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Biomedical subjects

J A Knight

Publications and source records attributed to J A Knight.

At least 55 records · Page 3Linked to original sources
PubMed1988

Serum lipoperoxidation products in an infant with hemolytic-uremic syndrome.

We detected increased concentrations of lipoperoxidation products, as malondialdehyde, in the serum of an infant with classic hemolytic-uremic syndrome. The concentrations declined when peritoneal dialysis was initiated and eventually returned to normal after clinical recovery. Our observation adds to the existing body of evidence that links the pathogenesis of hemolytic-uremic syndrome to peroxidative damage and to the rationale for using antioxidant agents as part of the therapy for this disease process.

Hemolytic-Uremic Syndrome↗
PubMed1988

Specificity of the thiobarbituric acid reaction: its use in studies of lipid peroxidation.

The thiobarbituric acid (TBA) reaction, quantified by colorimetry or fluorimetry, is the method most widely used for studying lipid peroxidation in both laboratory animals and in humans with disorders. However, concerns regarding its analytical specificity have often been expressed, because TBA reacts with a wide variety of chemical species to produce a pink to red color. In this study, we reacted TBA with various saturated and unsaturated aldehydes (both directly and in the presence of sucrose, fructose, and glucose), substituted pyrimidines, 2-deoxyribose, and N-acetylneuraminic acid. We also studied the TBA reaction with bilirubin, biliverdin, icteric serum, and serum containing hemolyzed erythrocytes, comparing the absorption spectra of these reaction products with that for malondialdehyde (MDA). The reaction products were also analyzed for MDA by high-performance liquid chromatography (HPLC). Although the TBA reaction with some of these compounds may not be important in biological studies, others could lead to misinterpretations of increased lipid peroxidation. Use of HPLC to quantify MDA is recommended because of its high analytical sensitivity and specificity, especially in the study of lipid peroxidation in human subjects.

Chromatography, High Pressure Liquid↗
PubMed1988

Urinary lipoperoxides quantified by liquid chromatography, and determination of reference values for adults.

Urinary lipoperoxides, measured as the malondialdehyde-thiobarbituric acid adduct, were quantified by adapting to urine the liquid-chromatographic method of Wong et al. (Clin Chem 1987;33:214-20) to plasma. Reference intervals for untimed urine specimens from 121 men, ages 16 to 67 years, and 107 women, ages 15 to 55, were determined. Their concentrations differed significantly (P = 0.015), males having a mean (and SD) of 0.89 (0.35) nmol of malondialdehyde per milligram of creatinine, females 0.78 (0.30). In both groups, the values were slightly skewed to the higher values. Our early studies suggest that measuring urinary lipoperoxide may have advantages over plasma in studying certain disorders. The presence of other urinary chromophores or TBA-reactive substances stresses the need for chromatographic techniques when lipoperoxides are measured in biological samples.

Adolescent↗
PubMed1987

Reference values for nickel concentrations in human tissues and bile.

Nickel concentrations in human tissues and gallbladder bile were determined by analysis of postmortem specimens from ten consecutive autopsies of adult persons. The tissue samples were collected and homogenized with precautions to avoid nickel contamination and were analyzed by electrothermal atomic absorption spectrophotometry with Zeemann background correction. In decreasing order of mean nickel concentrations, the following results were obtained (mean and range, microgram/kg dry weight, N = 7-10): lung 173 (71-371), thyroid 141 (41-240), adrenal 132 (53-241), kidney 62 (19-171), heart 54 (10-110), liver 50 (11-102), brain 44 (20-65), spleen 37 (9-95), and pancreas 34 (7-71). In five specimens of gallbladder bile, nickel concentrations averaged 2.3 +/- 0.8 micrograms/l (range 1.5-3.3). These data furnish reference values for use in evaluating tissue nickel concentrations in persons with occupational exposures to nickel, provide the first demonstration that nickel concentrations in thyroid and adrenal glands are approximately equal to those in lung and are higher than in other organs, and suggest that biliary excretion may be a significant route for the elimination of nickel in humans.

Adult↗
PubMed1987

Physicochemical characteristics and biological effects of nickel oxides.

Ten nickel oxides and nickel-copper oxides, which all contained NiO (bunsenite) as the predominant crystalline phase, were assayed as follows: in vitro dissolution tests in water and body fluids; in vitro phagocytosis tests in Chinese hamster ovary and C3H-10T1/2 cells; morphological transformation and cytotoxicity tests in cultured Syrian hamster embryo (SHE) cells; erythropoiesis stimulation assay by intrarenal administration to Fischer-344 rats; and scoring the renal histopathologic responses in rats killed 3 months post-injection. The test compounds differed substantially in their biological effects when tested in the various experimental systems. Based upon highly significant concordance of ranked results in the assays (P less than 0.001), six colligative biological attributes of the compounds were identified: (i) dissolution half-times in rat serum and renal cytosol; (ii) phagocytosis by C3H-10T1/2 cells; (iii) morphological transformation of SHE cells; (iv) erythropoiesis stimulation in rats; (v) induction of tubular hyperplasia in rat kidneys; and (vi) induction of arteriosclerosis in rat kidneys. Strong rank correlation (P less than 0.01) between results of the cell transformation and erythropoiesis stimulation assays is especially notable, since the compounds were tested by blind protocols in independent laboratories. The presence of high surface area and demonstrable Ni(III) were two physicochemical characteristics that were associated with the greatest biological effects of nickel oxides.

Animals↗
PubMed1987

Right ventricular blood temperature profiles for rate responsive pacing.

To establish the efficacy of a temperature-based pacemaker control algorithm, right ventricular temperature and heart rate were measured for 12-70 hours in eight patients (51 +/- 17 years) and in one normal volunteer (28 years) during a variety of activities including exercise, rest, sleeping, eating, drinking, and bathing. A diurnal variation in heart rate and temperature was observed. Drinking caused transient temperature changes (less than one minute); during eating, increases of 0.07-0.36 degrees C over 3-12 minutes were observed. An increase of 0.24 degrees C over 8.5 minutes was observed in one patient during bathing. An abrupt drop in temperature was typically observed at the onset of exercise, followed by a steady temperature rise. During treadmill exercise, after a drop (0.13-0.48 degrees C, Bruce n = 4; 0.16-0.34 degrees C, Naughton, n = 3) during the first 1-2 minutes, temperature rose steadily through the end of peak exercise (0.45-1.01 degrees C, Bruce; 0.28-0.47 degrees C, Naughton). A temperature dip was also observed when a patient was told exercise would start but the treadmill failed to turn on. The dip is probably secondary to changes in blood flow from the peripheral circulation to the central system at the onset of exercise. Repeated exercise separated by short rests caused progressive blunting of the initial dip. Right ventricular temperature changes in a predictable manner with daily activity, allowing a temperature algorithm to detect rest and exercise.

Adult↗
PubMed1987

Mutations in an upstream regulatory sequence that increase expression of the bacteriophage T4 lysozyme gene.

A P22 hybrid phage bearing the bacteriophage T4 lysozyme gene (e), as well as T4 sequences upstream from the lysozyme gene, was constructed. Amber mutations were introduced into gene e in the hybrid phage, and the resulting mutant phages were tested for the ability to form plaques on amber suppressor strains. Revertant phages that were able to form plaques on amber suppressors that did not suppress the parent amber mutant phages were isolated following UV mutagenesis. Secondary site pseudorevertants were identified among the revertants by a genetic test. Four of the suppressing secondary site mutations were mapped and sequenced. They were found to consist of small sequence alterations immediately upstream from gene e, all of which would tend to destabilize potential base-pairing interactions in the transcript. The mutations were shown to increase lysozyme expression when introduced into an otherwise wild-type hybrid phage, but were found to have little effect on transcription of the lysozyme gene.

Alleles↗
PubMed1987

Reference intervals for plasma lipoperoxides: age-, sex-, and specimen-related variations.

We measured lipoperoxides, as malondialdehyde (MDA), by liquid chromatography in plasma from 230 male and 148 female adult blood donors, to establish reliable reference values and to compare possible sex-, age-, and specimen-related differences. Our studies show that mean have higher MDA concentrations in plasma than do women (P less than 0.05), older men have higher values than younger men (P less than 0.05), and older women have higher values than young women (P less than 0.001). These age-related results support earlier studies in experimental animals that lipid peroxidation increases with increasing age. In addition, plasma from liquid EDTA-anti-coagulated blood has significantly lower MDA concentrations than does serum or plasma from blood treated with lithium heparin, sodium citrate, or CPDA-1 (P less than 0.001).

Adolescent↗
PubMed1987

Acute thymic involution and increased lipoperoxides in thymus of nickel chloride-treated rats.

Acute thymic involution occurred in male, Fischer-344 rats following a single injection of nickel chloride (0.5 mmol/kg, sc). In nickel-treated rats, the mean thymic weight became significantly decreased at 24 h, continued to diminish at 48 h, and reached 24% of the control value at 72 h post-injection. The ratio of thymic weight to body weight (mg/g) decreased from 1.24 +/- 0.05 (SD) in control rats to 0.30 +/- 0.05 in nickel-treated rats at 72 h post-injection (p less than 0.01). Concentrations of thymic lipoperoxides were assayed by the thiobarbituric acid reaction, with HPLC separation and spectrophotometric quantitation of the malondialdehyde-thiobarbituric acid complex. The mean concentration of thymic lipoperoxides was unchanged at 24 h, increased 2-fold at 48 h, and reached 8-times the control value at 72 h after nickel chloride injection. On histological examination, sections of thymus from nickel-treated rats showed moderate to profound depletion of cortical lymphocytes at 72 h post-injection. Marked degenerative changes were noted in cortical lymphocytes, with pyknosis and karyorrhexis; swelling and vacuolation were evident in thymic reticular epithelial cells. The time-courses of the biochemical and histopathological responses suggest that the lipid peroxidation may be an end-result, rather than a cause, of thymic involution and injury to thymic lymphocytes in nickel-treated rats.

Animals↗
PubMed1987

Lipoperoxides in plasma as measured by liquid-chromatographic separation of malondialdehyde-thiobarbituric acid adduct.

This assay of plasma lipoperoxides involves hydrolysis in dilute H3PO4 at 100 degrees C; complexation of malondialdehyde (MDA), a hydrolysis product, with thiobarbituric acid (TBA); methanol precipitation of plasma proteins; fractionation of the protein-free extract on a C18 column; and spectrophotometric quantification of the MDA-TBA adduct at 532 nm. The detection limit was 0.15 mumol of MDA per liter of plasma. Run-to-run precision (CV) averaged 8 to 13%. Analytical recovery of MDA after addition of tetraethoxypropane standards to 21 specimens of human or rat plasma averaged 98% (SD 7%). Lipoperoxide concentrations (as MDA) averaged 0.60 (SD 0.13) mumol/L in plasma specimens from 41 healthy persons and 1.4 (SD 0.3) mumol/L in plasma specimens from 12 control rats. Mean lipoperoxide concentrations were 1.5 to 2.3 times as great in plasma sampled from rats one to three days after subcutaneous administration of NiCl2 at dosages (250 to 750 mumol per kilogram body wt) previously shown to induce lipid peroxidation in lung, liver, and kidney.

Adult↗
PubMed1986

Low-level exercise testing after myocardial infarction. A useful guide to management.

Low-level exercise testing after acute myocardial infarction can be safely performed in the early recovery period before hospital discharge. It is a clinically useful procedure and has the following benefits. It identifies patients at high risk for recurrent acute coronary events within one year after acute myocardial infarction, permits evaluation of the effectiveness of drug therapy before hospital discharge, allows selection of patients for early coronary arteriography, and provides guidelines for activity in the immediate postinfarction period.

Angina Pectoris↗
PubMed1986

Comparison of biochemical markers between benign and malignant ovarian cysts.

To investigate the presumption that earlier diagnosis of ovarian tumors might lead to an improved outcome, we compared several substances in the fluid of benign and malignant ovarian cysts. Our results showed the following: (1) benign cysts were readily separated from malignant cysts on the basis of total lactate dehydrogenase (LD) activity and except for mucinous cysts, by their isoenzyme patterns. (2) Preoperative serum total LD activity and LD isoenzymes were of no diagnostic help in predicting the malignant tumors. (3) Carcinoembryonic antigen (CEA) levels usually differed greatly between benign and malignant cysts, although the benign mucinous cysts had CEA levels indistinguishable from malignant cysts. (4) Prominent quantitative differences between Roche and Abbott CEA activity were present in both benign and malignant cysts. (5) Preoperative serum CEA levels were not helpful in differentiating the benign from the malignant cysts.

Carcinoembryonic Antigen↗
PubMed1986

Stability of NADPH: effect of various factors on the kinetics of degradation.

Seeking to minimize degradation of NADPH during storage, reagent preparation, and assays, we investigated the effects of pH, temperature, and ionic strength as well as the effects of phosphate and acetate. NADH was also included for comparison. Our results indicate that the rate of degradation of NADPH is proportional most importantly to temperature and concentrations of hydronium ion, but also to concentrations of phosphate and acetate. The degradation rate decreased with increasing ionic strength at neutral pH, but increased slightly at lower pH. NADPH generally is less stable than NADH under the same conditions. The reaction orders with respect to hydronium ion and anions were near 1 for NADH degradation reactions, about 0.5 for NADPH. Rate constants for NADH and NADPH differed more at higher pH and lower phosphate and acetate concentrations.

Acetates↗
PubMed1985

Primary pulmonary hypertension in childhood: a report of two brothers.

We report 2 cases of primary pulmonary hypertension in brothers, 6 and 3 years old. Their lungs contained numerous plexiform vascular lesions. The literature is reviewed involving familial cases, especially those in which siblings were affected. Several of these cases lack the pathological verification necessary for acceptance as examples of plexogenic pulmonary arteriopathy.

Cardiomegaly↗