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Biomedical subjects

D X Liu

Publications and source records attributed to D X Liu.

At least 91 records · Page 5Linked to original sources
PubMed1990

Opioid and tachykinin peptides, and their precursors and precursor-processing enzymes, in human cerebrospinal fluid.

Opioid and tachykinin neuropeptides, which were derived from two biological sources (intact, and released from their corresponding precursors by the action of human cerebrospinal fluid (CSF) neuropeptidases), were characterized in human CSF by using a combination of post-high-performance liquid chromatographic (HPLC) detection techniques. Peptides were separated using gradient and isocratic reversed-phase HPLC. Radioimmunoassay measured immunoreactivity corresponding to several different individual neuropeptides including methionine enkephalin, leucine enkephalin, substance P and beta-endorphin. Commercial enzymes (trypsin, carboxypeptidase B) were used to release methionine- and leucine-enkephalin from precursors. Human CSF also served as a source of endogenous neuropeptidases. Mass spectrometry produced fragment ions that corroborated the amino acid sequence of methionine enkephalin and of substance P derived from both sources (intact, from precursors). These results demonstrated the presence of endogenous intact neuropeptides, several different neuropeptide-containing precursors and appropriate precursor-processing enzymes in human CSF for precursors of methionine enkephalin, leucine enkephalin, beta-endorphin1-31 and substance P.

Amino Acid Sequence↗
PubMed1990

A technique for temporal bone sections using non-decalcified frozen guinea pig cochleas: a study of succinic dehydrogenases.

We have developed a technique for sectioning temporal bones and have studied non-decalcified frozen guinea pig cochleas to localize succinic dehydrogenases. The technique is simple and practicable. The 6-microns sections used preserve both fine cochlear structure and satisfactory histochemical localization for identifying the succinic dehydrogenases. The technique can also be extended to immunological test, detecting transmitters and investigating enzymes in the cochlea.

Animals↗
PubMed1990

Norepinephrine and serotonin release upon impact injury to rat spinal cord.

Microdialysis sampling was used to characterize the release of norepinephrine and serotonin upon impact injury to the rat spinal cord. Increases in extracellular norepinephrine concentrations in response to injury were small and of short duration. In contrast, serotonin concentrations quickly rose 35-90 times following injury and took 30-45 min to return to control levels. Bleeding caused by injury was probably the major source of the increased serotonin levels. Our results allow a role for serotonin in secondary damage upon injury to the spinal cord but suggest that norepinephrine is not a very significant contributor to such damage.

Animals↗
PubMed1990

Relation between plasma atrial natriuretic peptide (ANP) and glomerular ANP receptors in 5/6 nephrectomized rats.

Chronic renal failure (CRF) was induced in male wistar rats (Group I) by 5/6 nephrectomy and the sham-operated ones served as control (Group II). The results showed that in Group I, plasma atrial natriuretic peptide (ANP) levels increased progressively as the Scr was elevated. Plasma R-A rose simultaneously compared to the normal (P less than 0.001). At the 20th week after operation, urine volume and Na decreased significantly (P less than 0.05). The number of glomerular receptors decreased markedly at the 12th week (P less than 0.05) and 20th week (P less than 0.01). Our data suggest that in 5/6 nephrectomized rats, the elevation of plasma ANP level might be partly caused by the damage of glomerular ANP receptors, and the elevated plasma ANP could not play its role in diuresis, natriuresis, blood pressure depression and R-A inhibition as a result of the damage of kidney ANP receptors.

Animals↗
PubMed1989

Small, but not large, unilamellar liposomes composed of dioleoylphosphatidylethanolamine and oleic acid can be stabilized by human plasma.

Small unilamellar liposomes, composed of dioleoylphosphatidylethanolamine (DOPE) and oleic acid (OA), prepared by sonication, were incubated in the presence of human plasma at 37 degrees C. The release of entrapped calcein after 8-h incubation was about 15% in plasma, compared with about 70% in phosphate-buffered saline under the same conditions. In contrast, dioleoylphosphatidylcholine (DOPC)/OA liposomes under the same conditions release about 70% in plasma and only 10% in PBS. Total release of calcein from the DOPE/OA liposomes was observed in a PBS solution containing bovine serum albumin, and the release was completely blocked by preincubation of the liposomes with plasma. These results indicate that the unstable DOPE/OA liposomes are stabilized by incubation with plasma. The stabilization process was very fast, being completed within 1 min. Only relatively small liposomes (d less than or equal to 200 nm) were completely stabilized by plasma; larger liposomes were progressively less stabilizable. SDS-polyacrylamide gel electrophoresis of liposomes which had been incubated with plasma and then washed indicated that several proteins were tightly associated with liposomes. Using liposomes containing [14C]OA, it was found that about 70% of the original OA was extracted after 1-h incubation with human plasma at 37 degrees C. Thin-layer chromatographic analysis of the plasma-treated liposomes showed the presence of the plasma lipids in the liposomes. These results suggest that liposomes composed of DOPE/OA are stabilized by protein and/or lipid components from human plasma and that the composition of the liposomes is altered. The mechanism of stabilization is discussed in terms of the surface pressure of small vesicles with a high degree of curvature.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1989

Characterization of plasma-stabilized liposomes composed of dioleoylphosphatidylethanolamine and oleic acid [published errtum appears in Biochem Biophys Res Commun 1989 Sep 29;163(3):1539].

We have previously reported that small unilamellar liposomes (d less than or equal to 200 nm) composed of dioleoylphosphatidylethanolamine and oleic acid can be stabilized by incubating with normal human plasma (Liu and Huang, Biochemistry 1989, in press). The stabilized liposomes were very stable even under relatively harsh conditions such as extreme pH, high salt and trypsin treatment. Fluorescence depolarization of diphenylhexatriene showed that the stabilized liposome had a high microviscosity in the lipid core, which did not decrease even after the majority of proteins were removed by trypsin. These data suggest that plasma proteins inserted into the lipid bilayer are probably responsible for the stabilization activity. After i.v. injection into mouse, stabilized liposomes showed a relatively low affinity to liver and spleen as compared to a conventional liposome composition.

Animals↗
PubMed1989

Identification of partial mutational sites in human mitochondrial DNA in the Chinese and its significance.

A simple method for the identification of mutational sites in human mitochondrial DNA (mtDNA) was described. It was based on the human Cambridge sequence as a relative standard sequence and a single base pair substitution in mtDNA as a unique mutational form. The partial mutational sites can be determined using this method which was characterized by combining the restriction mapping with the analysis for the table of human mtDNA potential mutational sites with rapidity and simplicity. In the meanwhile, six mtDNA mutational sites found in Chinese population were identified by means of this method.

China↗
PubMed1988

Opioid receptoractivity in CSF from an atypical lower back pain patient.

One patient's lumbar CSF sample out of 54 studied for lower back pain had an atypical metabolic profile of opioid receptoractivity. To test our hypothesis that neuropeptides play a role in human lower back pain, endogenous opioid receptoractivity was compared between a control and that atypical sample. Two lumbar puncture samples were obtained from those two patients, one before and one after clinical evaluation. Total opioid receptoractivity was measured in each sample before HPLC separation, and opioid receptoractivity was measured in each fraction after HPLC separation. The latter data represent a metabolic profile of opioid receptoractivity in the human lumbar CSF. Those data demonstrate that the atypical patient had opioid receptoractivity measurements (total and profile) differing in a qualitative and quantitative sense from the other 53 patients studied. CSF opioid receptoractivity reflects the metabolism of opioid neuropeptidergic systems in the physiology in those patients, and opioid peptides may play a role in lower back pain.

Back Pain↗
PubMed1988

Measurement of dynorphins with 3H-etorphine and canine limbic system receptors.

A canine limbic system preparation was used as the source of opioid peptide receptors to screen biologic extracts for the presence of opioid receptoractive peptides following their gradient RP-HPLC separation. Eight synthetic dynorphin peptides were studied for their ability to displace the commonly-used ligand 3H-etorphine from the canine limbic system P2 preparation. The peptides studied included the dynorphins 1-7, 1-8, 1-9, 1-10, 1-12, 1-13, 1-17, and dynorphin B. Two different types of opioid peptide molecules were utilized for the determination of the level of non-specific binding. In one study, methionine enkephalin, and in the second study each one of the eight corresponding dynorphins, was used for determination of non-specific binding. The experimental data indicated that 3H-etorphine bound to the canine limbic system P2 receptors, and that those dynorphins displaced effectively the 3H-etorphine from those receptors.

Animals↗
PubMed1988

Mitochondrial DNA polymorphism in Chinese.

Human mitochondrial DNA (mtDNA) restriction endonuclease fragment patterns were analyzed using placenta DNA isolated from 273 individuals representing four different nationalities, the Han, the Uygur, the Kazakh and the Hui populations. Thirty-eight fragment patterns (morphs) were observed with the enzyme ApaI, BamHI, EcoRI, HindIII, HinfI, HhaI, HapII, KpnI, Mbol, PstI, PvuII, SacI, ScaL and XhoI. Fourteen new morphs, including some only existing in individual racial and national populations were observed, which indicates that there is a significant difference in the distribution of mtDNA morphs among various national and racial populations. By comparison with the mtDNA sequences in primate species, some mtDNA ancestral morphs were found to be retained in Oriental population today. This result provided indirect evidence that Asia may be one of the human original sources. Genetic distances among four national populations computed and employed in construction of an average linkage tree suggested that the Uygur and the Kazakh populations combined to form a branch at first, then the Han and the Hui came together to form another one, and at last, these two branches converged into a stem. Again, it was found that the internal variation within the Uygur and the Kazakh populations was greater than that within the Han and the Hui populations. These results showed a relationship among the four different national populations in China based on the molecular level.

China↗
PubMed1986

Hemoglobinopathies in Xinjiang.

The present report summarizes the results of a search for hemoglobinopathies in 142,171 persons in Xinjiang, the results of structural analyses of abnormal hemoglobins in 134 families, and the incidence and distribution of abnormal hemoglobins and the thalassemias in eight ethnic groups or nationalities.

China↗