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Biomedical subjects

K L Johnson

Publications and source records attributed to K L Johnson.

104 records · Page 6Linked to original sources
PubMed1983

Circadian rhythm in acetaminophen toxicity: role of nonprotein sulfhydryls.

A circadian rhythm in the toxicity of acetaminophen administered at different times of the day was exhibited in male mice. Peak lethality (70% dead) occurred at 1800 hr and nadir lethality (10% dead) occurred at 1000 hr. Hepatic nonprotein sulfhydryl (NPS) concentrations also varied in a circadian manner and were found to exhibit an inverse relationship to the acetaminophen lethality rhythm, with the highest hepatic concentrations occurring at 1000 hr and the lowest concentrations occurring at 1800 hr. At 1800 hr when acetaminophen lethality was greatest and NPS levels the lowest, more reactive acetaminophen metabolites were found covalently bound to hepatic macromolecules as compared to those bound at 1000 hr when NPS levels were highest and acetaminophen lethality was lowest. Hepatic cytochrome P-450 levels measured at these two daily time periods did not differ. The plasma half-life of acetaminophen was significantly decreased at the 1000 hr time period as compared to the 1800 hr time period. These findings suggest that the normal daily changes in NPS levels may influence the lethality of acetaminophen.

Acetaminophen↗
PubMed1983

Species and sex differences in selenium inhibition of hepatic drug metabolism in rodents.

Hepatic microsomal drug metabolism was assessed in male and female rats, mice and hamsters 72 hr after administration of sodium selenite. The greatest inhibitory effect of selenium on hepatic drug metabolism occurred in male rats where the magnitude of reduction in microsomal metabolism by selenium treatment of ethylmorphine and aminopyrine was disproportionately greater than the decrease in either cytochrome P-450 levels or metabolism of aniline. In contrast, the inhibition of metabolism of the three substrates in female mice and the decrease in ethylmorphine-N-demethylase in male mice were similar in magnitude to the reduction observed in cytochrome P-450 content. Hepatic microsomal metabolism in male and female hamsters was relatively resistant to the inhibitory effects of selenium. The inhibition of drug metabolism by selenium may reflect a specific effect of selenium on selected isozymes of cytochrome P-450.

Aminopyrine↗
PubMed1983

Strategy production by young Down syndrome children.

A sample of young Down syndrome children was compared with three nonretarded samples, one equated for developmental age, one for language age, and one for ability to delay touching an attractive but prohibited stimulus. Results indicated that Down syndrome children were significantly less able to delay touching than were nonretarded children of similar developmental or language level; in addition, several kinds of within-task strategy behavior were identified that facilitated performance of the nonretarded children. These included turning attention, verbal and nonverbal, away from the stimulus. Implications for assessment were discussed, as were ramifications for the question of "developmental vs. difference" conceptualizations of mental retardation.

Child Development↗
PubMed1975

High-pressure liquid chromatographic determination of sulfamethazine residue in bovine tissue.

A sensitive high-pressure liquid chromatographic assay procedure is described for residues of sulfamethazine in bovine kidney, liver, muscle, and fat tissue at a sensitivity of 0.04 ppm. Studies were conducted using sulfamethazine-negative bovine tissue to ensure that the peak eluting at the indicated retention volume was sulfamethazine and that the recoveries from spiked tissues were consistent. Data are presented showing the levels of sulfamethazine in the tissue of 12 treated animals found by this technique. The method is more specific than the frequently used colorimetric methods and does not require the tedious separations involved in TLC assays.

Adipose Tissue↗
PubMedDate not supplied

Basics of flow cytometry.

The basics of flow cytometry are described. Cytometry is the measurement of cells; the flow cytometer performs this measurement quickly and reproducibly. Single cells in suspension are presented to a light source through hydrodynamic focusing. The resultant scattered light and fluorescence are collected and converted to electrical pulses, which are digitized for computer analysis. Frequency distributions can be viewed as single- or multiple-variable histograms for evaluating cell measurements. The versatility of flow cytometry is demonstrated by the types of samples it can analyze, characteristics it can measure, and applications in multiple laboratory sciences. Flow cytometry has been adapted easily and rapidly from a research tool to a clinically important procedure.

Clinical Laboratory Techniques↗
PubMedDate not supplied

Development of a vibratory white finger prevention program for shipyard workers: an exploratory study.

BACKGROUND: Vibratory White Finger (VWF) disease afflicts many shipyard workers who use vibrating tools over a period of years and can lead to a lifelong disability. Vascular symptoms include cold-induced spasms of the fingers and hands, blanching of the fingers, and atrophic skin changes in the fingertips. Sensorineural symptoms include numbness and tingling in the fingers and hands and reduced sensory perception and manipulative dexterity. The purpose of this study was to develop a screening program for shipyard workers, so that VWF disease could be identified and workers with the disease could be counseled on possible job changes involving reduced exposure to vibration. METHOD: This study was conducted during 1993. The subjects consisted of 39 users of vibrating tools and 10 nonusers. In the shipyard, each subject received a questionnaire dealing with VWF symptoms, followed by tests for multifrequency vibration thresholds, cutaneous sensitivity, and hand and finger strength. Each subject was subsequently examined outside the shipyard by a board-certified occupational health physician. RESULTS: Using discriminant analysis, statistical models for both the vascular and sensorineural stages of the disease were constructed. In general, there was a high level of agreement between the staging obtained from the statistical models and the outside physician's diagnoses, suggesting that the combination of questionnaire and test data was adequate for initial screening for this disease. CONCLUSION: It is not considered practical to perform a complete physician evaluation on every shipyard worker who is at risk for VWF. By using a structured questionnaire together with a limited number of VWF-related tests, and incorporating the data into a statistical model, it is possible to identify the priority candidates for physician follow-up and possibly alter the worksite to prevent serious disability.

Adult↗