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L Page

Publications and source records attributed to L Page.

At least 37 records · Page 2Linked to original sources
PubMed1996

Reclaiming midwifery.

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Continuity of Patient Care↗
PubMed1995

Quantitative cell line based bioassays for human cytokines.

Research in cytokine biology is ever increasing and it is clear that cytokines are involved in a wide range of pathological and physiological processes. The validity of such research relies heavily on the appropriate measurement of levels of cytokines in various biological samples. Amongst the currently available methods for measuring cytokine levels, it is only the biological assay of samples that can directly provide estimates of biologically active cytokines present in test samples. Of the several bioassay systems available for detecting cytokines, cell line based bioassays are the easiest to perform and provide the most precise and accurate data. The suitability of any cell line for bioassaying a particular cytokine depends on several criteria such as sensitivity, ease of growth maintenance, and cytokine specificity. The design and analysis of cell line bioassays is also important in providing valid estimates of cytokine levels. We review the most useful cell lines currently available for bioassaying cytokines and discuss the design advantages and limitations of cytokine bioassays.

Animals↗
PubMed1995

Change and power in midwifery.

Midwives are experiencing problems in playing their full part in the maternity services and the communities in which they practice. Mothers, babies, and families require greater care from these caregivers for healthier pregnancy and birth outcomes. Change to renew the power, skills, and knowledge of midwives is evident in many parts of the world. Processes of change require an examination of the purpose of midwifery. The starting point of change is an awareness of the meaning of birth to individuals and society, and of the role of midwives in supporting families around the time of birth. Midwives should use their power to resolve the considerable problems facing childbearing families, and to enrich the event.

Female↗
PubMed1994

Transforming growth factor-beta 1 blocks interleukin 4 induced cell proliferation by inhibiting a protein tyrosine phosphatase essential for signal transduction.

Transforming growth factor-beta 1 (TGF-beta 1) is a cytokine which exhibits pleiotropic effects on many cell types and cellular systems. TGF-beta 1 has been shown to play a modulatory role in haematopoiesis and immunoregulation, expressed through its ability to inhibit the activities induced by other cytokines; however, the mechanisms underlying this activity are currently unclear. The potency of this activity varies according to the selected stimulatory cytokine and we have found that the proliferation of leukaemic cell lines induced by interleukin 4 (IL-4) is particularly sensitive to inhibition by TGF-beta 1 and provides a useful model to study the mechanism of action of TGF-beta. We have previously shown that IL-4 mediated mitogenic signal transduction in human systems involves the induction of phosphatase activity leading to the dephosphorylation of an 80-kDa protein (p80). We now show that TGF-beta 1 inhibits IL-4 induced dephosphorylation of p80 in a dose responsive manner closely correlated with its ability to inhibit the biological activity of IL-4. This suggests that TGF-beta 1 is inhibiting the same protein-tyrosine-phosphatase required by IL-4 to transduce its mitogenic signal. The biochemical mechanism underlying the biological activity of TGF-beta 1 in inhibiting IL-4 bioactivity is therefore the blocking of post receptor binding signal transduction processes.

Amino Acids↗
PubMed1993

Identification of the formate dehydrogenases and genetic determinants of formate-dependent nitrite reduction by Escherichia coli K12.

The formate dehydrogenases of Escherichia coli involved in electron transfer from formate to nitrite (Nrf activity: nitrite reduction by formate) have been identified. No previously undescribed selenoprotein was detected in bacteria grown under conditions optimal for the expression of Nrf activity. The Nrf activities of single mutants defective in either FdhN or FdhH were between 50 and 60% that of the parental strain. A double mutant defective in both FdhN and FdhH retained less than 10% of the activity of the FdhN+ FdhH+ strain. No Nrf activity was detected in a triple mutant defective in FdhN, FdhH and FdhO or in the selC strain. It is concluded that all three of the known formate dehydrogenases of E. coli can contribute to the transfer of electrons from formate to the Nrf pathway. Mutants defective in Nrf activity and cytochrome c552 synthesis were isolated by insertion mutagenesis or identified amongst strains received from the E. coli Genetic Stock Center. The mutations were located in at least three regions of the chromosome, including the 92 to 94 minute region which includes fdhF, the gene encoding FdhH required for formate hydrogenlyase activity. Fine structure mapping by P1 transduction established that the nrf mutations in the fdhF region were due to defects in three separable loci, all of which were independent of but close to fdhF. Clones were isolated from a cosmid library that complemented a deletion extending from fdhF into a region essential for Nrf activity. From these clones, plasmids were isolated that complemented only some of the Nrf- mutations in the 92 to 94 minute region, confirming the presence of different operons essential for Nrf activity and cytochrome c552 synthesis in this region. Suggested reasons for this genetic complexity include the need for proteins involved in electron transfer from the various formate dehydrogenases to cytochrome c552, for the attachment of the haem group to the apocytochrome and for cytochrome c552 export into the periplasm.

Cloning, Molecular↗
PubMed1993

Restorative dentistry. Interactions with periodontics.

The integration of periodontal considerations with restorative planning is now the standard of care. Instilling motivation toward prevention continues to be one of our most challenging goals. A stable healthy periodontium and minimum restorative needs are the resulting rewards. With the use of available knowledge and microbial testing for both periodontitis and caries susceptibility, we now can offer our patients a higher likelihood of success in retaining natural teeth and implants.

Dental Caries↗
PubMed1992

Analysis of competence in cultured sea urchin micromeres.

Sea urchin embryo micromeres form the primary mesenchyme, the skeleton-producing cells of the embryo. Almost nothing is known about nature and timing of the embryonic cues which induce or initiate spicule formation by these cells. A related question concerns the competence of the micromeres to respond to the cues. To examine competence in this system we have exposed cultured sea urchin micromeres to an inducing medium containing horse serum for various periods of time and have identified a period when micromeres are competent to respond to serum and form spicules. This window, between 30 and 50 h after fertilization, corresponds to the time when mesenchyme cells in vivo are aggregating and beginning to form the syncytium in which the spicule will be deposited. The loss of competence after 50 h is not due to impaired cell health since protein synthesis at this time is not significantly different from controls. Likewise the accumulation of a spicule matrix mRNA (SM 50) and a cell surface glycoprotein (msp 130), both indices of micromere/mesenchyme differentiation, still occurs in cells that have lost competence to respond to serum by forming spicules. These experiments demonstrate that the acquisition and loss of competence in these cells are regulated developmental events and establish an in vitro system for the identification of the molecular basis for inductive signal recognition and signal transduction.

Animals↗
PubMed1991

Synthesis of phosphatidylethanolamine and ethanolamine plasmalogen by the CDP-ethanolamine and decarboxylase pathways in rat heart, kidney and liver.

Studies with mammalian cell lines have led to suggestions that mammalian tissues may derive all of their phosphatidylethanolamine (PE) from the decarboxylation of phosphatidylserine (PS), and also that the physiological significance of the CDP-ethanolamine pathway was the synthesis of ethanolamine plasmalogen. We have therefore investigated the biosynthesis of PE and ethanolamine plasmalogen via the CDP-ethanolamine and decarboxylation pathways in vivo in three rat tissues (heart, kidney and liver), which differ in ethanolamine plasmalogen content. In all three tissues [14C]ethanolamine was incorporated into both PE and ethanolamine plasmalogen, whereas [3H]serine was incorporated into only PS and PE fractions. When [14C]ethanolamine was introduced into the animals, the specific radioactivity of ethanolamine plasmalogen in the kidney was always greater than that of the PE fraction; in the heart the specific radioactivity of the ethanolamine plasmalogen fraction was similar to that of the PE fraction, whereas in the liver the specific radioactivity of the PE fraction was always greater than that of the ethanolamine plasmalogen fraction. The results obtained in this study indicate that: (1) the CDP-ethanolamine pathway is utilized for the synthesis of both PE and ethanolamine plasmalogen in all three tissues; (2) the decarboxylation pathway is utilized solely for the synthesis of PE; (3) serine plasmalogens are not formed by base-exchange reactions; (4) the relative utilization of the CDP-ethanolamine pathway for the synthesis of PE and ethanolamine plasmalogen varies among tissues. Our studies also revealed that the hypolipidaemic drug MDL 29350 is a potent inhibitor of PE N-methyltransferase activity in vitro and in vivo.

Animals↗
PubMed1990

Different physiological roles of two independent pathways for nitrite reduction to ammonia by enteric bacteria.

Operon fusion strains and mutants of Escherichia coli K-12 lacking the NADH-dependent nitrite reductase have been used to determine the regulation and physiological roles of two independent pathways for nitrite reduction to ammonia. Both the formate- and NADH-dependent pathways (Nrf and Nir, respectively) were totally repressed during aerobic growth, partially active during anaerobic growth in the absence of nitrite and further induced anaerobically by nitrite. Both were dependent upon a functional Fnr protein (a transcription activator of genes for anaerobic respiration). During anaerobic growth in the presence of nitrate, the Nir pathway was fully induced but Nrf was strongly repressed. Mutants defective in the NarL protein, which induces transcription of nitrate reductase genes but represses fumarate reductase genes in the presence of nitrate, were derepressed for Nrf activity during growth with nitrate, but the Nir enzyme was less active. The synthesis of Nrf components was also sensitive to glucose repression and weak activation by NarL during growth in the absence of nitrate. These data indicate that the Nir pathway provides a mechanism for detoxifying nitrite formed in the cytoplasm as a product of nitrate reduction. In contrast, the electrogenic reduction of nitrite by the Nrf pathway provides a secondary source of energy during anaerobic growth and is consequently repressed by the NarL protein when the thermodynamically more favourable electron acceptor, nitrate, is available. Two short DNA sequences, 5'-TACCAT-3' and 5'-CTCCTT-3', were found in the promoters of operons known to be activated or repressed by the NarL protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerobiosis↗
PubMed1990

Hydrolysis of 2-acyl-sn-glycero-3-phosphocholines in guinea pig heart mitochondria.

Although both 2-acyl-sn-glycero-3-phosphocholine and 1-acyl-sn-glycero-3-phosphocholine may be produced from phosphatidylcholine hydrolysis, studies on the former have lagged behind that of the latter. In this study a lysophospholipase A2 that hydrolyses 2-acyl-sn-glycero-3-phosphocholine has been characterized in guinea pig heart mitochondria. The lysophospholipase A2 activity was not dependent on Ca2+ and was inhibited differentially by saturated and unsaturated fatty acids. This lysophospholipase A2 activity was able to discriminate among different molecular species of 2-acyl-sn-glycero-3-phosphocholines when they were presented individually or in pairs. The order of decreasing rates of hydrolysis of different molecular species of 2-lysophosphatidylcholines, when the substrates were presented singly, was 18:2 greater than 20:4 greater than 18:1 greater than 16:0. A differential inhibition of the rate of hydrolysis of the individual substrates was observed when the substrates were presented in pairs. The degree of inhibition was dependent on the molar ratio of the mixed substrates. The characteristics of the enzyme suggest that involvement in the selective release of fatty acids from mitochondrial phosphatidylcholine would depend on a high selectivity of phospholipase A1 for different molecular species of phosphatidylcholine. A lysophospholipase A1 activity was also characterized in the mitochondria with a distinct acyl specificity from the lysophospholipase A2. Other characteristics of the two lysophospholipases suggest that the two reactions are not catalysed by the same enzyme.

Animals↗
PubMed1987

Acylation of 1-alkenylglycerophosphoethanolamine and 1-acylglycerophosphoethanolamine in guinea-pig heart microsomes.

Although the acylation of 1-alkenylglycerophosphocholine in mammalian heart is well documented, the acylation of 1-alkenylglycerophosphoethanolamine in the heart was not reported. In this study, the presence of acyl CoA: 1-alkenylglycerophosphoethanolamine acyltransferase in the guinea pig heart microsomes was demonstrated. 1-Alkenylglycerophosphoethanolamine acyltransferase displayed a high degree of specificity towards acyl-CoA. The order of reactivity with acyl-CoA was found to be: linoleoyl much greater than arachidonyl greater than palmitoyl greater than stearoyl = oleoyl. 1-Acylglycerophosphoethanolamine acyltransferase in the microsomes also exhibited specificity towards acyl-CoA in the following manner: linoleoyl greater than arachidonyl much greater than palmitoyl greater than oleoyl greater than stearoyl. However, such specificity appeared to be dependent on acyl-CoA concentration. The acyl-CoA specificities of both enzymes did not correlate with the C-2 acyl distribution observed in the corresponding microsomal phospholipids. Our results suggest that in addition to the acyl specificity of the acyltransferases, intracellular concentrations of acyl-CoAs may also have an important role in determining the observed acyl patterns of the phospholipids. Based on the acyl specificities, pH profiles, and their responses to heat inactivation and thiol reagents, we conclude that 1-alkenylglycerophosphoethanolamine acyltransferase and 1-acylglycerophosphoethanolamine acyltransferase in guinea-pig heart microsomes are not the same enzyme.

Acyl Coenzyme A↗