Search PubMed⌕ Search

Biomedical subjects

W J O'Brien

Publications and source records attributed to W J O'Brien.

At least 109 records · Page 6Linked to original sources
PubMed1982

Chemotherapy of herpetic keratitis induced by acyclovir-resistant strains of herpes simplex virus type 1.

The severity of herpetic keratitis induced by 9-(2-hydroxyethoxymethyl) guanine-resistant strains of herpes simplex virus was significantly reduced by cotherapy with 9-beta-D-arabinofuranosyladenine (ara-A) and 2-deoxycoformycin. Therapy with 5-trifluoromethyl-2'-deoxyuridine (F3TdR) significantly reduced the severity of keratitis induced by an acyclovir-resistant strain with a defective DNA polymerase. Therapy with 3 percent acyclovir ointment slightly reduced the number of herpetic lesions produced by either deoxypyrimidine kinase or DNA polymerase defective viruses, despite these viruses being 100 to 1000 times more resistant to acyclovir than the wildtype strain. Therapy with 3 percent ara-A ointment alone significantly reduced the severity of lesions produced by the wildtype herpes strain. Therapy with ara-A alone did not reduce the severity of disease induced by any of the acyclovir-resistant mutants. The sensitivity of the wildtype and mutant viruses to nucleoside analogs was confirmed by yield-reduction assays conducted with Vero cells. These studies indicate that cotherapy with ara-A and an adenosine deaminase inhibitor was a reasonable alternative therapy for keratitis due to mutants resistant to therapy with nucleoside analogs which require the virus-specified deoxypyrimidine kinase or DNA polymerase, while ara-A alone was not an effective alternative.

Acyclovir↗
PubMed1982

Effects of timoptic on corneal reepithelialization.

The effects of topical 0.5% Timoptic on the reepithelialization of rabbit corneas were compared to the effects observed in rabbits receiving either vehicle, phosphate-buffered saline (PBS), PBS containing 0.5% timolol maleate, or no treatment. The rate of epithelial wound closure was slowed, and epithelial DNA content was less in both Timoptic- and vehicle-treated corneas. Light microscopy showed that the epithelium of animals treated with either Timoptic or vehicle processed fewer cellular layers in the wounded areas as well as considerable disruption of the epithelial layer. The rate of DNA synthesis and the cyclic adenosine monophosphate content of the epithelial cells from all treatment groups were statistically the same. The impaired wound closure observed during Timoptic and vehicle treatment was probably due to the sloughing of cells caused by the 0.01% benzalkonium chloride in the vehicle and not to impaired healing caused by the metabolic effects of timolol meleate.

Animals↗
PubMed1982

Color analysis of dental modifying porcelains.

Sintered samples of modifying porcelains of various colors and manufacturers were analyzed using reflectance spectrophotometry. Color designations are reported according to practices of the Commission Internationale de l'Eclairage (International Commission for Illumination), and color names were assigned based on a method developed through a joint effort of the Inter-Society Color Council and the United States National Bureau of Standards (ISCC-NBS). Within samples labeled by the same color, differences among manufacturers were found in the color designations and names. These differences were noted in part by plots of the chromaticity coordinates of the samples. The ISCC-NBS method of designating colors is proposed as a uniform and descriptive color-naming method for modifier porcelain. Consistent color naming is a step in improving communication over the use of modifying porcelains.

Color↗
PubMed1982

The effects of methylprednisolone acetate on macromolecular synthesis and glucose oxidation in epithelial cells of the ocular surface.

Epithelial cells that re-epithelialized corneas after the normal corneal epithelium was removed limbus to limbus by scraping were found to be metabolically responsive to methylprednisolone acetate. Seventy-two hours after scraping, the re-epithelializing cells from steroid-treated animals were found to have a 26% slower rate of DNA synthesis, a 30% slower rate of glucose oxidation via glycolysis, and a 79% greater rate of RNA synthesis with no apparent change in gross protein synthesis as compared with vehicle-treated controls. The DNA content of the epithelial layer isolated from steroid-treated corneas was reduced by 31% as compared with that of vehicle-treated controls.

Amino Acids↗
PubMed1981

Cardiac catecholamine stores after cardiac sympathectomy, 6-OHDA, and cardiac denervation.

Sympathetic nerves are known to reach the heart via classical vagal pathways. Bilateral cervicothoracic sympathectomy (CS) might be expected therefore to leave significant amounts of releasable catecholamines in the myocardium if the vagi are left intact. Cardiac responses to tyramine (500 micrograms intracoronary) were compared in animals with CS, extrinsic cardiac denervation (CD), and chemical sympathectomy with 6-hydroxydopamine (6-OHDA). Dogs were placed on cardiopulmonary bypass and isovolumic pressures were recorded from the heart. In control animals, tyramine caused profound increases in rate (58%) and isovolumic pressures (86-170%). Ten CS animals demonstrated responses indistinguishable from control animals. Four CD and four 6-OHDA animals showed no response to tyramine. Cervical vagal stimulation after atropine in the CS animals produced tachycardia. Histofluorescent studies demonstrated the presence of significant numbers of cardiac adrenergic fibers in this group. The normal tyramine responsiveness of the CS animals was attributed to 1) significant numbers of vagal adrenergic fibers remaining in the heart after cervicothoracic sympathectomy, and 2) denervation supersensitivity, rendering the heart very responsive to the catecholamine that remains.

Animals↗
PubMed1981

Optical properties of direct restorative materials.

The contrast ratio, light reflectivity, scattering coefficient, and absorption coefficient of four composites and an unfilled resin were calculated algebraically from reflection spectrophotometric data using Kubelka's equations. The correlation coefficient between calculated and experimental values of contrast ratio was 0.9996. Values of infinite optical thickness ranged from 4.19 to 6.70 mm.

Acrylic Resins↗
PubMed1981

Translucency of human dental enamel.

Translucency of human dental enamel was determined by total transmittance of wavelengths from 400 to 700 nm. The transmission coefficient at 525 nm was 0.481 mm-1. Total transmission of light through human dental enamel increased with increasing wavelength. Human tooth enamel is more translucent at higher wavelengths. The translucency of wet human enamel and enamel after dehydration was also measured by total transmittance. The transmission coefficient at 525 nm decreased from 0.482 to 0.313 mm-1 after dehydration and was reversed on rehydration. The decrease in translucency occurred as a result of the replacement of water around the enamel prisms by air during dehydration.

Color↗
PubMed1981

Effects of nucleoside antivirals and their metabolites on the corneal endothelium.

The endothelial surface of rabbit corneas were perfused in vitro with bicarbonate Ringer's containing 5 mM glucose, 0.3 mM reduced glutathione, and various concentrations of nucleoside antivirals or their metabolites. During three hour perfusions, the swelling rates of corneas perfused with buffer containing either antivirals or metabolites were not significantly different from controls. Scanning electron microscopy of the endothelial cell layer revealed no structural abnormalities in any treatment group. One metabolite, fluoride ion, reduced endothelial glucose oxidation by about 60 percent when incubated with corneal tissue in vitro. The inhibition of glucose metabolism by fluoride ions was observed only at concentrations at least sixty times greater than would be anticipated in the anterior chamber of patients receiving topical F3TdR therapy. These studies indicate that 5-trifluoromethyl-2'-deoxyuridine, 5-iodo-2'-deoxyuridine, 9-(2-hydroxyethoxymethyl)-guanine, and their metabolites do not alter endothelial function when studied at physiological concentrations over a short term of exposure.

Acyclovir↗
PubMed1980

The effect of temperature and membrane lipid composition on the rate of beta-oxidation by Escherichia coli.

Escherichia coli, strain D-1ML, was grown to mid-exponential phase at 14, 30 or 43 degrees C. Membrane fractions were prepared from cells grown at each temperature and analyzed with respect to the unsaturated to saturated fatty acid ratio and the effect of temperature on the rate of catalysis by succinate dichlorophenol reductase and the membrane-bound acyl-CoA synthetase. The ratio of unsaturated to saturated fatty acids increased from 0.72 : 1.00 in cells grown at 43 degrees C to 1.46 : 1.00 in cells grown at 14 degrees C. The specific activity of succinate dichlorophenol reductase was increased by greater than two-fold in cells grown at 43 degrees C relative to the specific activity of the reductase from cells grown at 14 degrees C. In addition the activity of succinate dichlorophenol reductase responded to thermal phase transitions that were characteristic of membranes isolated from cells grown at the three different temperatures. In contrast the specific activity of acyl-CoA synthetase exhibited little or no variation as a function of the fatty acid composition of the membrane and the activity of the synthetase was not subject to thermal phase transitions. Comparison of Arrhenius plots of the oxidation of [U-14C]palmitoleate by whole cells and acyl-CoA synthetase activity with palmitoleate as substrate demonstrated that the two exhibited virtually identical Arrhenius activation energies and temperature optima. The Arrhenius plots of other soluble beta-oxidation enzymes do not resemble the provile of beta-oxidation. These data strongly suggest that the acyl-CoA synthetase which catalyzes the transport of fatty acids into E. coli by group translocation mechanism is the rate-limiting step in beta-oxidation in E. coli.

Chlorophenols↗
PubMed1980

Translucency of dental porcelains.

The translucency of comparable shades of five dental porcelains was determined. Both direct transmittance and total transmittance were measured at wavelengths of 400-700 nm. For 1 mm of porcelain, the values for direct transmittance were low and averaged 0.13 percent, whereas the values for total transmittance averaged 26.8 percent. Transmittance increased with increasing incident wavelength. These results indicated a high degree of light scattering.

Color↗
PubMed1980

The shear strength of dental porcelain.

The widespread use of porcelain in restorative dentistry is generally due to its esthetic appearance even though it is brittle. The transverse strength, or modulus rupture, averages around 108 MPa (16,000 psi) for aluminous porcelain and 88 MPa (13,000 psi) for feldspathic porcelain. The tensile strength, as determined by diametral compression, is approximately 29 MPa (4,200 psi) for opaque feldspathic porcelain and 40 MPa (5,800 psi) for gingival feldspathic porcelain. The compressive strength is reported to be 340 MPa (50,000 psi) for a feldspathic porcelain. These mechanical strength properties of dental porcelain confine its use to low stress-bearing restorations or to those restorations with a metal substrate.

Aluminum↗
PubMed1980

Base retention.

Explore the source record for details and available documents.

Denture Bases↗
PubMed1979

Measurement of corneal DNA content.

The amount of DNA in the corneal epithelium, stroma, and endothelium of both rabbit and bovine tissue was measured by a diphenylamine assay procedure. The results indicate that hot perchloric acid extraction is required to effectively solubilize the corneal DNA for assay. Rabbit corneal epithelium, stroma, and endothelium were found to contain 53.8, 1.7, and 4.3 microgram of DNA per milligram of tissue dry weight, respectively. Bovine corneal epithelium contained 15.8 microgram/mg DNA, stroma 0.6 microgram/mg DNA, and endothelium 3.1 microgram/mg. These data provide a basis for an expression of the cellularity of corneal layers.

Animals↗