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Biomedical subjects

R A Norton

Publications and source records attributed to R A Norton.

At least 19 recordsLinked to original sources
PubMed1997

Sterol utilization and metabolism by Heliothis zea.

Heliothis zea (corn earworm), an insect that fails to synthesize sterols de novo, was reared on an artificial diet treated with 18 different sterol supplements. Larvae did not develop on a sterol-less medium. delta 5-Sterols with a hydrogen atom, a methylene group, an E- or Z-ethylidene group, or an alpha- or beta-ethyl group (cholesterol, ostreasterol, isofucosterol, fucosterol, sitosterol, and clionasterol, respectively) at position C-24, and delta 5-sterols doubly substituted in the side chain at C-24 with an alpha-ethyl group and at C-22 with a double bond (stigmasterol) supported normal larval growth to late-sixth instar (prepupal: maturity). The major sterol isolated from each of these sterol treatments was cholesterol, suggesting that H. zea operates a typical 24-dealkylation pathway. The sterol requirement of H. zea could not be met satisfactorily by derivatives of 3 beta-cholestanol with a 9 beta, 19-cyclopropyl group, gem dimethyl group at C-4, a delta 5,7-bond or delta 8-bond, or by side chain modified sterols that possessed a delta 25(27)-24 beta-ethyl group, delta 23(24)-24-methyl group or 24-ethyl group, or delta 24(25)-24-methyl or 24-ethyl group. The major sterol recovered from the larvae (albeit developmentally arrested larvae) treated with a nonutilizable sterol was the test compound. Sterol absorption was related to the degree of sterol utilization. The most effective sterols absorbed by the insect ranged from 27 to 66 micrograms per insect, whereas the least effective sterols absorbed by the insect ranged from 0.6 to 6 micrograms per insect. Competition experiments using different proportions of cholesterol and 24-dihydrolanosterol (from 9:1 to 1:9 mixtures) indicated that abnormal development of H. zea may be induced on less than a 1 to 1 mixture of utilizable (cholesterol) to nonutilizable (24-dihydrolanosterol) sterols. The results demonstrate new structural requirements for sterol utilization and metabolism by insects, particularly with respect to the position of double bonds in the side chain and functionalization in the nucleus. The novel sterol specificities observed in this study appear to be associated with the dual role of sterols as membrane inserts (nonmetabolic) and as precursors to the ecdysteroids (metabolic).

Animals↗
PubMed1996

The challenge of irritable bowel syndrome.

Irritable bowel syndrome is a common disorder with symptom complexes that can include diarrhea, constipation, pain and bloating. After other disorders have been excluded, treatment should be directed at the predominant symptoms and gauged to their severity. A careful balance between a thoughtful investigation and the expense and dangers of overtesting must always be considered. Most patients continue to have persistent symptoms several years after the original diagnosis.

Adult↗
PubMed1995

A novel glass fiber disc culture system for testing of small amounts of compounds on growth and aflatoxin production by Aspergillus flavus.

A new method for growing Aspergillus flavus for experimental studies is presented. The system consists of a humidified vial with a thick septum pierced by a pin on which a glass fiber disc is affixed. The disc contains the test solution and inoculum plus medium. The method has been used to assess the effect of variations in culture conditions on production of aflatoxin B1 (AFB1). The AFB1 level was affected by the amount of medium placed on the disc and type of disc material. The results for different types of glass fiber and quartz discs were compared with AFB1 produced by fungus grown in liquid medium or on paper discs. When compared to a liquid medium culture there was a 15 to 20-fold increase in AFB1 for one type of disc. Incubations with less than 14 microliters of medium gave satisfactory results. A crude phosphatidylcholine preparation at a concentration of 0.7% of the medium resulted in a 4-fold increase in AFB1.

Aflatoxin B1↗
PubMed1995

Quantitation of steryl ferulate and p-coumarate esters from corn and rice.

The principal steryl ferulate and p-coumarate esters of different fractions from processed corn brans and corn oils, unrefined and refined, and from rice bran and rice bran oil were quantified by high-performance liquid chromatography. The results show that hexane-extracted corn oils yield more than five times the amount of esters compared to expeller processed oils. The yields of esters from bran and related products ranged from 0.07 to 0.54 mg/g of bran. Unrefined corn oils had levels from 0.18 to 8.6 mg/g for oil from hexane-extracted bran. By comparison, rice bran had ester levels of 3.4 mg/g of bran, and rice bran oil had levels of 15.7 mg/g of oil. The predominant esters from corn were sitostanyl and campestanyl ferulate, and sitostanyl and campestanyl p-coumarate. The principal esters from rice bran were cycloartenyl, 24-methylenecycloartanyl, and campesteryl ferulate. Rice bran oils had low levels of 24-methylenecycloartanyl but high levels of cyclobranol esters. The data presented provide a direct comparison of steryl ferulate and p-coumarate levels in the two cereals, and will aid in selecting the most suitable sources for the isolation of these compounds from corn products.

Chromatography, High Pressure Liquid↗
PubMed1991

Regulation of sterol biosynthesis in sunflower by 24(R,S),25-epiminolanosterol, a novel C-24 methyl transferase inhibitor.

Whereas sitosterol and 24(28)-methylene cycloartanol were competitive inhibitors (with Ki = 26 microM and 14 microM, respectively), 24(R,S)-25-epiminolanosterol was found to be a potent non-competitive inhibitor (Ki = 3.0 nM) of the S-adenosyl-L-methionine-C-24 methyl transferase from sunflower embryos. Because the ground state analog, 24(R,S)-oxidolanosterol, failed to inhibit the catalysis and 25-azalanosterol inhibited the catalysis with a Ki of 30 nM we conclude that the aziridine functions in a manner similar to the azasteriod (Rahier, A., et al., J. Biol. Chem. (1984) 259, 15215) as a transition state analog mimicking the carbonium intermediate found in the normal transmethylation reaction. Additionally, we observed that the aziridine inhibited cycloartenol metabolism (the preferred substrate for transmethylation) in cultured sunflower cells and cell growth.

Cell Division↗
PubMed1991

Efficacy of different anticoccidials against experimental coccidiosis in large white turkeys.

Two trials were conducted to compare the efficacy of currently approved anticoccidials for turkeys against challenge using a field isolate of mixed Eimeria species; E. adenoides, E. gallopavonis, and E. meleagrimitis. Poults in wire-floored cages were fed unmedicated diets from day-old to 3 wk of age. Diets were supplemented with either amprolium (AMP, 125 mg/kg), butynorate (BUT, 375 mg/kg), monensin (MON-60, 60 mg/kg; MON-100, 100 mg/kg), halofuginone (HAL; 3 mg/kg), zoalene (ZOA; 125 mg/kg), or sulfadimethoxine plus ormetoprim (SUL + ORM, 62.5 mg/kg and 37.5 mg/kg, respectively). After 2 days on the test diets, poults were individually weighed and inoculated with sporulated coccidial oocysts from the field isolate. Total fecal collections were obtained for Days 0 to 5 and 6 to 10 to estimate oocyst output. At 10 days postinoculation, the birds were individually weighed and killed to determine severity of intestinal lesions. The HAL and MON were most effective and AMP, ZOA, and SUL + ORM were least effective in maintaining weight and in reducing the severity of intestinal lesions. All the coccidiostats tested reduced oocyst passage, but poults fed HAL produced fewer oocysts. The results demonstrated differences in efficacy among anticoccidials with the more recently approved drugs providing the best protection against coccidiosis.

Amprolium↗
PubMed1991

Research note: use of fenbendazole for the treatment of turkeys with experimentally induced nematode infections.

Turkeys were raised under parasite-free conditions until 25 days of age at which time the birds were administered infective ova of Capillaria obsignata, Heterakis gallinarum, and Ascaridia dissimilis. At 28 days postinfection, four groups of birds were placed on rations medicated with fenbendazole at 15,30,45, or 60 ppm. These rations were given ad libitum for 6 consecutive days. At 31 days postinfection, five additional groups of birds were placed on rations medicated with fenbendazole at 15,30,45,60 or 120 ppm. These latter rations were given ad libitum for 3 consecutive days. One group of turkeys served as an unmedicated, infected control. Treatment group size ranged from 17 to 19 birds. All birds were necropsied 5 days after the medicated rations were withdrawn and nematode recovery was performed. Control birds harbored an average of 3.29 A. dissimilis, 12.06 H. gallinarum, and 65.94 C. obsignata. All but one of the fenbendazole-medicated groups showed 100% removal of A. dissimilis. The exception was that group that received fenbendazole at 15 ppm for 6 days, and that showed a 98.5% efficacy. The removal rate for H. gallinarum ranged from 78.6% (15 ppm for 3 days) to 100% (120 ppm for 3 days and 45 ppm for 6 days). The C. obsignata infections proved dose-limiting, with a removal rate ranging from 30.8% (15 ppm for 3 days) to 97.8% (45 ppm for 6 days).

Administration, Oral↗
PubMed1990

Zymosterol is located in the plasma membrane of cultured human fibroblasts.

Zymosterol (5 alpha-cholesta-8(9),24-dien-3 beta-ol) comprised a negligible fraction of the mass of sterol in cultured human fibroblasts but was well labeled biosynthetically with radioactive acetate. Treatment of cells with triparanol, a potent inhibitor of sterol delta 24-reductase, led to a marked increase in labeled zymosterol while its mass rose to 1 mol% of total sterol. All of this sterol could be chased into cholesterol. Furthermore, cell homogenates converted exogenous radiolabeled zymosterol to cholesterol. Three lines of evidence suggested that biosynthetically labeled zymosterol was associated with the plasma membrane. 1) About 80% of radiolabeled zymosterol was oxidized by the impermeant enzyme, cholesterol oxidase, in glutaraldehyde-fixed intact cells. 2) Sucrose density gradient analysis of homogenates showed that the equilibrium buoyant density profile of newly synthesized zymosterol was identical with that of the plasma membrane. 3) Newly synthesized zymosterol was transferred as readily from fixed intact fibroblasts to exogenous acceptors as was cholesterol. Given that cholesterol is synthesized within the cell, it is unclear why most of the zymosterol is in the plasma membrane. The pathway of cholesterol biosynthesis may compel zymosterol to flux through the plasma membrane. Alternatively, plasma membrane zymosterol may represent a separate pool, in equilibrium with the zymosterol in the intracellular biosynthetic pool.

Acetates↗
PubMed1988

Comparison of the chromatographic properties of sterols, select additional steroids and triterpenoids: gravity-flow column liquid chromatography, thin-layer chromatography, gas-liquid chromatography and high-performance liquid chromatography.

The chromatographic properties of approximately 100 sterols, select steroids of plant origin (sapogenins and steroidal alkaloids) and triterpenoids has been evaluated in this laboratory by monitoring their elution characteristics in adsorption (gravity column and thin-layer methods with and without the addition of silver nitrates), gas and reversed-phase high-performance liquid chromatography. The utility of each methodology to act in one or another chromatographic mode-separation, radio-chemical purification, quantitation and structural elucidation, is discussed. The importance of the tilt of the -OH group at C-3 as well as the polarity, size, an shape of the rest of the molecule as it effects the hydrogen-bonding ability of the -OH group is demonstrated through changes in chromatographic behavior that result from the step-wise introduction of double bonds, methyl, bromo, oxygen, nitrogen and cyclopropyl groups into 5 alpha-cholestanol. An independent aid in the structure identification and quantitation of the compounds was use of a multiple-wavelength diode array detector in which different wavelengths of the UV spectrum (200-400 nm) were simultaneously monitored following passage of the sample through a reversed-phase C18 column.

Chromatography, Gas↗
PubMed1986

Zinc oxide to induce molt in layers.

The effects of the addition of Zn as ZnO to diets to induce molt were evaluated against a fasted control. Experiment 1 involved 315 Leghorn hens, 15 months old, randomly distributed among five treatments, each replicated seven times with 9 hens per replicate. Hens fasted for 10 days were compared with hens fed diets to which ZnO was added at 10,000, 5,000, or 2,500 ppm for 7, 14, or 21 days. No significant differences were observed among treatments for days to return to 50% production, hen-day and hen-housed production, egg weight, grams egg per hen-day, grams of feed per gram egg, mortality, or Haugh units during the 22-week experimental period. Experiment 2 involved 420 Leghorn hens, 18 months old, randomly distributed among five treatments, each replicated seven times with 12 hens per replicate. Treatments involved fasting for 10 days or feeding diets with 10,000, 5,000, or 2,500 ppm ZnO fed for 7, 14, or 21 days. Hens fasted and hens fed diets with 10,000 ppm ZnO at the start of the experiment ceased production in significantly less time (4.6 to 6 days) than hens fed 5,000 ppm ZnO (14.3 to 14.9 days); however, days to return to 50% production from the start of the experiment did not differ among treatments. Feed consumption and feed cost per hen day during molt were lowest (P less than .05) in the fasted hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

International comparison of prevalence of resistance to antibiotics.

Prevalence of bacterial resistance to antibiotics was found to be substantially different in two separate regions of the world. The average percent resistant to individual antibiotics was nearly three times greater, and the percent of isolates resistant to six or more antibiotics 14 times greater among isolates at the Hôpital St Joseph in Paris than among those at the Peter Bent Brigham Hospital in Boston or at any of six US hospitals. Differences were not due to culture sampling or susceptibility testing methods used in the hospitals. Differences were nearly as great between isolates from patients recently admitted to the two hospitals, suggesting differences in the bacterial flora of their communities. Similar systematic comparisons of resistance prevalence in different parts of the world might help to define optimal antibiotic usage practices.

Anti-Bacterial Agents↗
PubMed1977

Linear and rod-shaped peptic ulcers.

Experience with the routine use of the pharmacologically aided, double-contrast examination to demonstrate various primary and healing ulcers over a six month period is assessed. Thirteen linear or rod-shaped ulcerations were diagnosed. It appears that gastric relaxation and the demonstration of fine mucosal relief are necessary to detect ulcers of linear or rod form.

Contrast Media↗