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Biomedical subjects

W Liu

Publications and source records attributed to W Liu.

At least 973 records · Page 54Linked to original sources
PubMed1991

Localization of 616 human chromosome 3-specific cosmids using a somatic cell hybrid deletion mapping panel.

A total of 5700 human chromosome 3-specific cosmid clones was isolated from a series of cosmid libraries constructed from somatic cell hybrids whose only human component was an entire chromosome 3 or a chromosome 3 containing an interstitial deletion removing 50% of long arm sequences. Several unique sequence chromosome 3-specific hybridization probes were isolated from each of 616 of these cosmids. These probes were then used to localize the cosmids by hybridization to a somatic cell hybrid deletion mapping panel capable of resolving chromosome 3 into nine distinct subregions. All 616 of the cosmids were localized to either the long or short arm of chromosome 3 and 63% of the short arm cosmids were more precisely localized. We have identified a total of 87 cosmids that contain fragments that are evolutionarily conserved. Fragments from these cosmids should prove useful in the identification of new chromosome 3-specific genes as well as in comparative mapping studies. The localized cosmids should provide excellent saturation of human chromosome 3 and facilitate the construction of physical and genetic linkage maps to identify various disease loci including Von Hippel Lindau disease and renal and small cell lung carcinoma.

Animals↗
PubMed1991

Second messenger-mediated actions of norepinephrine on target neurons in central circuits: a new perspective on intracellular mechanisms and functional consequences.

Ever since the initial demonstration of a widespread distribution of noradrenergic fibers to functionally diverse regions of the mammalian forebrain, there has been considerable interest in determining the electrophysiological effects of norepinephrine (NE) on individual neurons within these target areas. While early studies showed that NE could directly inhibit cell firing via increased intracellular levels of cyclic AMP, more recent work has revealed a spectrum of noradrenergic actions, which are more accurately characterized as neuromodulatory. More specifically, numerous experimental conditions have been described where NE at levels subthreshold for producing direct depressant effects on spontaneous firing can facilitate neuronal responses to both excitatory and inhibitory synaptic stimuli. The goal of this report is to review recent evidence which suggests that the various modulatory actions of NE on central neurons result from the activation of different adrenoceptor-linked second messenger systems. In particular, we have focused on the candidate signal transduction mechanisms that may underlie NE's ability to augment cerebellar and cortical neuronal responsiveness to GABAergic synaptic inputs. The consequences of such NE-induced changes in synaptic efficacy are considered not only with respect to their influences on feature extraction properties of individual sensory cortical neurons but also with regard to the potential impact such actions would have on the signal processing capabilities of a network of noradrenergically innervated cortical cells.

Action Potentials↗
PubMed1991

Effects of exogenous auxins on expression of lipoxygenases in cultured soybean embryos.

The expression of lipoxygenases (LOXs) is known to be developmentally regulated in soybeans (Glycine max. [L.] Merr.). Hormones have been firmly established as being involved in the growth and developmental processes of a number of plant species. Correlation between the expression of LOXs and the development and germination of soybean embryos suggests that plant hormones may affect the expression of LOXs. The present studies were conducted to investigate the effects of exogenous auxins on the expression of LOX isozymes and LOX activities in cultured cotyledon tissues of immature soybean seeds. The results revealed that at least one of the more acidic nonembryo LOX isozymes was induced by either alpha-naphthaleneacetic acid or indoleacetic acid but not by 2,4-dichlorophenoxyacetic acid after 4 days' exposure. Levels of LOX-1, -2, and -3 proteins and activities were significantly decreased by 2,4-dichlorophenoxyacetic acid 10 days after explanting. S1 analysis showed that embryo LOX messenger RNAs were detectable in the tissues treated with each of the auxins. The reduced levels of the embryo LOX proteins may, therefore, be regulated at the levels of translation, posttranslational modification, or degradation. The more acidic isozymes induced by alpha-naphthaleneacetic acid showed enzymatic activity and shared the same molecular mass and isoelectric point values as the germination-associated LOX isozymes found in hypocotyls and radicles, suggesting that those LOXs are involved in germination competency of soybean embryos.

Journal Article↗
PubMed1991

Mapping the receptor-recognition site of human transforming growth factor-alpha.

The receptor-recognition site human transforming growth factor-alpha (TGF alpha), a 50-residue tricyclic peptide with three disulfide bonds, was mapped by a set of 46 peptide analogs consisting of linear, monocyclic, bicyclic, and tricyclic structures representing individual and overlapping subdomains of human TGF alpha. Linear overlapping fragments ranging from 7 to 18 residues and spanning the entire length of TGF alpha as well as monocyclic analogs with one disulfide linkage were found to be inactive in both receptor-binding and mitogenic assays. Bicyclic analogs with two disulfide linkage and representing either the amino or carboxyl two-thirds of TGF alpha showed low activity at 0.1-0.9 mM concentrations. Tricyclic analogs containing all three disulfide linkages but lacking either the amino or carboxyl terminal heptapeptide was, respectively, 3% and 0.1% as active as TGF alpha. These results show that determinants for the receptor binding cannot be represented by a short continuous fragment or a single subdomain, but are located on a discontinuous surface on a folded structure with disulfide restraints. Furthermore, these results when combined with our previous results which shows that the middle subdomain (second disulfide loop) is not involved in the receptor binding suggest that the receptor-binding residues are constituted of three fragments located at the first and third subdomains as well as the external carboxyl peptide.

Amino Acid Sequence↗
PubMed1991

Contribution of the cell-surface-associated enzyme in the Zimmermann-Rosselet assay of outer membrane permeability of beta-lactam antibiotics.

Analysis of beta-lactam hydrolysis by intact cells of several strains of enteric bacteria suggests that a significant fraction of beta-lactamase molecules is present at a location directly accessible for the substrates in the medium. We propose a method to correct for the error introduced by these "surface-exposed" enzymes in the Zimmermann-Rosselet assay of outer membrane permeability.

Anti-Bacterial Agents↗
PubMed1991

Conversion of Bacillus subtilis 168 to a subtilin producer by competence transformation.

Subtilin is a ribosomally synthesized peptide antibiotic produced by Bacillus subtilis ATCC 6633. B. subtilis 168 was converted to a subtilin producer by competence transformation with chromosomal DNA from B. subtilis ATCC 6633. A chloramphenicol acetyltransferase gene was inserted next to the subtilin structural gene as a selectable marker. The genes that conferred subtilin production were derived from a 40-kb region of the B. subtilis ATCC 6633 chromosome that had flanking homologies to the B. subtilis 168 chromosome. The subtilin produced by the mutant was identical to natural subtilin in its biological activity, chromatographic behavior, amino acid composition, and N-terminal amino acid sequence.

Amino Acid Sequence↗
PubMed1991

Temporal pattern of nerve growth factor (NGF) binding in vivo and the in vitro effects of NGF on cultures of developing auditory and vestibular neurons.

NGF binding patterns reflect the presence of receptors for this growth factor. High specific binding of 125I 2.5 S-NGF was observed for the 11 gestation day (gd) statoacoustic ganglion (SAG) with lower levels recorded for both 14 gd acoustic ganglion (AG) and vestibular ganglion (VG) samples. Fourteen day AG cells were more than twice as active for binding NGF when compared to VG samples of the same gestational age. Both whole ganglion explants and dissociated cell cultures were grown in chemically defined medium for short term culture to assay changes in neurite outgrowth and survival of neurons in response to the addition of exogenous 2.5 S-NGF. The most vigorous neurite outgrowth and neuronal survival responses were produced by 11 gd SAG samples treated with NGF. Acoustic ganglion specimens of both 11 gd and 14 gd embryos were much more responsive to the neurotrophic effects of NGF when compared to the responses of their VG counterparts. There was a correlation between NGF binding ability and in vitro responsiveness to exogenous NGF. We hypothesize based on the results of this study that NGF (and/or a member of the NGF family of growth factors) is involved in the control of developmentally regulated neuronal cell death of SAG neurons and may play a role in the innervation of developing inner ear sensory structures.

Animals↗
PubMed1991

[Reconstitution of osteoinductive bone xenograft: bioassay in mice].

How to eliminate the antigenicity of bone xenograft while retaining its osteoinductive activities is an unsolved problem in the orthopaedic field. This paper reports an encouraging approach to the question by the following procedures extracting the bone morphogenetic protein (BMP) from cortical bone; eliminating the antigenicity of cancellous bone by chemical extraction; and reconstituting the graft with the treated cancellous bone serving as a delivery medium for BMP. This composite graft is accepted immunologically, and is also osteoinductive in the heterogenous host. In point of delivery medium of BMP, the cancellous bone xenograft is the best choice due to its abundant sources. Bioassay in mouse showed that the reconstituted graft, including only 0.5 mg BMP, demonstrated a definitive osteoinductive ability. In addition, this paper first furnished the information that the BMP aggregate from chemical extraction as described in the literature is also antigenic in the heterogenous host.

Animals↗
PubMed1991

[Changes in transmembrane action potentials and monophasic action potentials of phase 3 intraventricular block in rabbits].

The model of phase 3 intraventricular block was produced in 10 rabbits by giving 2.5% solution of potassium chloride intravenously under natural breathing and sinus rhythm. Transmembrane action potentials and monophasic action potentials were recorded respectively. The results showed that RP, APA, Vmax, MAPA and MVmax all decreased and both APD and MAPD shortened at the time of ventricular conduction block, when ventricular conduction was improved by vagal stimulation, RP, APA, Vmax, MAPA and MVmax all increased and both APD and MAPD lengthened. In addition, APD and MAPD measured at the same site in normal conduction, conduction block and conduction improved by vagal stimulation were in consensus.

Action Potentials↗
PubMed1991

[Clinical value of the Chengdu classification of non-Hodgkin's lymphomas].

Two hundred forty-nine cases of non-Hodgkin's lymphomas (NHL) were reviewed by using the working classification of NHL (Chengdu, 1985). The results showed that the patients of 249 cases of NHL ranging in age from 5 to 76 years, with the mean age of 42 of the types were separated into three major prognostic groupings as follows: 1. low (41 of 249 cases, small lymphocytic 27 cases, lymphoplasmacytoid 2 cases, follicular cleaved 7 cases, follicular cleaved and noncleaved 5 cases); 2. intermediate (58 of 249 cases, diffuse cleaved 28 cases, diffuse cleaved and noncleaved 27 cases, follicular noncleaved 3 cases); and 3. high grade malignancy (150 of 249 cases, diffuse noncleaved 49 cases, lymphoblastic 41 cases, immunoblastic 13 cases, polymorphic 39 cases, clear cell 2 cases, histiocytic 6 cases). Each group was significantly different from the others (P less than 0.05). The prognosis of patients with angioimmunoblastic lymphadenopathy like T-cell lymphoma (9 of 249 cases) was not more significant (P greater than 0.05) than that of patients with other polymorphic lymphoma (30 of 249 cases). The results showed this Chengdu classification of NHL is good for practice and usage in clinical evaluation and routine surgical pathology.

Adolescent↗
PubMed1991

[Status quo and prospects of oral liquid prepared from Chinese drugs].

This paper reviews the rise of oral liquids and their preparations, control standards, pharmacological research and clinical pharmacy, etc. On the basis of investigation, an overall discussion is given in respect to product variety and sale, pharmaceutical research and development, and social benefit from new products, so as to highlight the merits of Chinese medicinal materials.

Administration, Oral↗
PubMed1991

Comparison of enzymatic semisyntheses of peptide amides: human growth hormone releasing factor and analogs.

Enzymatic semisyntheses of growth hormone releasing factor (GRF), a 44-residue peptide amide hormone, from C-terminal acid precursors, are compared. A recombinant alpha-amidating enzyme was used to convert the glycine-extended precursor, GRF(1-44)-Gly-OH, to GRF(1-44)-NH2 in an essentially quantitative fashion. Trypsin was used to convert the precursors, GRF(1-43)-OH and GRF(1-44)-OH, to GRF(1-44)-NH2 (60 and 15% conversion, respectively) in a 75% v:v N,N'-dimethylacetamide solution containing a large excess of leucine amide. Carboxypeptidase Y catalyzed transpeptidations of the precursors, GRF(1-44)-OH and [Ala44]-GRF(1-44)-OH, to GRF(1-44)-NH2 in aqueous leucine amide solutions were also attempted. The trypsin catalyzed direct amidation of [Ala15]-GRF(1-29)-OH in concentrated ammonium acetate/ammonia buffer (95% 1,4-butanediol cosolvent) to form the superactive analog, [Ala15]-GRF(1-29)-NH2 (ca. 25% conversion at equilibrium), is also described.

Amino Acid Sequence↗
PubMed1991

[Autologous mixed lymphoma reaction in patients with malignant lymphoma].

Human T cells can be induced to proliferate in vitro when they are cocultured with autologous Non-T cells. This phenomenon has been termed the autologous mixed lymphocyte reaction, AMLR. In this study, AMLR was assessed in 14 untreated patients with lymphoma and 13 age-and-sex-matched healthy controls. This difference was significant (P less than 0.001), suggesting that patients with lymphoma may have impaired AMLR.

Adolescent↗
PubMed1991

[The regulating effect of electroacupuncture on gastroenteric electric activity in guinea pigs of peripheral vomiting].

Acute experiments were performed on 20 guinea pigs. The animals were divided at random into four groups of five each: the non-acupuncture group for control and three electroacupuncture groups (EA-I, EA-II, EA-III). Four pairs of platinum-wire electrodes were implanted under serosa of the antrum and corpus, duodenum, jejunum. The gastroenteric electric activity (GEA) was recorded in conscious and fasting state. Needling was applied at position 1 cm below the knee, corresponding to Zusanli. The peripheral vomiting model was established by infusion of CuSO4 into the stomach. Observation was made with regard to latency of vomiting induced by infusion of CuSO4, duration of the symptom, number of fits in the first five minutes after the attack began, and the variation of amplitude and frequency of GEA. The results were as follows: (1) The GEA of normal guinea pigs showed regular cyclic changes. After latency of 3.7 seconds following the infusion, symptom of vomiting began appear. The GEA returned to normal after latency of 60 minutes. (2) During vomiting, the GEA was characterized by a series of spikes which were seen more obviously in the antrum and corpus; during serious fits of vomiting, duodenum and jejunum were involved. The GEA showed disordered and quicker rhythm with higher amplitude and frequency. (3) EA could not affect the latency of the peripheral vomiting, but it could shorten the duration of the symptom. Results of group EA-II (p less than 0.001) showed EA could reduce the number of fits during the first five minutes; results of group EA-I (p less than 0.01) showed that EA could lower the amplitude and frequency of the GEA (p less than 0.05) that rose during vomiting.(ABSTRACT TRUNCATED AT 250 WORDS)

Acupuncture Therapy↗
PubMed1991

[Synthesis of small peptides containing hydroxy-amino-acid, and its effects on progesterone production].

Eleven peptides containing hydroxy-amino-acid have been synthesized manually by stepwise solid-phase method. Three of them were started on BHA-resin, the others on Merrifield-resin. TFMSA/TFA/p-cresol were used as cleaving reagent in all peptide-resin (1-11) cleavage. Furthermore, HF cleaving procedure was also used parallelly to five of those peptide-resins for contrast. No conspicuous difference in yield was found between TFMSA and HF. The purity of all products was checked by the profiles of analytical reversed phase HPLC (C-18) and the data of amino acid analysis. All synthetic peptides were tested for the effect on progesterone production by rat corpus luteum in vitro. Among them, three peptides, GlyTyr-NH2, LysTyr-NH2 and GlySer Lys-OH, showed significant effect (p less than 0.01) on inhibiting hCG-induced progesterone production.

Amino Acids↗