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Biomedical subjects

H Zhong

Publications and source records attributed to H Zhong.

At least 73 records · Page 4Linked to original sources
PubMed2000

Afferent input from rat slow skeletal muscle inhibits bioassayable growth hormone release.

The release of a bioassayable form of growth hormone (BGH), distinct from growth hormone as measured by immunoassay (IGH), from the rat pituitary into the blood is differentially regulated by afferent input from fast and slow skeletal muscles. Specifically, activation of low-threshold fast muscle afferents for 15 min increased plasma BGH by 217 and 295% and decreased pituitary BGH by 68 and 45% in male and female rats, respectively. In contrast, activation of slow muscle afferents inhibited BGH release, decreasing plasma BGH by approximately 60% and increasing pituitary BGH by 30-50% in male rats. Female rats from which food had been withheld for approximately 12 h had elevated basal plasma BGH levels, which then were decreased by 81% after slow muscle nerve stimulation. Plasma IGH concentrations were unchanged after any nerve stimulation condition. These results demonstrate that regulation of BGH release can be differentially mediated through low-threshold afferent inputs from fast or slow skeletal muscle. Furthermore, the results indicate that BGH responses are independent of gender or feeding status.

Afferent Pathways↗
PubMed2000

Molecular events implicated in brain tumor angiogenesis and invasion.

We have conducted studies designed to help elucidate the molecular mechanisms involved in brain tumor invasion and angiogenesis, which are critical in the growth of malignant tumors of the central nervous system. A variety of molecular factors have been implicated in these processes. Here we focus on three that are of particular importance in the progression of brain tumors. Angiopoietins are involved in the regulation of vascular development. Hypoxia inducible factor-1 is a transcription factor that up-regulates genes, including genes encoding vascular endothelial growth factor under hypoxic conditions. Focal adhesion kinase is associated with infiltration of tumor cells and angiogenesis.

Brain Neoplasms↗
PubMed2000

Activation of signal transducers and activators of transcription by alpha(1A)-adrenergic receptor stimulation in PC12 cells.

In PC12 cells stably expressing alpha(1A)-adrenergic receptors (ARs), norepinephrine (NE) activates several mitogen-activated protein kinase pathways and causes differentiation (). Using retroviral luciferase reporters, we found that NE also activated both signal transducers and activators of transcription (Stat) and gamma-interferon-activated sequence-mediated transcriptional responses, with maximal effects similar to those caused by interleukin-6 (IL-6). UTP and epidermal growth factor had no effect, whereas nerve growth factor caused a small Stat activation. Responses to NE were blocked by prazosin and depended on receptor density. Responses to NE were not blocked by inhibitors of mitogen-activated protein kinase kinase (PD98059), protein kinase C (GFX203290), Src (PP2), Jak2 (AG490), or the calcium chelator 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. The p38 mitogen-activated protein kinase inhibitors SB202190 and SB203580 blocked Stat activation by NE, the epidermal growth factor receptor inhibitor AG1478 caused a small inhibition, but the phosphoinositide 3 kinase inhibitor LY294002 potentiated both responses. Gel shifts confirmed formation of nuclear factors binding to both Stat and gamma-interferon-activated sequence consensus sequences in response to NE and IL-6. Immunoprecipitation experiments showed that IL-6 increased tyrosine phosphorylation of Stat1 and Stat3 in PC12 cells, whereas NE caused a sustained increase in tyrosine phosphorylation of Stat1. These results suggest that alpha(1A)-AR stimulation causes Stat-mediated transcriptional responses in PC12 cells that are not downstream of known second messenger or tyrosine kinase pathways.

Animals↗
PubMed2000

[Assessment of malaria DNA vaccines in mice and monkeys].

Cholera toxin B subunit is a good carrier protein and an effective adjuvant which can boost both cellular and humoral immunity. DNA fragments encoding B cell, Th cell and CTL epitopes of P. falciparum CS, MSA-1, MSA-2 and RESA antigens were cloned down-2 stream of cholera toxin B subunit gene in the same reading frame. High titer of anti-malaria epitopes antibodies and strong cellular immunogenicity were elicited after Balb/c mice were immunized three times with 100 micrograms recombinant plasmid DNA dissolved in 100 microliters PBS. A total of 120 vaccinees were challenged with mouse Plasmodium yoelli to investigate if cross protection existed. The protective efficacy was about 60%-80%. Four rhesus monkeys were challenged with 10(8) of P. cynomalgi, better results were obtained in the groups immunized with mixed plasmids including NANP, AWTE.

Animals↗
PubMed2000

[Induction of protective immune response in mice and rhesus monkeys by immunization with fusion protein of cholera toxin B subunit and multiples of Plasmodium falciparum].

Recombinant fusion protein of cholera toxin B subunit (CTB) and poly-valent protective epitopes of plasmodium falciparum was given to i.m. to C57BL/6j mice and rhesus monkeys three times. In rhesus monkeys, high level of antibodies for CTB (1:6400) and malaria epitopes (1:3200) amtobpdoes were elicited as well as the specific CTL activity for P. plasmodium. After the mice were challenged with sporozoites of P. yeolli, about 50% of them were protected from the patent infection. A blood-stage challenge with 10(8) of P. cynomolgi parasite were given to rhesus monkeys, which showed that two animals in control group were patent infection for at least 30 days, in contrast, the two animals immunized were recovered respectively at the day of 11 and 15 after challenges. The results suggested that cholera toxin acts as an effective adjuvent in the development of malaria vaccine.

Animals↗
PubMed2000

[Induction of protective immune responses in rhesus monkey by immunization with recombinant plasmids of polyvalent epitopes of Plasmodium falciparum using cholera toxin B as adjuvant].

The immunogenicity and protective efficacy of the DNA vaccine which include cholera toxin B subunit (CTB) and polyvalent protective epitopes of Plasmodium falciparum (awte gene) was assessed using rhesus monkeys as animal models. Recombinant plasmids of pCMV-CTB-AWTE were given to five rhesus monkeys three times with two weeks intervals by intramuscle (i.m.) route, immunization dose was 500 micrograms per plasmid per animal. High levels of anti-CTB and anti-malaria epitopes antibodies and P. falciparum epitope specific CTL activity were elicited. The vaccinated groups was challenged with 1.25 x 10(8) of P. cynomolgi parasites. All monkeys of the control group was patent for at least 34 days, the DNA vaccinated groups wasn't infected during the 60 days we detected. The cocktail DNA vaccine which contains multi-stage and multi-epitope antigen gene shows excellent immunogenicity and protective efficacy, the results also suggests that DNA vaccine plays an important role against malaria infection.

Animals↗
PubMed2000

Fiber size and myosin phenotypes of selected rhesus lower limb muscles after a 14-day spaceflight.

Muscle biopsies were taken from the rhesus (Macaca mulatta) soleus (Sol, a slow ankle extensor), medial gastrocnemius (MG, a fast ankle extensor), tibialis anterior (TA, a fast ankle flexor), and vastus lateralis (VL, a fast knee extensor) muscles in vivarium controls (n=5) before and after either a 14-day spaceflight (Bion 11, n=2) or a 14-day ground-based flight simulation (n=3). Myosin heavy chain (MHC) composition (gel electrophoresis), fiber type distribution (immunohistochemistry), and fiber size were determined. Although there were no significant changes, each muscle showed trends towards adaptation.

Animals↗
PubMed2000

[Expression and prognostic significance of multidrug resistance associated protein (MRP) gene in non-small cell lung cancer by in situ hybridization].

OBJECTIVE: To study the effect of MRP gene overexpression on prognosis of patients with non-small cell lung cancer (NSCLC). METHODS: Paraffin-embedded tissues from 47 cases of NSCLC who had undergone radical tumor resection were examined for expression of MRP gene mRNA by in situ hybridization using labelled digoxigenin probes combined with immunohistochemistry. All the patients were retrospectively followed-up. RESULTS: All of the 47 lung cancer specimens were found to have overexpression of MRP mRNA. It was significantly correlated with patients' survival period, response to chemotherapy, recurrence and mestastases after surgery, but was not correlated with histology, tumor size, node status, TNM stage, degree of differentiation, age and sex. CONCLUSION: Overexpression of MRP gene is a marker of prognostic significance in patients with NSCLC.

Adult↗
PubMed2000

[Measurement and evaluation of visual index in VDT operators under Multi-user system].

OBJECTIVE: To evaluate the visual function of the visual display terminal (VDT) operators under the Multi-user system. METHOD: Subjective symptoms of the VDT operators under the Multi-user system were measured before and after work in the field study. Visual indices were measured at 8:15, 9:15, 10:15, 11:15, or 12:15 a.m. RESULT: No discomfort symptom was observed during the working time, and Longitudino-Kinetic visual acuity, and Critical flicker frequency didn't decrease. Refraction showed no significant decrease as compared with that at 8:15 except that of right eye measured at 12:15. CONCLUSION: The Visual function of the VDT operators remained good in the Multi-user's system.

Adolescent↗
PubMed2000

Mechanical properties and fiber type composition of chronically inactive muscles.

A role for neuromuscular activity in the maintenance of skeletal muscle properties has been well established. However, the role of activity-independent factors is more difficult to evaluate. We have used the spinal cord isolation model to study the effects of chronic inactivity on the mechanical properties of the hindlimb musculature in cats and rats. This model maintains the connectivity between the motoneurons and the muscle fibers they innervate, but the muscle unit is electrically "silent". Consequently, the measured muscle properties are activity-independent and thus the advantage of using this model is that it provides a baseline level (zero activity) from which regulatory factors that affect muscle cell homeostasis can be defined. In the present paper, we will present a brief review of our findings using the spinal cord isolation model related to muscle mechanical and fiber type properties.

Animals↗
PubMed1999

Activation of tyrosine kinases by alpha1A-adrenergic and growth factor receptors in transfected PC12 cells.

We compared the role of tyrosine kinases in alpha(1A)-adrenergic receptor (AR) and growth factor receptor stimulation of mitogen-activated protein kinase pathways in PC12 cells. Norepinephrine (NE) (noradrenaline), epidermal growth factor (EGF) and nerve growth factor (NGF) caused different patterns of tyrosine phosphorylation in PC12 cells stably expressing alpha(1A)-ARs. NE increased tyrosine phosphorylation of focal adhesion-related kinase Pyk2 and a 70 kDa protein, probably paxillin, whereas EGF strongly stimulated tyrosine phosphorylation of the EGF receptor and cytokine-activated kinase Jak2. The EGF receptor inhibitor AG1478 inhibited activation of extracellular signal-regulated kinases (ERKs) by EGF but not by NE. EGF and NGF strongly activated tyrosine phosphorylation of Shc and caused association of Src-homology collagen (Shc) with growth-factor-receptor-bound protein 2 (Grb2); however, neither NE nor UTP caused substantial activation of the Shc/Grb2 pathway. NE, UTP, EGF and NGF all increased tyrosine phosphorylation of Src, and this was inhibited by the Src inhibitor PP2. However, PP2 inhibited ERK activation in response to NE and UTP, but not in response to EGF or NGF. PP2 also completely blocked NE-induced PC12 cell differentiation, but had no measurable effect on NGF-induced differentiation. These studies show that activation of mitogen-activated protein kinase pathways by G-protein-coupled receptors and tyrosine kinase receptors proceed through distinct molecular pathways in PC12 cells, and support an obligatory role for Src activation in mitogenic responses to alpha(1A)-ARs in these cells.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Overexpression of hypoxia-inducible factor 1alpha in common human cancers and their metastases.

Neovascularization and increased glycolysis, two universal characteristics of solid tumors, represent adaptations to a hypoxic microenvironment that are correlated with tumor invasion, metastasis, and lethality. Hypoxia-inducible factor 1 (HIF-1) activates transcription of genes encoding glucose transporters, glycolytic enzymes, and vascular endothelial growth factor. HIF-1 transcriptional activity is determined by regulated expression of the HIF-1alpha subunit. In this study, HIF-1alpha expression was analyzed by immunohistochemistry in 179 tumor specimens. HIF-1alpha was overexpressed in 13 of 19 tumor types compared with the respective normal tissues, including colon, breast, gastric, lung, skin, ovarian, pancreatic, prostate, and renal carcinomas. HIF-1alpha expression was correlated with aberrant p53 accumulation and cell proliferation. Preneoplastic lesions in breast, colon, and prostate overexpressed HIF-1alpha, whereas benign tumors in breast and uterus did not. HIF-1alpha overexpression was detected in only 29% of primary breast cancers but in 69% of breast cancer metastases. In brain tumors, HIF-1alpha immunohistochemistry demarcated areas of angiogenesis. These results provide the first clinical data indicating that HIF-1alpha may play an important role in human cancer progression.

Animals↗
PubMed1999

Molecular determinants of the modulation of cyclic nucleotide-activated channels by calmodulin.

The action of calmodulin (CaM) on target proteins is important for a variety of cellular functions. We demonstrate here, however, that the presence of a CaM-binding site on a protein does not necessarily imply a functional effect. The alpha-subunit of the cGMP-gated cation channel of human retinal cones has a CaM-binding site on its cytoplasmic N-terminal region, but the homomeric channel that it forms is not functionally modulated by CaM. Mutational analysis based on comparison to the highly homologous olfactory cyclic nucleotide-gated channel alpha-subunit, which does form a CaM-modulated channel, indicates that residues downstream of the CaM-binding domain on these channels are also important for CaM to have an effect. These findings suggest that a CaM-binding site and complementary structural features in a protein probably evolve independently, and an effect caused by CaM occurs only in the presence of both elements. More generally, the same may be true for other recognized binding sites on proteins for modulators or activators, so that a demonstrated physical interaction does not necessarily imply functional consequence.

Amino Acid Sequence↗
PubMed1999

Alpha1-adrenoceptor subtypes.

Alpha1-adrenoceptors are one of three subfamilies of receptors (alpha1, alpha2, beta) mediating responses to adrenaline and noradrenaline. Three alpha1-adrenoceptor subtypes are known (alpha1A, alpha1B, alpha1D) which are all members of the G protein coupled receptor family, and splice variants have been reported in the C-terminus of the alpha1A. They are expressed in many tissues, particularly smooth muscle where they mediate contraction. Certain subtype-selective agonists and antagonists are now available, and alpha1A-adrenoceptor selective antagonists are used to treat benign prostatic hypertrophy. All subtypes activate phospholipase C through the G(q/11) family of G proteins, release stored Ca2+, and activate protein kinase C, although with significant differences in coupling efficiency (alpha1A > alpha1B > alpha1D). Other second messenger pathways are also activated by these receptors, including Ca2+ influx, arachidonic acid release, and phospholipase D. Alpha1-adrenoceptors also activate mitogen-activated protein kinase pathways in many cells, and some of these responses are independent of Ca2+ and protein kinase C but involve small G proteins and tyrosine kinases. Direct interactions of alpha1-adrenoceptors with proteins other than G proteins have not yet been reported, however there is a consensus binding motif for the immediate early gene Homer in the C-terminal tail of the alpha1D subtype. Current research is focused on discovering new subtype-selective drugs, identifying non-traditional signaling pathways activated by these receptors, clarifying how multiple signals are integrated, and identifying proteins interacting directly with the receptors to influence their functions.

Adrenergic alpha-Agonists↗
PubMed1999

Direct comparison of GAPDH, beta-actin, cyclophilin, and 28S rRNA as internal standards for quantifying RNA levels under hypoxia.

The appropriate choice of an internal standard is critical for quantitative RNA analyses. As housekeeping genes, GAPDH, beta-actin, cyclophilin, and 28S rRNA are commonly employed as RNA internal standards with the assumption that their expression levels remain relatively constant in different experimental conditions. We tested this assumption under hypoxia (1% O2, 24 hours) compared to normoxia (20% O2, 24 hours) and compared RNA levels of these 4 housekeeping genes head to head using ribonuclease protection assays. Four biologically diverse cell lines with respect to clonal origin, neoplastic transformation, and growth rates were used in the comparison. Expression levels of 28S rRNA were constant, independent of O2 tension, but levels of GAPDH, beta-actin, and cyclophilin varied widely with hypoxia. In particular, GAPDH mRNA expression was increased by 21.2-75.1% under hypoxic conditions. Increased GAPDH transcription in hypoxia was correlated in the cancer cell lines with upregulation of the transcription factor Hypoxia Inducible Factor-1alpha protein levels in identical experimental conditions. These results suggest that 28S rRNA is a reliable internal control for comparative analyses of transcription under hypoxia; GAPDH appears particularly unfavorable for this purpose either in hypoxia or other experimental conditions that upregulate HIF-1alpha.

Actins↗
PubMed1999

Electrophysiological characterization of 5-HT receptors on rat petrosal neurons in dissociated cell culture.

The petrosal ganglion supplies chemoafferent pathways via the glossopharyngeal (IXth) nerve to peripheral targets which release various neurotransmitters including serotonin (5-HT). Here, we combined rapid 5-HT application with patch clamp, whole-cell recording to investigate whether 5-HT receptors are expressed on isolated petrosal neurons (PN), cultured from 7-12 day-old rat pups. In responsive cells, the dominant effect of 5-HT was a rapid depolarization associated with a conductance increase in approximately 43% of the neurons (53/123); however, in a minority population ( approximately 6%; 8/123), 5-HT caused membrane depolarization associated with a conductance decrease. In the former group, 5-HT produced a transient inward current (I5-HT) in neurons voltage-clamped near the resting potential ( approximately -60 mV); the effect was mimicked by the 5-HT3 receptor-specific agonist, 2-methyl-5-HT, suggesting it was mediated by 5-HT3 receptors. Further, I5-HT was selectively inhibited by the 5-HT3 receptor-specific antagonist MDL72222 (1-10 microM), but was unaffected by either 5-HT1/5-HT2 receptor antagonist, spiperone, or by 5-HT2 receptor-specific antagonist, ketanserin (50-100 microM). I5-HT displayed moderate inward rectification and had a mean reversal potential (+/-S.E.M.) of -4.3+/-6.6 mV (n=6). Application of 5-HT (dose range: 0.1-100 microM) produced a dose-response curve that was fitted by the Hill equation with EC50= approximately 3.4 microM and Hill coefficient= approximately 1.6 (n=8). The activation phase of I5-HT (10 microM 5-HT at -60 mV) was well fitted by a single exponential with mean (+/-S.E.M.) time constant of 45+/-30 ms (n=6). The desensitization phase of I5-HT was best fitted by a single exponential with mean (+/-S.E.M.) time constant of 660+/-167 ms (n=6). Fluctuation analysis yielded an apparent mean single-channel conductance (+/-S.E.M) of 2.7+/-1.5 pS (n=4) at -60 mV. In the minority ( approximately 6%) population of neurons which responded to 5-HT with a conductance decrease, the depolarization was blocked by the 5-HT2 receptor antagonist, ketanserin (50 microM). Taken together, these results suggest that 5-HT3 receptors are the major subtype expressed by rat petrosal neurons, and therefore are candidates for facilitating chemoafferent excitation in response to 5-HT released from peripheral targets.

Animals↗