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Biomedical subjects

M E Davis

Publications and source records attributed to M E Davis.

At least 37 records · Page 2Linked to original sources
PubMed2003

Genetic parameter estimates for serum insulin-like growth factor-I concentration and ultrasound measurements of backfat thickness and longissimus muscle area in Angus beef cattle.

A divergent selection experiment for serum IGF-I concentration began at the Eastern Ohio Resource Development Center in 1989 using 100 spring-calving (50 high line and 50 low line) and 100 fall-calving (50 high line and 50 low line) purebred Angus cows. Following weaning, bull and heifer calves were fed in drylot for a 140-d period. Real-time ultrasound measurements of backfat thickness and longissimus muscle area were taken on d 56 and 140 of the postweaning test. Only ultrasound data from calves born from fall 1995 through spring 1999 were included in the analysis. At the time of this study, IGF-I measurements were available for 1,521 bull and heifer calves, and ultrasound data were available for 636 bull and heifer calves. Data were analyzed by multiple-trait, derivative-free, restricted maximum likelihood methods. Estimates of direct heritability for IGF-I concentration at d 28, 42, and 56 of the postweaning period, and for mean IGF-I concentration were 0.26 +/- 0.07, 0.32 +/- 0.08, 0.26 +/- 0.07, and 0.32 +/- 0.08, respectively. Direct heritabilities for ultrasound estimates of backfat thickness ranged from 0.17 +/- 0.11 to 0.28 +/- 0.12, whereas direct heritabilities for longissimus muscle area ranged from 0.20 +/- 0.10 to 0.36 +/- 0.12, depending on the time of measurement and the covariate used for adjustment (age vs. weight). Direct genetic correlations of IGF-I concentrations with backfat thickness at d 56 and 140 and with longissiumus muscle area at d 56 and 140 averaged 0.02, 0.20, -0.08, and 0.23, respectively, when age was used as the covariate for both IGF-I and ultrasound measurements. Corresponding genetic correlations when age was used as the covariate for IGF-I and weight was used as the covariate for ultrasound measurements were 0.05, -0.07, -0.22, and -0.04, respectively. Therefore, the positive associations of serum IGF-I concentration with backfat thickness and longissimus muscle area at d 140 seem to have been partially mediated by weight. Results of this study do not indicate strong associations of serum IGF-I concentration with fat thickness or muscling of bulls and heifers during the postweaning feedlot period.

Adipose Tissue↗
PubMed2002

Effect of dietary mannan oligosaccharides and(or) pharmacological additions of copper sulfate on growth performance and immunocompetence of weanling and growing/finishing pigs.

Two experiments were conducted to determine the efficacy of mannan oligosaccharides (MOS) fed at two levels of Cu on growth and feed efficiency of weanling and growing-finishing pigs, as well as the effect on the immunocompetence of weanling pigs. In Exp. 1, 216 barrows (6 kg of BW and 18 d of age) were penned in groups of six (9 pens/treatment). Dietary treatments were arranged as a 2 x 2 factorial consisting of two levels of Cu (basal level or 175 ppm supplemental Cu) with and without MOS (0.2%). Diets were fed from d 0 to 38 after weaning. Blood samples were obtained to determine lymphocyte proliferation in vitro. From d 0 to 10, ADG, ADFI, and gain:feed (G:F) increased when MOS was added to diets containing the basal level of Cu, but decreased when MOS was added to diets containing 175 ppm supplemental Cu (interaction, P < 0.01, P < 0.10, and P < 0.05, respectively). Pigs fed diets containing 175 ppm Cu from d 10 to 24 and d 24 to 38 had greater (P < 0.05) ADG and ADFI than those fed the basal level of Cu regardless of MOS addition. Pigs fed diets containing MOS from d 24 to 38 had greater ADG (P < 0.05) and G:F (P < 0.10) than those fed diets devoid of MOS. Lymphocyte proliferation was not altered by dietary treatment. In Exp. 2, 144 pigs were divided into six pigs/pen (six pens/treatment). Dietary treatments were fed throughout the starter (20 to 32 kg BW), grower (32 to 68 kg BW), and finisher (68 to 106 kg BW) phases. Diets consisted of two levels of Cu (basal level or basal diet + 175 ppm in starter and grower diets and 125 ppm in finisher diets) with and without MOS (0.2% in starter, 0.1% in grower, and 0.05% in finisher). Pigs fed supplemental Cu had greater (P < 0.05) ADG and G:F during the starter and grower phases compared to pigs fed the basal level of Cu. During the finisher phase, ADG increased when pigs were fed MOS in diets containing the basal level of Cu, but decreased when MOS was added to diets supplemented with 125 ppm Cu (interaction, P < 0.05). Results from this study indicate the response of weanling pigs fed MOS in phase 1 varied with level of dietary Cu. However, in phase 2 and phase 3, diets containing either MOS or 175 ppm Cu resulted in improved performance. Pharmacological Cu addition improved gain and efficiency during the starter and grower phases in growing-finishing pigs, while ADG response to the addition of MOS during the finisher phase seems to be dependent upon the level of Cu supplementation.

Animal Feed↗
PubMed2002

Examination of the relationship between the estrogen receptor gene and reproductive traits in swine.

The relationship between estrogen receptor (ESR) genotype and reproductive traits in a population of Yorkshire, Large White, and crossbred animals was studied. Reproductive tract and litter data were analyzed for associations with ESR genotype, parity, and breed. Forty-six Yorkshire, 31 Large White, and 70 crossbred females from the above population were mated to Hampshire boars and slaughtered at 75 d of gestation. Data collected included ovulation rate, uterine horn length, number of fetuses, fetal weight, uterine weight, number of mummies, fetal sex, fetal placement, fetal survival, and fetal space. Data were analyzed using a model that included the fixed effects of ESR genotype, breed, parity, and all significant two-way interactions. Litter data representing 212 litter records were analyzed in a model that included the fixed effects of ESR genotype of dam, parity, farrowing month, dam breed, sire breed, and all significant two-way interactions. The ESR genotype was significantly associated with the total litter weight of piglets born and total litter weight of piglets born alive. Dams with the AA genotype had significantly (P = 0.04) heavier litters at birth (14.44 +/- 0.36 kg) than dams with the BB genotype (13.43 +/- 0.47 kg). Ovulation rate was significantly (P < 0.05) different between animals of parity 1 (17.22 +/- 0.41) and parity > or = 3 (19.92 +/- 0.85). Significant breed effects were observed for fetal weight, with purebred Large White animals having a greater fetal weight per horn (3,909 +/- 114 g) than purebred Yorkshire animals (3,553 +/- 92 g). Notable, but nonsignificant, trends with respect to ESR genotype were also observed for number of piglets alive at weaning and total litter weight at weaning. The ESR gene is positively associated with several previously uninvestigated reproductive traits.

Animals↗
PubMed2001

Shear stress regulates endothelial nitric oxide synthase expression through c-Src by divergent signaling pathways.

In this study, we defined the signaling cascade responsible for increased eNOS mRNA expression in response to laminar shear stress. This pathway depends on the tyrosine kinase c-Src because shear induction of eNOS mRNA is blocked by the c-Src inhibitors PP1 and PP2, as well as an adenovirus encoding kinase inactive c-Src. After activation of c-Src, this pathway diverges. One arm is responsible for the short-term (6 hour) increase in eNOS mRNA. This involves a transient, 1-hour increase in eNOS transcription, as detected by nuclear run-on, that is dependent on activation of Ras and is blocked by adenoviral infection with dominant negative Ras. Downstream of Ras, MEK1/2 and ERK1/2 are important in this pathway, as 2 inhibitors of MEK1/2, PD98059 and UO126, completely prevented this early increase in eNOS mRNA. ERK1/2 was rapidly phosphorylated in response to shear, and this was prevented by c-Src and Ras inhibition. Further, Raf is phosphorylated in response to shear stress, and this is prevented by c-Src inhibition, suggesting that Raf may transduce the signal between Ras and ERK1/2. The second arm of the pathway linking activation of c-Src to eNOS expression involves stabilization of eNOS mRNA by shear stress. This response to shear is completely abrogated by the c-Src inhibitor PP1 but not altered by Ras or MEK1/2 inhibition. Thus, c-Src plays a central role in modulation of eNOS expression in response to shear stress via divergent pathways involving a short-term increase in eNOS transcription and a longer-term stabilization of eNOS mRNA.

Animals↗
PubMed2001

Studies of the synthesis of SSZ-25 zeolite in a "mixed-template" system.

The synthesis of aluminosilicate zeolite, SSZ-25, is described using a two-component organic guest molecule strategy. This method has been recently described by us and is quite effective in crystallizing a variety of aluminosilicate zeolites with reduction in template cost. In this instance the original organic guest component used in the discovery of SSZ-25, N',N',N'-trimethyl-2-adamantammonium cation, is used in conjunction with a variety of smaller amines. The amine is the major organic component in the synthesis and the quaternary ammonium compound, while a minor component, is essential for structure direction to the desired zeolite product. Studies here show that the adamantyl component is preferentially taken up during crystal growth. Our studies showed that the use of the multi-organic component approach to synthesis resulted in a faster and cheaper route to crystallizing SSZ-25. The SSZ-25 has been described in the literature as having the MWW topology and as such has two different channel systems accessed by 10-ring openings; the channel systems do not intersect. One set of 10-rings open into large cavities. In this study we used NMR spectroscopy to examine the as-made materials and to see if the two organic components are used in different capacities in the synthesis, probing if the admantyl component is only found in these larger cavities. The crystalline products could be affected by solvent extraction with polar solvents like dimethylformamide: the X-ray powder patterns and elemental analyses changed with solvent treatment. The solvent-treated crystals were studied by NMR spectroscopy, elemental analysis, and argon adsorption. The two-component organic guest approach was also found to be quite flexible not only with regard to the amine, but also towards the quaternary ammonium compounds. Non-adamantyl polycyclic templates could be used, and polar but non-quaternized adamantyl derivatives also succeeded in directing towards SSZ-25 formation. On the other hand. in one instance it was shown that the two-component approach favors SSZ-25 as the kinetic product but at longer run times Ostwald ripening was observed, leading to the disappearance of SSZ-25 and formation of ferrierite zeolite and quartz.

Journal Article↗
PubMed2001

Characterization of Ti-Beta zeolites and their reactivity for the photocatalytic reduction of CO2 with H2O.

A characterization of Ti-Beta zeolites synthesized under various conditions as well as an investigation of their photocatalytic properties for the reduction of CO2 with H2O at 323 K to produce CH4 and CH3OH were carried out. In situ XAFS spectra measurements indicated that a highly dispersed tetrahedral titanium oxide species was present in the zeolite framework and an increase in the coordination number of the titanium oxide species by the addition of H2O and CO2 molecules could be detected. The Ti-Beta zeolite having a hydrophilic property (Ti-Beta(OH)) exhibited a more dramatic increase in the coordination number than the Ti-Beta(F) zeolite which had a hydrophobic property. These results suggest that CO2 and H2O molecules can be adsorbed efficiently onto the highly dispersed tetrahedrally coordinated titanium oxide species. UV irradiation of these Ti-Beta zeolite catalysts in the presence of H2O and CO2 led to the formation of CH4 and CH3OH. Ti-Beta(OH) exhibited a higher reactivity than Ti-Beta(F), while the selectivity for the formation of CH3OH on Ti-Beta(F) was higher than that for Ti-Beta(OH). These results indicated that the reactivity and selectivity of the zeolite catalyst can be determined by the hydrophilic and hydrophobic properties of the zeolites.

Journal Article↗
PubMed2001

Impact of blood serum insulin-like growth factor I on platelet-activating factor in bull spermatozoa.

The objective of this study was to examine differences in platelet-activating factor [1-O-alkyl-2-acetyl-sn-glycero-3-phosphorylcholine; PAF] in spermatozoa between two lines of Angus beef cattle divergently selected for blood serum insulin-like growth factor I (IGF-I) concentration. Endogenous lipids were extracted from the spermatozoa and endogenous PAF content was determined by radioimmunoassay. The amount of PAF detected in spermatozoa obtained from high IGF-I bulls (n = 8) ranged from 0.145 to 3.571 pM/10(6) cells. The level of PAF extracted from spermatozoa obtained from low IGF-I- bulls (n = 5) ranged from 0.001 to 1.024 pM/10(6) cells. Polynomial regression analysis revealed a significant cubic relationship (R(2) = 0.374; F = 6.292; P < 0.05) between spermatozoa PAF content and blood serum IGF-I concentration. Spermatozoa-derived PAF levels (mean +/- SEM) were significantly higher (P < 0.05) in the high IGF-I group (1.90 +/- 0.39 pM/10(6) cells) than in the low IGF-I group (0.59 +/- 0.20 pM/10(6) cells). High IGF-I bulls have a greater than three-fold higher PAF content in their spermatozoa than low IGF-I bulls. The data demonstrate that not only is PAF present in bull spermatozoa but that levels are significantly higher in individuals with high serum IGF-I concentrations.

Animals↗
PubMed2001

Induction of endothelial NO synthase by hydrogen peroxide via a Ca(2+)/calmodulin-dependent protein kinase II/janus kinase 2-dependent pathway.

We have recently demonstrated that hydrogen peroxide (H(2)O(2)) is an extremely potent stimulus of endothelial NO synthase (eNOS) gene expression. The present study was designed to identify the signaling mechanisms mediating this response. Induction of eNOS expression by H(2)O(2) was found to be Ca(2+) dependent, inasmuch as it was blocked by BAPTA-AM. Further studies have indicated that Ca(2+)/calmodulin-dependent protein kinase II (CaM kinase II) plays a critical role in mediating this response. Immunocytochemical staining with an anti-CaM kinase II antibody confirmed the expression of CaM kinase II in cultured bovine aortic endothelial cells. H(2)O(2) induced autophosphorylation of CaM kinase II and increased the activity of the enzyme, as assessed by an in-gel kinase assay. A specific inhibitor for CaM kinase II, KN93, and a calmodulin antagonist, W-7, attenuated eNOS induction by H(2)O(2). Further studies have indicated that janus kinase 2 is important in mediating increased eNOS expression in response to H(2)O(2) and likely is downstream from CaM kinase II. In conclusion, these data provide the first evidence that CaM kinase II plays a critical role in endothelial redox signaling. Regulation of eNOS via this pathway may represent an important vascular adaptation to oxidant stress.

Animals↗
PubMed2001

Association of a genetic marker with blood serum insulin-like growth factor-I concentration and growth traits in Angus cattle.

The objective of this research was to evaluate a biallelic genetic marker identified in the first promoter region of the bovine IGF-I gene. The point mutation was identified as a T-to-C transition by sequencing the polymorphic fragments. A PCR-RFLP procedure was developed for determining the marker genotypes. Marker genotypes were determined for 760 Angus calves from divergent lines that were created by selection for high or low serum IGF-I concentration (allele A: 63.9%, B: 36.1%). Data were analyzed using the multiple-trait derivative-free restricted maximum likelihood computer programs with animal models. The full animal model included fixed effects of marker genotype, birth year, season of birth, sex, age of dam, and selection line; random effects of animal, maternal genetic, and maternal permanent environmental effects; and a covariate for age of calf. Traits analyzed included blood serum IGF-I concentrations on d 28, 42, and 56 of the postweaning test, mean IGF-I concentration, birth weight, weaning weight, on-test weight, off-test weight, off-test hip height, postweaning gain, and weight gain during the 20-d period immediately after weaning. Results from the analysis across selection lines showed a significant association of the BB genotype with higher weight gain during the first 20 d after weaning and a slight dominance effect of the marker on postweaning gain. Analysis within the low IGF-I line also showed a significant association of the BB genotype with higher weight gain during the first 20 d after weaning and with on-test weight, although analysis within the high IGF-I line did not show any significant association. The associated effects of the marker need to be verified in other cattle populations.

Animals↗
PubMed2001

Cationic polymers for gene delivery: designs for overcoming barriers to systemic administration.

Cationic, polymer-based delivery systems have faced limitations in the systemic delivery of therapeutic gene drugs due to difficulties in formulation, in vivo stabilization, toxicity and low transfection efficiencies. Strategies for overcoming some of these barriers have utilized knowledge gained from the fields of colloidal stabilization and protein trafficking. This review highlights recent efforts in polycation preparations that include the development of new polymers for gene delivery, the modification of traditional polycations with hydrophilic polymers for salt and serum stability and the addition of bioactive functionalities to polymers for enhanced intracellular trafficking. These studies have resulted in polymer/DNA composites with increased stability and delivery efficiencies.

Active Transport, Cell Nucleus↗
PubMed2001

Bouveret's syndrome presenting as upper gastrointestinal hemorrhage without hematemesis.

A 74-year-old woman with a recent diagnosis of peptic ulcer disease diagnosed by endoscopy after presentation with an episode of upper gastrointestinal bleeding returned 6 1/2 weeks later with a 5-day history of nausea and vomiting without associated symptoms. An ultrasound was nondiagnostic except for a large gallstone and a poorly visualized gallbladder. Repeat endoscopy revealed a hard mass that was presumed to have formed secondarily to an ulcer-induced stricture, and a 6-cm filling defect just proximal to the duodenal bulb was seen on a preoperative upper gastrointestinal series. At laparotomy the mass was actually a large gallstone and two smaller stones, which had eroded into and become impacted in the duodenal bulb creating a gastric outlet obstruction. The stones were extracted via a duodenotomy, and the remaining portion of the gallbladder was removed with repair of the cholecystoduodenal fistula. The patient was discharged home after an uncomplicated postoperative course. Gastric outlet obstruction by a duodenal gallstone is a condition known as Bouveret's syndrome, which is a rare complication of gallstone disease. Upper gastrointestinal hemorrhage is an especially rare form of presentation.

Aged↗
PubMed2000

Transcriptional and posttranscriptional regulation of endothelial nitric oxide synthase expression by hydrogen peroxide.

Diverse stimuli, including shear stress, cyclic strain, oxidized LDL, hyperglycemia, and cell growth, modulate endothelial nitric oxide synthase (eNOS) expression. Although seemingly unrelated, these may all alter cellular redox state, suggesting that reactive oxygen intermediates might modulate eNOS expression. The present study was designed to test this hypothesis. Exposure of bovine aortic endothelial cells for 24 hours to paraquat, a superoxide (O(2)(-*))-generating compound, did not affect eNOS mRNA levels. However, cotreatment with paraquat and either Cu(2+)/Zn(2+) superoxide dismutase or the superoxide dismutase mimetic tetrakis(4-benzoic acid)porphyrin chloride increased eNOS mRNA by 2.3- and 2.2-fold, respectively, implicating a role for H(2)O(2). Direct addition of 100 and 150 micromol/L H(2)O(2) caused increases in bovine aortic endothelial cell eNOS mRNA that were dependent on concentration (ie, 3.1- and 5.2-fold increases) and time, and elevated eNOS protein expression and enzyme activity, accordingly. Nuclear run-on and 5, 6-dichloro-1-beta-D-ribofuranosylbenzimidazole-chase studies showed that H(2)O(2) caused a 3.0-fold increase in eNOS gene transcription and a 2.8-fold increase in eNOS mRNA half-life. Induction of eNOS by H(2)O(2) was not affected by the hydroxyl radical scavenger DMSO, mannitol, or N-tert-butyl-alpha-phenylnitrone, but it was inhibited by the antioxidants N-acetylcysteine, ebselen, and exogenously added catalase. Unlike H(2)O(2), the 4.0-fold induction of eNOS by shear stress (15 dyne/cm(2) for 6 hours) was not inhibited by N-acetylcysteine or exogenous catalase. In conclusion, H(2)O(2) increases eNOS expression through transcriptional and post-transcriptional mechanisms. Although H(2)O(2) does not mediate shear-dependent eNOS regulation, it is likely to be involved in regulation of eNOS expression in response to other physiological and/or pathophysiological stimuli.

Animals↗
PubMed2000

Differential regulation of vascular smooth muscle nuclear factor kappa-B by G alpha q-coupled and cytokine receptors.

NF kappaB has been implicated as a downstream effector of G alphaq-coupled receptor signaling, but whether these and cytokine receptors activate NF kappaB similarly remains unclear. Stimulation of rat vascular smooth muscle cell G alphaq-coupled P2Y nucleotide receptors with UTP induces luciferase transcription from a sensitive and specific NF kappaB dependent promoter. However, these responses are only;15% of that to the reference cytokine IL-1 beta. IL-1 beta is a powerful stimulator of I kappaB alpha degradation, RelA nuclear import, and isoform specific NF kappaB enhancer binding in vitro, responses that are not detectable after P2Y receptor stimulation. Expression of two trans -dominant NF kappaB polypeptides suppresses induction of the NF kappaB reporter and also IL-1 beta stimulated monocyte chemoattractant-1 mRNA, which is not induced by UTP. In contrast, UTP induces higher expression of the endogenous COX-2 and IL-6 mRNAs than does IL-1 beta, implying that G alphaq-coupled receptor evokes additional NF kappaB-independent transcription factors in regulating these two genes. P2Y receptors are as effective as the reference growth factor PDGF-BB at inducing CREB, AP-1, SRE and NFAT transcription, which are largely unaffected by IL-1 beta treatment. NF kappaB is less efficiently activated then several other transcriptional effectors of G alphaq-coupled receptor signaling in vascular smooth muscle cells, and is instead preferentially activated by inflammatory cytokines.

Animals↗