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Biomedical subjects

X Yang

Publications and source records attributed to X Yang.

At least 1,117 records · Page 62Linked to original sources
PubMed1991

beta-Alanyl-beta-alanine in cyclic beta-turned peptides.

In the present paper we describe the synthesis, purification, and single crystal x-ray analysis of the cyclic pentapeptide cyclo-(L-Pro-L-Pro-L-Phe-beta-Ala-beta-Ala). The peptide was synthesized by classical solution methods and the cyclization of the free pentapeptide was accomplished in good yields in diluted methylene-chloride solution using N,N-dicyclohexylcarbodiimide. The compound crystallizes in the monoclinic space group P21 from hot water with five solvent molecules. The Pro1-Pro2 peptide bond is cis and the molecular conformation is stabilized by an intramolecular hydrogen bond between the CO group of the beta-Ala5 and the NH of the Phe3 residue. The Pro1-Pro2 segment occupies the relative positions 2 and 3 of a type VIa beta-turn, while the L-phenylalanyl-beta-alanyl-beta-alanine segment is incorporated in a C13-like ring structure. The crystal packing is characterized by a network of 11 intermolecular hydrogen bonds involving all the remaining CO, NH, and the water molecules.

Crystallography↗
PubMed1991

Minimum mean square error estimation of connectivity in biological neural networks.

A minimum mean square error (MMSE) estimation scheme is employed to identify the synaptic connectivity in neural networks. This new approach can substantially reduce the amount of data and the computational cost involved in the conventional correlation methods, and is suitable for both nonstationary and stationary neuronal firings. Two algorithms are proposed to estimate the synaptic connectivities recursively, one for nonlinear filtering, the other for linear filtering. In addition, the lower and upper bounds for the MMSE estimator are determined. It is shown that the estimators are consistent in quadratic mean. We also demonstrate that the conventional cross-interval histogram is an asymptotic linear MMSE estimator with an inappropriate initial value. Finally, simulations of both nonlinear and linear (Kalman filter) estimate demonstrate that the true connectivity values are approached asymptotically.

Algorithms↗
PubMed1991

CO2 gas perfusion: improved efficiency and safety with sapphire-probe laser ablation of human artery.

CO2 gas has been proposed as a new perfusion medium for laser angioplasty. To compare CO2 gas with conventional saline perfusion, 146 fresh specimens of normal and atheromatous human artery were irradiated with a neodymium: yttrium-aluminum-garnet laser with a sapphire probe in flowing whole blood in an experimental circulation-occlusion model. The dimensions of the ablation crater and the extent of the surrounding tissue damage were measured microscopically. Significantly better ablation of atheromatous plaque was achieved with CO2 perfusion than with saline perfusion: mean ablation areas were 5.0 mm2 versus 2.8 mm2, respectively (P = .001, Student t test). In contrast, the ablation areas on normal vessel wall were identical (mean, 3.4 mm2) with the two perfusion media. Moreover, CO2 gas functioned as a negative contrast agent and facilitated direct monitoring of the laser recanalization procedure. On an experimental basis, CO2 gas perfusion seems to improve the efficiency and safety of laser ablation in human arteries.

Aged↗
PubMed1991

[Chemiluminescent immunoassay for insulin].

In this paper is reported solid phase chemiluminescent immunoassay for insulin with N-(4-aminobutyl)-N-ethylisoluminol (ABE1) labelled antibody and a double antibodies sandwich procedure. ABEI-CoCl2-H2O2 was used as the chemiluminescent system and the linear range of insulin was 0.3-150 microU/tube. The correlation coefficient of the log-log regression equation was 0.985 and the absolute limit of detection 0.32 microU/tube.

Humans↗
PubMed1990

Effect of 1-desamino-8-D-arginine vasopressin (DDAVP) on human platelets.

Intravenous infusion of 1-desamino-8-D-arginine vasopressin (DDAVP), an analog of arginine vasopressin (AVP), results in a rise in plasma levels of factor VIII coagulant activity and the von Willebrand factor. DDAVP infusion has been shown to shorten the prolonged bleeding time of patients with inherited platelet defects but the mechanism for this has not been fully clarified. There is little information available on the direct effect of DDAVP on platelets. We examined the effect of DDAVP on platelet responses, including Ca2+ mobilization, to understand the mechanisms by which DDAVP shortens the bleeding time in patients with primary platelet defects. In normal human platelets, DDAVP alone upto 100 microM did not induce aggregation, secretion or a rise in the intracellular Ca2+ concentration, monitored using quin2. In contrast AVP induced all three responses in a dose dependent manner. Interestingly preincubation of platelets with DDAVP at a 100-fold greater concentration inhibited the responses to AVP indicating that DDAVP does interact with the platelets. Moreover, DDAVP did not either potentiate or inhibit the responses to thrombin or ADP. These studies indicate that it is unlikely that the beneficial effect of DDAVP in patients with primary platelet defects is related to a direct stimulatory effect on platelets.

Adenosine Diphosphate↗
PubMed1990

Potential of hypertonic medium treatment for embryo micromanipulation: I. Survival of rabbit embryos in vitro and in vivo following sucrose treatment.

Rabbit zygotes and embryos were exposed to hypertonic sucrose in phosphate-buffered saline (SPBS). In experiment one, 144 zygotes shrank to 32-36% of their initial volume in 1.0 M SPBS within 30 min. Neither hypertonic treatment with 0.5 M or 1.0 M SPBS nor micropuncture of the zona pellucida after shrinkage affected embryo development into blastocysts in vitro (88%, 83%, and 82%, respectively), compared to that of the controls (93%, P greater than .05). In experiment two, 252 two- to four-cell- and 177 morula-stage embryos were exposed to isotonic PBS control or 0.5 M, 1.0 M, or 1.5 M SPBS for 30, 60, 90, 120, and 150 min before transfer to PBS (290 mOsm). Embryo development was significantly reduced (P less than .05) when embryos were exposed in 0.5 M and 1.0 M SPBS for more than 60 min or in 1.5 M SPBS for more than 30 min. In experiment 3, morulae exposed for 60 min to 0.5 M or 1.0 M SPBS shrank to 37-39% or 32-35% of their initial volume and then expanded to 87-94% or 81-90% of their initial volume, respectively, after being returned to isotonic PBS for 60 min, but embryos in 1.5 M SPBS had erratic osmotic behavior. In experiment four, 192 two- to four-cell embryos exposed to 0.5 M SPBS for 0, 30, and 60 min before transfer to oviducts of recipients resulted in the production of 39%, 42% and 31% young, respectively (P greater than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Potential of hypertonic medium treatment for embryo micromanipulation: II. Assessment of nuclear transplantation methodology, isolation, subzona insertion, and electrofusion of blastomeres to intact or functionally enucleated oocytes in rabbits.

The objective of this research was to study efficiency of embryo development following transfer of blastomeres into the perivitelline space of oocytes. Single blastomeres from 8-, 16-, and 32-cell embryos were obtained following mucin coat and zona pellucida removal by combined treatments with pronase and acidic phosphate-buffered saline (PBS, pH = 2.5). Blastomeres were separated by pipetting with a fire-polished micropipette following incubation in Ca+(+)-free PBS for 15 min at 39 degrees C. This procedure resulted in over 97% blastomere separation. For ease of blastomere insertion, oocytes were placed in droplets of 0.5 M sucrose in PBS (SPBS) during micromanipulation. To functionally enucleate oocytes some were stained with Hoechst 33342 DNA stain and irradiated. A single 8- or 16-cell blastomere was aspirated into an injection pipette (35 microns or 25 microns at the tip, respectively) and inserted into the perivitelline space of an irradiated or non-irradiated oocyte, but not fused with the oocyte. This micromanipulation procedure did not affect development of individual blastomeres into blastocysts or trophectoderm vesicles when compared with cultured control single blastomeres (P greater than .05). When the inserted blastomere was induced to fuse with an intact non-irradiated oocyte under an electric field, 56-57% were fused and 39-45% of the fused and activated oocytes developed to morulae or blastocysts. When an inserted blastomere (from 8-32-cell embryos) was induced to fuse with a functionally enucleated oocyte treated by Hoechst 33342 staining, followed by washing and UV-light irradiation, 63-66% of them were fused, but only 15-22% developed to the morula or blastocyst stage. This research demonstrated that the use of hypertonic medium treated oocytes greatly improved the ease and success rate of blastomere subzona insertion, but the value of functionally enucleated oocytes as recipient cells for nuclear transfer requires further investigation.

Animals↗
PubMed1990

Detection of pome fruit viroids by enzymatic cDNA amplification.

We have studied the detection of apple scar skin, dapple apple, and pear rusty skin viroids in nucleic acid extracts of infected pome fruit tissues by reverse transcription-polymerase chain reaction (RT-PCR) with viroid cDNA-specific primers. Analysis of RT-PCR-amplified products by gel electrophoresis or by Southern blot hybridization indicated that the new procedure is more sensitive than existing detection methods and provides information about viroid detection without requiring large samples or using molecular hybridization. Our results also suggest the potential utility of the PCR technology in detecting other viroids and possibly other plant pathogens.

Base Sequence↗
PubMed1990

Radiosensitivity, recovery and dose-rate effect in three human glioma cell lines.

The results of radiotherapy in the treatment of high-grade gliomas are disappointing. In this study three recently established cell lines from high-grade human gliomas have been found to exhibit a sensitivity that is at the resistant end of the spectrum of radiosensitivities seen in human tumour cells generally. The results support the view that inherent cellular radioresistance may be an important cause of failure in this disease. All three cell lines showed an increase in survival when the radiation dose rate was reduced. In split-dose experiments, recovery was found to increase with dose in a manner consistent with the predictions of the linear-quadratic equation.

Cell Line↗
PubMed1990

Population movement in Zhejiang province, China: the impact of government policies.

"China's urbanization policies include strict control of permanent migration to large cities, but encourage the growth of small cities and towns. Concurrently, temporary migration is widely permitted as a way to stimulate commerce. Data for Zhejiang province indicate that permanent mobility is largely directed toward urban places, that towns gain more than cities and that rural areas experience migration losses. Permanent migrants to urban places are selective of the better educated. Temporary migration is also urban directed but greater in volume than permanent migration, and places considerable strain on urban infrastructure. Government policies are a key to understanding the migration streams and migrant characteristics. The considerable net movement into cities suggests that strict control of city growth is more difficult to achieve than envisaged by policymakers." This is a revised version of a paper originally presented at the 1989 Annual Meeting of the Population Association of America (see Population Index, Vol. 55, No. 3, Fall 1989, p. 386).

Asia↗
PubMed1990

[Chemical composition of the penis and testes of deer before and after processing].

Compositional analysis has been made of Penis et testis Cervi before and after processing, taking extracts of EtOH (50%) and chloroform, nitrogen contents, ash contents, 18 amino-acids and 20 trace elements as chemical indexes. The result shows no remarkable difference between the raw and processed products. The processing procedure is only helpful in eliminating the fish mell and making grinding and extracting easier.

Amino Acids↗
PubMed1990

[Study on several systems used for chemiluminescent determination of horseradish peroxidase].

Four systems were studied used for chemiluminescent determination of HRP and the determination conditions optimized. In luminol-H2O2 (NaOH) system, HRP was determined conveniently in the range of 0.05-4 pmol, with a correlation coefficient of 0.998 for the linear log-log equation and a limit of detection of 16 fmol HRP. In pyrogallol-H2O2 (pH 6.5) system, 0.1-100 pmol of HRP were determined, based on three log-log regression equations with correlation coefficients of 0.997, 0.994 and 0.999, respectively, and limits of detection of 3-17 fmol HRP. Luminol-H2O2-para iodophenol system was used to determine HRP in the range to 10-50 fmol, based on the chemiluminescence intensity at 1 min and the correlation coefficient of the log-log equation being 0.996 with a limit of detection of 10 fmol HRP. When p-hydroxybiphenyl was used to take the place of p-iodophenol and the chemiluminescence intensity at 1 min or 3 min measured, 6-40 fmol HRP were determined with a correlation coefficient of 0.994 or 0.995 for the log-log equation and a limit of detection of 6.5 or 3.3 fmol HRP.

Horseradish Peroxidase↗
PubMed1990

[Serum isoforms of creatine kinase MM (MM3/MM1 ratio) in the diagnosis of acute myocardial infarction].

The reliability of serum MM3/MM1 ratio as a marker for AMI was evaluated in 81 consecutive coronary-care admission. Of these, 62 patients were diagnosed as definite infarction and 19 patients as angina, using WHO criteria. The MM3/MM1 ratio in the admission serum sample was 1.85 +/- 2.01 in 62 patients with definite infarction; in contrast, the MM3/MM1 ratio was 0.24 +/- 0.14 in 19 patients with angina (P less than 0.01 for MI group vs angina group). Among the AMI patients admitted within 12 h after onset, the diagnostic accuracy of the ratio MM3/MM1 was higher than CK, CK-MB, LDH, LD1/LD2 and GOT and similar to Mb in the initial serum samples. It seems that the MM3/MM1 ratio was a better enzyme marker than the others in the early stage of AMI, especially before 12 h.

Adult↗
PubMed1990

[Objective display on phenomena of propagated sensation along channels (PSC)--changes on the infrared thermal image channels pathway of upper extremity].

This paper reported the observed results on changes of the infrared thermal image of upper extremity induced by needle "Hega" (LI 4), "Daling" (P 7) and "Neiguan" (P6) points. The results indicated that 10 out of 23 cases whose higher and middle temperature bands of upper extremity distributed along the "Dachang" (Large Intestine) channels, when they felt phenomena of propagated sensation along the "Dachang" channels induced by needle "Hegu" points. Those effects did not appear in the objects who did not feel PSC along the "Dachang" channels induced by needled points. Above results provide an objective basis for the phenomena of channels and suggest that the phenomenon of PSC is an objective fact in human body.

Acupuncture Points↗
PubMed1990

[Objective observation on phenomena of sensation along channels (PSC) and QI reaching to affects area (QIRA)--the influence of acupuncture points on infrared thermal image of face].

Thirty three patients and nine volunteers were observed. 18 out of 33 patients felt PSC and Qi reaching to face induced by needle points. The QiRA rate was 80% in patients with face diseases. During acupuncture "Hegu" (LI 4) points, most of the patients felt PSC reaching to their faces and sensed heat in face. The infrared thermal image demonstrated that the temperature of face skin increase and the hyperthermal areas coincided basically with the pathway of "Yangming" channels. Those effects were more than the effects of the other objects who didn't feel PSC or sensed Qi reaching to face induced by needle "Hegu" (LI 4) or "Daling" (P 7) Points. The difference between the two groups was statistical significant. The temperature rising responses induced by needle points were not the results of natural fluctuation. The above results indicate that the PSC and QiRA is objective existence.

Acupuncture Points↗