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Biomedical subjects

R B Taylor

Publications and source records attributed to R B Taylor.

At least 37 records · Page 2Linked to original sources
PubMed1996

Determination of opiates in urine by capillary electrophoresis.

A method for the separation of a mixture of opiates comprising pholcodine, 6-monoacetylmorphine, morphine, heroin, codeine and dihydrocodeine by capillary electrophoresis using a running buffer of 100 mM disodium hydrogenphosphate at pH 6 is described. The characteristics of an analytical method based on this separation for the determination of these drugs following extraction from urine and using levallorphan as internal standard are reported. Detection limits in the region of 10 ng cm-3 are achieved when using electrokinetic injection. A comparison is made of the sensitivity and reproducibility of electrokinetic and hydrodynamic injection for these drugs. Data are presented to show the results obtained when the proposed method is applied to urine spiked with all the above opiates and also to urine from a subject following consumption of dihydrocodeine and pholcodine. The concentrations found are compared with those obtained by LC.

Chromatography, High Pressure Liquid↗
PubMed1996

Ecological assessments of community disorder: their relationship to fear of crime and theoretical implications.

Researchers suggest that fear of crime arises from community disorder, cues in the social and physical environment that are distinct from crime itself. Three ecological methods of measuring community disorder are presented: resident perceptions reported in surveys and on-site observations by trained raters, both aggregated to the street block level, and content analysis of crime- and disorder- related newspaper articles aggregated to the neighboring level. Each method demonstrated adequate reliability and roughly equal ability to predict subsequent fear of crime among 412 residents of 50 blocks in 50 neighborhoods in Baltimore, MD. Pearson and partial correlations (controlling for sex, race, age, and victimization) were calculated at multiple levels of analysis: individual, individual deviation from block, and community (block/neighborhood). Hierarchical linear models provided comparable results under more stringent conditions. Results linking different measures of disorder with fear, and individual and aggregated demographics with fear inform theories about fear of crime and extend research on the impact of community social and physical disorder. Implications for ecological assessment of community social and physical environments are discussed.

Adolescent↗
PubMed1996

Mechanism for synergism between sulphonamides and trimethoprim clarified.

Pseudomonas aeruginosa, Escherichia coli, Pseudomonas cepacia and Moraxella catarrhalis were selected for their markedly different resistance patterns to sulphonamides and trimethoprim. In addition, strains of E. coli and P. cepacia were selected having different resistance profiles to the inhibition of dihydropteroate synthetase and dihydrofolate reductase. All inhibitors of dihydropteroate synthetase combined in any combination with inhibitors of dihydrofolate reductase resulted in mutual enhancement of bacterial uptakes of the inhibitors and corresponding increased antibacterial activity of the combinations. High concentrations of sulphonamides or p-aminobenzoic acid plus trimethoprim caused a decrease in overall activity of the combination and indicated that both sulphonamides and p-aminobenzoic acid at high concentrations can interact with dihydrofolate reductase. The antibacterial activity of p-aminobenzoic acid at high concentrations is considered to be a blocking effect on dihydrofolate reductase even though p-aminobenzoic acid at low concentrations is an essential part of the synthesis of dihydrofolic acid. These findings support an alternative hypothesis for the mechanism of antibacterial action of individual antifolates and their mechanism of synergism in combination.

4-Aminobenzoic Acid↗
PubMed1995

Determination of proguanil and metabolites in small sample volumes of whole blood stored on filter paper by high-performance liquid chromatography.

A method is reported for the determination of proguanil and its two metabolites cycloguanil and 4-chlorophenylbiguanide in whole blood and plasma samples obtained by thumbprick and stored dry on filter paper. The sample preparation involves liquid extraction from the filter paper and subsequent solid-phase extraction using C8 Bond-Elut cartridges. Separation and quantification is by a previously reported ion-pairing high-performance liquid chromatographic system with ODS Hypersil as stationary phase and an 50:50 acetonitrile-pH 2 phosphate buffer mobile phase containing 200 mM sodium dodecylsulphate as ion-pairing agent. The analytical characteristics of the method are reported. Representative concentrations are shown as a function of time from a human subject after ingestion of a single 200-mg dose of proguanil hydrochloride. Typical ranges of concentration detected by the proposed method in human subjects were proguanil 12-900 ng/ml, cycloguanil 16-44 ng/ml and 4-chlorophenylbiguanide 1.5-10 ng/ml in whole blood.

Antimalarials↗
PubMed1995

Analysis of common opiates and heroin metabolites in urine by high-performance liquid chromatography.

A separation of heroin, 6-monoacetylmorphine, codeine, pholcodine, dihydrocodeine and morphine using a 200 x 2 mm I.D., 3 microns silica column with dichloromethane-pentane-diethylamine-methanol mobile phase is described. Data on the determination of these compounds in a urine matrix based on this separation using a solid-phase pretreatment with Bond Elut Certify cartridges and nalorphine as an internal standard are shown. The compounds listed can be quantified at levels below that generally accepted as the cut-off level for the screening for opiates by enzyme immunoassay (EMIT) with detection limits for the different opiates ranging from 4 to 20 ng ml-1. Comparative data are shown of subject urine samples assayed for opiates by both the enzyme immunoassay and the proposed method. The utility of the method for the elimination of so-called false positives detected by EMIT due to the presence of medically prescribed and non-prescription opiates in urine is discussed.

Chromatography, High Pressure Liquid↗
PubMed1995

Analysis of basic antimalarial drugs by CZE; Part 2. Validation and application to bioanalysis.

This report describes some of the quantitative aspects of the CZE separation of proguanil, chloroquine and their respective metabolites, the separations of which, by CE and MEKC, were reported in Part 1. Results obtained on the precision of migration time and peak areas using the alternative injection methods of vacuum and electrokinetic are described and discussed. The increase in concentration sensitivity using electrokinetic injection with an organic injection solvent reported in Part 1 is confirmed and the resultant limits of detection in urine reported. An assay method for these compounds in urine is described which incorporates a pretreatment stage of solid phase extraction and the main analytical parameters used in the validation of such an assay are reported. The limitation of the sample pretreatment used when applied to matrices of plasma and saliva are reported and discussed in the context of the electrokinetic injection method used.

Antimalarials↗
PubMed1995

The effect of phenylephrine on Müller muscle. A blepharogram study of eyelid motion.

PURPOSE: The blepharogram technique is used to study the effect of a drug on blinking. The authors show that ocular instillation of phenylephrine, a stimulant of Müller muscle of the eyelid, accelerates the up phase of the blink. METHODS: Motion of a tiny search coil glued to the eyelid moving in a weak magnetic field modifies an induced alternating current which is amplified and used to display the position of the upper eyelid in degrees on the ordinate of a graph with time in milliseconds on the abscissa. The graph is called a blepharogram. Blepharogram studies and individual blink analysis show the effect of phenylephrine on eyelid motion (blinking). RESULTS: Instillation of phenylephrine accelerated the up phase of the blink in all ten experimental subjects. In 65% of subjects, phenylephrine also produced or increased newly described N and M blepharogram patterns. CONCLUSION: This is the first instrumental detection of the effect of a pharmacologic agent on eyelid motion. The blepharogram technique provides insight into eyelid physiology and can be used to study any neuromuscular condition that affects eyelid motion.

Adult↗
PubMed1994

Heat stress interactions with protein, supplemental fat, and fungal cultures.

Cows that were subjected to hot environmental temperatures yielded less milk (3.1 kg/d) on a diet high in CP (18.4%) and of medium degradability (65%) than on diets high in CP of low degradability (59%) or medium in CP (16.1%). The high CP diets were associated with decreased DMI and higher water intake, ruminal NH4, and blood urea. Negative effects on yield from the high CP, medium degradability diet were not observed at moderate temperatures. Evaporative cooling of cows in hot weather resulted in a greater milk yield response to low versus medium rumen-undegradabale protein diets than for uncooled cows. Evaporative cooling of cows also affected response to protein quality. For cooled cows, high Lys diet (soybean, fish, and blood meals) increased milk yield 14% over that with low Lys diet (corn gluten meal), but, for uncooled cows, a high Lys diet only increased yield by 9%. Percentage of CP, degradability, and protein quality had no effect on body temperatures or respiration rates of lactating cows. Some, but not other, reports showed that supplementation of 2 to 2.5% fat to diets fed under hot summer conditions resulted in less yield response than when fat was added at moderate temperatures. In several studies, fungal cultures (3 to 5 g/d) in the diet decreased body temperatures and respiration rates in hot, but not cool, weather. Increased milk yields and cellulose digestibility also resulted from dietary fungal cultures in some, but not all, trials. The mechanism of action exerted by fungal cultures on body temperature and respiration rate is unclear.

Animal Feed↗
PubMed1993

Single dose pharmacokinetics of proguanil and its metabolites in pregnancy.

Plasma and whole blood concentrations of proguanil, its active metabolite cycloguanil, and the inactive metabolite 4-chlorophenyl-biguanide, were measured by HPLC in 10 healthy Karen women in the last trimester of pregnancy, following a 200 mg single oral dose of proguanil. Four of these women were restudied 2 months after delivery. The pharmacokinetic properties of proguanil were similar during and after pregnancy. Median peak plasma concentrations of proguanil during pregnancy and following delivery were 212 and 215 ng.ml-1, and occurred at 4.5 and 5 h, respectively. Mean plasma AUC values for proguanil during and following pregnancy were 94 and 98 ng.h.ml-1.kg-1, respectively. Corresponding whole blood AUC values were 361 and 396 ng.h.ml-1.kg-1. The mean elimination half lives and mean residence times of proguanil in plasma and whole blood were 12.3 and 19.6 h and 13.8 and 20.7 h respectively during pregnancy. Following pregnancy these values were 17.1 and 19.7 h for plasma and 19.7 h and 20.2 h for whole blood respectively. Mean peak plasma and whole blood concentrations of cycloguanil following pregnancy were 25 and 22 ng.ml-1 respectively. During pregnancy peak cycloguanil concentrations in both plasma and whole blood were markedly lower, 13 and 12 ng ml-1, respectively. Two pregnant women (neither of whom were restudied) were probably poor metabolisers of proguanil. The mean ratio of proguanil to cycloguanil plasma AUC was 16.7 in the third trimester of pregnancy and 7.8 following pregnancy, compared with less than 5 in previously reported studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Biguanides↗
PubMed1993

Dorsal root afferent influences on tonic firing of renal and mesenteric sympathetic nerves in rats.

After spinal cord transection in cats and rats, the activity of many sympathetic nerves is not entirely lost, and firing of other nerves continues unabated or is increased. This study was done to evaluate the importance of dorsal root afferent discharge on the generation of tonic sympathetic activity in renal and mesenteric postganglionic nerves in spinal rats and in rats with intact neuraxes. Sympathetic discharge was recorded in anesthetized rats, and peripheral afferent influences were eliminated by dorsal rhizotomy from T4 to L2. Activity of renal and mesenteric nerves was well maintained after high cervical and thoracic (T4) cord transections. Rhizotomy had no effect on sympathetic discharge in rats with intact neuraxes but decreased renal nerve activity significantly (-25%) in spinal rats. Because rhizotomy decreased mesenteric discharge in only three of six spinal rats, mean mesenteric nerve discharge was not decreased significantly. The decreased renal nerve discharge after dorsal rhizotomy could not be attributed to input from any specific spinal segment, and ipsilateral input was no greater than contralateral input. After rhizotomy, both renal and mesenteric nerves had substantial excitatory drive from the transected, deafferented spinal cord. These findings demonstrate that dorsal root afferent influences on spinal neurons can contribute to the generation of tonic discharge in some sympathetic nerves in spinal animals.

Afferent Pathways↗
PubMed1992

Prophylactic use of apraclonidine for intraocular pressure increase after Nd:YAG capsulotomies.

We evaluated the prophylactic effect of 1% apraclonidine HCl in controlling the increase in intraocular pressure after Nd:YAG posterior capsulotomy in a large, multicenter double-masked clinical trial. One hundred sixty-four patients were enrolled into the apraclonidine-treated group, and 165 into the vehicle-treated group. The incidence of increase in intraocular pressure (greater than 5 mm Hg) in the apraclonidine-treated group (7%, 11 of 163 patients) was significantly less than that in the vehicle-treated group (39%, 64 of 164 patients). Similarly, the mean maximal change in intraocular pressure in the apraclonidine-treated group (1.3-mm Hg decrease) was significantly different from the increase in the vehicle-treated group (5.3-mm Hg increase). Few adverse reactions were observed. The risk for significant loss of visual function after Nd:YAG laser posterior capsulotomy, combined with the efficacy and relative safety of prophylactic apraclonidine, suggest its addition to the treatment armamentarium.

Adrenergic alpha-Agonists↗
PubMed1992

Simultaneous determination of some antibacterial drugs in isosensitest broth using high-performance liquid chromatography with solid-phase extraction.

A method is described for the simultaneous determination of combinations of some antibacterial drugs in a matrix of isosensitest broth. A double solid-phase extraction procedure is described in which trimethoprim and dibromopropamidine isethionate together with 4-chlorophenylbiguanide as internal standard are freed from endogenous components by a cation-exchange extraction cartridge and subsequently removed and individually separated by reversed-phase ion-pair chromatography. Sulfadiazine, sulfamerazine and p-aminobenzoic acid, unretained by ion exchange, are similarly isolated for chromatography by adsorption on a CH-bonded phase cartridge and individually assayed using the same chromatographic system. The rationale of the pre-treatment and chromatography is described and the quantitative aspects of the analyses of selected combinations of these drugs are reported.

4-Aminobenzoic Acid↗
PubMed1992

Spinal stimulation to locate preganglionic neurons controlling the kidney, spleen, or intestine.

The organization of sympathetic preganglionic neurons may be a substrate for selective control of sympathetic outflow to different vascular beds. This study was done to determine the spinal segments containing preganglionic neurons controlling discharge of renal, splenic, and mesenteric postganglionic nerves. In urethan-anesthetized rats, preganglionic neurons were stimulated by microinjecting D,L-homocysteic acid (3 nl, 0.17 M) into the lateral gray matter of the third thoracic (T3) to the fourth lumbar (L4) spinal segments. Responses from all three nerves could be elicited from segments T4-T13. The greatest increases in renal nerve discharge were evoked from segments T8-T12, the largest increase of 59 +/- 9% elicited from T10. Increases in splenic and mesenteric nerve discharge were smaller and were evoked more uniformly from T4-L3. The largest increases in discharge of splenic and mesenteric nerves were 19 +/- 5% (from T5) and 26 +/- 4% (from T10), respectively. The widely overlapping spinal cord segments controlling these three organs suggest that location of the preganglionic neurons in different spinal segments is not part of the mechanism for selective sympathetic control. However, the larger renal nerve responses demonstrate that sympathetic output to these organs can be differentiated at the level of the spinal cord.

Animals↗
PubMed1991

Determination of teicoplanin in plasma using microbore high-performance liquid chromatography and injection-generated gradients.

A reversed-phase isocratic high-performance liquid chromatographic method for the determination of total teicoplanin in plasma is reported. The method developed uses a bracketing injection technique in conjunction with large injection volumes on a 1 mm diameter column to form a limited injection-generated gradient. The chromatography yields adequate resolution among all the major components for individual quantitation and also allows quantitation of total teicoplanin in plasma using ultraviolet detection. Pretreatment is by solid-phase extraction which uses C8 Bond Elut cartridges and gives effective clean up from endogenous materials. The method offers a faster and simplified means to determine total teicoplanin in plasma than those previously reported, and has a detection limit of 50 ng/ml.

Anti-Bacterial Agents↗