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Biomedical subjects

R L Bradley

Publications and source records attributed to R L Bradley.

At least 19 recordsLinked to original sources
PubMed2005

Soil factors controlling mineral N uptake by Picea engelmannii seedlings: the importance of gross NH4+ production rates.

* Hydroponic studies suggest that plant nitrogen (N) demand determines the rate of mineral N uptake; however, field observations show N limitation to be widespread. Field experiments are needed to understand soil factors controlling mineral N uptake. * We planted Picea engelmannii seedlings that had initially been grown from sterilized seeds, on a recently clearcut site. We applied a hybrid isotope dilution/pulse labelling technique to compare the gross production rate, concomitantly to the plant uptake rate, of soil mineral N. We also measured mineral N concentrations, microbial N, and percent ectomycorrhizal root tips. * Gross NH4+ production rate was the most important determinant of plant uptake rate. Exploratory path analysis suggested that plant uptake was also determined by microbial N, which was, in turn, determined by soil mineral N concentrations. Percent ectomycorrhizal root tips was negatively related to gross NO3- production rate and microbial N concentrations. * We conclude that nutrient flux density is important in controlling plant uptake. Mycorrhizal colonization may alter N dynamics in the rhizosphere without affecting mineral N uptake by seedlings.

Biological Transport, Active↗
PubMed2003

Inferred effects of cloud deposition on forest floor nutrient cycling and microbial properties along a short elevation gradient.

Cloud water deposition often increases with elevation, and it is widely accepted that this cloud water increases acid loading to upland forest ecosystems. A study was undertaken in south-eastern Quebec to determine if a 250 m elevation gradient (i.e. 420-665 m), along a uniform sugar-maple stand on the slope of Mount Orford, corresponded to a pH gradient in the forest floor and to predictable changes in soil nutrient availability and microbial properties. Precipitation data from a nearby study, and a photographic survey, provided presumptive evidence that this elevation gradient corresponded to a strong gradient in cloud water deposition. Forest floor temperature did not differ significantly across elevations. Forest floor moisture content was significantly higher, whereas pH and exchangeable Ca and Mg were significantly lower, at the higher elevations. Average seasonal net nitrification rates, determined by long-term laboratory incubations, did not differ significantly across elevations, whereas average seasonal net ammonification rates were significantly higher at higher elevations. Basal respiration rates and microbial biomass did not differ significantly across elevations, but metabolic quotient was significantly higher at higher elevations indicating possible environmental stress on forest floor microbial communities due to cloud water deposition. Anaerobic N mineralisation rates were significantly higher at higher elevations suggesting that N-limited microbial communities frequently exposed to cloud cover can be important short-term sinks for atmospheric N, thereby contributing to increase the active-N fraction of forest floors. We conclude that, where no significant changes in vegetation or temperature occur, elevation gradients can still be used to understand the spatial variability of nutrient cycles and microbial properties.

Altitude↗
PubMed2001

The adipocyte as a secretory organ: mechanisms of vesicle transport and secretory pathways.

Obesity is a common problem in western society that is directly linked to several disease processes and is associated with significant morbidity and mortality. Adipocytes--the primary site for energy storage (as triglycerides) and release--were long suspected to have an active role in regulating body weight homeostasis and energy balance. As a result, many studies have focused on finding abnormalities in adipocyte physiology and metabolism. An ever-increasing body of evidence indicates that, in addition to serving as a repository for energy reserves, adipocytes secrete a myriad of factors that comprise a complex network of endocrine, autocrine, and paracrine signals. Very little is known regarding the molecular mechanisms utilized by the adipocyte in regulating the biosynthesis and exocytosis of these secreted products. In order to gain a better understanding of these processes, we have examined the two classical secretory pathways: regulated and constitutive. Using leptin as a model adipocyte-secretory protein, this review focuses primarily on the latter pathway. This includes regulation of leptin synthesis and secretion by insulin and glucocorticoids and, more recently, the finding that the orexigenic neuropeptide, melanin-concentrating hormone (MCH), can stimulate leptin synthesis and secretion. This chapter also incorporates new data describing the partial purification and effect of insulin on leptin-containing vesicles in rat adipocytes. These data indicate that the majority of leptin trafficking occurs via a constitutive secretory pathway and that the primary acute insulin effect on leptin secretion is to increase leptin protein content. In addition, we describe the identification and characterization of the vesicle-associated protein, pantophysin, which may play a multifunctional role in vesicle biogenesis and transport.

Adipocytes↗
PubMed2000

Melanin-concentrating hormone regulates leptin synthesis and secretion in rat adipocytes.

Obesity is a common problem in Western society and is associated with significant morbidity and mortality. Energy homeostasis is regulated by a complex system involving both peripheral signals such as leptin and a number of orexigenic and anorectic neuropeptides. Obesity can result from dysregulation of the peripheral and/or central signals. Melanin-concentrating hormone (MCH) is a hypothalamic peptide that is important in the regulation of feeding behavior, primarily via uncharacterized signaling pathways in the central nervous system. Leptin, expressed in adipose tissue, mediates some of its actions through several hypothalamic neuropeptides, notably agouti-related peptide, proopiomelanocortin, and neuropeptide Y. Expression of leptin is regulated by dietary status, insulin, and glucocorticoids. Furthermore, certain neuropeptides may act on adipocytes. However, the potential effect of MCH has not been investigated. We report that MCH stimulates leptin mRNA expression and leptin secretion. MCH stimulated a 2-fold increase in leptin secretion by isolated rat adipocytes after 4 h of treatment. This increase in secreted leptin was preceded by a rapid and transient increase in ob mRNA levels; MCH stimulated a 2.5-fold increase in ob mRNA within 1 h of treatment, followed by a decline to basal levels within 4 h. In addition, we demonstrate that the MCH receptor SLC-1 is expressed in adipocytes, suggesting that fat cells may be targets of MCH or an MCH-like peptide under physiological conditions. Finally, using a radioimmunoassay, MCH/MCH-like peptide was detected in rat plasma. This study establishes a novel in vitro mammalian system for examining MCH signaling pathways.

Adipocytes↗
PubMed1999

Regulation of ob gene expression and leptin secretion by insulin and dexamethasone in rat adipocytes.

Leptin, the ob gene product, is produced by adipocytes, and it acts to decrease caloric intake and increase energy expenditure. To better understand the molecular mechanisms of hormone-regulated leptin synthesis and secretion, we assessed the ability of insulin and dexamethasone to acutely modulate ob gene expression and leptin secretion in rat adipocytes. Incubation of rat adipocytes with 100 nmol/l insulin for 2 h had no effect on ob mRNA levels, but it stimulated a twofold increase in leptin secretion. Dexamethasone (100 nmol/l) stimulated both a two- to fourfold increase in ob mRNA and a twofold increase in leptin secretion. Consonant with a posttranscriptional and transcriptional regulatory mechanism for insulin- and dexamethasone-stimulated leptin secretion, respectively, actinomycin D blocked dexamethasone-stimulated leptin secretion but did not affect insulin-stimulated leptin secretion. Cycloheximide treatment did not significantly affect ob mRNA accumulation, but it reduced total secreted leptin. Interestingly, however, insulin was still able to stimulate a twofold increase in leptin secretion. These data suggest that insulin, but not dexamethasone, is able to stimulate leptin secretion from a preexisting intracellular pool, although de novo protein synthesis is required for the full insulin-stimulated effect. Signaling pathways involved in leptin synthesis/secretion were also evaluated. The phosphatidylinositol 3-kinase inhibitor LY294002, the Map/Erk kinase inhibitor PD98059, and the immunosuppressant rapamycin had no effect on basal levels of leptin secretion. However, all three inhibitors markedly decreased both insulin- and dexamethasone-stimulated leptin secretion. These findings suggest a complex set of signaling pathways involved in mediating insulin- and dexamethasone-stimulated leptin synthesis and secretion.

Adipocytes↗
PubMed1999

Identification and control of processing variables that affect the quality and safety of fluid milk.

The objective of this study was to increase quality and safety of fluid milk by eliminating postpasteurization contamination as measured by extended shelf life. Milk shelf life was defined as the number of days for standard plate count to reach 20,000 CFU/ml in milk stored at 7 degrees C. Sequential analysis of the fluid milk processing system indicated filling machine and pasteurizer were significant sources of postpasteurization contamination. Aseptically sampled milk from the pasteurizer outlet indicated a maximum shelf life of more than 30 days could be achieved. The pasteurizer can be a source of contamination when inadequately cleaned or maintained. The filling machine was a significant source of contamination. Shelf life of milk in 236-ml containers was reduced 20 days compared with milk sampled before the filling machine. Carton-forming mandrels, filling heads, and airborne microorganisms were sources of contamination within the filling machine. Eliminating sources of postpasteurization contamination and proper cleaning followed by sanitizing with chlorine significantly increased milk shelf life in paperboard containers to 20.4 days from an initial shelf life of 9 days. Changing the sanitizing agent to peroxyacetic acid significantly increased milk shelf life to 33.9 days. Enclosing the filling chamber and adding sterile laminar flowing air significantly improved microbiological quality of air inside the chamber and reduced variance among milk shelf life samples.

Animals↗
PubMed1997

Cloning, sequencing, and regulation of the global nitrogen regulator gene ntcA in the unicellular diazotrophic cyanobacterium Cyanothece sp. strain BH68K.

In cyanobacteria, ammonium represses expression of proteins involved in nitrogen fixation and assimilation. The global nitrogen regulator gene ntcA encodes a DNA-binding protein, NtcA, that is a transcriptional activator of genes subject to nitrogen control. We report the cloning and sequencing of the ntcA gene from a nitrogen-fixing unicellular cyanobacterium, Cyanothece sp. strain BH68K. The gene comprises 678 nucleotides, and the deduced NtcA protein contains 226 amino acids with a predicted molecular weight of 25,026. In addition, ntcA mRNA levels were measured in cells grown under different nitrogen regimes. Under nitrogen-fixing conditions, ntcA transcripts were weakly expressed. Furthermore, ntcA expression was diminished or inversely proportional to nifHDK expression. Conversely, ntcA expression increased in nitrate-grown cells, and a concentration-dependent increase was seen in ammonium-grown cells up to 1 mM NH4Cl. These results indicate that ntcA is involved more in nitrogen assimilation than in nitrogen fixation and also imply that the rhythmic expression of ntcA and nifHDK transcription may be under the control of a circadian clock.

Aerobiosis↗
PubMed1995

Abnormal tympanography after supine bottle feeding.

OBJECTIVE: To determine whether bottle feeding with the infant in the supine position is related to entry of milk into the middle ear, thereby predisposing the infant to otitis media. STUDY DESIGN: Ninety children, aged 7 to 24 months, who were free of respiratory infection and had normal tympanograms initially, were bottle fed in either the supine or the semiupright position, and tympanography was repeated immediately afterward. RESULTS: Thirty-four (59.6%) of the 57 infants fed in the supine position had abnormal postfeeding tympanographic results compared with only five (15%) of the 33 infants fed in the semiupright position (p < 0.005). In addition, when the infants with abnormal tympanograms were placed in semiupright or prone positions for 15 minutes after feeding, the majority of tympanograms returned to normal. CONCLUSION: These data suggest that supine bottle feeding has a significant effect on middle-ear pressure dynamics, probably caused by the aspiration of milk into the ear. The results also suggest that repositioning infants after feeding may mitigate the effects of supine feeding, at least in healthy children. Although this study did not demonstrate that tympanographic abnormality definitely predisposes to otitis media, it provides more evidence to encourage the practice of feeding infants in a semiupright position.

Acoustic Impedance Tests↗
PubMed1992

Effective cleaning and sanitizing of polysulfone ultrafiltration membrane systems.

Polysulfone UF membranes that were soiled by Cheddar cheese whey were successfully cleaned in place. This cleaning procedure was completed in about 1 h. Most cleaning chemicals used were common and inexpensive. The cleaning procedure consisted of rinsing the membrane system for 2 min with water initially and after each cleaning solution. Sodium hydroxide at pH 11.0, with .1% of a nonionic surfactant added, was circulated for 20 min. After a 2-min rinse with water, a 1:1 mixture of nitric and phosphoric acids at pH 2 was circulated for 20 min and rinsed again with water. Finally, sodium hydroxide at pH 11.0, with 200 ppm of sodium hypochlorite added, was circulated for 20 min and rinsed. All cleaning solutions and all rinse waters were at 54 degrees C. Membranes cleaned by this procedure were found to be free from whey residue under examination by scanning electron microscopy. The cleaning process did not damage the membranes even when it was used continuously for 300 h. Microbial populations on the membrane were estimated by incubating small (4-cm2) sections of membrane in screw-cap vials filled with trypticase soy broth. From the portion of vials showing growth after 72 h at 32 degrees C, a most probable microbial population was calculated. Santizing cleaned polysulfone UF membranes with 100 ppm of sodium hypochlorite or 100 ppm of dichloroisocyanurate at 54 degrees C resulted in membranes free from viable microorganisms. When dichloroisocyanurate was used at 10 degrees C and 200 ppm, a most probable microbial population of 290/m2 was found. No microbial growth was detected when cleaned and sanitized membranes were stored in tap water for 24 h. This technique for cleaning UF membranes does not require the use of a holding solution containing santizers to control the growth of residual microorganisms.

Bacteria↗
PubMed1991

The involvement of photosystem II-generated H2O2 in photoinhibition.

The involvement of H2O2 generated by photosystem II (PSII) in the process of photoinhibition of thylakoids with a functional oxygen-evolving complex (OEC) was investigated. The rate of photoinhibition was decreased to the rate of loss of activity in the dark when bovine Fe-catalase was present during the photoinhibitory illumination. Photoinhibition was accelerated for both Cl(-)-depleted and Cl(-)-sufficient thylakoids when KCN was present to inhibit the thylakoid-bound Fe-catalase. We propose that these preparations become photoinhibited by reactions with H2O2 produced via oxidation of water by the Cl(-)-depleted OEC and by reduction of O2 at the QB site when PSII is illuminated without an electron acceptor.

Chlorides↗
PubMed1990

Use of the MANTRELS score in childhood appendicitis: a prospective study of 187 children with abdominal pain.

We report an evaluation of the MANTRELS clinical score in predicting appendicitis in a prospectively studied pediatric population presenting with abdominal pain. One hundred eighty-nine independent episodes from 187 children 2 to 17 years old were studied. For the groups as a whole and for the individual groups less than 16 years old, the score failed to satisfactorily discriminate those with appendicitis from those without. Had the MANTRELS score been used to determine observation and laparotomy in our patients, 21 additional patients would have been unnecessarily hospitalized, and 16 would have been subjected to unnecessary laparotomies. One patient would have received appropriate intervention earlier. In the 40 children 16 and 17 years old, the MANTRELS score adequately distinguished the two groups. A seven-variable discriminant function, derived from stepwise discriminant analysis, performed slightly better but showed essentially the same findings as the MANTRELS score. We believe the MANTRELS score failed to predict appendicitis in younger children because it does not contain variables that allow for separation of appendicitis from the numerous other conditions mimicking it in the pediatric population. The clinician remains the best judge of the acute abdomen in the pediatric age group.

Abdominal Pain↗
PubMed1990

Effective control of microbial populations in polysulfone ultrafiltration membrane systems.

Sanitizers currently used in the food industry are not efficient in destroying bacterial populations in polysulfone UF membrane systems. A new sanitizer composition that releases chlorous acid and chlorine dioxide from sodium chlorite at pH 2.7 was evaluated. Polysulfone UF membranes were soiled for 2.5 h by circulating and concentrating Cheddar cheese whey and skim milk. A cleaning regimen was established whereby acid and caustic cleaning solutions were circulated to clean the UF membrane system. Restoring permeate flux to initial values did not indicate that the system was effectively cleaned. The UF system was sanitized by recycling sanitizer solutions. Stainless steel and membrane surfaces were examined by swabbing to determine bacterial populations and sections of membranes were removed for examination using a scanning electron microscope. The new sanitizer appeared to control microbial populations effectively in UF membrane systems.

Animals↗
PubMed1988

Surgical management of otitis externa.

The surgical management of otitis externa is discussed in conjunction with failed medical management, primary causes, and proper case selection. The techniques of lateral ear canal resection and vertical ear canal ablation are described in detail.

Animals↗
PubMed1987

Pyometra in cats: 183 cases (1979-1984).

Pyometra was diagnosed in 183 cats. The most common signs detected by owners included vaginal discharge, anorexia, and lethargy. Main clinical findings on physical examination were vaginal discharge, abdominal distention, dehydration, palpable uterus, and pyrexia. Abdominal radiography revealed a large uterus in 138/169 cats. Most cats had leukocytosis with a left shift. Diagnosis of pyometra was confirmed at surgery in all cats on the basis of finding a large uterus containing purulent material. Clinical signs resolved in 168 cats after surgery; 15 cats (8%) died or were euthanatized. Postoperative complications in 20% generally resolved within 2 weeks after the cats were sent home. Signs detected by owners and results of physical examination in cats with pyometra were similar, but not as conspicuous as those reported in the dog. Mortality (8%) was similar to that seen in dogs.

Animals↗
PubMed1987

Evaluation of efficacy of four commercial enzyme-based cleaners of ultrafiltration systems.

Use of UF and RO in the dairy industry is rapidly expanding. Because the dairy industry demands high levels of cleanliness, this new technology requires close evaluation to assure adherence to these standards. Efficacy of four commercial enzyme-based cleaners (pH 7.0 to 8.4) in UF systems was determined by microbiological evaluation and permeate flux restoration. The UF system containing two polysulfone UF membranes in parallel, was soiled by recycling 380 L of sweet whey (40 degrees C) for 2.0 h followed by concentrating whey for .5 h. The cleaning cycle consisted of acid cleaner (.5 h, 40 degrees C), followed by enzyme cleaner (10.0 h, 40 degrees C), and rinsing (2.0 h, 40 degrees C). A chlorine sanitizer was circulated (5 min, 40 degrees C) and the unit containing sanitizing solution left idle overnight. Flux was determined and swabs and rinse water samples were taken immediately after soiling, after cleaning, and the next morning to check sanitizing. The four enzyme-based cleaners were unsatisfactory when microbiological criteria were considered. Loss of sanitizer strength and problems with yeast and especially mold growth over time also indicated lack of effective cleaning. Flux, however, was restored easily and did not correlate with efficacy of cleaning based on numbers of microorganisms remaining.

Dairying↗
PubMed1985

Use of microbial beta-lactamase to destroy penicillin added to milk.

A simple method is described for destruction of penicillin residues in bulk milk to an undetectable amount (less than .003 U/ml) with commercially available crude beta-lactamase enzyme. Milk containing .1 or .5 U/ml penicillin G was treated with .01 to 1.0 mU/ml of beta-lactamase (Bacillus cereus) for up to 96 h. The Bacillus stearothermophilus var. calidolactis assay was used to quantify penicillin in milk between .003 to 1.0 U/ml. The .5 U/ml of penicillin G was reduced to an undetectable amount within 18 h at 4 degrees C by 1.0 mU/ml of beta-lactamase. The development of titratable acidity over 5 to 6 h in contaminated milks treated with beta-lactamase and inoculated with Streptococcus thermophilus GH, Streptococcus cremoris, Streptococcus lactis, or a commercial starter culture was the same as for control milk samples containing no additives or only enzyme. Pilot-scale manufacture of Swiss and Cheddar cheeses from contaminated milks treated with beta-lactamase yielded cheeses of comparable quality, to control cheeses produced from penicillin-free milk. There were no delays in acid production as judged from pH measurements during production and ripening of the cheeses. About 50% of beta-lactamase activity added to milk remained after pasteurization at 63 degrees C for 30 min. The safety for human consumption of cheese containing small quantities of penicillin degradation products from milk treated with beta-lactamase remains to be established.

Animals↗