Biomedical subjects

H Guan

Publications and source records attributed to H Guan.

At least 55 records · Page 3Linked to original sources

PubMed1999

CT reconstruction by using the MLS-ART technique and the KCD imaging system--I: low-energy X-ray studies.

We investigated the use of the kinestatic charge detector (KCD) combined with the multilevel scheme algebraic reconstruction technique (MLS-ART) for X-ray computer tomography (CT) reconstruction. The KCD offers excellent detective quantum efficiency and contrast resolution. These characteristics are especially helpful for applications in which a limited number of projections are used. In addition, the MLS-ART algorithm offers better contrast resolution than does the conventional convolution backprojection (CBP) technique when the number of projections is limited. Here we present images of a Rando-head phantom that was reconstructed by using the KCD and MLS-ART. We also present, for comparison, the images reconstructed by using the CBP technique. The combination of MLS-ART and the KCD yielded satisfactory images after just one or two iterations.

Algorithms↗

PubMed1999

Contribution of cytochrome P-450 4A1 and 4A2 to vascular 20-hydroxyeicosatetraenoic acid synthesis in rat kidneys.

20-Hydroxyeicosatetraenoic acids (20-HETE), a biologically active cytochrome P-450 (CYP) metabolite of arachidonic acid in the rat kidney, can be catalyzed by CYP4A isoforms including CYP4A1, CYP4A2, and CYP4A3. To determine the contribution of CYP4A isoforms to renal 20-HETE synthesis, specific antisense oligonucleotides (ODNs) were developed, and their specificity was examined in vitro in Sf9 cells expressing CYP4A isoforms and in vivo in Sprague-Dawley rats. Administration of CYP4A2 antisense ODNs (167 nmol. kg body wt-1. day-1 iv for 5 days) decreased vascular 20-HETE synthesis by 48% with no effect on tubular synthesis, whereas administration of CYP4A1 antisense ODNs inhibited vascular and tubular 20-HETE synthesis by 52 and 40%, respectively. RT-PCR of microdissected renal microvessel RNA indicated the presence of CYP4A1, CYP4A2, and CYP4A3 mRNAs, and a CYP4A1-immunoreactive protein was detected by Western analysis of microvessel homogenates. Blood pressure measurements revealed a reduction of 17 +/- 6 and 16 +/- 4 mmHg in groups receiving CYP4A1 and CYP4A2 antisense ODNs, respectively. These studies implicate CYP4A1 as a major 20-HETE synthesizing activity in the rat kidney and further document the feasibility of using antisense ODNs to specifically inhibit 20-HETE synthesis and thereby investigate its role in the regulation of renal function and blood pressure.

Animals↗

PubMed1999

Subclavian steal syndrome: report of 28 cases.

OBJECTIVE: To study the experience in the treatment of subclavian steal syndrome (SSS) and the relation between SSS and the damage of brain. METHODS: In 28 patients with SSS, 23 were operated on. They complained of vertigo, TIA, and claudication of arms. One patient suffered from severe stem ischemia spasm. All the patients were subjected to subtraction angiography. Fifteen of them showed retrograde flow in the vertebral arteries. Transcranial Doppler revealed retrograde blood flow in 8 patients. Single photon emission tomography showed inadequate blood supply to the brain with affected subclavian arteries in 4 patients. Carotid-subclavian arterial bypass was performed in 16 patients, axilloauxillary bypass in 3, PTA in 1, and aorta-carotid graft bypass in 3. RESULTS: 13 patients (13/23) had their cerebrovascular symptoms relieved. Transcranial Doppler and emission tomography after operation showed nothing abnormal. CONCLUSION: SSS is harmful and the patients should be closely monitored by means of transcranial Doppler and emission tomography.

Adult↗

PubMed1999

[Responses of normal rat kidney to different ischemic ways].

OBJECTIVE: To evaluate the effects of different ischemic ways on rat kidneys. METHODS: Male Wistar rat kidneys were divided into sham operation (group A), continuous ischemia (group B), intermittent ischemia (group C), ischemic preconditioning (group D), and delayed effect of ischemic preconditioning group (group E). The functional and morphologic changes and levels of MDA of the kidneys which suffered from different ischemia were assessed. RESULTS: The functional indexes of the group C were similar to that of the sham group. In the group B, D and E, the rats showed acute renal failure. Morphological findings showed that the groups B, D and E had severe tubular necrosis (+ + + - + + + +) 24 hours after operation. The group C showed light tubular necrosis (+). 30 minutes after reperfusion, the level of MDA was significantly lower in the group C than in the groups B, D and E (P < 0.01). CONCLUSIONS: In a given ischemic period, the injury effect of intermittent ischemia-reperfusion was much lower than that of continuous ischemia-reperfusion. Experimentally, ischemic preconditioning did not have protective effect on rat kidneys, including "classic protection" and "protection of second window". Intermittent ischemia-reperfusion did not increase OFR and lipid peroxidation injury.

Animals↗

PubMed1999

[An experimental investigation of inhibition of interferon on lens epithelial cell growth in vitro].

OBJECTIVE: To investigate the inhibition of alpha-interferon (alpha-IFN) and gamma-interferon (gamma-IFN) on rabbit lens epithelial cell (RLEC) proliferation in vitro and their effective concentrations. METHODS: The second and third passage of RLEC were used for assay. Various concentrations of alpha-IFN or gamma-IFN were added into the culture medium and RLECs were exposed to these drugs. After 24 and 72 hours, the inhibition of RLECs was determined by counting the RLEC numbers on a counting plate and MTT colorimetric assay. RESULTS: Alpha-IFN and gamma-IFN may reduce the proliferation of RLECs at the concentration of 10(3) - 10(4) IU/ml. The inhibition of gamma-IFN was a little stronger than that of alpha-IFN. CONCLUSION: The experiment provides a scientific basis for selection of drugs to prevent after cataract.

Animals↗

PubMed1999

[Investigation of the diplopia after intraocular lens implantation].

OBJECTIVE: To investigate the pathogenesis, mechanism and prognosis of diplopia after cataract extraction with intraocular lens implantation (IOL). METHODS: Besides routine ocular examinations, refraction, ocular position, ocular movement, fusional function and image of diplopia were examined on all the patients. Forced duction was examined on partial patients. RESULTS: Among 24 cases with diplopia after IOL implantation, there were 19 cases of binocular diplopia and 5 cases of monocular diplopia. Of the binocular diplopia, there were 17 cases of strabismic diplopia and 2 cases of diplopia due to central fusional impairment. Of the cases with monocular diplopia, there were 4 cases resulted from operative complication and one case with congenital iridocoloboma. CONCLUSIONS: The pathogenesis of strabismic diplopia resulted from dysfunction of ocular movement is unknown. Most of the patients can obtain binocular vision by early active treatment. Monocular diplopia is partly resulted from operative complication.

Adult↗

PubMed1998

Purification and characterization of maize starch synthase I and its truncated forms.

Comparison of the protein sequences deduced from the cDNAs of maize granule-bound starch synthase, Escherichia coli glycogen synthase, and maize starch synthase I (SSI) reveals that maize SSI contains an N-terminal extension of 93 amino acids. In order to study the properties of maize SSI and to understand the functions of the maize SSI N-terminal extension, the gene coding for full-length SSI (SSI-1) and genes coding for N-terminally truncated SSI (SSI-2 and SSI-3) were individually expressed in E. coli. Here we describe for the first time the purification of a higher plant starch synthase to apparent homogeneity. Its kinetic properties were therefore studied in the absence of interfering amylolytic enzymes. The specific activities of the purified SSI-1, SSI-2, and SSI-3 were 22.5, 33.4, and 26.3 micromol Glc/min/mg of protein, respectively, which are eight times higher than those of partially purified SSI from developing maize endosperm. The full-length recombinant enzyme SSI-1 exhibited properties similar to those of the enzyme from maize endosperm. As observed for native maize enzyme, recombinant SSI-1 exhibited "unprimed" activity without added primer in the presence of 0.5 M citrate. Our results have clearly indicated that the catalytic center of SSI is not located in its N-terminal extension. However, N-terminal truncation decreased the enzyme affinity for amylopectin, with the Km for amylopectin of the truncated SSI-3 being about 60-90% higher than that of the full-length SSI-1. These results suggest that the N-terminal extension in SSI may not be directly involved in enzyme catalysis, but may instead regulate the enzyme binding of alpha-glucans. Additionally, the N-terminal extension may play a role in determining the localization of SSI to specific portions of the starch granule or it may regulate its interactions with other enzymes involved in starch synthesis.

Amino Acid Sequence↗

PubMed1998

Isolation and characterization of the zSSIIa and zSSIIb starch synthase cDNA clones from maize endosperm.

Two starch synthase clones, zSSIIa and zSSIIb, were isolated from a cDNA library constructed from W64A maize endosperm. zSSIIa and zSSIIb are 3124 and 2480 bp in length, and contain open reading frames of 732 and 698 amino acid residues, respectively. The deduced amino acid sequences of the two clones share 58.1% sequence identity. Amino acid sequence identity between the zSSIIa and zSSIIb clones and the starch synthase II clones of potato and pea ranges between 45 to 51%. The predicted amino acid sequence from each SSII cDNA contains the KXGGL consensus motif at the putative ADP-Glc binding site. Both clones also contain putative transit peptides followed by the VRAA(E)A motif, the consensus cleavage site located at the C-terminus of chloroplast transit peptides. The identity of the zSSIIa and zSSIIb clones as starch synthases was confirmed by expression of enzyme activity in Escherichia coli. Genomic DNA blot analysis revealed two copies of zSSIIa and a single copy of zSSIIb. zSSIIa was expressed predominantly in the endosperm, while transcripts for zSSIIb were detected mainly in the leaf at low abundance. These findings establish that the zSSIIa and zSSIIb genes are characteristically distinct from genes encoding granule-bound starch synthase I (Waxy protein) and starch synthase I.

Amino Acid Sequence↗

PubMed1998

Molecular cloning of starch synthase I from maize (W64) endosperm and expression in Escherichia coli.

A full length cDNA clone encoding a starch synthase (zSS) from maize endosperm (inbred line W64) was isolated and characterized. The cDNA clone (Ss1) is 2907 bp in length and contains an open reading frame of 1866 bp corresponding to a polypeptide of 622 amino acid residues including a transit peptide of 39 amino acids. The Ss1 cDNA clone was identified as zSSI by its direct alignment with sequences to: (i) the N-terminus obtained from the granule-associated form of the zSSI polypeptide, (ii) four internal peptide fragments obtained from the granule-associated form of the zSSI protein, and (iii) one internal fragment from the soluble form of the zSSI protein. The deduced amino acid sequence of Ss1 shares 75.7% sequence identity with rice soluble Ss and contains the highly conserved KSGGLGDV putative ADP-Glc binding site. Moreover, Ss1 exhibited significant activity when expressed in E. coli and the expressed protein is recognized by the antibody raised against the granule associated zSSI protein. Ss1 transcripts were detected in endosperm beginning at 15 days after pollination, but were not found in embryo, leaf or root. Maize contains a single copy of the Ss1 gene, which maps close to the Waxy locus of chromosome 9.

Amino Acid Sequence↗

PubMed1998

Feasibility of megavoltage portal CT using an electronic portal imaging device (EPID) and a multi-level scheme algebraic reconstruction technique (MLS-ART).

Although electronic portal imaging devices (EPIDs) are efficient tools for radiation therapy verification, they only provide images of overlapped anatomic structures. We investigated using a fluorescent screen/CCD-based EPID, coupled with a novel multi-level scheme algebraic reconstruction technique (MLS-ART), for a feasibility study of portal computed tomography (CT) reconstructions. The CT images might be useful for radiation treatment planning and verification. We used an EPID, set it to work at the linear dynamic range and collimated 6 MV photons from a linear accelerator to a slit beam of 1 cm wide and 25 cm long. We performed scans under a total of approximately 200 monitor units (MUs) for several phantoms in which we varied the number of projections and MUs per projection. The reconstructed images demonstrated that using the new MLS-ART technique megavoltage portal CT with a total of 200 MUs can achieve a contrast detectibility of approximately 2.5% (object size 5 mm x 5 mm) and a spatial resolution of 2.5 mm.

Algorithms↗

PubMed1998

Combining various projection access schemes with the algebraic reconstruction technique for low-contrast detection in computed tomography.

We separately applied three different projection access orders (the multilevel scheme (MLS), the sequence access scheme (SAS) and the random permutation scheme (RPS)) to the algebraic reconstruction technique (ART) in an attempt to improve low-contrast object detection in computed tomography (CT). We used both simulated (from various numbers of projections of low-contrast and contrast detail phantoms) and actual data (from megavoltage portal CT) during our study. When coupled with ART, SAS and RPS led to poor low-contrast detection and required multiple iterations for convergence. In contrast, one-iteration MLS yielded the most uniform reconstructions with the highest contrast-to-noise ratios. Therefore, MLS-ART provides the highest dose efficiency of all current reconstruction techniques for imaging low-contrast objects from a small number of projections.

Algorithms↗

PubMed1998

[Mechanism and treatment of malignant glaucoma].

OBJECTIVE: To investigate the possible mechanism and the treatment of malignant glaucoma. METHODS: The onsets of 34 eyes in 23 cases of malignant glaucoma were analyzed and the patients were treated with medicine, lens extraction, vitrectomy, anterior chamber plastic operation or combined procedures. RESULTS: The effective rate in medical treatment was 35.3%. Combined procedures (lens extraction associated with vitrectomy and anterior chamber plastic operation) were all successful. CONCLUSIONS: The possible mechanism of malignant glaucoma may be concerned with the formation of membranoid substance among vitreous face, ciliary body and posterior iris. Those who failured to medical therapy and were treated with combined operations may have good effect.

Adolescent↗

PubMed1998

[Expression of endothelin-1 and nitric oxide synthase mRNA in gastric mucosa of rats with cirrhosis and portal hypertensive gastropathy after disconnective operations].

OBJECTIVE: To investigate expression of endothelin-1 (ET-1) and nitric oxide synthase(NOS) gene in gastric mucosa in the rats with cirrhosis and portal hypertensive gastropathy (PHG) after disconnective operation. METHODS: Wistar rats were divided into three groups: normal (n = 12), cirrhosis and PHG (n = 12), and post-disconnective (n = 12). The rat models were induced by intraperitonal injection of thiocetamide for 16 weeks. The third group rats were reared for 3 months after the operations. ET-1 and NOS mRNA from the gastric mucosa of the three groups were measured quantitatively by Dot blot technique. RESULTS: ET-1 mRNA decreased in the PHG rats as compared to the nomal rats (P < 0.01). Further decrease was found in the post-disconnective rats (P < 0.01). NOS mRNA increased slightly in the PHG rats (P > 0.05) and increased obviously in the post-disconnective rats (P < 0.01). CONCLUSIONS: After the cirrhosis and PHG rats were subjected to disconnective operations, ET-1 was insufficient and NOS was too much in the gastric mucosa. These resulted in the gastric mucosal vessel dilatation. The imbalance of ET/NO proportion could partly attribute to rebleeding after disconnection.

Animals↗

PubMed1997

Comparing the properties of Escherichia coli branching enzyme and maize branching enzyme.

Escherichia coli glycogen branching enzyme (GBE) and maize starch branching enzymes I (SBEI) and II (SBEII) were expressed in E. coli and purified. E. coli GBE branched amylose at a higher rate than did SBEII, but branched amylose at a lower rate than did SBEI. Similar to SBEI, GBE branched amylopectin at a lower rate than did SBEII. High-performance anion-exchange chromatography analysis of the branched products produced by BE revealed the minimum chain length (cl) required for branching. While GBE and SBEII showed the same minimum cl [degree of polymerization (dp) 12] required for branching, SBEI had a slightly higher minimum cl (dp 16) requirement for branching. The major differences between GBE and SBE are their specificities in terms of the size of chains transferred. In comparison with SBE, GBE had a much narrower size range of chains transferred and transferred mainly shorter chains. While SBEI and SBEII produced a large number of chains ranging from dp 6 to over dp 30, GBE predominantly transferred chains ranging from dp 5 to 16 and produced only a very small number of long chains with dp greater than 20. Although it has been reported that SBEI and SBEII preferentially transfer longer and shorter chains, respectively (1), this study further defines the differences between SBEI and SBEII in the size of chains transferred. SBEI predominantly transfers longer chains with dp greater than 10, while producing few shorter chains with dp 3 to 5. In contrast, SBEII preferentially transfers smaller chains with dp 3 to 9, with the most abundant chains being dp 6 and 7. The significance of minimum chain-length requirement by SBE is discussed in setting the invariant size of amylopectin cluster size (9 nm).

1,4-alpha-Glucan Branching Enzyme↗

PubMed1997

Experimental study on modified treatment and endothelialization of bovine pericardial valves.

The purpose of this study were to confirm whether the modified treatment with L-glutamic acid could attenuate the calcification of the GA-fixed valves and improve its biocompatibility. Pericardial valves were routinely treated with GA and valves were treated with GA and 8% L-glutamic acid. The valves treated with these methods were implanted subcutaneously in rats. Calcium deposits of the valves collected at the 7th, 21st, 60th, 90th day were assessed by atomic absorption spectroscopy, and the pathologic changes were examined by light and electron microscopy. Cultured endothelial cells (ECs) were seeded onto the valves. The cell counts were determined at the 1st, 4th, 7th, 10th day after seeding. PGI2 in culture medium was tested at the 10th day. Transmission and scanning electron microscopy were used to observe the growth of ECs on the valves. Results showed that subsequent treatment with L-glutamic acid could significantly mitigate calcification of bovine pericardial valves as compared with simple GA-fixed valves (P < 0.01). ECs seeded on the GA treated valves died within 4 days. On the valves treated by modified method, ECs could proliferate and release PGI2. It is concluded that treatment with L-glutamic acid can markedly inhibit the calcification and improve the biocompatibility of bioprosthetical valves.

Animals↗

PubMed1997

Contribution of nitric oxide to the acute antihypertensive effect of blockers of AT1 angiotensin receptors in spontaneously hypertensive rats.

The acute vasodepressor effect of AT1 angiotensin receptor blockers losartan and CL329167 was compared in spontaneously hypertensive rats (SHR) pretreated and not pretreated with NG-monomethyl-L-arginine (LNMMA; 15 mg/kg i.v. bolus plus infusion at 10 mg/kg/h), an inhibitor of nitric oxide (NO) synthesis. The antihypertensive effect of losartan (30 mg/kg, i.v.) in SHR pretreated with LNMMA (-13 +/- 4 mmHg) was greatly diminished (P < 0.01) relative to the antihypertensive effect of losartan in SHR not pretreated with LNMMA (-44 +/- 8 mmHg). Similarly, the antihypertensive effect of CL329167 (5 mg/kg, i.v.) in SHR pretreated with LNMMA (-12 +/- 3 mmHg) was surpassed (P < 0.01) by the antihypertensive effect in SHR not pretreated with LNMMA. (-41 +/- 4 mmHg). However, pretreatment of SHR with LNMMA did not minimize the vasodepressor effect of prazosin, isoproterenol or sodium nitroprusside. The impairment in vasodepressor responsiveness to losartan in rats pretreated with LNMMA was not demonstrable in rats concurrently receiving sodium nitroprusside to correct for the loss of endogenous NO, or atrial natriuretic peptide which also increases vascular cGMP. These data suggest that a mechanism mediated by NO and/or cGMP is necessary for the full expression of the acute antihypertensive effect of AT1 angiotensin receptor blockers in SHR.

Angiotensin Receptor Antagonists↗

PubMed1997

[Effect of chicken bile on heart and blood pressure in animals].

In this paper, the effect of chicken bile on heart and blood pressure in animals was studied. The result shows that chicken bile(50 mg/kg, i.v.) can significantly reduce the normal blood pressure and hypertension induced by ephedrine in white rats. Chicken bile(1000 ppm) markedly inhibits myocardial contractive force, frequency and cardiac output of the isolated frog heart. But no influence was observed on the ECG in rabbits after administration of the bile (50 mg/kg, i.v.).

Animals↗

PubMed1997

RNA promoters located on (-)-strands of a subviral RNA associated with turnip crinkle virus.

Satellite (sat-) RNA C, one of the nonessential subviral RNAs of turnip crinkle virus (TCV), is dependent on the TCV-encoded RNA-dependent RNA polymerase (RdRp) for its replication. Earlier work showed that a stem-loop structure at the 3' end of (+)-strand sat-RNA C is required for synthesis of (-)-strands in vitro using a partially purified, template-specific TCV RdRp (Song C, Simon AE, 1995, J Mol Biol 254:6-14). Cis-sequences on (-)-strands of sat-RNA C that can serve as separate promoters in vitro have now been defined. Two promoter sequences are located on (-)-strand sat-RNA C, one comprising 11 bases located near the 3' end, and the other consisting of 14 bases located 41 bases from the 5' end. Both promoter sequences contain multiple consecutive C residues followed by multiple consecutive purines and have no obvious secondary structure, suggesting that, along with hairpin structures, specific primary sequences can be recognized by the TCV RdRp. The 3'-proximal promoter sequence directed synthesis from the 3' terminus using (-)-strand templates with the natural sat-RNA 3' end (AUCCC-3'). When plasmid-derived bases were present at the 3' ends of the templates, both promoter sequences could direct the RdRp to initiate transcription internally at the multiple consecutive C residues within the promoters. This result suggests that multiple consecutive C residues are important for transcription initiation and that natural 3'-end sequences, when located at 3' termini, help the RdRp to initiate at the 3' end of the molecule.

Carmovirus↗