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Biomedical subjects

W J Dunn

Publications and source records attributed to W J Dunn.

At least 19 recordsLinked to original sources
PubMed1992

A critical view of the rationale for routine, initial and periodic radiographic surveys.

Most dentists and dental faculties use an initial radiographic survey for the comprehensive-care patient rather than selective radiography, as recommended by professional organizations and radiation protection agencies. Survey or screening radiography has been justified in the belief that it is an essential health service designed to disclose serious occult disease and that failure to use such films might expose the dentist to successful malpractice litigation. However, incidence data indicate the chance of disclosing tumors, non-inflammatory cysts or other serious bone disease in the asymptomatic patient by screening jaw films is infinitesimal. On this basis, the practice is not justifiable as a public health measure, nor is the dentist who follows published national guidelines for prescription radiography vulnerable to successful litigation.

Canada↗
PubMed1988

QSAR approaches to predicting toxicity.

Due to the demands of time and the high cost of testing compounds for toxicity in test animals, it would be an advantage to be able to estimate the toxic response of chemical agents using theoretical approaches. Predicting whether a compound will be toxic or nontoxic is a classification problem and the methods of studying quantitative structure activity relationships (QSAR) can be used for this purpose [Hansch, C. (1969) Accounts Chem. Res., 2, 232]. It should be recognized, however, that formulating the QSAR problem as one of active vs. inactive makes it different from classical QSAR problems. This requires that methods be applied that can predict the category of a compound to be used, i.e., so-called methods of pattern recognition (Varmuza, K. (1983) J. Chem. Info. Comp. Sci. 23, 6) being required. There are several methods of pattern recognition that can be used with some being more suitable than others. The nature of this unique QSAR problem, the appropriate methods to apply, and some of the pitfalls of applying QSAR techniques to predicting toxicity are discussed.

Computer Simulation↗
PubMed1988

Choroidal malignant melanoma with early vitreous seeding.

Primary choroidal malignant melanoma with extension through the overlying retina is a rarely reported entity, and to our knowledge actual seeding of the vitreous has never been reported. The pathologic findings in a 41-year-old woman who presented with a large amelanotic subretinal mass near the optic disc of the right eye are discussed. Fundus examination preoperatively revealed a concentration of discrete, fleshy, oval to round, vitreous bodies of varying size, limited to the area overlying the mass. Histopathology of this tumor revealed a spindle cell posterior choroidal melanoma with marked atrophy of the overlying retina. At the apex, the retina was discontinuous and melanoma cells extended into the overlying vitreous. Some of the cells surrounded asteroid bodies overlying the tumor, altering their clinical appearance. This behavior, while only involving a small fraction of the tumor cells, may imply a more aggressive tumor.

Adult↗
PubMed1987

The role of solvent-accessible surface area in determining partition coefficients.

The logarithm of the partition coefficient (log P) of low-molecular-weight organic compounds is a physicochemical parameter used extensively in structure-biological activity studies to model interactions of the compounds with nonpolar phases in vitro and in vivo. The partition coefficient can be determined between water and a number of nonpolar solvents. The most common nonpolar solvent is 1-octanol, but solvents such as benzene, carbon tetrachloride, and chloroform are frequently used as models for the nonpolar phases. The functional relationship between chemical structure and partitioning is not well-understood. In this paper, partition coefficient data for 50 solutes in six nonpolar solvent systems are analyzed by using principal components analysis. The objective of the work is to explore the relationship between solute structure and partitioning behavior for simple organic compounds. Two structural factors are found to be important, with the isotropic surface area being the most important. The isotropic surface area can be used to estimate log P in some solvents and as an independent variable in quantitative structure-activity relationships (QSAR). This is illustrated by estimating the rate of epidermal diffusion of steroids.

Diffusion↗
PubMed1978

Structure-activity study of beta-adrenergic agents using the SIMCA method of pattern recognition.

The SIMCA method of pattern recognition (PaRC) was used to analyze structure-activity data for a series of phenethylamine agonists and antagonists of the beta-adrenergic receptor. On the basis of physicochemical substituent parameters the SIMCA method classified correctly 100% of the agonists and 88% of the antagonists. In addition, parameters derived from the class models were correlated with the biological activities of the agonists and antagonists, respectively. Test compounds not included in the initial data analysis were classified and their activities estimated. The applicability of pattern recognition in structure-activity studies in general is discussed.

Adenylyl Cyclase Inhibitors↗
PubMed1978

A structure-carcinogenicity study of 4-nitroquinoline 1-oxides using the SIMCA method of pattern recognition.

Structure-carcinogenicity data for a series of 4-nitro- and 4-hydroxyaminoquinoline 1-oxides were analyzed using the SIMCA method of pattern recognition. Using physicochemically based substituent constants to describe each compound, a principal components model was derived for the carcinogens. This model was 82% successful in predicting the carcinogenic potential of the compounds. For the 6-substituted compounds, a significant relationship between those structural parameters associated with carcinogenic potential and ability to stimulate unscheduled DNA synthesis was observed. In addition, other problems unique to the classification of carcinogens were discussed.

4-Hydroxyaminoquinoline-1-oxide↗
PubMed1978

Efficacy of monensin against coccidiosis in lambs.

Lambs fed monensin mixed in a complete fattening ration at concentrations of 5, 10, or 20 ppm were protected against death, impaired body weight gain, and diarrhea due to infections of Eimeria ninakohlyakimovae and E ahsata. Monensin given at the concentration of 10 ppm reduced oocyst passage and, at the concentration of 20 ppm, almost completely controlled oocyst passage. Protection was afforded by monensin given at the concentration of 5 ppm, although oocyst passage was excessive and body weight gains were suboptimal. Infected control lambs were severely affected, with mortality rate of 30% to 50% on days 14 to 18 and oocyst passage averaging 286,000,000 oocyst/lamb, Oocyst production peaks on days 12 to 15 and 21 to 27 correlated with the appearance of oocysts of E ninakohlyakimovae and E ahsata, respectively. Body weight gains and feed consumption of lambs fed monensin at the concentration of 10 or 20 ppm indicated that the drug was well tolerated at these dose levels and this route of administration. The compound was efficacious in Dorset and Suffolk X Hampshire lambs, and caused no problems when fed to pregnant ewes.

Animals↗
PubMed1977

Synthesis, physicochemical properties, and antitumor activities of analogs of 1-phenyl-3-benzyl-3-methyltriazenes.

To study the effect of substituents on the antitumor activities of analogs of 1-phenyl-3-benzyl-3-methyltriazenes, a series of compounds was designed and synthesized in which the substituent on the 1-phenyl was an electron-withdrawing group and the substituent on the 3-benzyl had a broad range of physicochemical properties. Of the 13 analogs prepared and tested against Sarcoma-180 in the mouse, five showed significant activity. The results were submitted to discriminant analysis to determine structure-activity relationships.

Animals↗
PubMed1976

Use of cluster analysis in the development of structure-activity relations for antitumor triazenes.

A series of antitumor triazenes in which the members of the series are physicochemically distinct was designed using the cluster analysis approach as proposed by Hansch and his co-workers. The series that resulted was tested against Sarcoma 180 in the mouse and the antitumor activities were analyzed using regression techniques. The structure-activity relations that resulted are discussed in terms of proposed mechanisms of action.

Animals↗