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Biomedical subjects

J A Walker

Publications and source records attributed to J A Walker.

At least 55 records · Page 3Linked to original sources
PubMed1996

A rat homolog of the mouse deafness mutant jerker (je).

An autosomal recessive deafness mutant was discovered in our colony of Zucker (ZUC) rats. These mutants behave like shaker-waltzer deafness mutants, and their inner ear pathology classifies them among neuroepithelial degeneration type of deafness mutants. To determine whether this rat deafness mutation (-) defines a unique locus or one that has been previously described, we mapped its chromosomal location. F2 progeny of (Pbrc:ZUC x BN/Crl) A/a B/b H/h +/- F1 rats were scored for coat color and behavioral phenotypes. Segregation analysis indicated that the deafness locus might be loosely linked with B on rat Chromosome (Chr) 5 (RNO5). Therefore, 40 -/- rats were scored for BN and ZUC alleles at four additional loci, D5Mit11, D5Mit13, Oprd1, and Gnb1, known to map to RNO5 or its homolog, mouse Chr 4 (MMU4). Linkage analysis established the gene order (cM distance) as D5Mit11-(19.3)-B-(17.9)-D5Mit13-(19. 2)-Oprd1-(21.5) - (1.2) Gnb1, placing the deafness locus on distal RNO5. The position of the deafness locus on RNO5 is similar to that ofjerker (je) on MMU4; the phenotypes and patterns of inheritance of the deafness mutation and je are also similar. It seems likely that the mutation affects the rat homolog of je. The rat deafness locus should, therefore, be named jerker and assigned the gene symbol Je.

Animals↗
PubMed1996

Chromosome content and ultrastructure of radiation-induced micronuclei.

Unrepaired or misrepaired radiation damage in mammalian chromosomes can result in micronucleus formation at the first cell division. This represents loss of genomic information which may cause cell death. To improve our understanding of the mechanism of radiation-induced micronucleus formation, we characterized micronucleus ultrastructure and identified the origin of micronucleus DNA. Immunofluorescence microscopy showed that micronuclei were structurally similar to main nuclei since they contained nuclear lamins A and C and were encapsulated by a network of vimentin intermediate filaments. The contents of radiation-induced micronuclei were characterized using fluorescence in situ hybridization to probe for DNA originating from chromosomes 2, 7, 11 and 16. We postulated that if incorporation of DNA into micronuclei were random, then the probability of chromosomal DNA in micronuclei would be related to the target, i.e. chromosome size. Our results demonstrated that incorporation of DNA from smaller chromosomes (11 and 16) was not different from expected values but incorporation of DNA from the larger chromosomes (2 and 7) was significantly greater than expected. Not all chromosomes in the human genome, therefore, were equally susceptible to genomic loss by micronucleus encapsulation. In conclusion, radiation-induced micronuclei have similar structural characteristics to main nuclei, chromosome damage and/or repair after ionizing radiation may be non-random, and micronucleus formation may reflect this variability.

Cell Nucleus↗
PubMed1996

Radiation-induced apoptosis in human lymphocytes: potential as a biological dosimeter.

We have tested the possibility of using apoptosis (programmed cell death) in human peripheral blood lymphocytes as a short-term biological dosimeter. Lymphocytes isolated from whole blood were irradiated in culture with 250 kVp x-rays or 60Co gamma rays. Two assays were used to measure apoptosis in lymphocytes after irradiation: in situ terminal deoxynucleotidyl transferase assay and fluorescence analysis of DNA unwinding assay. Similar qualitative and quantitative results were produced by the assays, supporting the notion that the fluorescence analysis of DNA unwinding assay measured DNA fragmentation associated with apoptosis. Induction of apoptosis in lymphocytes irradiated in vitro was proportional to dose and could be detected following exposures as low as 0.05 Gy. Lymphocytes from individual donors had reproducible dose responses. There was, however, variation between donors. X-ray and gamma-ray exposures induced similar levels of apoptosis at similar doses. The induction kinetics of apoptosis in vitro indicate a maximum is reached about 72 h after irradiation. In conclusion, the in vitro experimental evidence indicates that radiation-induced apoptosis in human lymphocytes has the kinetics, sensitivity, and reproducibility to be a potential biological dosimeter.

Adult↗
PubMed1996

Mapping of the metalloproteinase gene matrilysin (MMP7) to human chromosome 11q21-->q22.

The matrix metalloproteinase, matrilysin, is thought to play an important role in the early steps of tumor progression. We determined the chromosome location of the matrilysin gene (MMP7) by Southern and PCR analysis of two different panels of somatic cell hybrids and in situ hybridization of metaphase chromosomes. Matrilysin maps to the region, 11q21-->q22, adding MMP7 to the cluster of matrix metalloproteinase genes that have already mapped to this region.

Base Sequence↗
PubMed1996

Technical note: a simple, rapid assay for alpha-amylase in bovine pancreatic juice.

A procedure is described for the determination of alpha-amylase activity in bovine pancreatic juice. Bovine pancreatic juice was incubated with potato amylopectin for 6 min, and then alkaline potassium ferricyanide was added to stop the enzymatic reaction. Tubes were placed in a boiling water bath for 10 min and then cooled, and 40 mL of distilled water was added. Optical density was read at 420 nm, and the amount of end product (reducing sugars) was determined by comparison with maltose standards. Ten dilutions of bovine pancreatic secretion were assayed to determine the intraassay precision of this method, resulting in a CV of 1.05%. A pooled sample was assayed five times over five separate days to determine the interassay precision, resulting in a CV of 7.3%. This alpha-amylase assay provides a repeatable, rapid, and economical determination of alpha-amylase activity from bovine pancreatic juice.

Animals↗
PubMed1996

Factors associated with cognitive recovery after cardiopulmonary resuscitation.

BACKGROUND: A range of neuro-cognitive sequelae, from mild intellectual impairments to brain death, have been reported in survivors of aborted sudden cardiac death. PURPOSE: To determine to what extent, if any, factors associated with cardiopulmonary resuscitation, left ventricular function, and mood state are related to outcomes in five cognitive areas, namely orientation, attention, memory, reasoning, and motor performance. METHODS: Repeated measures were used to assess cognitive outcomes in 45 sudden cardiac arrest survivors over the 6 months following cardiopulmonary resuscitation. A battery of neuro-psychological tests was used to assess cognitive outcomes and psychological status over time. The relationship of the cardiopulmonary resuscitation, left ventricular function, and psychological variables to cognitive outcomes were assessed at each data point. The independent variables included time to cardiopulmonary resuscitation, time to defibrillation, duration of cardiopulmonary resuscitation, time to awakening, ejection fraction, New York Heart Association Class I to IV, tension, anger, and depression. RESULTS: During hospitalization 38 of the 45 survivors (84%) had mild to severe deficits in one or more cognitive areas; 19 of 38 survivors (50%) continued to be impaired in one or more cognitive areas at 6 months. Of these, all had mild to severe deficits in at least one aspect of memory, with delayed recall the most frequent impairment. Time to awakening accounted for a unique portion of the variance in orientation and memory outcomes over time. The left ventricular function variables accounted for a significant portion of the variance in motor speed. CONCLUSIONS: Our results suggest that half of the long-term survivors of aborted sudden cardiac death are cognitively intact 6 months after resuscitation but that 25% have moderate to severe impairment in memory, which could hamper and/or preclude the resumption of prearrest roles.

Analysis of Variance↗
PubMed1995

Codominant effects of the fatty (fa) gene during early development of obesity.

Expression of a single copy of the rat obesity fatty (fa) gene may affect energy balance. To test this hypothesis, the effects of zero, one, and two copies of fa on early growth were evaluated, using a molecular genetic method for counting fa alleles inherited by 7- and 14-day-old F2 offspring of a BN/Crl x Crl:ZUC-fa F1 intercross. Litter and sex effects were controlled by multiple-regression analysis, allowing genotype effects on the weights of body, inguinal adipose pads, interscapular brown adipose tissue, and liver to be isolated. At 7 days of age, the fa copy number had linear effects on body and inguinal adipose pads weight. At 14 days of age, the fa copy number had linear effects on body, inguinal adipose pads, and interscapular brown adipose tissue weights and an additional quadratic effect on inguinal adipose pads weight. Thus fa has codominant effects on growth during the first week of life. The recessive effects of fa on growth appear during the second week of life.

Adipose Tissue↗
PubMed1995

Influence of ruminal or abomasal starch hydrolysate infusion on pancreatic exocrine secretion and blood glucose and insulin concentrations in steers.

Seven Holstein steers (234 +/- 6.4 kg) surgically fitted with pancreatic cannulas, ruminal and abomasal infusion cannulas, and hepatic-portal vein catheters were used in a 4 x 7 incomplete Latin square design experiment to examine the influence of ruminal and abomasal carbohydrate infusion on enzyme secretion and composition of pancreatic juice. Four treatments were arranged in a 2 x 2 factorial: 1) ruminal starch hydrolysate (SH; 34.2 g/[h.site]) or abomasal water and 2) abomasal SH or ruminal water. Starch hydrolysate is raw cornstarch that has been partially digested by a heat-stable alpha-amylase. Experimental periods were 14 d with 9 to 10 d of adaptation, 4 d of pancreatic collection, and blood collection on d 14. Abomasal SH infusion tended (P < .10) to increase pancreatic fluid secretion. The pH of pancreatic juice was higher (P < .01) for ruminal SH infusion, and abomasal SH infusion tended (P < .10) to result in lower pH of pancreatic juice. alpha-Amylase concentrations (units/milliliter and units/milligram of protein) and secretion (units/hour) were less (P < .002) for abomasal SH infusion. Chymotrypsin concentration (units/liter; P < .01) and secretion (units/hour; P < .10) were less for abomasal SH infusion; however, a rumen x abomasal interaction was found (P < .05). Chloride concentration (milligrams/deciliter) and secretion (milligrams/hour) were increased (P < .01) for abomasal SH infusion. Abomasal SH infusion resulted in increased (P < .01) portal blood glucose concentrations; however, portal plasma insulin concentration was not affected (P > .10). Abomasal SH infusion altered alpha-amylase secretion in steers, but ruminal SH infusion had minimal effect on alpha-amylase secretion. These changes suggest abosamal infusion of SH may negatively impact secretion of pancreatic alpha-amylase.

Abomasum↗
PubMed1995

Analysis of heroin drug seizures by Micellar Electrokinetic Capillary Chromatography (MECC).

A rapid procedure using Micellar Electrokinetic Capillary Chromatography (MECC) is presented for the quantitation of illicit heroin samples. This analytical system resolves heroin from accompanying impurities and adulterants enabling accurate quantitation via the use of an internal standard. An aqueous run buffer consisting of 40 mmol sodium dodecyl sulfate, 8.5 mmol sodium phosphate, 8.5 mmol sodium borate and 15% acetonitrile is used with a 27 cm x 50 microns fused silica capillary column. Linearity, accuracy and reproducibility studies of heroin using this method are established. Comparisons to a commonly used gas chromatographic method show excellent correlation. Due to its high resolution and speed, this MECC system also serves as a screening procedure to detect impurities and adulterants present in heroin samples. Relative migration times of various opiates and adulterants are reported. With minor exceptions, complete separation of numerous compounds is achieved within five minutes, including compounds that are difficult to analyze by gas chromatography such as morphine, O6-acetylmorphine, aspirin and salicylic acid.

Chromatography, Gas↗
PubMed1994

Delayed recovery of endothelium-dependent vasodilation in regenerating arterioles of skeletal muscle autografts.

This study investigated the responses of regenerating arterioles in grafted skeletal muscle to the endothelium-dependent dilator acetylcholine (ACh); the substrate for endothelium-derived relaxing factor (EDRF), L-arginine (L-Arg); and sodium nitroprusside (SNP). Additionally, responses of graft arterioles to the endothelium-independent substances adenosine (Ado) and norepinephrine (NE) were measured. The retractor muscle of hamsters was removed, placed in a myotoxic solution, and grafted into its original site. The graft revascularized spontaneously by sprouting of vessels in surrounding tissue. Quantification of changes in arteriolar luminal diameter was accomplished using in vivo video microscopy at 30, 45, and 60 days postgrafting. In 30-day grafts, there was little or no response to topically applied ACh or L-Arg. By 45 days, arteriole response to 10(-6), 10(-5), and 10(-4) M ACh and 10(-4) L-Arg was 0, 4, 20, and 17% of the control response, respectively. SNP (10(-6)-10(-4) M) produced approximately 50% of the control response at both 30 and 45 days. By 60 days the response of graft arterioles to ACh, L-Arg, and SNP was not different from controls. Arteriolar response in 30-day grafts to Ado (10(-6)-10(-4) M) was significantly attenuated, but was not different from control by 45 days. Responsiveness of arterioles to NE had recovered to control levels by 30 days postgrafting. These data indicate that the restoration of endothelium-dependent regulation of arteriolar dilation lags behind endothelium-independent, receptor-mediated mechanisms. The diminished response of regenerating arterioles may be related to dysfunctions in both the synthetic pathway for EDRF and the guanylate cyclase/cGMP mechanism for vascular smooth muscle cell relaxation and/or flow-dependent mechanisms of blood flow regulation.

Acetylcholine↗
PubMed1994

Evaluation of nutrient utilization in the canine using the ileal cannulation technique.

Nine mature mongrel dogs were used to evaluate a surgical technique for the cannulation of the terminal ileum and used in two experiments to determine the effect of carbohydrate source on starch and dry matter digestion. Dogs (16.2 +/- 2.0 kg body weight; means +/- SD) were fitted with an ileal T-cannula constructed of polyvinyl chloride pipe. The cannula was inserted into the terminal ileum approximately 10 cm proximal to the ileocecal junction and the cannula was exteriorized through a small incision on the right flank. Dogs recovered quickly from surgery (5d). A preliminary study using Cr:EDTA in the food indicated that sampling for 12 h postprandially allowed near complete representation of digesta flow for a meal; peak flow occurred 4-to 8-h postfeeding. Two experiments were performed evaluating the effect of carbohydrate source on ileal starch and dry matter digestibility. Dogs were fed two meals daily with Cr2O3 used as a digesta marker. Diets contained 67% extruded grain (corn, rice, oats or barley) and 33% canned meat supplement on a dry matter basis. Starch digestion was complete (> 98%) within the small intestine and was unaffected by carbohydrate source. In experiment 1, prececal and total tract dry matter digestibilities were higher for rice than corn, and in experiment 2, barley was higher than oats. The ileal T-cannula allows for measurement of small intestinal nutrient disappearance without the confounding effects of colonic microflora. This method may be useful when applied to the study of other nutrients in dogs.

Animal Feed↗
PubMed1994

The relation of documented coronary artery disease to levels of total cholesterol and high-density lipoprotein cholesterol.

Recommendations for identifying persons at high risk for coronary heart disease are based primarily on levels of total and low-density lipoprotein cholesterol. We examined whether, given knowledge of these levels, information on the high-density lipoprotein cholesterol level would improve the prediction of arteriographically documented coronary artery disease among 591 men. We found that even at levels of total and low-density lipoprotein cholesterol considered desirable, high-density lipoprotein cholesterol was inversely related to disease severity. For example, among the 112 men with a total cholesterol level <180 mg per dl, the mean occlusion score (representing the overall severity of disease) was 107 among men with a high-density lipoprotein cholesterol level < or = 30 mg per dl vs a mean score of 52 among men with levels > or = 45 mg per dl. Furthermore, men with low levels of both low-density lipoprotein cholesterol (< 110 mg per dl) and high-density lipoprotein cholesterol (< or = 30 mg per dl) had as much occlusive disease as did men with high levels of both lipoprotein fractions. Given information on the ratio of high-density lipoprotein cholesterol to total cholesterol, the actual levels of the lipoprotein fractions did not improve disease prediction. Our results emphasize the importance of considering high-density lipoprotein cholesterol when assessing coronary heart disease risk.

Adult↗
PubMed1994

Sequence specificity of furin, a proprotein-processing endoprotease, for the hemagglutinin of a virulent avian influenza virus.

The virulence of avian influenza viruses correlates with the sensitivity of their hemagglutinin (HA) to cellular proteases. Furin, a proprotein-processing subtilisin-related endoprotease, is a leading candidate for the enzyme that cleaves the HA of virulent avian viruses. We therefore compared the specificity of furin with those of proteases in a variety of cultured cells and in a rat Golgi fraction, using the HA cleavage mutants of a virulent avian influenza virus, A/Turkey/Ireland/1378/85 (H5N8). The results indicated similar sequence specificities among the endoproteases when purified furin was used. In experiments with the vaccinia virus expression system, overexpressed furin cleaved mutant HAs that were not recognized by the endogenous proteases, resulting in an apparent broader specificity of furin. These findings authenticate the proposed role of furin as an HA-activating protease in vivo and caution against the use of expression vectors to study protease sequence specificity.

Amino Acid Sequence↗
PubMed1994

Effects of slaframine and 4-diphenylacetoxy-N-methylpiperidine methiodide (4DAMP) on pancreatic exocrine secretion in the bovine.

Three Holstein steers (345 +/- 22 kg) surgically fitted with a pancreatic cannula were used in two 3 x 3 Latin square design experiments to examine the effects of slaframine (SF), a muscarinic agonist, or 4-diphenylacetoxy-N-methylpiperidine methiodide (4DAMP), an M3 muscarinic glandular receptor antagonist, on pancreatic exocrine secretion. Pancreatic exocrine secretion was collected for 8 h postdosing at 30-min intervals beginning 1 h postfeeding. In experiment 1, steers were dosed with 0, 25, or 50 micrograms.kg-1 body weight (BW) of SF. Secretion of pancreatic juice and the pH of the secreted juice increased linearly (p < 0.05) with SF; however, secretion rate showed a time by treatment interaction (p < 0.05), as treatments converged 7 h postdosing. Trypsin secretion tended (p < 0.10) to show a quadratic response to SF administration, with the 25 micrograms SF.kg-1 BW dose having the lowest value. In experiment 2, steers received 50 micrograms.kg-1 BW of SF (positive control), 113 micrograms.kg-1 BW of 4DAMP (isosmolar with SF), or both. SF caused a greater pancreatic fluid secretion (p < 0.10) than 4DAMP, with SF plus 4DAMP intermediate. A time by treatment interaction (p < 0.04) was found, since treatments converged 8 h postdosing. Trypsin secretion was higher (p < 0.05) for SF than the other treatments. Chymotrypsin, alpha-amylase, and protein secretion were not affected. SF and 4DAMP alter pancreatic fluid secretion in the steer but have minimal effects on enzyme secretions.

Alkaloids↗
PubMed1993

The measurement of physical activity in bone density research.

Physical activity is often recommended as a method to prevent or treat osteoporosis. Nevertheless, it is difficult to interpret the research findings upon which this recommendation is made because of problems measuring physical activity. Studies investigating the bone density-physical activity association were reviewed. Physical activity was measured by participation in a specific form of exercise, questionnaire and interview, mechanical devices, and physiological markers of activity. In about half of the exercise participation studies, grouping criteria were problematic for the nonexercise or control group. Many discrepancies were found in the questionnaire and interview studies. Overall, little information was reported with respect to reliability or validity of measures, thereby hampering comparisons across studies. These measurement issues can provide nurses with a new perspective for evaluating studies that report the impact of physical activity on bone mass and other health outcomes as well.

Bone Density↗
PubMed1993

Importance of conserved amino acids at the cleavage site of the haemagglutinin of a virulent avian influenza A virus.

The virulence of avian influenza A viruses depends on the cleavability of the haemagglutinin (HA) by an intracellular protease at multiple basic amino acids. Although previous studies have demonstrated the importance of these amino acids for processing by the cellular protease, with emphasis on conserved residues near the cleavage site, the minimal requirements for cleavage remain unknown. By expressing site-specific mutants of the HA of a virulent avian influenza virus, A/turkey/Ireland/1378/85 (H5N8), in the simian virus 40 system and testing for their cleavability by an endogenous protease in CV-1 cells, and their fusion activity in a polykaryon formation assay, we were able to show that glycine at the amino terminus of HA2 is not essential for cleavage and that maximal cleavage requires at least five basic residues at the cleavage site, when carbohydrate is nearby. Moreover, we confirmed, that a conserved proline upstream of the cleavage site is not essential for HA cleavage or fusion activity, and that lysine replacement of the carboxyl-terminal arginine of HA1 abolishes cleavability. These findings should help identify the proteases responsible for intracellular cleavage of the HA of virulent avian influenza viruses.

Amino Acid Sequence↗