Biomedical subjects

L Liu

Publications and source records attributed to L Liu.

At least 1,171 records · Page 65Linked to original sources

PubMed1992

Stimulation by TGF beta of chick embryo fibroblasts--inhibition by an IGFBP-3.

The multiple effects of TGF beta on cell proliferation are not well understood. Our results show that TGF beta was a good but transient mitogen for chick embryo fibroblasts. DNA synthesis was three- to fourfold increased, even at high concentrations of TGF beta. We did not show a bimodal effect. An inhibitor of cell growth, that inhibits 100% of stimulation induced by serum in CEF, was purified to homogeneity from medium conditioned by mouse 3T3 cells. This inhibitor has been shown to be an IGF-binding protein (mIGFBP-3). In the present work, this mIGFBP-3 inhibited the TGF beta stimulation by about 50%, while the stimulation induced by PDGF or insulin was not inhibited by mIGFBP-3. Furthermore, TGF beta stimulation, in the presence of a high concentration of insulin in conditions which would saturate IGF receptors, was not significantly inhibited by mIGFBP-3. All together these results suggest that a part of the mitogenic effect of TGF beta may be through increasing IGF secretion and eventually other growth factors such as PDGF (as suggested previously).

3T3 Cells↗

PubMed1992

Lens structures exist transiently in development of transgenic mice carrying an alpha-crystallin-diphtheria toxin hybrid gene.

The development of lens structures in transgenic mice (lnl mice) which carry the diphtheria toxin A chain-coding sequence under the control of the alpha-crystallin promoter is examined here in detail. The initial stages of lens development during embryonic days 10.5 to 12.5 (E10.5-E12.5), including the invagination of the surface ectoderm to form a lens vesicle, closure of the vesicle to form a lens cup, and initial appearance of the lens itself, appeared identical in histologic analyses of lnl mice and genotypically wild-type littermate controls. However, by E12.5, cells in the central posterior lens of developing lnl mice appeared to be vacuolated and undergoing necrosis. This necrosis was quite prominent at E14.5 and the overall lens size was significantly reduced. The lenses of lnl mice continued to be present but were significantly smaller throughout embryonic development. The cells of these lenses were capable of undergoing biochemical differentiation, reacting with antibodies to both alpha- and beta-/gamma-crystallin. alpha-Crystallin expression was initiated at the appropriate time (E10.5) and maintained in most cells of lnl lenses. The expression of beta-/gamma-crystallins was surprising as these crystallins are expressed later in lens development after normal expression of alpha-crystallin and after the anticipated time of expression of the diphtheria toxin transgene. Despite extensive necrosis and cell death, lens structures persisted in lnl mice and disappeared only in the early postnatal period between days 3 and 6. Throughout the perinatal period, the remaining lens cells expressed both alpha- and beta-/gamma-crystallins. Prenatal development of the retina and ciliary body was relatively normal although the eye was significantly reduced in overall size. Some additional developmental defects were noted including persistent hyaloid artery and thickened cornea. In the perinatal period the rapidly expanding retina filled the entire eye leaving essentially no anterior or posterior chamber. These results clearly indicate that lens cells which are the target of diphtheria toxin-mediated cell ablation techniques persist for a significant time during development and thus place limitations on the interpretations of results obtained using this technique.

Animals↗

PubMed1992

Cell and species distribution of prolactin-inducible annexin I mRNA.

The major prolactin-induced gene in the Columbid cropsac (cp35) is a unique member of the annexin (lipocortin/calpactin) gene family, most closely related to mammalian annexin I. Because no other annexins are known to be regulated by a specific hormonal signal, we have analyzed the distribution of annexin I mRNAs which hybridize to cp35 cDNA by comparing several tissue and cell systems. In addition we have used in situ hybridization to locate the expression of cp35 mRNA in the cropsac. Of nine separate organs extracted only cropsac, spleen, trachea, intestine, and lung expressed easily detectable levels of annexin I mRNA. Heart, liver, kidney, and skeletal muscle did not consistently express detectable annexin I. Prolactin (PRL) injection had no measurable effect on the mRNAs expressed in any of the tissues other than cropsac. Mammalian cell lines which respond to PRL (COMMA-D, HC11) were probed for expression of cp35-hybridizing mRNAs. These cell lines contained high levels of annexin I mRNA, but the mRNA level was not stimulated by PRL. Lactating mouse mammary gland did not contain measurable RNAs for either annexin I or II. In situ hybridization of cropsac sections showed that high-level expression of annexin I (cp35) mRNA was localized in the differentiating layer of the cropsac mucosal epithelium after PRL stimulation. It was not abundant in either the proliferating layer or the outermost desquamating layer of cells. These experiments argue that mRNAcp35 expression is a unique component of the PRL-induced differentiation response of cropsac and that closely related mRNAs are expressed in some, but not all, other tissues of the pigeon.

Animals↗

PubMed1992

Failure of rivalry at low contrast: evidence of a suprathreshold binocular summation process.

Presentation of different images to the two eyes normally results in a time-varying alternation between the two images (binocular rivalry). However, we find that when orthogonal gratings are viewed dichoptically at low contrast, a stable summation between the two images is perceived in the form of a dichoptic plaid. The range of perception of the dichoptic plaid depends on spatial frequency, contrast and luminance of the gratings. This phenomenon differs from the "false fusion", a fleeting summation of different images perceived only under very brief presentation of the stimuli. The observations suggest that there exists a neural process that performs a summation of dissimilar images, and that is distinct from the competitive process of suppression and binocular rivalry.

Contrast Sensitivity↗

PubMed1992

High-level expression of staphylococcal nuclease R gene in Escherichia coli.

Staphylococcal nuclease R, an analogue of nuclease A, was overproduced under the transcriptional control of the bacteriophage lambda PRPL promoters regulated by temperature sensitive repressors. The expression level reached 200-300 mg l-1 and showed little host dependence in different strains. The investigations of the recombinant nuclease R have revealed that the amino terminal formyl methionine residue of the nuclease is precisely processed, the protein consists of 155 amino acid residues. The experiment shows that the pBV221-DH5 alpha is a quite suitable vector-host system for high-level expression and precise processing of heterologous genes in Escherichia coli. The comparative studies between the codons used in the staphylococcal nuclease R gene and the optimal codon usage in E. coli indicate that high level expression of heterologous genes in E. coli may not always require a high degree of codon usage bias.

Amino Acid Sequence↗

PubMed1992

Age-related changes in the proportion of amyloid precursor protein mRNAs in Alzheimer's disease and other neurological disorders.

In the human brain, alternative splicing of amyloid precursor protein (APP) gene transcript generates at least three types of mRNA coding for APP770, APP751 and APP695. The former two types harbor, but the latter one lacks a domain of Kunitz-type serine protease inhibitor (KPI). We studied, by using the RNase protection technique, the expression of APP mRNAs in brains of Alzheimer's disease (AD) and other neurological disorders with special reference to aging. We found that the ratio of (APP770 mRNA+APP751 mRNA)/APP695 mRNA in the frontal cortex increased approximately 1.5-fold in AD compared with other neurodegenerative or cerebrovascular disorders. The ratio in other neurological disorders did not change significantly from control even in their affected brain regions. On the other hand, we found a positive correlation between the ratio and age; the ratio (y) increased gradually with the advance of age (x) as expressed by y = 0.005x + 0.014 (r = 0.372) for the AD group, and y = 0.004x -0.037 (r = 0.486) for the non-AD group. These correlations indicate that the AD brain reached the same ratio of KPI-harboring to lacking APP mRNAs a few decades earlier than the non-AD brain in senescence. This finding of AD-specific and age-related change led us to the idea that a relative increase in KPI-harboring APPs over a KPI-lacking APP may perturb normal degradation of APPs, thereby leading to deposition of beta A4 protein as amyloid.

Aging↗

PubMed1992

Synthesis and secretion by mouse 3T3 cells of an inhibitor of cell growth (mIGFBP-3): correlation with cell proliferation.

Our results show that stimulation by serum of dense cultures of 3T3 cells rapidly induced increased synthesis of a growth inhibitor (mIGFBP-3) capable of binding IGF. mIGFBP-3 was secreted by stimulated cells immediately after its synthesis, and accumulated in the medium. Accumulation of mIGFBP-3 in the medium increased, as a function of growth factor (bFGF, PDGF, insulin) concentrations and time. bFGF was the best stimulatory factor for both DNA synthesis and accumulation of mIGFBP-3 in the first 24 h of incubation. DNA synthesis was arrested after 48 h of incubation with bFGF when accumulation of mIGFBP-3 was maximal. Since we showed that mIGFBP-3 is able to inhibit bFGF stimulation of DNA synthesis in mouse fibroblasts, it is possible that the accumulation of mIGFBP-3 induces a feedback regulation of cell growth.

3T3 Cells↗

PubMed1992

Direct gene transfer into nonhuman primate myofibers in vivo.

Previously, we showed that rodent muscle has the ability to take up and express plasmid genes injected intramuscularly. This study now demonstrates that nonhuman primate muscle also has this ability to express injected plasmids. A scaled-up version of the standard large preparation of plasmid DNA allowed several tens of milligrams of CCC plasmid DNA to be relatively easily produced and administered to monkeys. After the injection of the E. coli beta-galactosidase reporter gene in pRSVLac-Z, foreign gene expression was localized to both type I and type II myofibers. The luciferase reporter gene in pRSVL was used to quantify the amount of expression. The multiple implantation of plasmid DNA pellets was more efficient in expressing luciferase than the injection of DNA in normal saline. Luciferase activity persisted for at least 4 months after injection. However, the luciferase expression was considerably less than that in rodents. Preliminary studies explored why expression was less in monkeys. Of particular interest was the increased thickness of the perimysium of monkeys as compared to that in rodents. This increased connective tissue may decrease delivery of the plasmid DNA to the myofibers. Anti-nuclear or anti-DNA antibodies were not observed, even after repetitive DNA administrations, and no adverse effects were observed in any of the monkeys.

Adenosine Triphosphatases↗

PubMed1992

Lack of correlation between DNA methylation and hepatocarcinogenesis in rats and hamsters treated with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone.

Previous studies have demonstrated that the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) induced liver tumors in F344 rats but not in Syrian golden hamsters. The aim of this study was to determine whether there was a correlation between the persistence of O6-methylguanine (O6-mGua) adducts and the rate of recovery of O6-methylguanine-DNA methyltransferase (O6-mGuaT) after depletion in the liver and susceptibility to NNK in F344 rat and Syrian golden hamster injected s.c. with NNK (80 mg/kg). The levels of both 7-methylguanine and O6-mGua reached a maximum 24 h after NNK treatment. O6-mGua in NNK-treated rat liver was undetectable after 48 h. In the rat, the depletion of O6-mGuaT activity occurred within 4 h following NNK treatment. A subsequent rapid recovery of enzyme activity was observed 36 h after NNK exposure. In contrast, high levels of O6-mGua persisted in hamster liver DNA and no O6-mGuaT activity was detected up to 336 h after NNK injection. Thus, the persistence of O6-mGua in hamster liver is most likely related to a lack of recovery of the O6-mGuaT. These results suggested that factors other than O6-mGua may be determining NNK-induced hepatocarcinogenesis in rats. An aldehyde generated by alpha-hydroxylation of NNK, 4-oxo-4-(3-pyridyl)butanal, inhibited O6-mGuaT activity in rat hepatocytes, suggesting that this aldehyde contributes to the carcinogenicity of NNK by inhibiting this repair enzyme.

Animals↗

PubMed1992

Bioactivation of aflatoxin B1 by lipoxygenases, prostaglandin H synthase and cytochrome P450 monooxygenase in guinea-pig tissues.

In the present investigation, we have examined the role of lipoxygenases in the bioactivation of aflatoxin B1 (AFB1) in hepatic and extrahepatic tissues. The enzyme activities were evaluated by determining [3H]AFB1-DNA adduct formation. The results demonstrated that both purified soybean lipoxygenase and guinea-pig tissue cytosolic lipoxygenases were able to activate AFB1 to form [3H]AFB1-DNA adduct(s). The reaction was completely inhibited by nordihydroguaiaretic acid (NDGA, 0.1 mM), a lipoxygenase inhibitor and an antioxidant, but not by indomethacin (0.1 mM), an inhibitor of prostaglandin H synthase (PHS), indicating that this reaction is associated with lipoxygenase activity, and/or is involved in a peroxyl radical process. While purified lipoxygenase showed arachidonic acid (AA)-dependent properties, the omission of AA did not diminish guinea-pig tissue cytosolic [3H]AFB1-DNA adduct formation, possibly because AA was released from lipid particles by AFB1. Within the range of hemoglobin (Hb) concentrations found in lung, kidney and liver cytosols (1.4-11.1 microM) and microsomes (0-0.5 microM), neither pure Hb, nor Hb of cytosols or microsomes from whole blood caused detectable AA-dependent AFB1-DNA binding. This indicates that Hb, as a contaminant with quasi-lipoxygenase activity, did not contribute to AFB1 activation attributed to guinea-pig tissue lipoxygenases. [3H]AFB1 concentrations at half-maximal DNA binding rate of pulmonary cytochrome P450 monooxygenases (P450) and lipoxygenases were similar, though P450 had a much higher maximum DNA binding rate. Pulmonary microsomal PHS activity for AFB1 activation was too low for its half-maximal binding concentrations of [3H]AFB1 and maximum rate to be accurately determined. In kidney, maximum rates for lipoxygenase, PHS and P450 were similar, whereas half-maximal binding concentrations for reactions by lipoxygenase and P450 were lower compared to that of PHS. The half-maximal binding concentration of hepatic lipoxygenase was significantly lower than those for PHS and P450. Hepatic half-maximal binding concentrations for PHS and P450 were similar, though P450 had a much higher maximum rate than PHS and lipoxygenases. These data suggest that lipoxygenase-catalyzed AFB1 activation can occur at low AFB1 concentrations. This may be important in view of human exposure to low AFB1 concentrations and predominant lipoxygenase activity in human airway epithelial cells. When expressed per gram of tissue, renal and hepatic PHS activities and renal lipoxygenase activities for AFB1 activation were similar, and higher than the activity of pulmonary PHS, while pulmonary PHS activity for the oxidation of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) was similar to that in liver and lower than that in kidney.(ABSTRACT TRUNCATED AT 400 WORDS)

Aflatoxin B1↗

PubMed1992

Induction of Pseudoactinorhizae by the Plant Pathogen Agrobacterium rhizogenes.

Infection of Elaeagnus angustifolia cotyledonary wounds by Agrobacterium rhizogenes strain NCPPB 2659 resulted in the formation of pseudoactinorhizae on roots differentiated from callus. These pseudoactinorhizal root nodules were anatomically indistinguishable from the actinorhizae induced by the plant's microsymbiont Frankia. This unusual hairy root phenotype provides support for the concept that the genetic program for actinorhiza morphogenesis resides in the plant's genome.

Journal Article↗

PubMed1992

Different spatial tunings for ON and OFF pathway stimulation.

We compared the spatial tuning of sensitivity to luminance increments and decrements in three types of localized stimulus presentation with a smooth spatiotemporal envelope. The first type consisted of spatiotemporal Gabor grating functions with either a positive or a negative bias in luminance. The spatial tuning showed a substantially narrower bandwidth and greater peak sensitivity for the positive Gabors. A similar description could be applied to the results for detection of spots with a 2-D difference-of-Gaussian profile, although the shape of the tuning function differed in several respects. We also used the biased Gabor modulation in a contrast self-masking paradigm, where the increment (or decrement) was presented against a steady background with the same spatial configuration, over a range of base contrasts. At medium spatial frequencies the biased masking functions were similar to those typically found for unbiased gratings, in showing a threshold facilitation (dipper) at low contrast, and sub-Weber masking behaviour at higher contrasts. At low spatial frequencies, however, a pronounced asymmetry appeared. Stimuli with a positive bias again showed typical masking behaviour, but a virtually flat masking function was obtained for negative bias stimuli. We conclude that stimuli without abrupt luminance transients reveal pronounced differences in the spatial tuning of responses to positive and negative stimuli, which probably reflect differences in the neural connectivity of the ON and OFF processing systems.

Contrast Sensitivity↗

PubMed1992

Anatomy of the renal innervation: intrarenal aspects and ganglia of origin.

The intrinsic innervation of the kidney is described based on studies using ultrastructural, fluorescent, immunocytochemical, and autoradiographic techniques. The efferent sympathetic innervation reaches all the segments of the renal vasculature and to a much lesser extent the tubular nephron. The afferent renal nerves are localized predominantly in the pelvic region, the major vessels, and the corticomedullary connective tissue. The pathways of the renal innervation to the corresponding ganglia, as reported from observations resulting from the combination of axonal transport labeling and immunocytochemical methods, are presented. In the rat the ganglia of origin of the sympathetic efferent innervation include T13-L1 ipsilateral and contralateral paravertebral ganglia and the prevertebral superior mesenteric and celiac ganglia. The sensory afferent innervation presents a different segmental distribution of the dorsal root ganglia for the right and left kidney. For the left kidney, the corresponding ganglia extend from T8 to L2 with the greatest numbers in T12 and T13. For the right kidney, ganglia as high as T6 and as low as L2 harbor neurons innervating the kidney. Current knowledge of the anatomical bases of the function of the renal nerves is discussed.

Animals↗

PubMed1992

[Effect of panaxatriol saponins isolated from Panax notoginseng (PTS) on myocardial ischemic arrhythmia in mice and rats].

PTS, one of the major effective components of Panax notoginseng was found to exert remarked antiarrhythmic activities on coronary artery ligation induced ischemic and reperfused arrhythmias in rats. PTS also reduced the size of myocardial infarct. For i.v. CaCl2-Ach induced atrial fibrillation and/or flutter in mice, PTS produced a significant protective effect. In addition, PTS showed an action of prolonging the life under the condition of normobaric hypoxia.

Animals↗

PubMed1992

[Dynamic changes of pulmonary glucocorticoid receptor in endotoxin-induced lung injury].

The changes of maximal binding capacity (Bmax) of glucocorticoid receptor (GCR) in the endotoxin-induced lung injury were observed by using radioligand binding assay. The content of glucocorticoid (GC) and the activity of phospholipase A2 (PLA2) were also measured. The results showed that the level of GCR in lung cytoplasma decreased continuously after endotoxin infusion, and its affinity decreased in the late phase while PLA2 activity markedly increased. There was a negative correlation between the Bmax of GCR and PLA2 activity (r = -0.87, P < 0.01). These findings indicated that there is a secondary alteration in GCR during endo toxin-induced lung injury, and that the GC hypofunction caused by reduced GCR binding capacity may be of importance in the development of ARDS.

Animals↗

PubMed1992

[Plasma fibronectin determination in acute bacterial pneumonia].

Plasma fibronectin (PFn) level was measured with immunoelectrophoresis in 40 healthy adults and 30 patients with acute bacterial pneumonia. The results showed that PFn was considerably lowered in acute bacterial pneumonia (214.49 +/- 77.84 micrograms/ml) when compared with that of healthy controls (292.48 +/- 43.11 micrograms/ml), (P less than 0.001). In the pneumonia group (10 severe cases) the level of PFn was significantly lowered than that in the moderate or mild cases (127.45 +/- 31.03 micrograms/ml vs. 255.11 +/- 54.16 micrograms/ml), (P less than 0.001). In 11 cases of recovering pneumonia, PFn was significantly higher than that in exacerbation period (213.13 +/- 41.32 micrograms/ml vs. 154.52 +/- 51.27 micrograms/ml) (P less than 0.001). We think that PFn level is helpful to evaluate the clinical course and prognosis of acute bacterial pneumonia.

Adolescent↗

PubMed1992

[Effect of sodium 18 beta-glycyrrhetate on experimental arrhythmia].

The effect of sodium 18 beta-glycyrrhetate (SGA) on experimental arrhythmia was investigated. The result shows that SGA strongly counteracts arrhythmia induced by chloroform of chloroform adrenaline, lengthens the appearance time of arrhythmia induced by CaCl2, slightly retards the heart rate of rats and rabbits, and partly antagonizes the acceleration effect of isoproterenol on rabbit hearts.

Animals↗

PubMed1992

[The respiratory facilitating effects by electrical and chemical stimulation of central nucleus amygdala].

Experiments were performed on fifty urethan anesthetized (1 g/kg) rabbits of both sexes, vagotomized and spontaneously breathing. The respiratory responses to electrical and chemical stimulation of ACE were observed. The results were as follows: 1. Long train electrical stimulation of ACE caused significant respiratory facilitating effects: inspiratory prolongation and increase of respiratory rate and depth. 2. Short brust of electrical stimulation administered in ACE during the mid inspiratory and expiratory phases elicited the prolongation of inspiratory phase and the expiratory off-switch (EO-S) effect, respectively. 3. Microinjection of monosodium L-glutamate (MSG) (1 mol/L, 1 microliter) into ACE produced the similar respiratory effects as that of electrical stimulation. 4. Control experiments had no significant effect on respiration. The results showed that the activation of neurons in ACE caused facilitation of respiration. It is suggested that ACE region may take an important part in facilitating the basic respiratory rhythm.

Amygdala↗