Biomedical subjects

L Chen

Publications and source records attributed to L Chen.

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

PubMed1995

Gonadotropin-stimulated regulation of blood-follicle barrier is mediated by nitric oxide.

Although initially described over 30 years ago, the blood-follicle barrier has remained a biological enigma. In this study, we characterize the blood-follicle barrier with respect to its regulation of intrafollicular inter-alpha-trypsin inhibitor protein (I alpha I) influx after an ovulatory stimulus. We have found that I alpha I is localized within the ovarian vasculature but is excluded from the follicular compartment until an ovulatory stimulus is given. Within minutes after an ovulatory dose of human chorionic gonadotropin, I alpha I is localized within the follicular fluid of responding follicles where this protein becomes associated with and stabilizes the newly synthesized hyaluronic acid-rich cumulus extracellular matrix. Analysis of this process has shown that intravenous injection of sodium nitroprusside or excess substrate for nitric oxide synthase, L-arginine, mimics the effect of gonadotropic hormones on the influx of I alpha I into the follicular compartment of preovulatory follicles. Moreover, intravenous injection of specific nitric oxide synthase inhibitors, NG-nitro-L-arginine methyl ester and NG-nitro-L-arginine, inhibits gonadotropin-mediated intrafollicular influx of I alpha I and also inhibits ovulation in the mouse.

Alpha-Globulins↗

PubMed1995

Regulation of lineage-specific transcription of the sucrase-isomaltase gene in transgenic mice and cell lines.

Sucrase-isomaltase (SI), a gene expressed exclusively in absorptive enterocytes, was used to examine the molecular mechanisms that regulate cell-specific gene expression in the intestinal epithelium. Transgenic mice were made with a construct containing nucleotides -8,500 to +54 of the mouse SI gene linked to a human growth hormone reporter gene. In adult transgenic animals, high-level transgene expression was limited to the small intestine, with low levels of ectopic expression in the colon. In contrast to the endogenous gene that is expressed only in enterocytes, the transgene was expressed in all four cell lineages, including enterocytes, enteroendocrine, goblet, and Paneth cells. To examine this process of lineage-specific expression further we studied Caco-2 and COLO DM cell lines, which model enterocytes and enteroendocrine cells, respectively. Reminiscent of results in transgenic animals, only Caco-2 cells transcribed the endogenous SI gene, whereas both Caco-2 and COLO DM cells supported transcription from chimeric SI reporter gene constructs. Taken together, these data suggest that each intestinal cell lineage has the cellular machinery to transcribe the SI gene. Moreover, these findings imply that transcription is normally repressed in nonenterocytic cells, possibly via a transcriptional silencer residing outside of the region of the SI gene examined in these studies.

Animals↗

PubMed1995

Mechanisms of iron-induced proximal tubule injury in rat remnant kidney.

The proposition that proximal tubule (PT) iron accumulation may cause PT injury by lysosomal destabilization or reactive oxygen species generation in human and animal chronic renal disease was examined in partially nephrectomized [remnant kidney (RK)] and sham-operated (SO) Wistar rats. Electron microscopic histochemistry with horseradish peroxidase indicated iron uptake into and release from lysosomes. PT cytoplasmic iron was seen in RK but not in SO by energy-dispersive X-ray spectrometry. Total (9.66 +/- 1.89 vs. 3.30 +/- 0.31 nmol/mg protein; P < 0.01), low-molecular-weight (1.39 +/- 0.09 vs. 0.91 +/- 0.07; P < 0.001), and catalytic iron (1.88 +/- 0.27 vs. 1.28 +/- 0.09; P = 0.05) were higher in RK cytoplasm than in SO. Lysosomal enzyme activity was greater in RK than in SO [e.g., N-acetyl-beta-D-glucosaminidase (NAG): 0.75 +/- 0.05 vs. 0.57 +/- 0.06 mumol p-nitrophenol.h-1.mg protein-1; P < 0.05] and was increased further by chronic iron loading (e.g., RK and NAG: 0.84 +/- 0.04 vs. 0.60 +/- 0.07; P < 0.05). There was no enzymatic evidence of lysosomal fragility, and chronic iron loading of RK decreased fragility as assessed by NAG release (1.36 +/- 0.14 vs. 2.17 +/- 0.14; P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

A new method to localize brain nuclei for surgery in extrapyramidal disease.

A CT localization method to be used with the Leksell stereotactic system was employed to locate the ventral lateral nucleus of the thalamus (VL) and globus pallidus (GP) for treating extrapyramidal disease (EPD). The study comprised 100 normal adults and 70 cases of EPD, and results in both populations were compared. The 70 cases of EPD were studied ventriculography, and 30 normal adults were studied my MRI. Results indicate the accuracy of localization of the primary targets was 94.25% with the CT localization method described herein and 88.9% in the control group. In conclusion, the new CT localization method is a valuable technique to locate brain nuclei and to replace ventriculography with stereotactic surgery in the treatment of EPD patients.

Adolescent↗

PubMed1995

Heterogeneity in vascular smooth muscle responsiveness to angiotensin II. Role of endothelin.

We compared the role of endothelium and of endothelin in mediating the vasoconstrictor responses to angiotensin II (Ang II) in three vascular smooth muscle preparations--aorta, mesenteric artery, and tail artery--isolated from adult male Sprague-Dawley rats. The vasoconstrictor potency for Ang II in blood vessels with endothelium varied in the following rank order: aorta > mesenteric artery > tail artery. Although the maximal tension responses to Ang II were similar for mesenteric and tail arteries, it was significantly lower in aorta. Endothelium removal led to a leftward shift in the concentration-response curves to Ang II in the aorta but a rightward shift in the mesenteric artery. Strikingly, Ang II failed to evoke tension responses in tail artery in the absence of endothelium. The endothelin-A (ETA)-selective antagonist BQ-123 blocked the responses to Ang II in a noncompetitive manner, with partial and complete attenuation of responses in the endothelium-intact mesenteric and tail artery preparations, respectively. In contrast, BQ-123 did not affect the responses to Ang II in the aorta. BQ-123 also failed to affect the responses to Ang II in endothelium-denuded mesenteric artery rings. The Ang II type 1 (AT1) receptor-selective antagonist losartan competitively blocked the responses to Ang II in the three tissues (pA2, 8.3 to 8.7) when endothelium was present. These data suggest that there are endothelium-dependent regional variations in vascular tissue sensitivity to Ang II.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗

PubMed1995

Breast cancer selective gene expression and therapy mediated by recombinant adenoviruses containing the DF3/MUC1 promoter.

The high molecular weight mucin-like glycoprotein, DF3 (MUC1), is overexpressed in the majority of human breast cancers. Here we demonstrate that replication defective recombinant adenoviral vectors, containing the DF3 promoter (bp -725 to +31), can be used to express beta-galactosidase (Ad.DF3-betagal) and the herpes simplex virus thymidine kinase (HSV-tk) gene (Ad.Df3-tk) in DF3 positive breast carcinoma cell lines. In vivo experiments using breast tumor implants in nude mice injected with Ad.DF3-betagal demonstrated that expression of the beta-galactosidase gene is limited to DF3-positive breast cancer xenografts. Moreover, in an intraperitoneal breast cancer metastases model, we show that i.p. injection of Ad.DF3-tk followed by GCV treatment results in inhibition of tumor growth. These results demonstrate that utilization of the DF3 promoter in an adenoviral vector can confer selective expression of heterologous genes in breast cancer cells in vitro and in vivo.

Adenoviruses, Human↗

PubMed1995

Patterns of localization and cytoskeletal association of two vegetally localized RNAs, Vg1 and Xcat-2.

In Xenopus, localization of a rare class of mRNAs during oogenesis is believed to initiate pattern formation in the early embryo. We have determined the pattern of RNA localization for one of these RNAs, Xcat-2, which encodes a putative RNA-binding protein related to Drosophila nanos (Mosquera, L., Forristall, C., Zhou, Y. and King, M. L. (1993) Development 117, 377-386). Xcat-2 is exclusively localized to the mitochondrial cloud in stage I oocytes, moves with this body into the vegetal cortex during stage II and, later, partitions into islands consistent with it being a component of the germ plasm. As previously shown, Vg1 is not localized to the vegetal cortex until stage IV and distributes to all vegetal blastomeres during development. We found a direct correlation between the localized condition of these RNAs and their recovery in a detergent-insoluble fraction. We present evidence suggesting that differential RNA binding to a cytoskeletal component(s) in the vegetal cortex determines the pattern of inheritance for that RNA in the embryo.

Animals↗

PubMed1995

Clinical factors and angiographic features associated with premature coronary artery disease.

BACKGROUND: Clinical, angiographic, and biochemical features may differ in young patients with coronary heart disease compared with older patients. METHODS: We compared clinical and angiographic characteristics in 100 male patients with clinical onset of disease at age < or = 45 years (group 1) with those of 100 older male patients (clinical onset of disease at > or = 60 years) (group 2). All patients had documented coronary artery disease. The two patient groups were compared in terms of the pattern of angina at disease onset, angiographic features, and coronary risk factors. RESULTS: Seventy-six patients in group 1 and 49 patients in group 2 presented with acute coronary syndromes (unstable angina or myocardial infarction) at clinical disease onset (p < 0.001). Compared with patients in group 2, younger patients (group 1) showed a preponderance of single-vessel disease (54 vs 36%; p < 0.001) and complex stenosis morphologic features (59 vs 36%; p < 0.01). Family history of coronary artery disease (39 vs 11%; p < 0.001) and smoking (73 vs 46%; p < 0.001) were also more prevalent in younger patients. Mean plasma total cholesterol level was 6.4 +/- 1.3 mmol/L in group 1 and 6.1 +/- 1.2 mmol/L in group 2 (p = NS). Younger patients, however, had lower high-density lipoprotein (HDL) cholesterol (0.9 +/- 0.2 mmol/L and 1.1 +/- 0.4 mmol/L; p < 0.01) and higher plasma triglyceride levels compared with patients of group 2 (2.7 +/- 1.3 mmol/L vs 2.1 +/- 1.1 mmol/L; p < 0.001). CONCLUSIONS: Patients with premature coronary disease referred to coronary angiography commonly have unheralded acute onset of symptoms, angiographically complex stenosis morphologic features, and less extensive coronary artery disease. In addition to previously identified risk factors such as family history and smoking, we observed that high plasma triglyceride and low HDL cholesterol levels are associated with premature coronary artery disease.

Adult↗

PubMed1995

Autocrine feedback death and the regulation of mature T lymphocyte antigen responses.

Antigen-induced T cell death is an important regulatory mechanism in the peripheral immune system. Evidence suggests that this process depends on T cell growth-inducing lymphokines such as IL-2 and occurs in proportion to the degree of T cell receptor occupancy. Strong T cell receptor stimulation leads to the synthesis of death molecules such as Fas ligand and tumor necrosis factor that cause T cell suicide. We propose that T cell death under these circumstances is the culmination of a feedback control mechanism termed propriocidal regulation or autocrine feedback death that regulates the expansion of specific T cell clones under conditions of high lymphokine and antigen load. In a quasi-stochastic system such as the antigen receptor repertoire, feedback information may be essential for the appropriate regulation of peripheral immune responses. Our understanding of this feedback mechanism affords a means to manipulate antigen-specific T cell death in vivo. The application of this approach to the therapy of T cell-medicated immunological diseases is discussed.

Animals↗

PubMed1995

The mechanism of action for the block of NMDA receptor channels by the opioid peptide dynorphin.

Dynorphin is one of the endogenous opioids that modulates the excitability of nociceptive (pain-sensing) neurons. We have shown recently that dynorphin blocks NMDA-activated currents directly without the participation of kappa-opioid receptors. In order to understand the mechanism underlying this novel action of dynorphin, we examined, in detail, the interactions between dynorphin and NMDA receptors in isolated trigeminal neurons. Dynorphin reversibly blocks NMDA-activated current (INMDA). The onset and recovery of the block were determined with concentration jump experiments. The association rate (k+) of dynorphin(1-17) is 4.9 x 10(6) sec-1 M-1 and the dissociation rate (k-) is 7.5 sec-1. The apparent dissociation constant (KD) of dynorphin, calculated from these rate constants, is 1.6 microM. Dynorphin does not change the EC50 of NMDA, nor the potentiating action of glycine. The binding site for dynorphin is distinct from that of Zn2+ or H+. Upon treatment with the disulfide reducing agent dithiothreitol (DTT), NMDA receptors become less susceptible to dynorphin block. The affinity of dynorphin for the modified NMDA receptors is reduced by 2.7-fold. In analyses of single NMDA channels in cell-free patches, we found that dynorphin shortens the mean open time, decreases the probability of opening of NMDA channels, but has no effect on the single channel conductance. These results suggest that dynorphin interacts with a site conformationally linked with the redox site(s) on the NMDA receptor, thus altering the gating properties of the channel.

Animals↗

PubMed1995

[Single channel analysis of aconitine blockade of calcium channels in rat myocardiocytes].

Ventricular myocardiocytes from neonatal Wistar rats were isolated and cultured. Aconitine, Ca2+ channel blocker verapamil or Ca2+ channel activator BAY K8644 were added to the bath solution separately. Using the cell-attached configuration of the patch clamp technique, the single channel activities of L type Ca2+ channel were recorded before and after addition of all three drugs. The results showed the blocking effect of aconitine (50 micrograms.ml-1) on L type Ca2+ channels. Its mechanism may be relevant to the decrease in both open state probability and the mean open time of Ca2+ channel. The difference was statistically significant compared with control group (P < 0.01). The amplitude of Ba2+ currents, which flow through open L type Ca2+ channel was unchanged.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1995

Biochemical and biophysical characteristics of mitochondria in the hypertrophic hearts from hypertensive rats.

A comparative study of the biochemical and biophysical characteristics of myocardial mitochondria was conducted in 16-weeks-old male stroke-prone spontaneously hypertensive rats (SHRsp) and normotensive Wistar-Kyoto control rats (WKY) (n = 6-12). Cardiac and ventricular weights of SHRsp were significantly higher than those of the WKY group. The average amounts of mitochondria (Mit) and sarcoplasmic reticulum (SR) proteins isolated from the ventricle of SHRsp were 37% and 25% greater, respectively, when compared with those of WKY. Mit cytochrome c oxidase activities (mumol/min/mg) were 4.63 +/- 0.71 for SHRsp and 5.55 +/- 0.50 for WKY myocardium (mean +/- s), so that the activity of the former was significantly reduced by 17% (P < 0.01). Mit Ca2+, Mg(2+)-ATPase activity (mumol/min/mg) of SHRsp was 24% lower than that of WKY myocardium (P < 0.01). The fluorescence polarization of myocardial Mit membrane labelled with DPH (1, 6-diphenyl-1, 3, 5-hexatriene) in hypertensive rats was not different from that in control rats. The spectra of intrinsic protein fluorescence in 300-380 nm at an excitation wavelength of 290 nm were also identical in the Mit or SR between SHRsp and WKY myocardium. An ultrastructural analysis showed that there were more new-born Mit with smaller volumes and an increased number of isolated Mit in vitro from SHRsp myocardium, while there were larger Mit volumes isolated from WKY myocardium. These results demonstrated the disorder of mitochondrial energy metabolism in hypertrophied myocardium from SHRsp, which may be involved in the abnormality of myocardial calcium metabolism.

Animals↗

PubMed1995

Dorsal scapular nerve compression. Atypical thoracic outlet syndrome.

The dorsal scapular nerve and long thoracic nerve of 10 cadavers (20 sides) and 36 patients with dorsal scapular nerve compression were studied anatomically. The origin of the dorsal scapular nerve of a section frequently shared a common trunk with the long thoracic nerve, and went through the scalenus medius anterointernally and posterolaterally with the presence of some tendinous tissues. Leaving the long thoracic nerve, it might give branches to the shoulder and the subaxillary region and finally have the branches join the long thoracic nerve again. The compression of the section near the origin caused discomfort and sourness of the neck, shoulder and back region. Clinically, the severance of the scalenus anterior and medius ameliorated or relieved the compression of the dorsal scapular nerve. Complete decompression required cutting of the scalenus medius and its tendinous tissue superficial to the dorsal scapular nerve. Among 24 sides of 22 patients undergoing surgery, the symptoms of 20 sides of 19 patients were completely or partially relieved.

Adult↗

PubMed1995

[Clinical observation and study of blood phosphate concentration changes in postoperative patients].

Blood phosphate concentration of 257 postoperative patients in the ICU was determined through the molybdenum-blue developing method. The results showed that 136 cases had hypophosphatemia (blood phosphate concentration < 0.8mmol/L), bearing an incidence of 52.9%, which indicated that the occurrence of hypophosphatemia was associated with patients' age, primary disease and postoperative intravenous hypertonic glucose solution transfusion. Meanwhile, the existance of hypophosphatemia was often complicated by hypocalcemia (83.1%), hyponatremia (76.4%), and hypokelemia (37.5%), and furthermore, was in connection with organ dysfunction or failure. Of the 40 death cases among all 257, 31 endured hypophosphatemia (77.5%). Hence, prompt diagnosis and active prevention and treatment of hypophosphatemia are essential to raise the cure rate of surgical critical patients.

Adolescent↗

PubMed1995

[Experimental comparison of the analgesic action of Aconitum and its processed products].

This paper deals with the effects of crude Aconitum and Aconitum processed by a new method of moistening and steaming, and by method of pharmacopoeial stipulation on the analgesic action with writhing test and hot plate test in mice. The result shows that the Aconitum processed by new method No 1, which applies moistening in water for 48h and then heating with high pressure steam (68.65kPa, 115 degrees C) for 2h has an advantage over that processed according to pharmacopoeial routine (P < 0.05).

Aconitum↗

PubMed1995

[Pathological and immunohistochemical studies on primary nasal mucosal malignant melanoma].

The pathological and immunohistochemical features of primary nasal mucosal malignant melanoma (PNMMM) were reported in 40 cases. The results showed that approximate 70% of PNMMM was polypoid. The principal features were the mixed existance of different cellular patterns and morphologies. Immunohistochemically, PNMMM reactivity to S-100 protein and vimentin was 90% and 77.5%, respectively, along with no reactivity to Keratin. We believe that PNMMM may arise from preexistant melocytes in nasal mucosa. Histological pleomorphism and immunohistochemical reactivity to S-100 protein and vimentin were of importance for diagnosis of PNMMM, especially for the amelanotic type.

Adult↗

PubMed1995

Analysis of plasma and urinary tea polyphenols in human subjects.

Tea has been shown to inhibit chemically induced tumorigenesis in many animal models, but the effects of tea consumption on human carcinogenesis are not conclusive. In order to develop biomarkers for tea consumption, we developed methods for the analysis of tea polyphenols in human plasma and urine samples using HPLC with the coulochem electrode array detection system. (-)-Epigallocatechin-3-gallate (EGCG), (-)-epigallocatechin (EGC), (-)-epicatechin-3-gallate (ECG), and (-)-epicatechin (EC) are the major polyphenols in green tea. Most of the tea polyphenols were in their conjugated forms in the plasma and urine. The samples were incubated with a mixture of beta-glucuronidase and sulfatase to generate the free form of tea polyphenols. After extraction into ethyl acetate and separation by reversed-phase chromatography, EGCG, EGC, and EC were identified on the basis of their retention times and electrochemical characteristics. Due to the high selectivity of the detection mode, interference was minimized. Good quantitative relationships were established for a large concentration range of tea polyphenols. The limits of detection for EGCG, EGC, ECG, and EC were from 0.5 to 1.5 ng/ml of plasma or urine sample. After ingestion of 1.2 g of decaffeinated green tea in warm water, the plasma samples collected at 1 h from 4 human volunteers contained 46-268 ng/ml of EGCG, 82-206 ng/ml of EGC, and 48-80 ng/ml of EC. ECG was not detected in plasma samples. The maximum urinary excretion of EGC and EC occurred at 3-6 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

[Changes of HDL-receptor of hepatic cell membrane in rabbit model of calcium bilirubinate cholangiolithiasis].

HDL-receptor of the hepatic cell membrane and Fch level of the hepatic tissue in the rabbit model of calcium bilirubinate cholangiolithiasis were examined. The results showed: (1)the HDL-receptors' Bmax of the biliary obstruction and infection (BOI) and biliary obstruction (BO) groups decreased during the 1st week after operation (P < 0.01); they were only 69.09% and 49.09% of that in the control group respectively, and the lowered level continued until the 6th week; the Kd values of BOI and BO groups were not different from that of the control group during the 1st week, but they were significantly higher in the 6th week after operation (P < 0.01); (2)the Fch levels of the hepatic tissue were slightly decreased in all experimental groups (P < 0.05). We concluded that under the conditions of biliary obstruction and infection, there was a disorder of the HDL receptors of hepatic cell membrane. At the early stage of biliary obstruction and infection, the receptors decreased in number, and at the later stage, the affinity changed and less HDL entered into the hepatic cell. Then the precurser cholesterol pool for BA biosynthesis narrowed. Thus, BA secreted from the liver cells into genetic elements possibly promote the formation of the calcium bilirubinate gallstones.

Animals↗