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Biomedical subjects

W Liu

Publications and source records attributed to W Liu.

At least 1,027 records · Page 57Linked to original sources
PubMed1986

Effect of three pyrethroids on blood feeding and fecundity of Aedes aegypti.

Caged Aedes aegypti were exposed to a range of concentrations of d-phenothrin, d-allethrin and tetramethrin in a wind tunnel. Mortality, blood engorgement and egg production among these mosquitoes and their progeny were recorded. Tetramethrin was the most effective (LC50 of 0.0017%), followed by d-phenothrin (LC50 0.0031%) and d-allethrin (LC50 0.01%). Blood engorgement was decreased by treatment with each pyrethroid at the high concentration (0.002%, 0.003% and 0.01% respectively). Treatment with d-phenothrin or d-allethrin decreased egg production, but tetramethrin increased oviposition. These effects had ceased in the F2.

Aedes↗
PubMed1985

Reactivation kinetics of diethylphosphoryl acetylcholine esterase.

The kinetics of reactivation of diethylphosphorylated acetylcholine esterase by pyridine-2-aldoxime methochloride has been studied using the approach of following the course of the hydrolysis of acetylcholine during the reactivation of the phosphorylated enzyme by the reactivator [Tsou, C.-L. (1965) Acta Biochem. Biophys. Sin. 5, 398-417]. Equations are derived based on the scheme of the formation of a complex between the phosphorylated enzyme and the reactivator and the rate of dissociation of this complex is not necessarily faster than the dephosphorylation and regeneration of the active enzyme. The regenerated enzyme then reacts with the substrate through an acetyl-enzyme intermediate as generally depicted. The equation obtained for product formation during the course of reactivation contains two exponential terms and this is in accord with the experimentally observed biphasic reaction. By making the assumption that the dissociation of the phosphorylated enzyme-reactivator complex is much faster than the dephosphorylation reaction, the above equation can be simplified to a form containing only one exponential term. By following the course of the reactivation reaction with the conventional approach of taking aliquots and assaying for enzyme activity recovery, it would appear likely that one would miss the initial stage of this biphasic reaction.

Acetylcholinesterase↗
PubMed1985

Chloride secretory mechanism induced by prostaglandin E1 in a colonic epithelial cell line.

Confluent T84 monolayers grown on permeable supports and mounted in a modified Ussing chamber secrete chloride (Cl-) in response to prostaglandin E1. The threshold stimulation was observed at 10(-9) M and a maximal effect at 10(-6) M. Unidirectional flux studies showed an increase in both serosal to mucosal and mucosal to serosal Cl- fluxes with 10(-6) M prostaglandin E1; the increase in serosal to mucosal Cl- flux exceeded the increase in mucosal to serosal flux, resulting in net Cl- secretion. Na+ transport was not affected in either direction and the changes in net Cl- flux correlated well with the changes in short circuit current. To identify the electrolyte transport pathways involved in the Cl- secretory process, the effect of prostaglandin E1 on ion fluxes was tested in the presence of putative inhibitors. Bumetanide was used as an inhibitor for the basolaterally localized Na+,K+,Cl- cotransport system whose existence and bumetanide sensitivity have been verified in earlier studies (Dharmsathaphorn et al. 1984. J. Clin. Invest. 75:462-471). Barium was used as an inhibitor for the K+ efflux pathway on the basolateral membrane whose existence and barium sensitivity were demonstrated in this study by preloading the monolayers with 86Rb+ (as a tracer for K+) and simultaneously measuring 86Rb+ efflux into both serosal and mucosal reservoirs. Both bumetanide and barium inhibited the net chloride secretion induced by prostaglandin E1 suggesting the involvement of the Na+,K+,Cl- cotransport and a K+ efflux pathways on the basolateral membrane in the Cl- secretory process. The activation of another Cl- transport pathway on the apical membrane by prostaglandin E1 was suggested by Cl- uptake studies. Our findings indicate that the prostaglandin E1-stimulated Cl- secretion, which is associated with an increase in cyclic AMP level, intimately involves (a) a bumetanide-sensitive Na+,K+,Cl- cotransport pathway that serves as a Cl- uptake step across the basolateral membrane, (b) the stimulation of a barium-sensitive K+ efflux mechanism on the basolateral membrane that most likely acts to recycle K+, and (c) the activation of a Cl- transport pathway on the apical membrane that serves as a Cl- exit pathway.

Alprostadil↗
PubMed1984

Alternative conformational states in the ribosome-associated 5.8S RNA.

Two conformations of the 5.8S rRNA have been distinguished by gel electrophoresis. Diethyl pyrocarbonate and dimethyl sulphate reactivity were used to probe these conformational states in both the free molecule and those associated with 28S RNA or the ribosome. Both conformations could be demonstrated in each case and in every instance four residues, C50, A52, G53, C54, which were strongly reactive in the faster-migrating conformation were essentially unreactive in the slower-migrating form. These results suggest that the two conformations differ in the degree to which the tertiary structure is folded and raise the possibility that the 5.8S rRNA functions in translation by switching between alternative conformational states.

Animals↗
PubMed1983

Structure of the ribosome-associated 5.8 S ribosomal RNA.

The structure of the 5.8 S ribosomal RNA in rat liver ribosomes was probed by comparing dimethyl sulfate-reactive sites in whole ribosomes, 60 S subunits, the 5.8 S-28 S rRNA complex and the free 5.8 S rRNA under conditions of salt and temperature that permit protein synthesis in vitro. Differences in reactive sites between the free and both the 28 S rRNA and 60 S subunit-associated 5.8 S rRNA show that significant conformational changes occur when the molecule interacts with its cognate 28 S rRNA and as the complex is further integrated into the ribosomal structure. These results indicate that, as previously suggested by phylogenetic comparisons of the secondary structure, only the "G + C-rich" stem may remain unaltered and a universal structure is probably present only in the whole ribosome or 60 S subunit. Further comparisons with the ribosome-associated molecule indicate that while the 5.8 S rRNA may be partly localized in the ribosomal interface, four cytidylic acid residues, C56, C100, C127 and C128, remain reactive even in whole ribosomes. In contrast, the cytidylic acid residues in the 5 S rRNA are not accessible in either the 60 S subunit or the intact ribosome. The nature of the structural rearrangements and potential sites of interaction with the 28 S rRNA and ribosomal proteins are discussed.

Animals↗
PubMed1983

Multiple-locus departures from panmictic equilibrium within and between village gene pools of Amerindian tribes at different stages of agglomeration.

A comparative analysis of departures from multiple-locus Hardy-Weinberg equilibrium is presented for a set of four tribal Indian groups (the Yanomama, Makiritare, Wapishana and Ticuna) from the lowlands of South America. These tribes span a range of agglomeration and acculturation from the most traditional, swidden horticulturalists to frontier townspeople. The small-group social organization typical of traditional horticulturalists leads to substantial departures from tribal panmixia, as manifested by the distribution of multiple-locus genotypes both within and between villages. Within villages, the departures from single-locus Hardy-Weinberg equilibrium are small and nonsignificant, but the departures from gametic equilibrium (independence of loci) are substantial, even for the unlinked loci we have used to characterize these populations. The departures from single-locus homogeneity across villages are also substantial. One of the normal concomitants of increasing acculturation in this setting is an increase in agglomeration. As agglomeration increases, the departures from multiple-locus panmixia decrease, a process that can be very rapid. We discuss both the shifting balance theory of evolution and punctuated evolutionary rates in light of the small group social organization that must have obtained throughout most of human evolution.

Brazil↗
PubMed1983

Serum proteins in healthy Basenjis and Basenjis with chronic diarrhea.

A serologic survey was conducted to characterize the electrophoretic patterns of serum proteins in healthy Basenji dogs (n = 137) and Basenjis with chronic diarrhea (n = 32). Serum protein electrophoresis values for Basenjis were similar to previously reported values from dogs of other breeds. Dogs with histologically confirmed lymphocytic-plasmacytic enteritis had a statistically significant (P less than 0.05) decrease in total protein, albumin, and albumin/globulin ratio. alpha 2-Globulin and gamma-globulin values were significantly increased in old dogs (9 years of age or older) with lymphocytic-plasmacytic enteritis. Although not statistically significant, gamma-globulin values were generally increased in Basenjis with lymphocytic-plasmacytic enteritis when compared with the values in age-matched clinically healthy Basenjis.

Alpha-Globulins↗
PubMed1982

Effect of localized trauma and temporary splinting on immature skeletal muscle and mobility of the femorotibial joint in the dog.

The right pelvic limbs of 2 groups of dogs were splinted in extension for 2 weeks. In 1 of these groups, the dogs were anesthetized and the distal portion of the quadriceps femoris muscle was traumatized before splinting. Two groups of control dogs were also used; neither group was splinted, but 1 group was anesthetized, and their muscles were traumatized. The range of motion of the femorotibial joint was measured in all 4 groups before splinting and 3 and 9 weeks after splinting. Types I and II muscle fiber diameters and percentages were also recorded at 3 and 9 weeks in all groups. Flexion of the femorotibial joint was limited after splinting (P less than 0.001), but less so after trauma and splinting than after splinting alone (P less than 0.0001). A reversible type I fiber atrophy occurred in most restricted muscles (P less than 0.001) and early type II fiber atrophy was seen in a few muscles after trauma and splinting (P less than 0.002). Multifocal fiber necrosis was the only irreversible change seen after 3 weeks of splinting with or without concurrent muscle trauma. Relative fiber percentages did not change appreciably during splinting or recovery.

Animals↗
PubMed1981

Aryl hydrocarbon hydroxylase in human prostate.

Aryl hydrocarbon hydroxylase (AHH) was present in explant cultures of human prostate obtained from surgery of benign prostatic hyperplasia and was inducible by benz[a]anthracene (BA). The induction of AHH ranged from 14- to 150-fold when compared with control values and 10-fold variation of AHH inducibility among individuals was observed. Epithelial cells grown from human prostate tissue also contained measurable AHH activity and AHH was inducible by BA and 7,12-dimethylbenz[a]anthracene (DMBA). Inducibility of AHH by BA ranged from 2- to 63-fold. The inducibility of AHH by DMBA was always less than that by BA. In cells treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), there were no changes in AHH activity. These findings support the view that the human prostate is susceptible to environmental polycyclic hydrocarbon carcinogens and that environmental and occupational factors might contribute to the etiology of human prostatic carcinoma.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1979

Consulting to children in crisis.

Although community consultation is common for psychiatrists, such activity is usually carried out on an elective rather than emergency basis. In a world troubled by community disaster situations--children are often at risk. Psychiatrists, through the use of skillful crisis consultation, can be of great help to these young people. This report describes the effort of a mental health consultation team to meet the needs of a large population of children under acute stress.

Acculturation↗