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H Guan

Publications and source records attributed to H Guan.

At least 73 records · Page 4Linked to original sources
PubMed1996

Analysis of the active center of branching enzyme II from maize endosperm.

Analysis of the primary structure of mBEII, with those of other branching and amylolytic enzymes as reference, identifies four highly conserved regions which may be involved in substrate binding and in catalysis. When one of the amino acid residues corresponding to the putative catalytic sites of mBEII, i.e., Asp-386, Glu-441, and Asp-509, was replaced, activity disappeared. These putative catalytic residues are located in three different regions (regions 2-4) of the four highly conserved regions (regions 1-4) which exist in the primary structure of most starch hydrolases and related enzymes, including branching enzymes. Region 3, which contains Glu-441 as one of the putative catalytic residues, was located downstream of the carboxyl-terminal position previously reported. The importance of the carboxyl amino acid residues was also demonstrated by chemical modification of the branching enzyme protein using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1996

Computed tomography using algebraic reconstruction techniques (ARTs) with different projection access schemes: a comparison study under practical situations.

In a previous report we presented a novel ART technique with the projections arranged and accessed in a multilevel scheme (MLS) for efficient algebraic image reconstruction, but whether the scheme is still superior in real situations where the data are noisy is unknown. In this paper, we make a detailed comparison between MLS and the other two conventional projection access orderings in ART: the random permutation scheme (RPS) and the sequential access scheme (SAS). By simulating reconstructions of a human head using different sizes of detector, taking different numbers of projections, each measurement under a different number of photons, a full mapping of the reconstruction accuracy measured by correlation coefficient for the three schemes has been made. Test results demonstrate that one-iteration MLS produces the best reconstruction in many situations. It outperforms one-iteration RPS when the noise level is low. SAS in many cases can never attain the image quality of one-iteration MLS, even with many more iterations. A convergence test using different initial guesses also demonstrates that MLS has less initial dependence. In the Fourier domain, it also represents an efficient and fast implementation of the Fourier slice theorem.

Adult↗
PubMed1996

Nitric oxide and the depressor response to angiotensin blockade in hypertension.

We investigated the contribution of nitric oxide to the short-term blood pressure reduction caused by interruption of the renin-angiotensin system in angiotensin-dependent hypertension. The blood pressure of rats made hypertensive by coarctation of the aorta between the renal arteries at their origin fell after administration of the angiotensin-converting enzyme inhibitor ramiprilat (2 mg/kg IV; -75 +/- 5 mm Hg) or the angiotensin II antagonist losartan (30 mg/kg IV; -79 +/- 6 mm Hg). But the antihypertensive effect of these agents was attenuated in rats pretreated with NG-nitro-L-arginine methyl ester (10 mg/kg IV) to inhibit nitric oxide synthesis (ramiprilat, -23 +/- 7 mm Hg; losartan, -37 +/- 5 mm Hg). In rats made hypertensive by long-term infusion of angiotensin II (60 ng/min IV, 6 to 7 days), the vasodepressor response to discontinuation of the angiotensin II infusion also was attenuated by pretreatment with the nitric oxide synthesis inhibitor (-52 +/- 7 versus -31 +/- 7 mm Hg); this attenuation was not demonstrable in rats receiving sodium nitroprusside (1 microgram.kg-1.min-1 IV) to replace the loss of endogenous nitric oxide (-72 +/- 9 mm Hg). Pretreatment with NG-nitro-L-arginine methyl ester did not interfere with the vasodepressor effect of sodium nitroprusside or prazosin in rats with aortic coarctation-induced hypertension or with the blood pressure reduction caused by discontinuation of an infusion of phenylephrine in rats made hypertensive by long-term administration of this drug. These data suggest a contribution of nitric oxide to the blood pressure reduction caused by interruption of the renin-angiotensin system in models of established angiotensin-dependent hypertension.

Angiotensin II↗
PubMed1996

The cloning, sequence analysis, and expression in E. coli of coat protein gene of grapevine fanleaf virus Gh.

Fragments of 5' end and 3' end of the coat protein gene of a Chinese strain grapevine fanleaf virus (GFLV-Gh) were separately amplified through RT-PCR. The two products were cloned and ligated into a complete full-length coat protein gene via an inherent BgIII restriction site. The entire gene contains 1512 nucleotides which encode a 504 amino acids coat protein, molecular weight approximately 56 kDa. Comparison with GFLV F-13 shows 88.4% homology in nucleotides and 95.8% similarity in deduced amino acid residues. Also this coat protein gene was expressed in E. coli DH 5 alpha.

Amino Acid Sequence↗
PubMed1996

[Gastric devascularization for acute gastric mucosal lesion and bleeding].

Thirteen patients with acute gastric mucosal lesion and bleeding were treated with gastric devascularization. Of all, 11 apparently stopped bleeding, two failed to respond to the procedure, one rebled, and three died. Clinical analysis of the patients suggested that low blood pressure, damage of liver function, serious infection, acidosis and uremia were precipitating factors of the disease and for AGML in portal hypertension, the effect of this procedure was poor. Meanwhile, the etiology and pathological mechanism of AGML, the selection of operation types for the disease, and the anatomical and physiological bases of gastric devascularization were also discussed.

Adult↗
PubMed1996

[Tolerance to rat parathyroid allograft induced by depletion of Ia+ donor cells plus short course cyclosporine].

In this study, Ia+ donor cells of rat parathyroid allografts were depleted by anti-Ia monoclonal antibody plus complement. The secreting function of treated glands as well preserved. Then we transplanted the treated glands into subcapsular of the recipient kindey, and the median survival time (MST) of the allografts were 60 days, compared with 14 days in the fresh PTG group (P < 0.01). If the recipients received 25 mg/kg cyclosponine for three days before transplantation, the MST of about 60% PTG allografts was more than 150 days, with P < 0.01 in comparison with the control group (short course CyA alone, MST: 70 days). These results indicate that long-term survival of rat parathyroid allografts can be achieved by depletion of Ia+ donor cells and short course pretreatment of the recipient with CyA.

Animals↗
PubMed1996

[A clinical analysis on 131 senile cases with diplopia].

OBJECTIVE: To approach the pathogenic features of senile diplopia to elevate the rate of accurate clinical diagnosis and the therapeutic effect of treatment. METHODS: Prism, synoptophore, Hess' screen and red glass test were used to examine the ocular position, muscle movement and diplopia image in 131 cases (aged 60 or older). Biochemical examination of blood and imaging diagnosis were also involved. RESULTS: Among 131 cases, 120 (91.6%) suffered from binocular diplopia and 11 cases (8.4%) monocular diplopia. The majority of cases (110/120) with binocular diplopia were of ocular dyscinesia type resulting from intracranial vascular diseases, while the majority of cases with monocular diplopia resulted from complications of intraocular operation. CONCLUSIONS: Most of the diplopia in the aged are binocular one whose main cause is ocular dyscinesia resulting from vascular diseases. The cause of monocular diplopia in most of the cases is frequently due to the complications of intraocular operation. The authors emphasize a thorough examination of patients with diplopia.

Aged↗
PubMed1995

Maize branching enzyme catalyzes synthesis of glycogen-like polysaccharide in glgB-deficient Escherichia coli.

The structure of alpha-glucan, isolated from wild-type Escherichia coli B, a glycogen branching enzyme (BE)-deficient E. coli AC71 (glgB-), or from AC71 transformed with genes coding for maize BEI and BEII individually as well as with both genes, was analyzed by high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection. Transformation of the maize BE gene(s) in AC71 (glgB-) showed complementation in branching activity. Analysis by HPAEC revealed different structures between glycogen of E. coli B and alpha-glucan of AC71 transformed with a different maize BE gene(s). The individual chains of the alpha-glucan debranched with isoamylase were distributed between chain length (CL) 3 and > 30 and the chain with CL 6 was the most abundant. In comparison with the glycogen of E. coli B, the alpha-glucan of AC71 transformed with the maize BE gene(s) consisted of a lesser amount of chains with CL 7-9 and a larger amount of chains with CL > 14. It also showed a broad peak with chains of CL 9-12 as in maize amylopectin. This study provides in vivo evidence that glycogen BE and maize BE isozymes may have different specificities in the length of chain transferred. Furthermore, this study suggests that the specificity of glycogen synthase and starch synthase and their concerted action with BE play an important role in determining the structure of the polysaccharide synthesized.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1995

Calcium- and protein kinase C-dependent basal tone in the aorta of hypertensive rats.

We examined the regulatory influence of nitric oxide on development of calcium- and protein kinase C-dependent basal tone in rings of thoracic aortas from rats with aortic coarctation-induced hypertension and from normotensive controls. Aortic rings from hypertensive rats but not those from normotensive rats, bathed in Krebs' bicarbonate buffer and subjected to 2 g of passive stretch, were relaxed by removal of calcium from the buffer and by the protein kinase C inhibitors staurosporine and calphostin C. Protein kinase C activity was much greater in homogenates of aortae from hypertensive rats than in those from normotensive controls (2124 +/- 785 versus 608 +/- 73 pmol.min-1.mg protein-1, respectively). Relaxant responses to removal of calcium and to staurosporine were greater in aortic rings rubbed to remove the vascular endothelium than in endothelium-intact rings (-1.07 +/- 0.12 versus -0.70 +/- 0.10 g tension/mg tissue, respectively, for calcium removal and -1.10 +/- 0.12 versus -0.65 +/- 0.08 g tension/mg tissue, respectively, for staurosporine). Treatment with an inhibitor of nitric oxide synthesis increased calcium-dependent tone in both intact and endothelium-denuded aortic rings from hypertensive rats. Conversely, the administration of sodium nitroprusside or L-arginine reversed tone in both intact and denuded aortic rings from hypertensive rats, but acetylcholine reversed tone only in intact rings. The relaxant effects of these agents were paralleled by increases in cyclic guanosine monophosphate in aortic tissue. We conclude that aortic rings from rats with aortic coarctation-induced hypertension display calcium-dependent, protein kinase C-mediated tone in the absence of exogenous vasoconstrictors.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1995

[Clinical analysis of iatrogenic pseudoaneurysms].

The surgical management of 9 patients with false aneurysms resulting from iatrogenic injury was reviewed. The principal symptoms were local pain in 8 patients, neuralgia syndrome in 3, and rupture in 2. In the series, swelling or pulsatile mass was present in 7 patients. Only 5 patients were noted to have an artery bruit at the time of examination. Of these patients, 6 were diagnosed clearly before operation and all of the pseudoaneurysms were confirmed surgically. Surgical treatment was carries out in 8 patients including emergency operation in 3. Postoperative complications were rather high (25%), but fortunately, there was no operative mortality in this series. The etiological diagnostic method and the principles of surgical management were discussed.

Adolescent↗
PubMed1995

[Experimental study of implantation of autologous vascular endothelial cells on dacron grafts].

Ten mongrel dogs underwent carotid artery bypass 17 times with dacron grafts, 4mm in inner diameter and 5cm in length. The grafts in experimental group A were immediately seeded with autologous endothelial cells harvested by 0.25% trypsin solution (n = 7). The grafts in experimental group B were seeded with autologous endothelial cells cryopreserved in liquid nitrogen for 1 week (n = 3). The grafts in contrast group was not seeded with any endothelial cells implanted in the contralateral carotid arteries in group A (n = 7). The number of endothelial cells harvested in the two groups was 0.9 +/- 0.3 x 10. Factor VIII related antigen stain method confirmed the cells harvested by 0.25% trypsin solution to be endothelial cells. The grafts were removed and studied at the end of 2, 4, and 6 week after implantation. The total patency rate of group A was 85.7% (6/7), and that of the contrast group 57% (4/7). The weight of thrombus in group A was 40.6 +/- 36.9mg and the contrast group 85.9 +/- 26.3mg (P < 0.01). Scanning electron microscopy revealed that the cells at the middle segment of the grafts in the group A and B had the characteristics of ellipse, and tight intercellular junction, while the middle segment grafts in contrast group were covered by platelets, erythrocytes, leukocytes and fibrin. Transmission electron microscopy, factor VIII related antigen stain method, and vimentin stain method demonstrated that the cells in the group A and B showed characteristics of endothelial cells. It was concluded that endothelialization of the dacron grafts could be accelerated and the quality could be improved by immediate seeding with endothelial cells or by seeding with endothelial cells cryopreserved in liquid nitrogen for 1 week.

Animals↗
PubMed1994

A projection access order for speedy convergence of ART (algebraic reconstruction technique): a multilevel scheme for computed tomography.

The practical performance of algebraic reconstruction techniques (ART) for computed tomography (CT) depends heavily on the order in which the projections are considered. Complete orthogonalization, notwithstanding its theoretical justification, is not feasible because the computational time is prohibitive. The authors report here a scheme that yields the most efficient reconstruction without orthogonalization: projections are organized and accessed in a nominally multilevel fashion. Each level makes the best use of the image information reconstructed in the preceding levels. If the number of projections is a power of two. Then the access orders are exactly that for the 1D FFT. The authors' scheme can be easily implemented. Using it, one iteration of ART yields a high-quality image. Experimental results of this algorithm are demonstrated and compared with the results from the conventional sequential method and also random ordering. Comparisons show that this scheme is superior. ART is better in image quality than the Fourier back-projection algorithm, at least for a smaller number of projections. Since the authors have made it much more efficient in computational speed, ART could now find widespread use in medical imaging.

Algorithms↗
PubMed1994

Vascular responsiveness to nitric oxide synthesis inhibition in hypertensive rats.

We contrasted in normotensive and hypertensive rats the effect of inhibition of nitric oxide synthesis on isometric tension development by aortic rings bathed in Krebs' bicarbonate buffer. NG-Nitro-L-arginine methyl ester (L-NAME) (3 x 10(-4) mol/L) increased tension (82 +/- 11% of the response to 120 mmol/L potassium chloride) in rings of thoracic aorta taken from hypertensive rats 7 to 14 days after aortic coarctation, whereas rings of abdominal aorta from below the coarctation were unresponsive, as were rings of thoracic aorta from rats with deoxycorticosterone-salt-induced hypertension and from the corresponding normotensive controls of either model of hypertension. The contractile response to L-NAME in aortic rings of rats with aortic coarctation was reversed by L-arginine (1 mmol/L), attenuated by removal of the endothelium, and blunted by the protein kinase C inhibitor staurosporine but was unaffected by inhibition of cyclooxygenase, scavengers of superoxide anion, or blockade of receptors for angiotensin, norepinephrine, serotonin, or endothelin. In additional experiments we contrasted the effect of L-NAME (10 mg/kg IV) on the blood pressure of sham-operated rats and rats with aortic coarctation after pretreatment of animals in both groups with DuP 753 (30 mg/kg IV) to achieve blood pressure equalization. The pressor response to L-NAME was twofold greater in rats with aortic coarctation than in sham-operated controls. That pressor and aortic constrictor responsiveness to L-NAME are increased after aortic coarctation suggests that a mechanism of vasodilation, mediated by nitric oxide, is preferentially manifested in rats with aortic coarctation-induced hypertension.

Animals↗
PubMed1994

[Surgical treatment thoracoabdominal aortic aneurysms with blocking of aorta at short intervals].

Visceral ischemia and deterioration in renal function is common cause of morbidity in patients with thoracoabdominal aortic aneurysm surgically treated. Two patients with huge thoracoabdominal aortic aneurysm were surgically treated by a new technique of shunting. The operation was performed by using a synthetic artificial graft, which was sutured to the iliac artery by end to side anastomosis, and the upper end of the graft was anastomosed to the cut end of the thoracic aorta by end-to-end method. Compared with the traditional temporary shunting, there are several advantages in using the improved shunting technique. First, by so doing the ischemic time of various viscera could be fractionated and shortened, just about 17 minutes. visceral ischemic complication can be avoided. Second the pseudoaneurysm produced by the traditional method of temporal shunting could be prevented by the improved method. Third, on account of the ischemic time of the viscera is decreased, operation could be done under normal temperature without need for hypothermia. In treating a case of huge thoracoabdominal aortic aneurysm, successful result could hardly be obtained without good prepostopoerative care. We should also emphasize that the improvement of some surgical technique is also important.

Adult↗
PubMed1994

[Subclavian steal syndrome: a report of 25 cases].

From 1982 to 1992, 25 patients with subclavian steal syndrome (SSS) were admitted with 20 undergoing surgery. Etiology included atherosclerosis 56% (14/25), Takayasu's disease 36% (9/25), 14 of them were smokers. Stenosis or occlusion of the left subclavian artery were found in 14, the right in 7, and bilateral in 4. 14 cases had vertigo symptoms, 24 cases had claudication of the arm, 9 of them complained transient ischemic attack (TIA). Carotid to subclavian bypass were performed for 15 cases. Two patients underwent axilloaxillary bypass with evidence of both clinical and laboratory improvement. Aorta-Carotid graft bypass was done in 2 cases with good result in one. PTA was done for a girl with innominate severe stenosis but symptom recurred three months later. Symptoms of the upper extremity ischemia were relieved in 75% of the patients, and of the cerebrovascular ischemia in 50%. Our conclusion is that surgical therapy remains the treatment of choice in symptomatic patients.

Adult↗