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Biomedical subjects

J D Walker

Publications and source records attributed to J D Walker.

At least 145 records · Page 8Linked to original sources
PubMed1973

Aliphatic hydrocarbons of Cladosporium resinae cultured on glucose, glutamic acid, and hydrocarbons.

The carbon source markedly influenced the qualitative and quantitative composition of cellular hydrocarbons in Cladosporium resinae. Total lipid and hydrocarbon content was greater in cells grown on n-alkanes than in cells grown on glucose or glutamic acid. Glucose-grown cells contained a spectrum of aliphatic hydrocarbons from C(7) to C(36); pristane and n-hexadecane comprised 98% of the total. Cells grown on glutamic acid contained C(7) to C(23) hydrocarbons; n-tridecane, n-tetradecane, n-hexadecane, and pristane made up 74% of the total. n-Decane-grown cells yielded C(8) to C(32) compounds, and n-hexadecane (96%) was the major hydrocarbon. Cells grown on individual n-alkanes from C(11) to C(15) all contained C(11) to C(28) hydrocarbons, and cells grown on n-hexadecane contained C(11) to C(32) hydrocarbons. In n-undecane-grown cells, n-hexadecane and pristane made up 92% of the total, but in cells grown on C(12) to C(16)n-alkanes the major cellular hydrocarbon was the one on which the cells were grown. This suggests that cells cultured on n-alkanes of C(12) or longer accumulate n-alkanes prior to oxidizing them.

Alkanes↗
PubMed1973

Pathway of n-alkane oxidation in Cladosporium resinae.

Pathways of initial oxidation of n-alkanes were examined in two strains of Cladosporium resinae. Cells grow on dodecane and hexadecane and their primary alcohol and monoic acid derivatives. The homologous aldehydes do not support growth but are oxidized by intact cells and by cell-free preparations. Hexane and its derivatives support little or no growth, but cell extracts oxidize hexane, hexanol, and hexanal. Alkane oxidation by extracts is stimulated by reduced nicotinamide adenine dinucleotide (phosphate). Alcohol and aldehyde oxidation are stimulated by nicotinamide adenine dinucleotide (phosphate), and reduced coenzymes accumulate in the presence of cyanide or azide. Extracts supplied with (14)C-hexadecane convert it to the alcohol, aldehyde, and acid. Therefore, the major pathway for initial oxidation of n-alkanes is via the primary alcohol, aldehyde, and monoic acid, and the system can act on short-, intermediate-, and long-chain substrates. Thus, filamentous fungi appear to oxidize n-alkanes by pathways similar to those used by bacteria and yeasts.

Alcohols↗
PubMed1969

The conversion of testosterone to 5 alpha-androstan-17 beta-ol-3-one (dihydrotestosterone) by skin slices of man.

The conversion of testosterone-1,2-(3)H to dihydrotestosterone by slices of human skin obtained from various anatomical sites in 112 normal subjects and three individuals with the syndrome of testicular feminization has been measured under standardized conditions. Very low rates of dihydrotestosterone formation were observed in sites obtained from the mons or from miscellaneous areas of the trunk and limbs of the control subjects. The mean rates of conversion were very high, however, in slices of skin obtained from several perineal sites (labia majora, scrotum, prepuce, and clitoris). Furthermore, as measured here, the rate of dihydrotestosterone formation by prepuce rises during the 3 months after birth and then falls progressively thereafter, reaching a level in the adult that is almost as low as that observed in the slices of nonperineal skin from all ages. In the patients with testicular feminization dihydrotestosterone formation by slices of skin obtained from the mons was within the normal range, whereas the rates observed in labia majora were lower than the average values obtained in the normal subjects.

Adolescent↗
PubMedDate not supplied

Left ventricular and myocyte structure and function following chronic ventricular tachycardia in rabbits.

Recent studies have shown that chronic pacing induced tachycardia in large animals such as dogs and pigs causes congestive heart failure accompanied by myocyte contractile abnormalities, neurohormonal activation, alterations in sarcolemmal receptor systems, and changes in myocardial structure. However, fundamental studies directed at identifying basic contributory mechanisms responsible for the development of this form of heart failure are problematic in these large animals. Accordingly, the present study examined the direct effects of pacing induced tachycardia upon LV and myocyte structure and function in the adult rabbit. Twelve adult rabbits (New Zealand White; 3.5-4.5 Kg) underwent 30 days of pacing induced ventricular tachycardia (VT; right ventricular paced, 400 bpm) and 12 additional age and weight matched rabbits served as controls. Echocardiography revealed increased LV end-diastolic dimension (1.92 +/- 0.04 vs 1.10 +/- 0.20 cm; p < 0.05) and decreased fractional shortening (41.5 +/- 3 vs 22.3 +/- 4%; p < 0.05) in the VT group compared to controls with no change in LV mass. Steady-state isolated myocyte contractile function was significantly reduced in the VT group compared to control. For example, isolated myocyte velocity of shortening was 41 +/- 2 microns/s in the VT group compared to 84 +/- 5 microns/s for controls (p < 0.05). In the presence of 8 mM extracellular Ca2+, myocyte velocity of shortening was 40% lower in the VT group compared to controls. Finally, myocyte contractile responsiveness with beta-adrenergic receptor stimulation was reduced by 52% in the VT group compared to controls. Isolated myocyte length significantly increased in the VT group compared to control (157 +/- 3 vs 128 +/- 2 microns; p < 0.05) with a concomitant decrease in cross-sectional area (274 +/- 6 vs 400 +/- 31 microns 2; p < 0.05). Myocyte myofibril volume fell by 27% in the VT group compared to control with no change in mitochondrial percent volume. In summary, this study demonstrated that chronic pacing induced tachycardia in rabbits caused: 1) LV dilation and dysfunction, 2) depressed isolated myocyte contractile function and inotropic responsiveness, and 3) alterations in myocyte structure and composition. The changes in LV and myocyte function and structure following chronic tachycardia in rabbits are similar to that reported previously with tachycardia induced heart failure in larger animals. These findings suggest that this rabbit model of chronic tachycardia may provide a useful and practical means by which to examine basic mechanisms responsible for the development of congestive heart failure.

Animals↗
PubMedDate not supplied

The viability and possible applications of high resolution mark replicator casting compound in document examination.

Mark replicator casting compounds are commonly associated with recovering toolmark detail. A series of experiments was designed to identify the possible applications, and assess the overall viability, of using mark replicator compound to record indentations on questioned documents. The trials included testing the effect of Isomark High Resolution Mark Replicator on different paper-based substrate types, and observing in particular, any damage that it may cause. The experiments also tested the effect that the mark replicator has on subsequent fingerprinting techniques. It was found that the mark replicator successfully recorded indentations on paper and card surfaces. In some cases, the mark replicator caused staining on some of the surfaces and had a negative effect on the quality of fingerprints subsequently developed.

Journal Article↗
PubMedDate not supplied

Ballpoint ink flakes as indicators of added entries.

Examiners were asked to determine if an entry made in a diary had been completed at one time, or if the last sentence of the entry had been added later. Standard non-destructive ink differentiation techniques did not show any differences in the ballpoint pen ink used. Dried flakes of ballpoint pen ink were present in the initial stroke of the questioned sentence, but did not appear elsewhere in the entry. Experiments were undertaken to ascertain if these dried flakes could be attributed to a time delay or some other cause. Experimentation showed that ink flakes occurred only after periods of non-use of the ballpoint pens in the sample. Caution is urged in applying this finding to actual case work.

Forensic Medicine↗
PubMedDate not supplied

Quantitative prediction of biodegradability, metabolite distribution and toxicity of stable metabolites.

An evaluation of the capability of organic chemicals to mineralize is an important factor to consider when assessing their fate in the environment. Microbial degradation can convert a toxic chemical into an innocuous one, and vice versa, or alter the toxicity of a chemical. Moreover, primary biodegradation can convert chemicals into stable products that can be difficult to mineralize. In this paper, we present some new results obtained on the basis of a recently developed probabilistic approach to modeling biodegradation based on microbial transformation pathways. The metabolic transformations and their hierarchy were calibrated by making use of the ready biodegradability data from the MITI-I test and expert knowledge for the most probable transformation pathways. A model was developed and integrated into an expert software system named CATABOL that is able to predict the probability of biodegradation of organic chemicals directly from their structure. CATABOL simulates the effects of microbial enzyme systems, generates the most plausible transformation pathways, and quantitatively predicts the persistence and toxicity of the biodegradation products. A subset of 300 organic chemicals were selected from Canada's Domestic Substances List and subjected to CATABOL to compare predicted properties of the parent chemicals with their respective first stable metabolite. The results show that most of the stable metabolites have a lower acute toxicity to fish and a lower bioaccumulation potential compared to the parent chemicals. In contrast, the metabolites appear to be generally more estrogenic than the parent chemicals.

Animals↗
PubMedDate not supplied

Comparison of undergraduate pediatric dentistry clinical procedures from 1982-83 through 1996-97.

Using the information obtained from the Collegiate Patient Management System a comparison of average numbers of procedures performed by third year dental students from 1983/84 to 1996/97 was made. The data were grouped in order to compare Group I (1983/1989) to Group II (1990/1997). Student's t-tests were performed to determine significant differences between the groups for the various procedures. The number of new patients in Group I was only 8.2 compared to Group II--7.9 and the total number of new and recall patients seen by students was Group I--33.5 compared to Group II--29.9. Students in Group I performed 19.3 one-surface restorations compared to 11.8 (p = .0001) in the later group and 9.5 two-surface restorations compared to 6.0 (p = .0003) for the 1990's group. Stainless steel crowns, pulpotomies, extractions and sealants were also compared. The total numbers of patients visits was 66.8 in GRP I compared to 49.6 (p;eq.0001) in GRP II. There has been a decrease in most student experiences in the undergraduate pediatric dental clinic in the past 15 years.

Child↗
PubMedDate not supplied

A clinical review of preventive resin restorations.

Since the 1981-1982 academic year, the University of Iowa Department of Pediatric Dentistry had placed approximately 2000 composite/sealants or preventive resin restorations in children's molars. When these children appeared again for examination or treatment, their restorations were evaluated for retention, maintenance, and quality. Results were encouraging: more than 80 percent of the sealant material was "all present"; and more than 98 percent of the composite restorative material was rated quite satisfactory (the "Alfa" category).

Bisphenol A-Glycidyl Methacrylate↗