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M W Smith

Publications and source records attributed to M W Smith.

At least 163 records · Page 9Linked to original sources
PubMed1991

Developmental control over vitamin-D-induced calbindin gene expression during early differentiation of chicken jejunal enterocytes.

In situ hybridization and immunocytochemical techniques have been used to examine the distribution of vitamin-D-induced calbindin mRNA and calbindin protein in enterocytes lining the crypts and villi of chicken small intestine. Basal villus enterocytes contained approximately twice as much calbindin but over three times as much calbindin mRNA compared to values found in basal crypt and upper villus enterocytes, all values being measured 2 days after vitamin D injection into D-deficient chickens. Virtually no calbindin mRNA was detected in tissues taken from control D-deficient birds. Direct proportionality found between calbindin mRNA and calbindin content in enterocytes of basal crypt, mid and upper villus suggests pre-translational control over calbindin synthesis. The implications of possible inefficient translation of calbindin mRNA in basal villus enterocytes are discussed. Present methods of analysis provide a novel way to study mechanisms controlling gene expression throughout the whole process of enterocyte differentiation.

Animals↗
PubMed1991

Postnatal development of lamb intestinal digestive enzymes is not regulated by diet.

1. Change in digestive enzyme activities determined biochemically in brush-border membrane vesicles and cytochemically in isolated villi of lamb proximal intestine has been related to diet, intestinal structure and rumen development during the first 10 weeks of postnatal life. 2. Lactase activity halved, dipeptidylpeptidase IV activity doubled and aminopeptidase N and alkaline phosphatase activities remained constant during this period of development. Maintaining lambs on a milk replacer diet for 5 weeks after birth had no effect on this pattern of postnatal change in digestive enzyme activities. 3. Structural changes accompanying these selective effects on enzyme expression included a halving of villus height and a doubling of villus width. Villus surface area remained unaffected by these changes in height and width of villi. Crypt depth doubled during the first 10 weeks of postnatal life. Maintaining lambs on a milk replacer diet for 5 weeks did not affect this pattern of change in intestinal structure. 4. It appears from these results that postnatal decrease in lactase and increase in dipeptidylpeptidase IV activities are not regulated by factors such as diet, rumen development, or changes in intestinal structure. Attention is drawn to differences encountered between these results and a postnatal modification of glucose transport which clearly is dependent on diet.

Alkaline Phosphatase↗
PubMed1991

Ontogenic development of lamb intestinal sodium-glucose co-transporter is regulated by diet.

1. The ontogenic development of the intestinal Na(+)-glucose co-transporter was measured in lambs as a function of diet. Transport activity was assayed in brush-border membrane vesicles and the expression of transport protein in the brush-border membrane determined by Western analysis. 2. Na(+)-dependent D-glucose transport increased to a maximum (300-700 pmol mg-1 s-1) within the first 2 weeks of birth and then declined to negligible amounts (less than 10 pmol mg-1 s-1) over the next 8 weeks. There was no further change over the next 2-3 years. Early changes were associated with modifications in both the maximum velocity Vmax for transport and expression of carrier protein in the brush-border plasma membrane. 3. Maintaining lambs on a milk replacer diet beyond the normal weaning period prevented the normal decline in the expression of Na(+)-glucose co-transport. At 5 weeks the transport rate was 433 +/- 150 pmol mg-1 s-1 in lambs maintained on milk replacer, but only 79 +/- 40 pmol mg-1 s-1 in normally reared control lambs. 4. Infusing the proximal intestine of 2- to 3-year-old sheep with 30 mM-D-glucose for four days increased the rate of transport 40- to 80-fold above that found in control animals perfused with mannitol. A similar but smaller increase was observed in one animal perfused with the non-metabolizable sugar alpha-methyl-D-glucopyranoside. The induced increase in glucose transport was correlated with the expression of the co-transporter protein in the brush-border plasma membrane. 5. It is concluded that the age-related decline in Na(+)-glucose co-transport in the sheep intestine is directly due to the decrease in D-glucose (and D-galactose) reaching the small intestine after development of the rumen. These results further suggest that luminal sugar substrates for the co-transporter promote both the maintenance and the up-regulation of the brush-border transport protein and it is the intact sugar itself which controls gene expression during enterocyte maturation.

Animals↗
PubMed1991

Oxidative injury induces influx-dependent changes in intracellular calcium homeostasis.

Understanding of the mechanisms of cell injury and cell death is fundamental to the understanding of both protection against and initiation of cell injury and cell death. We subjected primary cultures of proximal tubular epithelium (PTE) from adult rats to an exogenous oxidative stress, generated by xanthine/xanthine oxidase (X/XOD), and studied its effect on the concentration of cytosolic ionized calcium ([Ca2+]i) by means of digital imaging fluorescence microscopy (DIFM) using a cytosolic calcium probe, fura-2. Exposure to 25 mU/ml X/XOD caused notable increases in [Ca2+]i detectable within 15 sec and increasing to micromolar levels with time. Experiments with Ca(2+)-free medium containing ethylene glycol-bis(beta-aminoethyl ether)N,N,N',N'-tetraacetic acid (EGTA) showed that the increase of [Ca2+]i was due to influx from the extracellular space. Smaller and slower increases in [Ca2+]i were seen after exposure to lower concentrations of X/XOD (5 and 10 mU/ml). PTE injury and killing were assessed by measuring the release of cytosolic lactate dehydrogenase (LDH), exclusion of trypan blue, and observation of morphologic changes. Exposures to the 25 mU/ml concentration of X/XOD caused significant LDH release after 2 hr and correlated with trypan blue staining of exposed cells. Again, lesser concentrations of X/XOD resulted in a slower release of smaller amounts of LDH, and thus delayed trypan blue staining. Cytoplasmic bleb formation was seen by phase microscopy within minutes of exposure to 25 mU/ml, followed by cell rounding, retraction, and disintegration. Transmission electron microscopy revealed a progression of changes characteristic of lethal cell injury, beginning with dilatation of the endoplasmic reticulum, detachment of ribosomes, condensation of mitochondria, and chromatin clumping and terminating with mitochondrial swelling and formation of intramitochondrial flocculent densities. These studies clearly show that notable increases of [Ca2+]i precede both sub-lethal and lethal changes in rat PTE. These results indicate that interventions designed to minimize or to accelerate calcium entry could be of importance in cell preservation or cell killing, respectively, and therefore to therapeutic strategies for myocardial infarction, stroke, or shock in the former instance and for cancers in the latter.

Animals↗
PubMed1991

Pharmacokinetic and other related factors affecting psychotropic responses in Asians.

The last decade has witnessed substantial progress in our understanding of ethnic differences and similarities between Asians and other ethnic groups in response to various psychotropics. Capitalizing on recent advances in cross-cultural and psychobiological research methodology, a number of recent studies have suggested a special sensitivity of Asians to various psychotropic medications. Whereas pharmacokinetic differences have been consistently found with haloperidol and some benzodiazepines, results of studies focusing on tricyclic antidepressants (TCAs) have remained inconclusive. In addition, ethnic differences in protein binding and in the pharmacodynamics of some of these drugs have also been reported. Future studies should explore newer assay methods and imaging techniques capable of measuring receptor-drug interactions, in addition to utilizing existing research methodologies to more systematically scrutinize the nature and extent of such differences. They should be designed not only to ascertain differences in drug responses, but also to examine genetic and environmental (e.g., diet, exposure to enzyme inducers) factors that may contribute to these differences. Pharmacogenetic probes could be used in combination with studies examining pharmacokinetic and pharmacodynamic issues for such purposes.

Asian↗
PubMed1991

Psychopharmacologic considerations in the treatment of black American populations.

Although striking ethnic differences in pharmacologic responses to various medications have been documented in the general medical literature, there is a paucity of such information in the psychopharmacologic literature. Recent work has provided a number of studies that illustrate interesting inter-ethnic pharmacogenetic, pharmacokinetic, and pharmacodynamic differences. In general, however, such studies have reported inconsistent findings relative to dose response relationships with various psychotropics. Results of our literature review, with a particular focus on black Americans, suggest that the lack of consistency in these investigations is largely attributable to various methodological and design problems. Prominent among these problems are: diagnostic misclassification, treatment of various ethnic groups in a homogeneous undifferentiated manner, lack of appropriate control for age and gender, and minimal consideration for chronicity of illness. As a result, though there exist some interesting data suggesting inter-ethnic genetic and kinetic differences, the extant literature on black Americans and other ethnic groups should be evaluated with some caution. The purpose of this article is to provide a systematic review of the existing psychopharmacologic literature on the black American population.

Black or African American↗
PubMed1991

Ethnic psychopharmacology: the Hispanic and Native American perspective.

There is ample evidence attesting to differences in drug response and disposition among certain ethnic groups. The existing body of knowledge concerning pharmacological issues in the Hispanic and Native American ethnic groups, however, is both meager and confusing. In this article, the authors first attempt to briefly characterize these increasingly important ethnic groups, citing recent population figures and epidemiological findings. This is followed by a review of several existing retrospective studies concerning the pharmacological treatment of patients belonging to these groups. Recent findings in the area of pharmacogenetics are critically appraised and other factors influencing drug responsiveness are also examined. The clinical significance of this research for the optimal treatment of patients in cross-cultural settings is highlighted. The need for further research that would both fortify and clarify the available information with respect to these issues and the Hispanic and Native American populations is obvious.

Ethnicity↗
PubMed1991

Salmonella-induced M-cell formation in germ-free mouse Peyer's patch tissue.

M cells present in Peyer's patch tissue transport enteric antigens for presentation to underlying lymphoid tissue to initiate immune responses against intestinal infection. Present work investigates how interactions taking place between bacteria, epithelial cells, and immunocytes could contribute to initial detection and later elimination of enteric antigens. Oral infection of germ-free mice with Salmonella typhimurium aroA- caused a twofold to threefold increase in M cell numbers, crypt depth, and enterocyte migration rate after 7 days. These changes were accompanied by a twofold increase in follicle-associated epithelial tissue (FAE)-associated CD4+ and a threefold decrease in FAE-associated CD8+ counts. Salmonella also increased M-cell numbers shortly after infection. Other effects on crypt size and spleen weight took longer to develop. Salmonella probably creates M cells by changing the local subepithelial immune environment in the lymphoid follicle.

Animals↗
PubMed1990

Cell loss and class distribution of TH-I cells in the substantia nigra of the neurological mutant, weaver.

Eight-week-old homozygous weaver mutant mice and littermate wildtype controls were perfused with a buffered acrolein and paraformaldehyde solution. The brains were subsequently removed, blocked and sectioned on a vibratome. Representative sections through the midbrain were incubated overnight with an antibody for tyrosine hydroxylase. Visualization of the antibody was achieved using the peroxidase-antiperoxidase technique. The immunoreactive cells in the substantia nigra were examined to determine the subclasses of cells that are affected when dopaminergic neurons are lost in these mutants. Class distributions were determined and the data were subjected to chi 2 analyses. The results indicate a significant loss of tyrosine hydroxylase-immunoreactive cells in both the pars compacta and pars lateralis that is dependent upon the group and the region being studied. In addition, distributional shifts within the classes of labeled neurons suggest that there is an increase in the small neurons over the expected numbers in both divisions of the substantia nigra.

Animals↗
PubMed1990

Galactose inhibits lactase expression by mouse jejunal enterocytes.

Present work uses a combination of quantitative cytochemistry and measurements of cell migration rates to describe galactose effects on lactase expression by mouse enterocytes. Mice fed galactose were found to eat less, weigh less and drink more than mice maintained on a low-carbohydrate isocalorific diet. The enterocyte migration rate in these mice was also only one third of that determined in low-carbohydrate-fed animals. The rate at which lactase activity increased in the brush border membrane of migrating enterocytes was 3-times greater in low-carbohydrate- compared with galactose-fed mice. The time during which this increase persisted was, however, 3-times less in low-carbohydrate-fed animals. The maximum rate of sucrase-maltase appearance, measured as control in these experiments, remained unaffected by galactose feeding. Galactose effects on lactase expression might in part result from mice being unable to metabolise this substrate. Previously it has been stated that galactose increases lactase biosynthesis in rat intestine (Koldovsky, O., Bustamonte, S. and Yamada (1981) In Mechanisms of intestinal adaptation (Robinson, J.W.L., Dowling, R.H. and Ricken, E.O., eds.), pp. 153-156, MTP Press, Lancaster). This result is discussed in relation to the opposite finding reported in the present work for mouse jejunal enterocytes. The need to relate enzyme appearance to age and developmental state of enterocytes in this type of study is also emphasized.

Animals↗
PubMed1990

Nucleotide sequence and characterization of the 39K gene region of Autographa californica nuclear polyhedrosis virus.

The complete nucleotide sequence of the Pstl-K fragment of the Autographa californica nuclear polyhedrosis virus (AcMNPV) genome was determined. This region of the genome contains the delayed early 39K gene and V-ubi, a viral protein with homology to ubiquitine. In addition, Pstl-K potentially encodes five other proteins. Hybrid-select translation mapped nine viral-specific proteins to this fragment. Three proteins were observed with both early and late RNA; two of them comigrated with proteins directed by transcripts made from the 39K open reading frame (ORF). One protein which was only seen with hybrid-selected late RNA comigrated with ubiquitin. A correction of previously published sequence data indicates that there is an additional AUG codon upstream of the 39K ORF. This AUG codon is located 8 nucleotides downstream of the early transcription initiation site. The methionine codon is followed by codons for three amino acids and a termination codon. The 39K ORF is located 102 nucleotides downstream of the minicistron. In vitro transcription-translation experiments confirmed that the downstream AUG serves as the initiation codon for the 39K ORF. Radioimmunoprecipitation experiments indicated that the Pstl-K-encoded 39K protein reacted with antiserum raised against a previously described nuclear matrix-associated 39K protein.

Amino Acid Sequence↗
PubMed1990

Effects of genetic selection on growth rate and intestinal structure in the domestic fowl (Gallus domesticus).

1. Pieces of small intestine taken from chickens subjected previously to continuous selection, relaxed selection or no selection for rapid growth were used to estimate villus surface area and microvillus development to determine what effects genetic selection might have on factors controlling intestinal function. 2. Crypt size and the rates at which enterocytes migrated out of crypts were also measured, after injection of tritiated thymidine, to determine the time course of microvillus elongation. 3. Differences in growth rates measured between highly selected, relaxed selected or unselected birds were found to be correlated with parallel changes in villus surface area. Selection for growth did not change the density, dimensions or pattern of development of enterocyte microvilli. Microvilli did, however, produce a maximal 20-fold increase in villus surface area under all conditions. 4. Crypt size and enterocyte migration rates did not vary significantly between tissue taken from unselected and relaxed selected chickens. Tissue taken from highly selected birds had a crypt size and enterocyte migration rate 40% higher than values found for the other two groups of chickens. 5. The possibility that early genetic selection increased growth potential by uncoupling diet-induced changes on crypt hyperplasia from secondary effects on villus structure, and that later selection increased growth potential by increasing appetite, is discussed.

Animals↗
PubMed1990

Simultaneous exploitation of different peptide permeases by combinations of synthetic peptide smugglins can lead to enhanced antibacterial activity.

Various synthetic, peptide prodrugs (smugglins) were tested alone and in combination for activity against Escherichia coli. The smugglins may be transported through any of three peptide permeases, and once inside the bacteria are activated by intracellular peptidase action to release their intrinsically impermeant, antibacterial moieties. When each such antibiotic peptide present in a mixture was accumulated via a different permease, synergistic effects could be observed. Synergy was also found when smugglins were combined with other non-peptide antibiotics. The principle of using smugglin combinations could extend the scope of their application, and should minimise the potential problem that can arise from the occurrence of resistant, transport mutants. The smugglin interactions were studied using a modified microtitre plate assay.

Anti-Bacterial Agents↗
PubMed1990

Possible lymphocyte effects on lactase expression by mouse jejunal enterocytes.

Jejunal intraepithelial lymphocyte numbers fall and lactase activity increases during early infection with the intestinal parasite Nematospiroides dubius. Both these variables later return to values found in control mice. These results support the view that local immune reactions, suppressed by the presence of N. dubius, normally inhibit lactase expression by mouse enterocytes.

Animals↗
PubMed1990

Abnormal expression of dipeptidylpeptidase IV activity in enterocyte brush-border membranes of children suffering from coeliac disease.

Dipeptidylpeptidase IV (DPP IV) activity has been shown cytochemically to decrease significantly in enterocytes of children suffering from coeliac disease. This decrease is due to a halving of the time available for enterocytes to express DPP IV in their brush-border membranes during development. This effect is compared with previous results showing coeliac disease to inhibit disaccharidase activities selectively.

Alkaline Phosphatase↗
PubMed1990

Chloride conductance and intracellular chloride accumulation in mouse Peyer's patch enterocytes.

1. Measurements of membrane potential, Cl- conductance and intracellular Cl-, K+, Na+ and H+ activities have been carried out in the follicle-associated epithelium of the mouse Peyer's patch to characterize further the physiological properties of antigen-transporting M cells, enterocytes and intraepithelial lymphocytes. 2. Intraepithelial lymphocytes, identified in random impalements as a second negative jump in membrane potential (Vm), were found to have higher K+ and H+ activities, lower Na+ and Cl- activities and higher negative values for Vm than either of the other two epithelial cell types. Cl- activity in these cells was higher than that predicted from the Nernst equation. 3. M cells identified as having the first negative jump in Vm in impalements involving intraepithelial lymphocytes were unable to accumulate Cl-. They also had a lower Vm than that found in apparently fully differentiated enterocytes. This Vm was partly depolarized at a low Cl- concentration. 4. Apparently fully differentiated enterocytes could be further divided into two populations depending on whether the Vm could or could not be partly depolarized by a low Cl- concentration. The mean Vm and intracellular Cl- activity of Cl(-)-sensitive cells, measured in high Cl- medium, were less than values found for Cl(-)-insensitive enterocytes. Cl- was only accumulated by enterocytes showing no depolarization at low external Cl- concentration. 5. The Vm of mature villus enterocytes was the same as that determined for Cl(-)-insensitive follicle-associated enterocytes. Villus enterocyte Vm was not depolarized at a low Cl- concentration. 6. The present ability to distinguish two apparently large populations of follicle-associated enterocytes having M cell-like or villus enterocyte-like properties is discussed in relation to current theories describing how M cells might be formed. The presence of a Cl- conductance in M cell enterocytes, the inability to accumulate Cl- and the maintenance of a low Vm could aid endocytosis of macromolecules across the apical membrane.

Animals↗
PubMed1990

Brush-border membrane alkaline phosphatase activity in mouse Peyer's patch follicle-associated enterocytes.

1. Using a new method of quantitative cytochemistry to determine alkaline phosphatase activity, it was possible to identify M cells and distinguish two further types of enterocytes present in mouse Peyer's patch follicle-associated epithelial tissue. 2. A quantitative description of these three cell types was provided by making direct absorbance measurements of enzyme reaction product on the luminal surface of individual follicle-associated enterocytes. M cells having a negligible alkaline phosphatase activity had a mean absorbance of 6 +/- 2 arbitrary units. The other two populations of enterocytes had overlapping but significantly different mean absorbances of 20 +/- 2 and 30 +/- 3 arbitrary units. 3. M cells accounted for 3.2 +/- 1% of the total number of cells present in the apical part of the follicle-associated epithelium. This percentage is a minimum value describing an extreme example of cells having M cell-like characteristics. The remaining epithelial cells were divided equally between those having high and low alkaline phosphatase activities in their brush-border membranes. A small percentage of cells having low alkaline phosphatase activities could perform M cell functions. 4. Results obtained suggest that reduced alkaline phosphatase activity and brush-border membrane Cl- conductance can both be used as differentiation markers to identify a large population of poorly differentiated enterocytes present in mouse follicle-associated epithelial tissue.

Alkaline Phosphatase↗