Biomedical subjects

M Li

Publications and source records attributed to M Li.

At least 829 records · Page 46Linked to original sources

PubMed1996

Validation of transonic small animal flowmeter for measurement of cardiac output and regional blood flow in the rat.

The objective of the present study was to validate a transonic flowmeter system with two probes (model 3SS for cardiac output (CO) and 1RB for organ flows) in Sprague-Dawley (SD) rats first by measuring blood flow through pump-infused isolated renal artery and ascending aorta, and then through measurements of CO and renal, mesenteric, and hindquarter blood flow (RBF, MBF, HBF) in vivo. We measured in vivo baseline flow and changes in flow induced by dopamine and propranolol for CO, prostaglandin E2 (PGE2), and angiotensin II (AII) for RBF and pentobarbital sodium for MBF and HBF. Correlations between meter and pump flow were linear (r = 0.999, p < 0.001) with close agreement both in ascending aorta and renal artery flow measurements. The baseline values were 15 +/- 0.7 ml/100 g/min for CO, 4 +/- 0.1 ml/100 g/min for RBF, 7 +/- 0.3 ml/100 g/min for MBF, and 6 +/- 0.3 ml/100 g/min for HBF, respectively. The system reliably detected increase and/or decrease in CO and regional blood flows. The transonic flowmeter system is accurate, highly reproducible, and compatible with other established techniques for measuring CO and regional blood flows in the rat.

Angiotensin II↗

PubMed1996

Phenotypic changes and loss of melanoma-specific endogenous C-type retroviruses in BL6 melanoma cells transfected with the H-2Kb gene.

The murine B16 melanoma and its sublines are low or totally deficient in expression of the H-2Kb class I major histocompatibility complex (MHC) gene. In clones derived from the B16F10BL6 subline, expression of the transfected or endogenous H-2Kb gene resulted in alterations of various phenotypic properties of these melanoma cells, among which was the loss of melanoma-associated antigen (MAA) expression. Because our previous immunoelectron microscopy studies showed that MAA was associated with a C-type ecotropic retrovirus specific for melanomas of C57BL/6 origin, we examined the effect of class I H-2Kb as well as class II H-2IAk gene expression on retrovirus production in subclones of BL6 melanoma cells. Here we have shown that expression of the transfected or endogenous H-2Kb gene resulted in the loss of production of budding, MAA-specific, C-type retrovirus particles. Northern blot analysis demonstrated expression of ecotropic retroviral mRNAs in both particle-producing and non-producing BL6 melanoma clones. Southern blot analysis of high-molecular-weight cellular DNAs using an ecotropic env-specific DNA probe indicated that the parental BL6-8 melanoma cells contained the C57BL/6 endogenous ecotropic MuLV (Emv-2) and at least three additional, novel ecotropic retroviral DNAs. Restriction enzyme analysis of the proviral DNA suggests that the loss of retrovirus production in the H-2Kb-expressing melanoma clones is the result of multiple rearrangements in the novel proviral DNAs. Thus, phenotypic changes observed in the H-2Kb gene-transfected BL6 melanoma cells were associated with loss of endogenous melanoma-specific ecotropic retrovirus production.

Animals↗

PubMed1996

Loss of intracisternal A-type retroviral particles in BL6 melanoma cells transfected with MHC class I genes.

Electron microscopy of B16 melanoma and its sublines revealed that these cells produce numerous intracisternal A-type retroviral particles (IAPs). To identify and sequence the melanoma-associated IAPs of C57BL/6 mice, a cDNA library was constructed from IAP-producing BL6.8 cell RNA and screened using MIA14 IAP DNA as a probe. A 6-8 kb mRNA was identified that represents the full-length message for a new subfamily of IAP, termed MeIAP. The melanoma-derived IAP cDNA showed high similarity to MIA14 with major differences in the LTR. A nine base motif of the R region showed that this IAP differs from other previously sequenced IAPs. Analysis of the individual clones from BL6 melanoma revealed that IAPs were produced only in the clones that failed to express H-2Kb molecules. No IAPs were found in the melanoma clones that expressed endogenous H-2Kb. To analyse further the association between MHC class I genes and IAP production, the H-2Kb-negative clones of BL6 melanoma were transfected with various H-2 genes. Transfection of the H-2Kb or H-2Kd, but not H-2Dd or H-2Ld genes resulted in the elimination of IAPs. Northern blot analysis revealed that loss of IAPs in the H-2K gene-transfected BL6 melanoma cells was due to lack of IAP transcripts. Elimination of IAPs in the H-2Kb-positive BL6 melanoma cells was also accompanied by alterations in expression of various cellular genes and changes of their phenotypic properties.

Animals↗

PubMed1996

Dehydroepiandrosterone does not prevent adrenocorticotrophin-induced hypertension in conscious rats.

1. We tested the hypothesis that dehydroepiandrosterone (DHEA), which prevents dexamethasone-induced hypertension in rats, may block adrenocorticotrophin (ACTH) hypertension, which has been presumed due to corticosterone excess. The blood pressure and metabolic effects of DHEA (18 mg/kg per day) were examined in sham and ACTH-treated (0.5 mg/kg per day) conscious Sprague-Dawley rates (n = 20). 2. ACTH but not sham injection increased blood pressure, water intake and urine output and decreased bodyweight. 3. DHEA administration for 10 days did not alter blood pressure or metabolic effects in either sham or ACTH-treated rats. 4. DHEA, which is known to block dexamethasone-induced hypertension, did not modify ACTH-induced hypertension in the rat. This suggests either that ACTH-induced hypertension is not simply a consequence of glucocorticoid activity or that the action of DHEA in dexamethasone hypertension is not through blocking the glucocorticoid receptor.

Adrenocorticotropic Hormone↗

PubMed1996

Growth inhibition of a human oral bacterium Porphyromonas gingivalis by rat cysteine proteinase inhibitor cystatin S.

Agar diffusion analysis demonstrated that rat cystatin S, a cysteine proteinase inhibitor, inhibited the growth of all tested strains of a human oral, Gram-negative anaerobic periodontopathogen Porphyromonas gingivalis. Its specific inhibitory activity against this tissue-invasive bacterium but not against other tested oral bacterial species emphasized the importance of specific cysteine proteinases for growth of P. gingivalis.

Animals↗

PubMed1996

Borrelia burgdorferi supercoiled plasmids encode multicopy tandem open reading frames and a lipoprotein gene family.

DNA sequencing and Southern blot analyses of a Borrelia burgdorferi DNA fragment encoding a signal sequence led to the discovery of a genetic locus, designated 2.9, which appears to be present in at least seven copies in virulent B. burgdorferi 297. DNA sequence analysis of these regions revealed that each 2.9 locus contained an operon of four genes (ABCD) and open reading frames designated rep+ (positive strand) and rep- (negative strand) which encoded multiple repeat motifs. Downstream of the rep+ gene(s) in six of the completely cloned and sequenced 2.9 loci also were lipoprotein (LP) genes possessing highly similar signal sequences but encoding variable mature polypeptides. The lipoproteins could he separated into two classes on the basis of hydrophilicity profiles, sequence similarities, and reactivity with specific antibodies. The 2.9 loci were localized to two (20- and 30-kb) supercoiled plasmids in B. burgdorferi 297. Northern (RNA) blot analysis established that the 2.9 ABCD operon was only minimally expressed, whereas the rep- gene(s) and at least three of the seven LP genes were expressed by B. burgdorferi in vitro. A single putative promoter element was identified by RNA primer extension analysis upstream of the ABCD operon, whereas a number of potential promoter regions existed upstream of the LP genes. The combined data indicate that the ABCD operon, rep+ and rep- genes, and LP genes are separately transcribed during in vitro growth. The 2.9 loci possess a repetitiveness, diversity, and complexity not previously described for B. burgdorferi; differential expression of these genes may facilitate the spirochete's ability to survive in diverse host environments.

Amino Acid Sequence↗

PubMed1996

Modulation of calcium currents by electrical activity.

Electrical activation of mouse dorsal root ganglion (DRG) neurons in cultures for 1-2 days produced a downregulation of voltage sensitive calcium currents, which persisted for > or = 24 h after stimulation was terminated. This regulation varied with different patterns of activation. Both the magnitude and time course of regulation of the low-threshold voltage-activated (LVA) and high-threshold voltage-activated (HVA) currents were differentially sensitive to neural impulse activity. Tonic stimulation at 0.5 Hz did not affect the HVA currents, but 2.5 Hz did produce a significant decrease. Phasic stimulation (10 Hz for 0.5 s every 2 s) with an average frequency of 2.5 Hz produced significantly more downregulation of HVA currents than did the tonic 2.5-Hz stimulation. The efficacy of phasic stimulation varied inversely with the interval between bursts. Thus phasic stimulation of 10 Hz for 0.5 s but delivered every 4 s produced no effects on HVA currents. Stimulation optimal for downregulation of Ca2+ currents also produced a decreased binding by the DRG neurons of an L-type Ca2+ channel antagonist. This suggests a downregulation by electrical activity of the number of Ca2+ channels, rather than an alteration in a constant number of channels. Depression of LVA currents was produced by all stimulus patterns tested, including 0.5-Hz tonic stimulation. Chronic stimulation with a stimulation pattern that downregulated Ca2+ currents also produced a slowing of the increase in intracellular Ca2+ (as measured by Fura-2/AM) that is produced acutely by repetitive stimulation. This is consonant with earlier studies of intracellular Ca2+ concentration kinetics in growth cones.

Animals↗

PubMed1996

Identification of two novel point mutations in the human protein S gene associated with familial protein S deficiency and thrombosis.

Individuals with thrombosis who were believed to possess associated familial protein S deficiency were analyzed for mutations in the protein S gene by a two-step process. First, the individuals were analyzed for protein S Pro626 A/G dimorphism in both their genomic DNA and reverse-transcribed (RT) polymerase chain reaction (PCR)-amplified cDNA from peripheral blood cell mRNA. If a heterozygote expressed both alleles at the mRNA level at this site in genomic DNA, a search for point mutations was made by direct cDNA sequencing. RT-PCR amplification of exons 1-6 with mRNA from two twin sisters, each of whom has severe type I protein S deficiency, revealed both larger and smaller fragments in addition to the expected 504-base pair fragment in normal individuals. A donor splicesite mutation at position +4 of the 5' end of intron A was subsequently identified in both sisters and their mother. This mutation would lead to incorrect precursor mRNA splicing and the observed cDNA products. Translation of the altered mRNAs would result in a truncated protein without biological activity. In a second family, cDNA sequencing revealed a T-->G mutation at codon 603 (Ile-->Ser) in exon 15 of the protein S gene in an individual with protein S deficiency (mixed type) and a history of thrombosis. The same mutation was also detected in the proband's mother and grandmother, both of whom also exhibit protein S deficiency and thrombotic disease. This mutation occurs within a disulfide loop of protein S that is believed to be responsible for binding to C4b binding protein and may result in greater affinity between protein S and C4b, consequently leading to thrombotic disease.

Adult↗

PubMed1996

L-arginine prevents corticotropin-induced increases in blood pressure in the rat.

In this study we examined whether L-arginine treatment could prevent corticotropin (ACTH)-induced increases in blood pressure in the Sprague-Dawley rat. Sixty rats were randomly divided into six groups (n = 10): sham injection, ACTH injection (0.5 mg/kg per day in divided doses), L-arginine (0.6%) in food plus sham injection, L-arginine plus ACTH treatment, D-arginine (0.6%) in food plus sham injection, and D-arginine plus ACTH. Systolic pressure, water intake, urine volume, body weight, plasma and urinary electrolytes, and serum corticosterone concentrations were measured. ACTH increased systolic pressure (from 127 +/- 2 to 165 +/- 6 mm Hg, P < .001), water intake, and urine volume and decreased body weight body weight. L-Arginine reduced ACTH-induced blood pressure rises (130 +/- 3 mm Hg, P < .001) but had no effect on blood pressure in sham-treated rats. D-Arginine did not affect blood pressure in sham-treated rats, and systolic pressure in D-arginine+ACTH-treated rats was similar to that of ACTH-treated rats. L-Arginine decreased serum corticosterone concentrations in sham-treated rats (424 +/- 42 versus 238 +/- 25 ng/mL, P < .01), but D-arginine had no effect. However, both drugs decreased serum corticosterone concentrations in ACTH-treated rats (1071 +/- 117 versus 739 +/- 95 and 695 +/- 72 ng/mL for L- and D-arginine, respectively; both P < .05). As L-arginine but not D-arginine prevented ACTH-induced increases in blood pressure in Sprague-Dawley rats and both L- and D-arginine reduced serum corticosterone concentrations in ACTH-treated rats, the effects of L-arginine in preventing ACTH-induced hypertension were not simply a consequence of decreased corticosterone secretion.

Adrenal Glands↗

PubMed1996

Detection of extended distribution of beta2-thyroid hormone receptor messenger ribonucleic acid (RNA) in adult rat brain using complementary RNA in situ hybridization histochemistry.

In situ hybridization histochemistry using a complementary RNA probe, directed at the entire length of the thyroid hormone receptor beta2 (TRbeta2)-specific region (-56 to 495 bp), was used to evaluate expression of TRbeta2 messenger RNA (mRNA) in coronal sections of adult rat brain. An extended distribution and intense expression of TRbeta2 mRNA was found in several regions of rat brain, including regions where TRbeta2 mRNA had not been previously identified using PCR or in situ hybridization histochemistry. These areas included hippocampus (dentate gyrus and C1, -2, and -3), cerebral cortex (predominantly layer 3), arcuate nucleus, median eminence, medial geniculate nucleus, tegmental bundle, medial and lateral lemniscus, Purkinje layer of the cerebellum, and several brain stem nuclei. In conclusion, we have developed a highly sensitive and specific method to demonstrate TRbeta2 mRNA expression in adult rat brain. The present findings are in agreement with immunoreactive TRbeta2 studies of rat brain and argue against the presence of an unidentified T3-binding protein to explain the previous discordant results of TRbeta2 mRNA and protein studies. In addition, the specificity of distribution of TR beta2 mRNA to certain brain nuclei, particularly those involved in hearing, implies a specific functional role of this receptor subtype and provides a physiological basis to understand the effects of hypothyroidism on brain development.

Animals↗

PubMed1996

Selective loss of small myelinated fibers in the lateral corticospinal tract due to midbrain infarction.

Small myelinated fibers in the lateral corticospinal tract (LCST) were selectively diminished as compared with large myelinated fibers in a patient with an old paramedian midbrain infarct involving the red nuclei, oculomotor nuclei, and inferior olivary pseudohypertrophy. Although the physiologic function of small myelinated fibers in the LCST is unknown in humans, we hypothesize that some of these fibers may include the rubrospinal tract.

Cerebral Infarction↗

PubMed1996

Abnormally expressed low-voltage-activated calcium channels in beta-cells from NOD mice and a related clonal cell line.

A macroscopic low-voltage-activated (LVA) inward current was found in pancreatic beta-cells isolated from NOD mice. However, this current was not present in nondiabetic prone mouse (e.g., Swiss-Webster) pancreatic beta-cells. We performed pharmacological analyses on this current in NOD insulinoma tumor cells (NIT-1). This cell line was developed from pancreatic beta-cells of a transgenic NOD mouse. The sodium-channel blocker, tetrodotoxin (TTX; 2 micromol/l) had no effect on this LVA current. The amplitudes of currents elicited by a -20 mV test pulse retained similarity when the extracellular sodium concentration was increased from 0 to 115 mmol/l; when the extracellular calcium concentration was decreased from 10 to 2 mmol/l, there was an approximate 50% reduction of this current elicited by a -30 mV test pulse. Neither the L-type calcium-channel blocker, nifedipine (3 micromol/l), nor the N-type calcium-channel blocker, omega-CgTx-GVIA (1 micromol/l), at -30 mV produced an appreciable effect. The T-type calcium-channel blockers, nickel (3 micromol/l) and amiloride (250 micromol/l), effectively reduced the peak of this current. In 2 mmol/l calcium external solution, the threshold of voltage-dependent activation of this calcium current was approximately -65 mV, and the peak current occurred at -20 mV. Half-maximum steady-state inactivation was around -43 mV. The mean time constant of slow deactivating tail currents generated by a preceding 20 mV pulse was 2.53 ms. The intracellular free calcium concentration was two- to threefold higher in NOD mouse pancreatic beta-cells compared with Swiss-Webster pancreatic beta-cells. We concluded that there are LVA calcium channels abnormally expressed in NOD mouse beta-cells. This LVA calcium channel may be factorial to the high cytosolic free calcium concentration observed in these cells, and thereby may contribute to the pathogenesis of NOD mouse beta-cells.

Amiloride↗

PubMed1996

Chromosome 3 allelic losses and microsatellite alterations in transitional cell carcinoma of the urinary bladder.

A deletion analysis of chromosome 3 was conducted in 72 cases of transitional cell carcinoma of the urinary bladder using seven microsatellites spanning the 3p arm and two additional microsatellites in 3q. Results showed that 19 of 72 (26.4%) cases had deletions in one or more 3p regions. Two regions of frequent deletion were identified: 3p12-14 and 3p21-23. Less frequent deletions at 3p24.2-25 were also observed. Deletions at 3p were weakly correlated with tumor grade, but strongly with pathological stage. Among 70 cases with histological grade available, 4 of 29 (13.8%) grade 1 and 2 tumors, and 15 of 41 (36.6%) grade 3 tumors showed allelic losses in one or more of the 3p regions studied (P = 0.055). Among 69 cases with pathological stage available, none of 27 superficial carcinomas (pTa, pTis, and pT1) showed 3p deletions, whereas 18 of 42 (42.9%) muscle invasive lesions (pT2, pT3, and pT4) displayed allelic losses at 3p (P < 0.001). In addition, 12 cases showed microsatellite instability, but there was no correlation between abnormalities and tumor grade or stage. No correlation was found between deletions at 3p21-23 and microsatellite instability. In conclusion, deletions at three discrete regions of 3p were identified in bladder carcinoma, suggesting the involvement of candidate tumor suppressor genes residing in these regions. Moreover, detection of allelic losses in these regions was associated with higher tumor grade and more advanced stage, suggesting their potential involvement in bladder tumor progression.

Biomarkers, Tumor↗

PubMed1996

[Chemical constituents of Taxillus levinei (Merr.) H.S.Kiu].

Four compounds were isolated from the leaves of Taxillus levinei and identified as protocatechuic acid, isoquercitrin, quercetin-3-O-(6"-galloyl)-beta-D-glucoside and quercetin-3-O-beta-D-glucuronide on the basis of chemical properties and spectral data. These compounds were obtained from T. levinei for the first time.

Drugs, Chinese Herbal↗

PubMed1996

[Percutaneous microwave coagulation therapy for hepatocellular carcinoma--study on its therapeutic effect in surgical cases].

Six patients with hepatocellular carcinoma were subjected to percutaneous microwave coagulation therapy (PMCT) by ultrasonic guiding. The size of the main tumor in the present cases was limited to not more than 2 cm. From 18 to 48 days after PMCT, each patient was subjected to surgery and pathological examination. By macroscopic observation, the PMCT area including both non-tumor and tumor regions looked yellowish white, and the boundary was clearly recognized. In the histological examination, the coagulation area surrounded by fibrous capsule was found, and deletion of nuclei and changes in stainability were observed in the marginal region. These changes indicated obvious coagulation necrosis, but the changes became less intense toward the center in the area, and in some portions, the tissue was indistinguishable from viable cells by light microscopy. In 2 cases out of the 6, part of the tumor remained outside the coagulation area. Since only the area determined by the microwave electrode is coagulated to cause necrosis on PMCT, sufficient safety margin should be required.

Aged↗

PubMed1996

[Receptor mechanism of dynorphin A in rat secondary spinal cord injuries].

OBJECTIVE: To clarify the effects of dynorphin A on secondary spinal cord injuries. METHODS: Spinal cord injured rat model made according to modified Allen's method was used by comparing the effect of intrathecal dynorphin A antiserum and that of its receptor antagonist nor-BNI. RESULTS: The recovery of the muscle tension and motor function of the hindlimb in dynorphin antiserum group was markedly faster than that in both control and nor-BNI groups. Also, the recovery of motor function in the nor-BNI group was favorable at the early stage of injury, compared to the control group. Pathological observation showed that the residual area of the spinal cord in dynorphin A1-13 antiserum group was larger than that in both control and nor-BNI groups. The residual area of the spinal cord in the nor-BNI group was also larger than that in the control group. CONCLUSION: These observations support the hypothesis that dynorphin contributes to certain pathophysiological changes following traumatic SCI through both opiate-receptor mediated and nonopioid mechanisms.

Animals↗

PubMed1996

[A serological study on the infection of Helicobacter pylori among children].

Using ELISA method, anti-H. pylori IgG and IgM were detected in 181 sera from patients (aged 2-14 years) complaining of repeated midepigastical pain and 152 sera of controls. The positive rate of anti-H, pylori IgG in the patients was 53%, significantly higher than those of control groups (34.6%-35%), (P < 0.05). The presence of anti-H. pylori IgG in serum can assist in the diagnosis of H. pylori, but can not indicate the existence of H. pylori. There were no evident relationships between level of antibodies (anti-H. pylori IgG and IgM) and the degree of H. pylori infection, or the duration of disease. Children's H. pylori infection increases with age. Elder children have the same positive rate of anti-H. pylori IgG as adults. Hence, eradication of H. pylori infection should be focused not only on adults but also on children.

Adolescent↗

PubMed1996

[Effects of different modes for health education on mothers' knowledge of baby feeding].

To study the effects of existing different modes of health education on mothers' knowledge in feeding babies and young children, 414 mothers with their babies aged 0 to 18 months were interviewed with an ad hoc questionnaire in urban and rural areas in Guangdong Province during February to April, 1995. Results revealed that the best source of mothers' nutritional knowledge was derived from a comprehensive mode of health education, the others from mass media and medical care professionals, and the last one from mothers' relatives and friends. Prenatal training course for baby feeding was one of the effective measures in nutritional education, but its effects depended on mothers' occupation and cultural level. Baby-friend hospitals played an important role in improvement of mothers' knowledge level in breast-feeding. It suggests comprehensive education channel, training course for pregnant women, baby-friend hospitals, and so on, all are major means of nutritional education for baby feeding.

Adult↗