Search PubMed⌕ Search

Biomedical subjects

X F Li

Publications and source records attributed to X F Li.

At least 91 records · Page 5Linked to original sources
PubMed1994

[Relationship between effect of tetrandrine on pleurisy and phospholipase A2].

A model of pleurisy was established with an intrapleural injection of carrageenan (Car, 10 mg.kg-1) in rats to explore the anti-inflammatory action of tetrandrine (Tet) and its mechanism. After the injection of Car, the exudate, protein and neutrophils appeared in the pleural cavity of rats at 2 h, then increased progressively, and reached a peak level at 12 h and remained high up to 48 h. The phospholipase A2(PLA2) activity of neutrophils (Neu-PLA2) and of the acellular component (ACC-PLA2) in the pleural exudate intensified at 2 h, rose to maximal intensity at 8 h, and started to decline at 48 h. The changes of the amount of exudate, protein content and neutrophil count, and parameters indicating the inflammatory response, were closely related to that of the PLA2 activity (r = 0.749-0.928, P < 0.05 or 0.01). By ig gavage of Tet (10-80 mg.kg-1) to rats at 30 min before and 4 h after the injection of Car, the inflammatory parameters were reduced and the PLA2 activity was inhibited, dose-dependently. The reductions of the inflammatory parameters were significantly associated with the inhibition of the PLA2 activity (r = 0.928-0.993, P < 0.05 or 0.01). These results indicate that Tet has a fine anti-inflammatory action and its mechanism may involve the inhibition on the activation and release of PLA2 of inflammatory cells.

Alkaloids↗
PubMed1993

Determination of the degree of cure of dental resins using Raman and FT-Raman spectroscopy.

FT-IR spectroscopy has traditionally been used to determine the degree of conversion of dental resins. FT-Raman scattering provided an alternate method of obtaining degrees of conversion for these systems and was particularly useful for measuring spectra of materials without any sample preparation. Raman and FT-Raman spectroscopy gave identical results, but the latter technique was preferred for the highly fluorescent samples often encountered in commercial composites. Linear calibration curves were obtained for the aromatic mixtures Bis-GMA/TEGDMA and Bisphenol-A/TEGDMA using C = C/phi, and for the wholly aliphatic mixture EGDMA/EGDA using C = C/C = O, over a wide range of mole ratios. If both the mole and intensity ratios [C = C/phi or C = C/C = O] were known for an uncured dental resin, then the degrees of conversion could be obtained for the cured materials using Raman spectroscopy. However, if the mole ratios for the uncured resin were unknown, then the degree of conversion depended on the calibration curve, since the Raman scattering cross section of the vibrational modes depended on the molecules to which they were attached.

Benzhydryl Compounds↗
PubMed1993

Transforming growth factor-beta (TGF-beta)-mediated immunosuppression in the tumor-bearing state: enhanced production of TGF-beta and a progressive increase in TGF-beta susceptibility of anti-tumor CD4+ T cell function.

The present study deals with the effect of transforming growth factor-beta (TGF-beta) on anti-tumor immune responsiveness at various stages of the tumor-bearing state. Spleen cells from BALB/c mice bearing a syngeneic tumor (CSA1M) 1-3 wk after inoculation with CSA1M cells produced interleukin-2 (IL-2) and macrophage-activating factor (MAF)/interferon-gamma (IFN-gamma) upon in vitro culture without addition of exogenous tumor antigens. This lymphokine production was achieved through collaboration between anti-CSA1M CD4+ T cells and antigen-presenting cells that had been pulsed with CSA1M tumor antigens in vivo in the tumor-bearing state. The IL-2-producing capacity of CD4+ T cells reached the maximal level as early as one week after tumor implantation but decreased with the progress of tumor-bearing stages. In contrast, the capacity of CD4+ T cells to produce MAF/IFN-gamma was not affected but was maintained at high levels even late in the tumor-bearing state. The addition of recombinant TGF-beta (rTGF-beta) to cultures of spleen cells from various tumor-bearing stages resulted in the suppression of lymphokine production. However, the magnitude of the TGF-beta-induced suppression varied depending on which tumor-bearing stages of splenic cells were tested as a responding cell population; it was slight in cells from early (1-3 wk) tumor-bearing stages but increased in cells from donor mice at later tumor-bearing stages. Thus, spleen cells from late tumor-bearing stages with weak but significant IL-2-producing and considerable MAF/IFN-gamma producing capacities failed to produce these lymphokines when rTGF-beta was present in cultures. A progressive increase in the TGF-beta susceptibility was also observed for IL-4-producing Th2 as well as IL-2/MAF-producing Th1 cells. In addition, increased levels of TGF-beta were detected in plasma from tumor-bearing mice at late stages. Taken together, these results indicate that tumor-bearing mice exhibit enhanced production of TGF-beta as well as a progressive increase in the susceptibility of anti-tumor CD4+ T cells to TGF-beta-induced suppressive mechanisms.

Animals↗
PubMed1993

The effects of alpha-adrenoceptor agonists on intracellular Ca2+ levels in freshly dispersed single smooth muscle cells from rat tail artery.

1. The presence of functional alpha-adrenoceptors in freshly dispersed single smooth muscle cells from rat tail arteries was investigated by use of selective alpha-adrenoceptor agonists and antagonists. 2. Cirazoline, a selective alpha 1-adrenoceptor agonist, caused a prazosin-sensitive, rapid but transient increase in intracellular Ca2+, which was partially inhibited by the voltage-dependent Ca2+ channel blocker, nifedipine. 3. TL99, an alpha 2-adrenoceptor agonist, in the presence of prazosin, initiated a slow and sustained increase in intracellular Ca2+ which was partially inhibited by yohimbine and almost completely blocked by nifedipine. 4. In rat tail artery, the effects (dose-response and time-response curves) of cirazoline and TL99 on intracellular Ca2+ levels in freshly dispersed single smooth muscle cells were comparable with those obtained with organ bath studies of ring preparations of artery. 5. In freshly dispersed single smooth muscle cells, the time-course response curves induced by the selective alpha 1-adrenoceptor agonist, phenylephrine and the selective alpha 2-adrenoceptor agonist, UK14304, were similar to those observed with cirazoline and TL99, respectively. 6. These results indicate that: (a) functional alpha 1- and alpha 2-adrenoceptors are present in freshly dispersed single smooth muscle cells from rat tail artery and (b) alpha 1- and alpha 2-adrenoceptors are coupled to different cellular processes that lead to an increase in intracellular Ca2+.

Adrenergic alpha-Agonists↗
PubMed1992

Particular types of tumor cells have the capacity to convert transforming growth factor beta from a latent to an active form.

We investigated the capacities of various tumor types to generate an active versus latent form of transforming growth factor beta (TGF-beta) in its culture supernatants (SNs). Tumor cell lines were divided into three types depending on the form and magnitude of TGF-beta detected in their culture SNs: some (2 of 7 lines) generated mostly an active form (Type A); others (4 of 7) generated exclusively a latent form (Type B); and the remaining line (1 of 7) produced only marginal levels of active/latent TGF-beta (Type C). When Type A tumor cells were cultured at lower numbers, cultures failed to generate active TGF-beta. However, the addition of Type B tumor cell culture SNs containing only a latent form of TGF-beta resulted in the generation of the potent activity of active TGF-beta. This capacity was observed for another Type A tumor but not for other types (Type B and Type C). An active form of TGF-beta was detected in culture SNs of Type A tumor cells as early as 3-6 h after the addition of Type B tumor culture SNs. The emergence of an active form of TGF-beta was also observed in cultures of Type A tumor cells, the protein synthesis of which was almost completely inhibited by pretreatment with cycloheximide. Moreover, the Type B tumor SN used for the induction of active TGF-beta activity was found to contain latent TGF-beta with an apparent molecular weight of about 200,000. Type A tumor cells were also capable of generating active TGF-beta by the addition of recombinant TGF-beta of latent form with a small molecular weight (about 60,000), although the generation of active TGF-beta was much weaker after the addition of small latent TGF-beta than after the addition of large latent TGF-beta. Taken collectively, these results indicate that particular types of tumor cells have the capacity to generate an active form of TGF-beta and that such capacity can be attributed to their potential to convert TGF-beta from a latent (mainly large type) to an active form.

Animals↗
PubMed1992

A review of the effects of long-acting progestogen-only contraceptives on ovarian activity.

Progestogen-only contraception acts mainly by blocking cervical mucus and preventing sperm penetration through it does have a variable pattern of contraceptive effects on the endometrium and ovary. In contrast with the complete suppression of ovarian function with combined pill or injectable use, a variable degree of endocrine activity is demonstrated in women choosing a long-acting progestogen-only contraceptive. This degree of suppression of ovarian activity explains the decrease in systemic side-effects, the rapid resumption of ovulation and recovery of fertility following the discontinuation of the method. New delivery systems of progestogens, the vaginal ring and implant, offer better and more consistent contraceptive effects.

Cervix Mucus↗
PubMed1992

Effects of cross-gender steroid hormone treatment on prolactin concentrations in humans.

It is well known that peripheral prolactin levels are significantly higher in menarcheal women than in men. Higher levels of prolactin in menarcheal women are related to exposure to higher levels of estrogen in women than in men. Increased exposure to androgens in men has also been proposed as a possible reason to account for lower prolactin levels in men; however, this suggestion has not been conclusively proven. The current study sought to evaluate the cross-gender effects of male and female hormones on basal levels and the pituitary store of prolactin in humans. Four groups of individuals were involved: normal men and women, male and female transsexuals primed with female hormones and testosterone, respectively for at least 6 months. A metoclopramide challenge test was carried out on each subject of each group. Subjects were rested for 1 h, with an indwelling catheter in the antecubital vein, before a blood sample was collected for estimation of basal hormone levels. Following an oral ingestion of 10 mg of metoclopramide, blood samples were collected at 15, 30, 60, 90, 120, 150 and 180 min. Prolactin, estradiol and testosterone concentrations were measured by radioimmunoassay. Basal levels as well as metoclopramide-induced releases of prolactin (as measured by area under the curve) in normal women were significantly higher (p less than 0.05) than corresponding levels in normal men. Following long-term priming with female hormones, the pattern of response to metoclopramide in male transsexuals was dramatically changed.(ABSTRACT TRUNCATED AT 250 WORDS)

Estradiol↗
PubMed1991

Transforming growth factor-beta-induced inhibition of T cell function. Susceptibility difference in T cells of various phenotypes and functions and its relevance to immunosuppression in the tumor-bearing state.

The present study investigates the nature of humoral component(s) generated in tumor-bearing hosts to induce immune dysfunction of T cells. Cell-free ascitic fluid and culture supernatant (SN) were obtained from the ascites and cultures allowing MH134 hepatoma cells to grow. These ascites and SN samples were tested for their abilities to influence the generation of CTL responses to TNP and alloantigens. The generation of the anti-TNP CTL responses that require self H-2-restricted CD4+ Th cells was markedly suppressed by addition of the ascites or SN under conditions in which these samples did not inhibit anti-allo CTL responses capable of using alternate pathways of allo-restricted CD4+ and CD8+ Th. The activation of CD8+ CTL precursors and CTL activity were also resistant to the ascites or SN. The ascites- or SN-induced suppressive effect to which CD4+ Th were most susceptible was found to be mediated by transforming growth factor-beta (TGF-beta) activity, because: 1) the TGF-beta activity was detected in the MH134 ascites and culture SN; 2) the suppression of CD4+ Th function required for anti-TNP CTL responses was almost completely prevented by addition of anti-TGF-beta antibody to cultures and; 3) rTGF-beta also induced similar patterns of immunosuppression to those observed by ascites or SN. These results indicate that TGF-beta produced by tumor cells induces deleterious effects on T cell, especially on the CD4+ Th subset, and provide an explanation for the molecular mechanism underlying the previously observed CD4+ Th-selective suppression in the tumor-bearing state.

Animals↗
PubMed1991

Perception of acoustic source characteristics: walking sounds.

The current study investigated the ability of subjects to perceive source characteristics (the gender of a human walker) of a naturally occurring auditory event (human walking). A number of acoustic properties were measured and subjected to statistical analyses in order to identify those properties that differentiate male and female walking footsteps. A principal component analysis on the statistical properties of the spectral energy distributions then identified two classes of information that were important in determining subject perception of the gender of a walker: (1) the spectral peak which integrates the information about the spectral central tendency of frequency and shape of the spectral peak; and (2) the contribution of high-frequency spectral components. A follow-up experiment then manipulated these spectral properties to verify their contributions in the perceptual classification of walker gender. Additionally, the effect of shoe on the gender judgement in walking sequences was assessed by having both male and female walkers wear male's shoes.

Acoustics↗
PubMed1991

[Exploration of the application of harmonic analysis in the study of genetics].

Taking the accumulation process of protein and oil in rapeseed as an example, the paper explores the possibility of application of harmonic analysis to describing the quantitative change process of biological characters. Some genetic rules involved in the phenotype processes of characters are discovered through decomposing genetic quantity from the dynamic change processes of the characters. The preliminary conclusion is that there are two prevailing simple-harmonic oscillators in the accumulation processes of protein and oil in rapeseed, which are inheritable. This shows that harmonic analysis opens up a new explorative way by which genetic rules of the phenotype processes of biological characters can be revealed.

Animals↗
PubMed1991

[Effects of sodium 18 beta-glycrrhetinic acid on the production of active oxygen species and the concentration of intracellular free Ca2+ in rat neutrophils].

The effects of sodium 18 beta-glycyrrhetinic acid (SGA) on the production of active oxygen species (AOS) and the concentration of intracellular free Ca2+ ([Ca2+]i) in the rat neutrophils were studied by the methods of luminoldependent chemiluminescence and calcium indicator Fura-2 loading. The results showed that SGA 0.8-12.7 mumol.L-1 selectively inhibited calcium inophore A-23187-stimulated AOS production with IC50 1.4 mumol.L-1, while SGA 25.4-203 mumol.L-1 stimulated neutrophils to generate AOS and potentiated the action of chemotactic peptide f-MLP on inducing AOS production. SGA 25.4-203 or 6.3-50.7 mumol.L-1 depressed the [Ca2+]i rise in neutrophils stimulated by A-23187 or f-MLP; in the contrast, verapamil or diltiazem has higher effective concentration more than 100 or 200 mumol.L-1 to f-MLP and left [Ca2+]i rise induced by A-23187 unaffected. SGA 101.5-203 mumol.L-1 also caused [Ca2+]i rise in neutrophils. The result analysis indicate that the effect of SGA on AOS production has no relationship with its regulation to [Ca2+]i in neutrophils.

Animals↗
PubMed1990

Categorical perception of nonspeech chirps and bleats.

Mattingly, Liberman, Syrdal, and Halwes, (1971) claimed to demonstrate that subjects cannot classify nonspeech chirp and bleat continua, but that they can classify into three categories a syllable place continuum whose variation is physically identical to the nonspeech chirp and bleat continua. This finding for F2 transitions, as well as similar findings for F3 transitions, has been cited as one source of support for theories that different modes or modules underlie the perception of speech and nonspeech acoustic stimuli. However, this pattern of finding for speech and nonspeech continua may be the result of research methods rather than a true difference in subject ability. Using tonal stimuli based on the nonspeech stimuli of Mattingly et al., we found that subjects, with appropriate practice, could classify nonspeech chirp, short bleat, and bleat continua with boundaries equivalent to the syllable place continuum of Mattingly et al. With the possible exception of the higher frequency boundary for both our bleats and the Mattingly syllables, ABX discrimination peaks were clearly present and corresponded in location to the given labeling boundary.

Animals↗
PubMed1989

The effects of chronic vitamin A excess on bone remodeling in aged rats.

This study was conducted to assess the effects of long-term ingestion of moderate excesses of vitamin A on trabecular bone remodeling in the fifth lumbar vertebral body of aged rats. Eighteen-month-old rats were fed diets with vitamin A content equal to the daily requirement (DR), 2-fold, and 5-fold the DR along with calcium content of either the DR or 0.3-fold the DR, for 14 months each. As expected, serum concentrations of 1,25-dihydroxyvitamin D were higher in the reduced than in the normal calcium intake groups (65.1 +/- 2.4 SEM vs 47.8 +/- 2.1 pg/ml, P less than 0.001). Calcium balance was more positive at the higher than the lower calcium intake (5.7 vs 0.9 mg, P less than 0.001) but was unaffected by vitamin A intake. Histomorphometric analysis of the fifth lumbar vertebral body revealed that the 2-fold but not the 5-fold excess in vitamin A intake resulted in a 15% increase in percentage of trabecular bone (P less than 0.02). The low calcium diet depressed bone growth (total bone tissue) but did not affect percentage of trabecular bone. Several effects of the vitamin A excess and low calcium diet were noted along the trabecular surface including increased mineral apposition rate and resorption surfaces and decreased formation surfaces. The net effect of vitamin A on trabecular bone of the rat varies as intake begins to exceed the DR. At a 2-fold excess, a modest favorable effect on percentage of trabecular bone was observed.

Aging↗
PubMed1989

Hemin-induced erythroid differentiation changes the sensitivity of K562 cells to tumor necrosis factor-alpha.

Tumor necrosis factor-alpha (TNF) can inhibit the growth of erythroid progenitors (erythroid colony-forming units [CFU-E] and erythroid burst-forming units [BFU-E]) at picomolar concentrations, but only if added within the first 48 h of culture. These data suggested that cells undergoing erythroid differentiation become resistant to TNF. To test this hypothesis, K562 cells were treated with hemin to induce erythroid differentiation and then tested for their sensitivity to TNF in terms of growth and TNF receptor expression. TNF inhibited the growth of untreated K562 cells, but not hemin-treated K562 cells. Untreated K562 cells expressed TNF receptors, whereas few hemin-treated K562 cells expressed TNF receptors within 24 h of exposure to hemin. These data show that K562 cells induced to differentiate along the erythroid pathway are resistant to TNF because they lack TNF receptors and suggest that the resistance of erythropoietin-treated human bone marrow cells to TNF added after 48 h of culture may also reflect loss of TNF receptors associated with erythroid differentiation.

Cell Differentiation↗
PubMed1989

[Preliminary study on the virulent difference between viral strains isolated from Rattus norvegicus and Apodemus agrarius in Fujian Province].

Virulence between virus strains of hemorrhagic fever with renal syndrome (HFRS) from R. norvegicus and A. agrarius were different, besides the diversity in their epidemiological feature, clinical symptoms and antigenicity. Virulence of the virus strains from R. norvegicus, especially those from nonepidemic areas, were weak than those from A. agrarius. Sucking mice might be used for determining virulence of the virus strains from various source. Foci of HFRS had been in southern Fujian, but human cases of HFRS had rarely been found, or only a few mild cases were found in a few areas. This might be related to weaker virulence of the virus strains from R. norvegicus. The prevalent degree of the disease might be related to HFRSV of wild rattus type in the area.

Animals↗
PubMed1989

[Differentiation of the type of EHF antibodies by RPHI].

This article reports the use of for differentiation of the type of EHF antibodies. A total of 58 convalescent-phase sera from EHF patients in natural foci of predominant Apodemus type of EHF and in those of Rattus type of EFH were examined. In the former 34/36 (94.44%) belonged to Apodemus type, and in the latter 22/22 (100%) belonged to Rattus type. Both RPHI and HI obtained the same result in differentiation of the type of EHF antibodies. RPHI possesses sensitivity and specificity in EHF diagnosis, and may be used for differentiation of the type of EHF antibodies.

Animals↗