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G Chen

Publications and source records attributed to G Chen.

At least 559 records · Page 31Linked to original sources
PubMed1997

Effect of K(+)-channel blockers on ACh-induced hyperpolarization and relaxation in mesenteric arteries.

Acetylcholine (ACh) induces endothelium-dependent hyperpolarization in the rat mesenteric artery in the presence of the nitric oxide synthase inhibitor N omega-nitro-L-arginine. We have now studied the effects of K(+)-channel blockers on the hyperpolarization responses to ACh in resting and norepinephrine-contracted rat mesenteric arteries. We also measured tension simultaneously to determine whether the inhibitory effects of these agents on relaxation could be correlated to their effects on hyperpolarization. Glibenclamide had no significant effect on the hyperpolarization or relaxation. Tetraethylammonium (TEA, 5 mM) inhibited the hyperpolarization to ACh significantly to a similar extent in both the resting and norepinephrine-stimulated arteries. Charybdotoxin (100-150 nM) caused only a small but significant inhibition. Apamin (0.3 microM) was the most effective in inhibiting the hyperpolarization in resting arteries. It was less effective in the norepinephrine-contracted arteries. A combination of apamin and charybdotoxin completely abolished the hyperpolarization responses in both conditions. The relaxation to ACh was correlated to hyperpolarization. In all cases, the inhibition of the relaxation by the K(+)-channel blockers could be accounted for by their effects on the hyperpolarization. These results indicate that Ca(2+)-activated K(+)-channels, especially those sensitive to apamin, may be the major ion channels mediating endothelium-dependent hyperpolarization to ACh.

Acetylcholine↗
PubMed1997

Adenosine modulation of calcium currents and presynaptic inhibition of GABA release in suprachiasmatic and arcuate nucleus neurons.

Adenosine modulation of calcium channel currents and synaptic gamma-aminobutyrate (GABA) release was investigated with whole cell voltage-clamp recordings in rat suprachiasmatic nucleus (SCN) and arcuate nucleus cultures (n = 94). In SCN cultures, approximately 70% of the neurons showed a reversible inhibition of whole cell barium currents on the application of adenosine or its analogues. Adenosine at 1 microM reduced the amplitude of the barium currents by approximately 27%. In contrast to the significant reduction in the amplitude, the rising and decaying phases of the barium currents, and the inverted bell shape of the current-voltage curve of the barium currents, were not changed by adenosine. The adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA; 100 nM) and the adenosine A2 receptor agonist N6-[2-(3,5-dimethoxyphenyl)-ethyl]adenosine (DPMA; 100 nM) inhibited the barium currents by 21% and 16%, respectively, in SCN neurons, indicating both A1 and A2 receptor actions. The A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (100 nM) significantly reduced the effect of CPA but did not change the effect of DPMA on the barium currents. In the presence of tetrodotoxin to block action potentials, the frequency, but not the amplitude, of miniature inhibitory postsynaptic currents was significantly reduced (46%) by 1 microM adenosine, suggesting a presynaptic mechanism of adenosine action. In support of this suggestion, the postsynaptic GABA receptor responses were not influenced by 1 microM adenosine in the majority of SCN neurons. Most solitary self-innervating SCN neurons in microisland cultures were GABAergic. In these cells, the evoked autaptic GABA release (inhibitory postsynaptic current) was significantly inhibited by adenosine (37%), CPA (27%), and DPMA (28%), indicating that both A1 and A2 receptors were present in presynaptic axons. Similar to the effect in SCN neurons, adenosine inhibited both barium currents and GABA release in arcuate neurons. The reduction of whole cell barium currents by adenosine (1 microM), CPA (100 nM), and DPMA (100 nM) was 24, 17, and 19%, respectively. In solitary self-innervating arcuate neurons, adenosine inhibited the evoked GABA release (inhibitory postsynaptic current) by approximately 48%. We conclude that both adenosine A1 and A2 receptors are present in the SCN and arcuate nucleus of the hypothalamus. Adenosine inhibits calcium currents and presynaptically reduces inhibitory GABA neurotransmission.

Adenosine↗
PubMed1997

Local and propagated vascular responses evoked by focal synaptic activity in cerebellar cortex.

We investigated the local and remote vascular changes evoked by activation of the cerebellar parallel fibers (PFs). The PFs were stimulated (25-150 microA, 30 Hz) in halothane-anesthetized rats equipped with a cranial window. The changes in arteriolar and venular diameter produced by PF stimulation were measured with the use of a videomicroscopy system. Cerebellar blood flow (BFcrb) was monitored by laser Doppler flowmetry and the field potentials evoked by PF stimulation were recorded with the use of microelectrodes. PF stimulation increased the diameter of local arterioles (+26 +/- 1%, mean +/- SE) in the activated folium (n = 10, P < 0.05). The vasodilation was greatest in smaller arterioles (16.5 +/- 0.8 microm), was graded with the intensity of stimulation, and was less marked than the vasodilation produced by hypercapnia in comparably sized vessels (+58 +/- 5%, CO2 pressure = 50-60 mmHg, n = 8). In addition, the vasodilation was greatest along the horizontal beam of activated PFs and was reduced in arterioles located away from the stimulated site in a rostrocaudal direction. The increases in vascular diameter were associated with increases in BFcrb in the activated area (+55 +/- 4%, n = 5). PF stimulation increased vascular diameter (+10 +/- 0.5%, n = 10) also in larger arterioles (30-40 microm) located in the folium adjacent to that in which the PFs were stimulated. Higher-order branches of these arterioles supplied the activated area. No field potentials were evoked by PF stimulation in the area where these upstream vessels were located. The data suggest that increased synaptic activity in the PF system produces a "local" hemodynamic response mediated by synaptic release of vasoactive agents and a "remote" response that is propagated to upstream arterioles from vessels residing in the activated folium. These propagated vascular responses are important in the coordination of segmental vascular resistance that is required to increase flow effectively during functional brain hyperemia.

Animals↗
PubMed1997

High levels of Gs alpha in platelets of euthymic patients with bipolar affective disorder.

OBJECTIVE: Previous investigations have suggested the involvement of signal-transducing guanine-nucleotide-binding proteins (G proteins) both in the mechanism of action of lithium and in the pathophysiology of bipolar affective disorder. To determine whether such G protein abnormalities are a trait phenomenon, the authors investigated the levels of G protein alpha subunits in platelets and lymphocytes of euthymic patients with bipolar affective disorder. METHOD: Selective antibodies were used to quantitate levels of G protein alpha subunits regulating adenylylcyclase activity (Gs alpha-both 45- and 52-kDa forms- and Gil-2 alpha) and those regulating phosphoinositide turnover (Gq/11 alpha) in both platelets and lymphocytes of 44 euthymic patients with bipolar affective disorder and 27 matched comparison subjects. RESULTS: Levels of both Gs alpha 45 and Gs alpha 52 were higher in the platelets of the euthymic bipolar patients (both bipolar I and bipolar II) than in those of the comparison subjects. CONCLUSIONS: These findings are consistent with previous reports of high Gs alpha levels in bipolar affective disorder and, furthermore, suggest that such levels may be a trait abnormality for this condition.

Adult↗
PubMed1997

Orbital development in long-term survivors of retinoblastoma.

PURPOSE: To determine the effects of enucleation, irradiation, and age at diagnosis on bony orbital growth in long-term survivors of retinoblastoma using measurements based on computed tomographic (CT) imaging. PATIENTS AND METHODS: We used CT obtained at a median age of 13 years to measure orbital volume and configuration in 54 patients who had been treated for retinoblastoma a minimum of 5 years previously. RESULTS: Enucleation and high-dose orbital irradiation (> 35 Gy) both independently adversely affected orbital development (P = .014 and P = .022, respectively). Orbital volume differences for children treated when < or = 1 year old were no greater than those for children treated when older than 1 year of age. In children treated for bilateral retinoblastoma, the impact of enucleation on orbital development was not statistically different from that of irradiation (P = .13). Small implants (12 to 14 mm in diameter) were more commonly associated with smaller orbital volumes. Migration of orbital implants was associated with the smaller orbital sphere size in children < or = 1 year of age (P < .035). CONCLUSION: Treatment for retinoblastoma compromises orbital development. Resulting orbital asymmetry seems to be at least partially related to the size of the implant. Detailed imaging-based measurements of orbital volume and configuration may aid the planning for cosmetic and reconstructive surgery in those who develop orbital asymmetry.

Age Factors↗
PubMed1997

Clearance of 125I-labeled interleukin-6 from brain into blood following intracerebroventricular injection in rats.

To test the hypothesis that interleukin-6 (IL-6) induced within the brain can be released into peripheral blood, 125I-labeled IL-6 was injected into the lateral cerebral ventricle of rats, and its concentration in peripheral blood followed serially. Acid-precipitable tracer appeared within 5 min of injection and entered the blood following first-order kinetics (fractional rate, 0.0116 +/- 0.0022/min). Comparison of areas under the curve of intracerebroventricular (icv) vs. iv injection showed that 37.1-46.5% of tracer injected into the lateral cerebral ventricle appeared in the blood over a 4-h period. icv IL-6 exits at least in part via venous drainage (superior sagittal sinus/aortic concentration gradient was 1.47 +/- 0.23 and 3.05 +/- 0.87 in two separate groups). Prior icv injection of human IL-1beta (100 ng) did not alter rate of degradation or of exit ofradioiodine-labeled IL-6 from the brain. These studies indicate that a relatively high proportion of IL-6 that arises in the brain enters the peripheral circulation. Direct secretion of IL-6 from brain to blood may be a mechanism by which the brain modifies peripheral metabolic, endocrine, and immune activity.

Animals↗
PubMed1997

Nasopharyngeal carriage of penicillin-resistant Streptococcus pneumoniae in children with sickle cell disease.

OBJECTIVE: We studied the prevalence of nasopharyngeal (NP) carriage, antimicrobial susceptibilities, and serotypes of Streptococcus pneumoniae (SP) in children with sickle cell disease (SCD) in the Mid-South. In addition, we examined risk factors for NP carriage of penicillin-resistant SP (PRSP). STUDY DESIGN: Between July 1994 and December 1995, we obtained NP cultures from 312 children with SCD followed at the Mid-South Sickle Cell Center, 208 (67%) of whom were receiving penicillin prophylaxis. RESULTS: Among the 312 patients, colonization with SP occurred in 42 (13%), 30 (71%) of whom were receiving penicillin prophylaxis. Twenty-three of the 42 SP isolates (55%) were resistant to penicillin; 5 of the 23 (22%) were highly resistant. PRSP organisms were also resistant to cefotaxime (43%), trimethoprim-sulfamethoxazole (57%), and erythromycin (22%). Serotypes 6A, 6B, 14, 19A, and 23F accounted for 19 (90%) of 21 resistant strains. Children who were treated with antibiotics during the preceding month were more likely to carry PRSP than children who were not treated. CONCLUSIONS: There is a high prevalence of NP carriage of PRSP in children with SCD in the Mid-South, which raises concerns regarding the continued effectiveness of penicillin prophylaxis in these children. Further studies on the antimicrobial susceptibilities of resistant organisms and the relationship between NP carriage of SP and invasive disease are needed before developing new recommendations for prophylaxis and treatment.

Adolescent↗
PubMed1997

Chemical analysis of single cells and exocytosis.

Recent advances in the development of microscale analytical techniques have allowed minute amounts of compounds of biological interest to be monitored in microenvironments. Microcolumn separation techniques, such as microcolumn liquid chromatography and capillary electrophoresis, provide a means of obtaining high-efficiency separations of analytes in picoliter to femtoliter volume samples. Voltammetric microelectrode techniques, such as amperometry and fast-scan cyclic voltammetry, are ideally suited for monitoring transiently occurring chemical events in cellular and subcellular processes owing to their rapid response times and small structural dimensions. The principles and applications of these techniques in single-cell analysis are discussed throughout this review. Multicomponent separations and quantitations of large invertebrate neurons of the land snail Helix neurons and the pond snail Planorbis corneus dopamine neurons, and of small mammalian cells, bovine adrenal cells, rat PC12 cells, and human lymphocytes, by use of microcolumn liquid chromatography and capillary electrophoresis are presented. Electrochemical monitoring of neurotransmitter exocytosis from single adrenal cells, from PC12 cells, and from the cell body of the Planorbis dopamine neuron is highlighted. Results obtained from both separation and voltammetric techniques in single-cell analyses will provide a better understanding of cellular and/or neuronal chemistry and biology in complicated living environments.

Adrenal Medulla↗
PubMed1997

beta-cell function in normal rats made chronically hyperleptinemic by adenovirus-leptin gene therapy.

Leptin was overexpressed in the liver of normal Wistar rats by infusing recombinant adenovirus containing the cDNA encoding leptin. Plasma leptin levels rose to 12-24 ng/ml (vs. <2 ng/ml in control rats), and food intake and body weight fell. Visible fat disappeared within 7 days. Plasma insulin fell to <50% of normal in association with hypoglycemia, suggesting enhanced insulin sensitivity. Although beta-cells appeared histologically normal, the pancreases were unresponsive to perfusion with stimulatory levels of glucose and arginine. Since islet triglyceride content was 0, compared with 14 ng/islet in pair-fed control rats, we coperfused a 2:1 oleate:palmitate mixture (0.5 mmol/l). This restored insulin responses to supranormal levels. When normal islets were cultured with 20 ng/ml of leptin, they too became triglyceride-depleted and failed to respond when perifused with glucose or arginine. Perifusion of fatty acids restored both responses. We conclude that in normal rats, hyperleptinemia for 2 weeks causes reversible beta-cell dysfunction by depleting tissue lipids, thereby depriving beta-cells of a lipid-derived signal required for the insulin response to other fuels.

Adenoviridae↗
PubMed1997

[Effect of platelet derived growth factor on the growth of human glomerular mesangial cells in vitro].

OBJECTIVE: To study the effect of plateletderived growth factor (PDGF) on the growth of human glomerular mesangial cells (MsC) in vitro. METHODS: Immunohistochemistry for the detection of BrdU positive cells; [3H] proline incorporation for the bioactive assay of total amount of collagen; and Northern blot analysis for the determination of fibronectin (FN) alpha 1 (IV) collagen and c-myc mRNA expression. RESULTS: The cell labelling index (LI) of BrdU incorporation in the PDGF group is 34.5% higher than that in the normal group, which was 19.5% (P < 0.01), The total amount of collagen secreted by MsC within cells and outside of cells in the PDGF group were 2.69 +/- 0.60% and 3.87 +/- 0.65% respectively, much higher than that of the normal group, which were 1.25 +/- 0.50% and 1.61 +/- 0.51% respectively (P < 0.01). Northern blot analysis revealed an increase of FN, Col IV, c-myc mRNA levels in the PDGF group. CONCLUSION: PDGF can stimulate cell proliferation, synthesis of collagen and enhance FN, Col IV, c-myc mRNA expression. It is possible that PDGF may play an important role in the development and progression of glomerulopathy.

Cell Division↗
PubMed1997

[Severe combined immunodefficiency disease, 4 autopsy case reports].

OBJECTIVE: To study the pathological changes of severe combined immunodefficiency disease (SCID). METHODS: 4 cases with SCID proven by autopsy examination. RESULTS: All patients were male with an average age of 5 moths. The major clinical manifestations included severe repeated infection with bacteria, virus, fungi and pneumocystis carinii. Autopsy examination revealed hypoplasia of thymus, spleen and lymph nodes. 1 case died from pneumocystis carinii pneumonia and BCG vaccine disease, 2 cases died of severe general infection and 1 case died from large cell lymphoma. CONCLUSIONS: The main diagnosis criteria for SCID are hypoplasia of both T and B lymphocytes, the pathologic changes of SCID are very complex.

Cytomegalovirus Infections↗
PubMed1997

[Preliminary study on pathophysiological basis of liver-blood deficiency syndrome].

By ways of HPLC and RIA, multiple laboratory parameters were determined simultaneously in 84 patients of iron--deficiency anemia (IDA) or chronic aplastic anemia (CAA) with Liver-Blood Deficiency Syndrome (LBDS) diagnosed by differentiation of TCM. The results showed that LBDS had some pathophysiological characteristics such as decreased function of sympathicus and adrenal medulla axis, increasing of L-EK, lower energy metabolism of erythrocyte, lower rate of body metabolism, sodium and water imbalance, and abnormalities in hemorrheology and erythrocyte deformability. It is suggested that the patients with LBDS are in a state of protective compensation in blood volume regulation.

Adolescent↗
PubMed1997

[Pharmacokinetics and efficacy of low-dose all-trans retinoic acid in the treatment of acute promyelocytic leukemia].

A clinical trial was conducted in order to evaluate the therapeutic effect and side effects of low-dose all-trans retinoic acid (ATRA) in the treatment of acute promyelocytic leukemia (APL). First of all, we compared the pharmacokinetic features in normal individuals with a single oral dose of ATRA at 15 mg/m2 and 45 mg/m2, respectively. The results showed that maximal plasma concentration with oral ATRA at 15 mg/m2 was high enough (10(-6) mol/L) to induce APL cell differentiation. Based on these results, 27 cases of de novo APL patients were treated with oral ATRA at a dose of 15-20 mg/m2/day and 24 of the 26 (92%) evaluable cases achieved clinical complete remission (CR) after 13 to 67 dyas of ATRA treatment. No patient experienced retinoic acid syndrome (RAS) and DIC. The Cmax with a single dose of ATRA on day 1 of treatment and immediately after obtaining of CR with ATRA in three cases demonstrated similar values in one patient and an about 2 fold decrease in two patients. Moreover comparison with a relatively well-matched previous group of 20 APL patients treated with high-dose ATRA showed that low-dose ATRA is as effective as high-dose in treating APL patients and may provide the advantages of decrease of the degree of hyperleukocytosis and side effects.

Adolescent↗
PubMed1997

[Tracheobronchoplasty: a report of 40 cases].

Tracheo bronchoplastic surgery with or without simultaneous arterioplasty was porformed in 40 cases of various bronchopulmanary diseases (benign in 8 and malignant 32). The operation consisted of reconstruction of trachea in 3 cases, plastic carinoplasty 2 cases, and bronchoplasty and pulmonary arterioplasty 1 case, sleeve resection of bronchus 34 cases, 4 cases (10%) had postoperative complications. Two cases (5%) died shortly after operation. Thirty-eight cases recovered. Thirty cases of malignant tumor were followed up from 1 to 10 years. The survival rates were 83.3% (25/30), 53.3% (16/30), 40% (12/30), 23.3% (7/30) at 1, 3, 5 and 10 years respectively. We discussed indication, anesthetic management, surgical procedure and results. The indication must be controlled strictly. The operative procedure and postoperative management must be further improved because the complications and mortality of tracheobronchoplasty are higher than those of conventional resections.

Adolescent↗
PubMed1997

[Clinical observation on pars plana lensectomy-vitrectomy preserving lens anterior capsule].

OBJECTIVE: To investigate the therapeutic effect of combined operation on cataract complicated with vitreous pathology. METHOD: 19 patients (20 eyes) with coexisting cataract and vitreous opacification or endophthalmitis or intraocular foreign bodies were operated with pars plana lensectomy-vitrectomy preserving lens anterior capsule. The ciliary sulcus intraocular lenses (IOLs) were primarily implanted for sixteen eyes of 19 cases in the operation. RESULTS: All cases were followed up for 12-36 months. Visual acuities of 18 cases were improved, 7 eyes between 0.3-0.5, 11 eyes beyond 0.5, the best one at 1.2. Anterior capsule opacification occurred merely in one eye, and in others the capsule kept being transparent. CONCLUSION: Preserving anterior lens capsule in the operation is beneficial to the insertion of IOL, and the anterior segment is affected slightly, thus it is a promising method for treating cataract complicated with vitreous opacification.

Adult↗
PubMed1997

[Purification and properties of inulinase from Aspergillus niger].

The main component of inulinase was purified from fermentation broth of Aspergillus niger 319 to homogeneity by using ammonium sulfate fraction, ion-exchange chromatography on DEAE-cellulose column and Sephadex G-100 gel filtration. The specific activity was as 67 folds at the fermentation broth, and the yield was 25.5%. The inulinase, containing 13.92% of carbohydrate, was a monomer protein with a molecular weight of 28,000 Dalton; and its isoelectric point was pH 5.4. The optimal pH and temperature of the inulinase was pH 5.0 and 60 degrees C, respectively. The enzyme was strongly inhibited by heavy metal ions of Hg2+, Pb2+ and Cu2+. The optimal substrate for the enzyme was inulin and the product was only fructose, but it also had invertase activity with the I/S of 0.348. The Km and Vm of the inulinase was 6.25 mmol/L and 67.11 mumol.mg-1.min-1, respectively.

English Abstract↗
PubMed1997

[Effect of levodopa on visual evoked potential in amblyopia].

PURPOSE: To evaluate the efficacy of levodpa treatment for amblyopia. METHODS: The patients with amblyopin were given a single dose of levodopa, and the normal control group was established with the other normal eye in unilateral amblyopia. Their pattern visual evoked potential(PVEP) were tested before and after taking levodopa. RESULTS: After taking a single dose of levodopa, the PVEP in the normal eyes showed that the N1P1 amplitudes evoked by middle spatial frequency stimuli and the P1N2 amplitudes evoked by high spatial frequency stimuli increased, however, in the amblyopic eyes showed that the N1 latency evoked by low spatial frequency stimuli and P1 latency evoked by middle spatial frequency decreased. CONCLUSION: A single dose of levodopa administration can induce improvement of PVEP in the amblyopic eyes, and levodopa may be efficacious in the amblyopic therapy.

Adolescent↗