent fashion, whereas injections of a GABAB antagonist CGP 35,348 (1, 2.5 and 5 micrograms/side) into the same sites decreased these seizures dose-dependently. The effect of R-baclofen (200 ng/side) on spike and wave discharges could be blocked by a subsequent injection of CGP 35,348 (1 microgram/side) at the same site. Injections of R-baclofen (200 ng) or CGP 35,348 (5 micrograms) into the midline thalamus had no effect on these seizures. In non-epileptic rats, bilateral injections of R-baclofen (1 microgram/side) into the specific relay nuclei induced synchronized rhythmic oscillations on the cortical electroencephalogram. The results suggest that GABAB receptors in the ventrolateral thalamus and in the reticular nuclei are involved in an oscillatory activity which underlies the rhythmic spike and wave discharges recorded during spontaneous generalized non-convulsive seizures.

Animals↗
PubMed1992

Calcium antagonistic effects of carbamazepine as a mechanism of action in neuropsychiatric disorders: studies in calcium dependent model epilepsies.

Carbamazepine (CBZ) is used in neurology for the treatment of epilepsies and trigeminal neuralgia and in psychiatry for the prophylactic treatment of affective and schizoaffective psychoses. Since a common mechanism of epilepsies and affective psychoses might be increased intracellular calcium ion levels, CBZ action was analyzed in penicillin, caffeine and low Mg2+ induced model epilepsies which have been shown to be suppressed specifically by organic calcium antagonists. In CA3 and CA1 areas of hippocampal slice preparations of guinea pigs CBZ reduced paroxysmal depolarizations and extracellular field potentials (EFP) in a typical time and concentration dependent manner as it is known from calcium antagonists. Furthermore, subthreshold concentrations of the organic calcium antagonist verapamil intensified the action of CBZ. NMDA induced increases of the discharge rate of EFP were, however, unaffected by CBZ.

Animals↗
PubMed1992

Smoking and lung cancer in China: combined analysis of eight case-control studies.

Smoking is well established as a principal risk factor for lung cancer. The risk of lung cancer is about ten times higher in smokers in Western countries. In China, a number of epidemiological studies have investigated the association between lung cancer and smoking and in the present paper, a combined analysis of eight such case-control studies is described. The summary odds ratio (OR), calculated by the Mantel-Haenszel method, and attributable risk (AR) of lung cancer associated with smoking were calculated from the combined data which were obtained from a literature review. The eight case-control studies were conducted in Beijing, Shanghai, Shenyang, Nanjing, Harbin, Zhengzhou, Taiyuan, and Nanchang, yielding a total of 4081 lung cancer cases and 4338 controls. The summary OR of lung cancer associated with smoking was 2.17 (95% CI (confidence interval): 1.98-2.39). The OR were 3.09 (95% CI: 2.61-3.66) for males and 2.30 (95% CI: 1.96-2.69) for females. The AR were 38.2% for both sexes, 56.7% for males and 25.5% for females. Risks of 1.00, 1.03, 2.04, and 3.33 showed a dose-response relationship between lung cancer and number of cigarettes smoked per day. There were also significant dose-response relationships of lung cancer with duration of smoking (OR = 1.00, 1.02, 2.66), and age at start of smoking (OR = 1.00, 3.30, 2.36, 1.18). The OR and AR of lung cancer associated with smoking in China were much lower than those reported in Western countries and the possible reasons for this are discussed.

Case-Control Studies↗
PubMed1992

Abscisic acid accumulation in leaves of two contrasting hybrid poplar clones affected by nitrogen fertilization plus cyclic flooding and soil drying.

Cuttings of hybrid Populus clones Tristis and Eugenei growing in pots in a greenhouse were treated with nitrogen fertilizer at two rates and subjected to repeated soil flooding or drying. Periodically, gas exchange measurements and radioimmunoassays, to determine abscisic acid (ABA) concentrations, were made on recently mature leaves.In both clones, photosynthesis and stomatal conductance were depressed five days after flooding, but leaf ABA concentrations remained relatively constant. In contrast, an initial, 9-day period of soil drying resulted in substantial ABA accumulation in leaves, which closely correlated with declines in photosynthesis and conductance. A second soil drying cycle of up to 9 days was less effective in modifying gas exchange and leaf ABA concentrations. High-N supply stimulated leaf ABA production as the soil dried. On the resumption of watering, gas exchange in Tristis recovered fully and rapidly and leaf ABA concentrations quickly returned to control values, whereas gas exchange in Eugenei recovered slowly and leaf ABA concentrations remained high for longer.Gas exchange in Eugenei was unaffected by soil drying until leaf ABA concentrations exceeded 100 ng g(dw) (-1), whereas Tristis showed a reduction in stomatal conductance and photosynthesis at leaf ABA concentrations of only 10 ng g(dw) (-1). A rise in internal CO(2) concentrations was associated with increased leaf ABA concentrations in Tristis, but not in Eugenei. Clonal differences in the relationship between gas exchange and leaf ABA concentration suggest contrasting physiological strategies for survival under prolonged drying conditions.

Journal Article↗
PubMed1992

Recombinant interleukin-6 protects mice against experimental bacterial infection.

Because of reports of high levels of interleukin-6 (IL-6) in patients during infection, we studied the role of IL-6 in experimental infection. Mice infected with the facultative intracellular pathogen Listeria monocytogenes displayed high levels of IL-6 in their sera and tissues, particularly the spleen, 1 to 3 days after infection. At this time, the IL-6 titers correlated with bacterial numbers in individual mice and in groups of mice given graded doses of Listeria organisms. However, the presence of IL-6 in serum declined after 4 days, even when a large initial dose of bacteria meant that bacterial numbers were still increasing at this time. Recombinant mouse IL-6 injected intraperitoneally before infection protected mice in a dose-dependent manner. It was effective when given 4 h before infection but not when administration was delayed for 24 h postinfection. It is therefore believed that IL-6 plays a role in early priming of the immune response to infection. Its exact function in this model is being investigated.

Animals↗
PubMed1992

Mortality among workers in a thorium-processing plant--a second follow-up.

A second follow-up of mortality was carried out for workers employed in a thorium-processing plant between 1915 and 1973. The study group comprised 3796 workers (3119 men and 677 women). Of the whole group, 926 (761 men and 165 women) were deceased and 2620 (2161 men and 459 women) were still alive, while 250 (6.6%) were lost to follow-up. For the male workers, the standardized mortality ratio (SMR) for all causes of death was 1.12 with a 95% confidence interval (95% CI) of 1.05-1.21. The SMR for the male workers was also significantly increased for all cancers (SMR 1.23, 95% CI 1.04-1.43) and lung cancer (SMR 1.36, 95% CI 1.02-1.78). For the female workers, the SMR was 0.74 (95% CI 0.63-0.86) for all causes and 0.53 (95% CI 0.35-0.78) for all cancers. The results of a Poisson regression analysis showed that there was no significant effect of the selected factors on lung cancer mortality.

Cause of Death↗
PubMed1992

Long-stay older patients in acute hospitals: are they bed blockers?

This analysis of the use of acute hospitals by older people identifies the extent of long stays by elderly patients and the eventual outcomes of these stays in terms of separations to residential care or the community. The effect of casemix on length of stay and differences associated with location of hospital are also discussed. Less than 0.5% of all acute hospital inpatients are older people who could be considered nursing home type patients. These patients use some 9% of all acute bed days and, in most cases, these beds would otherwise be unoccupied. It is unlikely therefore that they are 'blocking' beds that could be used to relieve waiting lists.

Aftercare↗
PubMed1992

[Changes in glomerular polyanions and ultrastructure induced by protamine in rats].

Perfusion of rat kidneys with polycation protamine, resulted in pathologic alterations of glomeruli very similar to those observed in minimal change nephrotic syndrome in human. In the experimental model, colloidal iron stained kidney tissue sections were analyzed quantitatively by image analyzer and stereology in combination with the observation of other glomerular ultrastructure. The mean thickness of foot processes and the foot processes making up the volume fraction of glomerular capillary were determined. The studies showed that there was a significant decrease in glomerular polyanions of kidneys perfused with protamine as compared with that of the control group (P < 0.01). The glomerular alterations included swelling and fusion of foot processes and narrowing or loss of filtration slits. Electron-dense particles formed by binding of protamine to polyanions were seen primarily in the lamina rara externa of glomerular basement membrane and also along the lamina rara interna and on the foot process surface, which showed the distribution feature of glomerular filter. These results suggest that the ultrastructure alterations of glomeruli may result from the neutralization of polyanions by perfusion with protamine.

Animals↗