Search PubMed⌕ Search

Biomedical subjects

Q Xu

Publications and source records attributed to Q Xu.

At least 433 records · Page 24Linked to original sources
PubMed1992

Synthesis, characterization, and antitumor activity of new chloroethylamine platinum complexes.

A series of cis-bis-(2-chloroethylamine)platinum(II) and platinum(IV) complexes were synthesized and characterized by elemental analysis, IR, and 1H and 195Pt NMR spectroscopic techniques. Complexes were tested in vitro against murine L1210 leukemia and human ovarian A2780 cell lines and in vivo against the L1210 leukemia model. Some of these complexes showed excellent antitumor activity in both systems. However, all were inactive against cisplatin-resistant A2780/CP cells.

Animals↗
PubMed1992

Hexaamminecobalt(III) binding environments on double-helical DNA.

Previous cation nmr evidence suggests that univalent cations such as Na+ bind to DNA in a diffuse, nonspecific manner, whereas di- and trivalent cations show distinct binding heterogeneity. Here are reported 59Co- and 23Na-nmr measurements of the %GC dependence of the DNA binding behavior of the trivalent hexaamminecobalt(III) cation. When Co(NH3)6Cl3 titrations are performed on one mammalian and three bacterial DNAs, evidence is found for at least three distinct classes of bound Co(NH3)6(3+). A comparison of titration curves for all four DNAs demonstrates that an increase in GC content correlates with an increase in the fraction of specific Co(NH3)6(3+). binding sites. For M. lysodeikticus DNA (72% GC), a slowly exchanging class of bound 59Co(NH3)6(3+) is apparent. This class of sites is saturated at very low binding densities (between 0.02 and 0.03 cobalt cations per DNA phosphate). At higher binding densities (greater than 0.03), the signal due to slowly exchanging 59Co(NH3)6(3+) disappears into the noise, and a single 59Co(NH3)6(3+) signal is observed. Within the sensitivity limitations of these measurements, no evidence for slowly exchanging bound 59Co(NH3)6(3+) could be found for any of the other DNAs, for which a single, rapidly exchanging 59Co(NH3)6(3+) signal is observed at all binding densities. For this rapidly exchanging signal, for all four DNAs, the measured 59Co(NH3)6(3+) nmr parameters depend significantly on (a) binding density and (b) GC content of the DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

The influence of bile salts on small intestinal motility in the guinea pig in vitro.

The effect of bile salts on intestinal motility is unclear. In the current study, isometric contractions of the guinea pig terminal ileum were examined in vitro. Dose-response curves to known agonists cholecystokinin (CCK), bethanechol, and KCl were constructed alone and in the presence of atropine (10(-6) mol/L), tetrodotoxin (10(-6) mol/L), and different bile salts, namely, taurodeoxycholate, tauroursodeoxycholate, taurocholate, glycodeoxycholate, and glycoursodeoxycholate. These bile salts, at levels as low as 5 and 50 mumol/L, significantly depressed (P less than 0.05) CCK-induced contractions throughout the dose-response curves and were concentration dependent. This depressant effect was not dependent on the bile salt species or any apparent physicochemical differences between them. The inhibitory effect was also specific for certain agonists such as CCK (the action of which was partially mediated by cholinergic nerves, being depressed by atropine and abolished by tetrodotoxin), field stimulation, and nicotine. Bile salts had no effect on either bethanechol- or KCl-induced contractions. Such bile salt inhibition of excitatory, cholinergic, enteric neurons may slow transit through the ileum, enhancing the time for absorption and conserving the bile salt pool.

Animals↗
PubMed1992

Characterization and developmental expression of Xenopus C/EBP gene.

The Xenopus homolog of the transcription factor C/EBP (CCAAT/enhancer core binding protein), cloned from an adult Xenopus liver cDNA library, encodes a protein whose sequence is 67% homologous to that of rat C/EBP at the amino acid level, with virtually identical sequence of the basic-zipper region at the carboxyl terminus. As determined by gel electrophoretic mobility shift assays, the protein synthesized from xC/EBP cDNA bound specifically to the consensus binding site for C/EBP-like proteins. Northern blotting and RNase protection revealed a single species of xC/EBP mRNA of 2.7 kb which was most abundant in adult Xenopus liver, with smaller amounts in spleen, kidney, oviduct and brain and undetectable in heart and skeletal muscle. Although a small amount of this transcript could be detected in unfertilized eggs and early embryos, its accumulation rose sharply at the onset of metamorphosis (stage 55/56), and continued to increase through metamorphic climax to reach its highest level in stage 66 froglet liver, but thereafter declining in adult liver. In situ hybridization revealed a uniform pattern of distribution of xC/EBP mRNA in the liver and fat body throughout metamorphosis. Towards the end of metamorphosis, high levels of xC/EBP mRNA were detected in epithelial cells of the digestive tract. However, the spatial pattern of cells expressing the transcript changed markedly in the developing kidney. Our results suggest that xC/EBP may be involved as a transcription factor in the establishment of the adult phenotype during post-embryonic development of Xenopus.

Amino Acid Sequence↗
PubMed1992

Induction of arteriosclerosis in normocholesterolemic rabbits by immunization with heat shock protein 65.

Previous studies have established the presence of high numbers of activated T lymphocytes and "aberrant" expression of major histocompatibility complex class II antigens by endothelial and smooth muscle cells in human atherosclerotic lesions, implicating the involvement of a local cellular immune response. The identity of the antigen(s) eliciting this immune response, the extent of their effect, and the atherogenic stage at which they occur remain to be determined. In the present studies, 120 normocholesterolemic New Zealand White rabbits were immunized one or more times with various antigens, with or without adjuvants. The antigens and adjuvants included human or rabbit atherosclerotic lesion proteins, ovalbumin, Freund's complete and/or incomplete adjuvants, recombinant mycobacterial heat shock protein 65 (hsp65), and two hsp-free adjuvants, Ribi complete adjuvant and lipopeptide. In addition, some groups received a high-cholesterol diet. Sixteen weeks after the first immunization the animals were killed, and arteriosclerotic lesions in the intima of the aortic arch were found to have developed only in those animals immunized with antigenic preparations containing hsp, either in the form of whole mycobacteria or as purified recombinant hsp65, although their serum cholesterol levels were normal. No arteriosclerotic changes exceeding those of controls were found in the other groups, irrespective of the antigen used. Immunohistopathologic examination revealed that the lesions contained 20% T cells, 10-30% macrophages, and 10-40% smooth muscle cells. Analysis of the peripheral blood T-lymphocyte proliferative responses revealed that the occurrence of lesions was positively correlated with the presence of hsp65-reactive T cells, suggesting that hsp65 is involved in the induction of arteriosclerotic lesions. Furthermore, combined immunization with hsp-containing material and a cholesterol-rich diet provoked development of significantly more severe atherosclerosis and the appearance of characteristic foam cells. We conclude that an (auto)immune response to hsp may initiate the development of atherosclerosis and that a high blood cholesterol level is only one albeit a very important risk factor.

Animals↗
PubMed1991

Influence of the 53 kDa glycoprotein on the cooperativity of the Ca(2+)-ATPase of the sarcoplasmic reticulum.

Previous results from this laboratory suggest that the 53 kDa glycoprotein (GP-53) of rabbit skeletal muscle sarcoplasmic reticulum membrane (SR) may influence coupling between Ca2+ transport and ATP hydrolysis by the Ca(2+)-ATPase. Here we report evidence that GP-53 may influence the cooperative behavior of the Ca(2+)-ATPase. The ATPase activity of the Ca(2+)-ATPase displays negative cooperative dependence (Hill coefficient n less than 1) on [MgATP] and has positive cooperative dependence (n greater than 1) on [Ca2+]free. We have determined the degree of cooperativity for native SR vesicles, SR preincubated with antiserum against GP-53 or preimmune serum, and SR partially extracted with KCl-cholate. Our results show that SR preincubated with preimmune serum or SR treated with cholate in 50 mM KCl (yielding membranes rich in GP-53) demonstrate a cooperative dependence of Ca(2+)-ATPase activity on both [ATP] and [Ca2+] similar to that of untreated SR. SR preincubated with anti-GP-53 antiserum (which causes an uncoupling of Ca2+ transport from ATP hydrolysis) or SR extracted with cholate in 1 M KCl (yielding membranes depleted of GP-53) displays decreased positive cooperative dependence on [Ca2+] and decreased negative cooperative dependence on [ATP]. The results are consistent with the interpretation that GP-53 may influence the cooperative behavior of the Ca(2+)-ATPase.

Adenosine Triphosphate↗
PubMed1991

Ontogeny of the production of an estrogen-regulated eosinophil chemotactic factor in the rat uterus.

The ontogeny of an estrogen-induced eosinophil chemotactic activity in the uterus after estrogen administration and its regulation by progesterone was studied in neonatal rats at 3, 7, 10, and 13 days of age. These results were compared with the increase in peroxidase activity and the secretion of complement component C3 by the uterus. No chemotactic activity was observed in animals younger than 14 days, and after this age the estrogen regulation of the response was also prevented by the co-administration of progesterone. The secretion of complement C3 appeared earlier, at 10 days of age. It was also observed that the uterus of 3-7-day-old rats responded to estrogen by increasing the secretion of two proteins of 36 and 110 kDa. No further regulation or synthesis was observed with increasing age for these two proteins.

Aging↗
PubMed1991

[Characterization of HDL receptor and its ligand in cultured smooth muscle cells isolated from rabbit aorta].

The characteristics of HDL3 binding sites on cultured smooth muscle cells originally isolated from rabbit aorta were studied with 125I-labelled rabbit HDL3. The results indicated that specific and high-affinity HDL3 binding sites were present on the surface of smooth muscle cells (Bmax = 0.321 micrograms/mg cell protein; KD = 5.6 x 10(-8) mol/L). The presence of a high concentration of non-labelled apo A1 blocked the 125I-HDL3 binding rate by 50%. 125I-HDL3 pretreated (blocked) with rat antirabbit apo A1 IgG lost up to 70% of its original binding activity. Additionally, rabbit apo A1 was isolated, purified and its amino acid composition analyzed. The binding rate of 125I-HDL3 to smooth muscle cells was not affected by the presence of various concentrations of cholesterol. It was also relatively unaffected by trypsin or pronase treatment and independent of Ca2+ concentration. The optimal temperature and pH were 4 degrees C and 2 respectively. All of these characteristics differ from those of the LDL receptors. These results suggest that apo A1 is a major ligand of HDL3 receptors.

Animals↗
PubMed1991

[Effect of rhizoma Zingiberis on anoxic or cooled mice].

The anti-anoxic experiments have indicated that the petroleum ether extract of Rhizoma Zingiberis can prolong the survival time in mice poisoned by KCN or under the condition of normobaric hypoxia, as well as decapitation-induced gasping duration in mice, but can not prolong the survival time in mice poisoned by NaNO4. The anti-anoxic action might be related to the reduction rate of O2 consumption of the body. The aqueous extract of Rhizoma Zingiberis does not possess the above-mentioned anti-anoxic action. Both extracts do not affect the survival time in cooled mice.

Animals↗
PubMed1991

The effect of estradiol on the production and secretion of complement component 3 by the rat uterus and surgically induced endometriotic tissue.

We have recently demonstrated that glandular epithelial cells isolated from human endometriotic tissue synthesize and secrete complement component 3 (C3). Furthermore, because C3 is capable of producing many of the immunological activities known to be associated with human endometriosis, we studied the production, secretion, and regulation of C3 using the rat model for endometriosis. Endometriosis was surgically induced in 20 adult female rats. The animals were then ovariectomized and one half were treated with estradiol (E2) for 3 days. Uterine luminal epithelial cells synthesized and secreted C3 only after E2 administration, whereas the uteri from control animals did not produce C3. In contrast, the ectopic endometrium from control animals produced and secreted C3, and this expression was strongly upregulated by in vivo E2 administration. We conclude that surgically induced endometriosis in the rat has properties biochemically independent from the intact uterus and may serve as a useful model to further investigate the regulation of C3 synthesis from human endometriosis.

Animals↗
PubMed1990

Domain structure in yeast tRNA ligase.

Yeast tRNA ligase is one of two proteins required for the splicing of precursor tRNA molecules containing introns. The 95-kDa tRNA ligase has been purified to homogeneity from a strain of Escherichia coli which overexpresses the protein. The ligation reaction requires three enzymatic activities: phosphodiesterase, polynucleotide kinase, and ligase. By partial proteolytic digestion, we have produced fragments of tRNA ligase which contain the constituent activities. These results provide evidence for a model in which the three constituent activities of ligase are located in three distinct domains separated by protease-sensitive regions. We have also located the active adenylylated site in the ligase domains. It is lysine-114. The tRNA ligase sequence in this region has limited homology to the active-site region of T4 RNA ligase.

Adenosine Triphosphate↗
PubMed1990

The stimulation of uterine complement component C3 gene expression by antiestrogens.

We have previously demonstrated that complement component C3 is regulated by estradiol in the rat uterus. The antiestrogens tamoxifen, LY117018, and LY156758 exert both agonist and antagonist effects on the immature rat uterus. In this study, these three antiestrogens also stimulated an increase in the synthesis and secretion of C3. The combination of LY117018 and estradiol did not increase C3 to a greater extent than LY117018 alone, which suggests a similar mechanism of regulation. The regulation may be transcriptional since both estradiol and tamoxifen increase the concentration of C3 mRNA. Results of in situ hybridization revealed that the increase in C3 mRNA occurred in the luminal epithelial cells. Although the induction by estradiol and the antiestrogens was similar in most aspects, the time course for tamoxifen-stimulated synthesis differed from estradiol in that the time required to achieve maximal concentrations of C3 was delayed by 12 h with tamoxifen. This pattern did not appear to be related to the time it took to convert tamoxifen to 4-hydroxytamoxifen since the C3 response for these antiestrogens were identical. The antiestrogen-stimulated increase in C3 synthesis and mRNA concentration was prevented by the co-administration of progesterone lending support to the hypothesis that the antiestrogens regulate C3 synthesis via a mechanism similar to estrogen.

Animals↗
PubMed1990

The projection of spinocerebellar neurons from the sacrococcygeal region of the spinal cord in the cat. An experimental study using anterograde transport of WGA-HRP and degeneration.

The projection from the sacro-coccygeal region of the spinal cord to the cerebellum was studied by two different techniques in the cat. In five cats wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) was injected caudal to a preceding unilateral cordotomy at the sacral level, aimed at interrupting the spinocerebellar tracts on one side completely, and the distribution of WGA-HRP labeled mossy fibers and mossy fiber terminals was studied in the cerebellum. In three additional cats, degenerating fibers were examined in Fink-Heimer stained sections following unilateral transection of the lateral and ventral funiculi at L7 or S3 level. In the WGA-HRP experiments the labeled mossy fiber terminals were located bilaterally in lobules I-V. Most of them were found in the anterior part of lobule II. In addition, labeled terminals were observed in sublobule VIIIB and in pars copularis of the paramedian lobule, contralateral to the cordotomy. The terminals in the anterior lobe were concentrated in longitudinal zones parallel to the mid sagittal plane. In lobule II, the terminals were most abundant in the superficial, apical parts of the folia. Some presumed terminals were also seen in the cerebellar nuclei. Labeled fibers were found contralateral, but not ipsilateral to the cordotomy in the superior and inferior cerebellar peduncles, as well as in the spinal cord rostral to the cordotomy. The results of the degeneration experiments were the same as those of the WGA-HRP experiments with regard to the detailed projections in the cerebellar cortex. This is strong support against the possibility that WGA-HRP labeled cerebellar mossy fiber terminals, following WGA-HRP injections in the spinal cord, would represent terminals of collaterals of retrogradely labeled neurons. It also lends strong support in favour of WGA-HRP as a reliable anterograde tracer for studying cerebellar cortical projections of spinocerebellar neurons in the cat.

Animals↗
PubMed1989

Cytoarchitectonic organization of the spinal cord in the rat: II. The cervical and upper thoracic cord.

A laminar cytoarchitectonic scheme of the cervical and upper thoracic segments of the rat spinal cord is presented in which Rexed's principles for the cat are applied. The material examined in the current investigation consists of 50-80 microns-thick unstained or Nissl-stained sections, and 2 microns-thick plastic-embedded sections stained with paraphenylenediamine. The cytoarchitectonic organization was found to be basically similar to that of the cat. As in our previous study of the cytoarchitectonic organization of the lower thoracic and lumbosacral spinal cord (Molander et al.; J. Comp. Neurol. 230:133-141, '84), the borderlines between the laminae were often found to be ambiguous, suggestive of zones of transition rather than sharp borders. In addition to the laminar scheme, the distribution of certain important cell groups, including the column of Clarke, the central cervical nucleus, the lateral cervical nucleus, the lateral spinal nucleus, and the internal basilar nucleus, is described.

Animals↗
PubMed1989

Evaluation of anti-allergic effects of 1-substituted 2-n-butyl-methylenedioxy indenes.

The effects of ten 1-substituted 2-n-butyl-5,6-methylenedioxyindenes on mice and guinea pigs were investigated for their allergic reactions in the development of a new anti-allergic drug. Anti-allergic effects were determined by testing the effect of agents on passive cutaneous anaphylaxis (PCA) in mice and Schultz-Dale reaction in guinea pig tracheal muscle. 2-Butyl-1-[N-methyl-N-[2-(N',N'-dimethylamino) ethyl]amino]5,6- methylenedioxyindene (1) indicated the most potent anti-allergic activity. Since our previous experiments indicated that 2-n-butyl 3-dimethyl amino-5,6-methylenedioxyindene (MDI-A) and its derivatives showed a potent anti-allergic effect by interfering with the calcium (Ca) movement in the allergic reaction in guinea pigs, the effect of 1 and MDI-A on allergic reaction and Ca-induced contraction of tracheal muscle in these animals were compared. The present data indicate the superiority of 1 in both reactions.

Animals↗