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Biomedical subjects

R A Reeves

Publications and source records attributed to R A Reeves.

At least 37 records · Page 2Linked to original sources
PubMed1995

Cloning, sequencing, and expression of a xylanase gene from the extreme thermophile Dictyoglomus thermophilum Rt46B.1 and activity of the enzyme on fiber-bound substrate.

A genomic library of the Dictyoglomus sp. strain Rt46B.1 was constructed in the phage vector lambda ZapII and screened for xylanase activity. A plaque expressing xylanase activity, designated B6-77, was isolated and shown to contain a genomic insert of 5.3 kb. Subcloning revealed that the xylanase activity was restricted to a internal 1,507-bp PstI-HindIII fragment which was subsequently sequenced and shown to contain a single complete open reading frame coding for a single-domain xylanase, XynA, with a putative length of 352 amino acids. Homology comparisons show that XynA is related to the family F group of xylanases. The temperature and pH optima of the recombinant enzyme were determined to be 85 degrees C and pH 6.5, respectively. However, the enzyme was active across a broad pH range, with over 50% activity between pH 5.5 and 9.5. XynA was shown to be a true endo-acting xylanase, being capable of hydrolyzing xylan to xylotriose and xylobiose, but it could not hydrolyze xylobiose to monomeric xylose. XynA was also shown to hydrolyze xylan present in Pinus radiata kraft pulp, indicating that it may be of use as an aid in pulp bleaching. The equivalent xylanase gene was also isolated from the related bacterium Dictyoglomus thermophilum, and DNA sequencing showed these genes to be identical, which, together with the 16S small-subunit rRNA gene sequencing data, indicates that Rt46B.1 and D. thermophilum are very closely related.

Amino Acid Sequence↗
PubMed1995

Correction of the beta-mannanase domain of the celC pseudogene from Caldocellulosiruptor saccharolyticus and activity of the gene product on kraft pulp.

The celA, manA, and celB genes from Caldocellulosiruptor saccharolyticus compose a cellulase-hemicellulase gene cluster and are arranged on a 12-kb C. saccharolyticus genomic fragment of the recombinant lambda bacteriophage NZP lambda 2. The beginning of a fourth open reading frame (celC) which was homologous to the C. saccharolyticus manA and celA genes was located at the 3' end of the 12-kb NZP lambda 2 genomic fragment. Genome-walking PCR was used to isolate DNA fragments downstream of the C. saccharolyticus celB gene, and the entire nucleotide sequence of celC was obtained. From the preliminary nucleotide sequence, celC appeared to encode yet another multidomain bifunctional enzyme (CelC) consisting of an N-terminal endo-1,4-beta-D-glucanase domain (75% similar to CelA domain 1), two central cellulose-binding domains, and a C-terminal endo-1,4-beta-D-mannanase domain (98% similar to ManA domain 1). However, upon completion of the celC sequencing, two -1 frameshifts were identified in the region encoding the putative CelC mannanase domain. The isolated CelC mannanase domain exhibited no beta-mannanase activity, which supported this observation. Recombinant PCR was used to correct the celC frameshifts by inserting the appropriate nucleotides into the gene. The repaired celC fragment containing the base insertions (manB) expressed strong beta-mannanase activity on soluble mannan substrates and showed significant activity on kraft pulp as judged by the release of reducing sugars.

Bacterial Proteins↗
PubMed1995

White coat effect in treated hypertensive patients: sex differences.

Ambulatory blood pressure recordings were performed in patients receiving anti-hypertensive therapy to determine the prevalence of a white coat effect and to evaluate the importance of the sex of the patients with higher office vs. ambulatory blood pressure (BP) readings. A white coat effect (office--ambulatory BP > or = 20/10 mm Hg) was present in 106 of 152 treated hypertensive patients who had a mean office BP (mm Hg) of 174 +/- 2/94 +/- 1 compared with a mean awake ambulatory BP of 137 +/- 2/81 +/- 1 (P < 0.001). A severe white coat effect (office--ambulatory BP > or = 40/20 mm Hg) was observed in 49 of 152 patients with office BP (183 +/- 3/96 +/- 2) being higher (P < 0.001) than mean awake ambulatory BP (134 +/- 2/77 +/- 1). A white coat effect was present in 70 of 87 women but only in 36 of 65 men (P < 0.001). Similarly, a severe white coat effect was seen in 41 of 87 women but only in 8 of 65 men (P < 0.001). Female sex and office SBP were significantly (P < 0.001) correlated with the presence of a white coat or severe white coat effect. Thus, female patients with treated hypertension are more likely than men to have a white coat component to their high office BP readings. These sex differences in white coat effect should be considered in future studies involving patients with hypertension based on high office readings.

Age Factors↗
PubMed1994

Secondary structure model for an unusual SSU rRNA from the extremely thermophilic bacterium strain AZ3 B.1.

The SSU rRNA gene of the extremely thermophilic bacterium strain AZ3 B.1, encodes an rRNA containing four large inserts. A secondary structure model has been constructed which predicts that the inserts form large stem loop structures with a common sequence motif at the base of the helices. To date, these structures have only been detected in related, thermophilic organisms.

Bacteria, Anaerobic↗
PubMed1994

Phylogeny and lipid composition of Thermonema lapsum, a thermophilic gliding bacterium.

1,490 nucleotides of the 16S rRNA gene of a Gram-negative, thermophilic and gliding bacterium, Thermonema lapsum, have been sequenced. Phylogenetic analysis indicates that T. lapsum is related to cytophaga-flavobacteria-bacteroides (CFB) and is confirmed by the identification signature nucleotides that define this group. Further phylogenetic analysis indicates that T. lapsum forms the deepest branch in the CFB group; this observation was confirmed by the identification of unique nucleotide and nucleotide pairs which separate T. lapsum from all other members of this group. The phospholipid fatty acid (PLFA) profile also confirmed that T. lapsum is related to the cytophaga-flavobacteria-bacteroides group and also to selected members of the genus Flexibacter; the PLFA profile is unique to T. lapsum.

Bacteria, Aerobic↗
PubMed1994

Who wants to eliminate heart disease?

Twenty-seven physicians and nine pharmacists at one University teaching hospital identified their preferred way of dying after attaining average life expectancy. Respondents' ranking of modes of dying showed high agreement (for physicians, W = 0.65, p < 10(-16)). Disease category, rapidity of death, and their interaction (ANOVA, all p < 0.0001) influenced choice. "Rapidly fatal cardiac death" was overwhelmingly preferred. Cancer and slowly fatal central nervous system disorders were rated last. Eliminating cardiovascular disease would necessarily increase the likelihood of other modes of death. If these respondents represent "informed consumers", then reducing cardiac death at normal life expectancy may be contrary to Western society's preferences.

Adult↗
PubMed1993

Report of the Canadian Hypertension Society Consensus Conference: 4. Hypertension in the elderly.

Several knowledge gaps, which made evidence-based guidelines impossible in 1985, have since been filled. There is now unequivocal evidence that treatment of isolated systolic hypertension benefits elderly patients, as does treatment beyond the age of 75 years. Pseudohypertension, although occasionally problematic, is not common and is not a reason to neglect the treatment of elderly patients, including those with isolated systolic hypertension. In general, long-term antihypertensive treatment of the elderly is well tolerated and does not cause important decreases in mental function. Comparative drug studies continue to accumulate; most show no clinically significant general differences between drugs, aside from the somewhat decreased efficacy and tolerability of beta-blockade in elderly patients. As in the young, certain drugs may be preferred in the presence of other conditions--e.g., congestive heart failure or diabetes.

Aged↗
PubMed1993

Evaluation of the pharmacokinetic and pharmacodynamic interaction between quinidine and nifedipine.

Quinidine and nifedipine appear to be subject to metabolism by the same isozyme of cytochrome P-450. In addition, both drugs have been reported to alter the pharmacokinetics of other compounds. To investigate a potential interaction, 10 healthy subjects (five male, five female) received quinidine sulfate (200 mg orally), nifedipine (20 mg orally), or the combination of both drugs every 8 hours for 4 doses using a randomized, cross-over study design with a 2-week washout period between treatments. Drug concentration, heart rate, and mean arterial pressure were measured at frequent intervals after the final dose. Quinidine concentrations were unchanged by the co-administration of nifedipine. Nifedipine area under the curve (AUC0-8) increased 36.6% from 333 to 455 micrograms.hr/L (P < .05) after quinidine administration. Heart rate was significantly higher in the nifedipine-quinidine treatment at 0.5, 1.0, 1.5, and 2.0 hours when compared with either drug alone. The maximum increase in heart rate (17.9 beats/minute) occurred at 0.5 hours after nifedipine administration and was significantly correlated with serum concentrations at that time (r = .78). These results suggest that quinidine inhibits nifedipine metabolism, and this pharmacokinetic interaction results in enhanced pharmacologic response.

Administration, Oral↗
PubMed1993

Phylogeny of twenty Thermus isolates constructed from 16S rRNA gene sequence data.

The sequences of the 16S rRNA genes of 20 Thermus isolates were determined to a high fidelity by using automated DNA sequencing and fluorescent-dye-labelled primers. The strains tested included members of the three validly named Thermus species and representatives of major taxonomic clusters defined previously for this genus. The parsimony method was used to reconstruct the phylogeny of the strains from the aligned sequences, and a bootstrap analysis revealed a number of well-supported clades. Our results are not consistent with groupings inferred from numerical taxonomy data but support the conjecture that the genus Thermus contains more species than the three currently recognized species.

Base Sequence↗
PubMed1993

Reproducibility of ambulatory blood pressure and assessing treatment withdrawal in hypertension trial.

Ambulatory blood pressure monitoring (ABPM), like casual blood pressure (BP), is imperfectly reproducible between visits. The reproducibility of ABPM is less than the reproducibility predicted from a simple model of random variation of BP. This suggests either increased technical error in the technique, an element of increased biologic variability, or both. In addition, ABP shows a between-day variation (add about 6 to 7 mm Hg diastolic, similar in magnitude to what is observed with casual BP) which cannot be obviated by the average of many within-day measurements. The reliability of ABPM, although conventionally judged excellent at about RI = 0.75, is insufficient to avoid misclassification errors and regression to the mean when BP cutpoints are employed. About 40% of patients apparently failing treatment withdrawal at a threshold of +2 SD, or about 95 mm Hg diastolic ABP, will be false-positive failures when categorized by a single ABP. Despite the inconvenience, obtaining an average of two or more ABP measurements on different days may be cost-saving to a clinical trial because of the improved reproducibility; other costs may exceed $1000 per entrant.

Ambulatory Care↗
PubMed1992

Reproducibility of nurse-measured, exercise and ambulatory blood pressure and echocardiographic left ventricular mass in borderline hypertension.

OBJECTIVE: To compare the short-term reproducibility of four diagnostic tests: resting blood pressure, exercise blood pressure, non-invasive daytime ambulatory blood pressure and echocardiographic left ventricular mass. DESIGN: Blinded, prospective test-retest (reliability) study. SETTING: Hypertension research units in two teaching hospitals. PARTICIPANTS: Six normal volunteers and 22 patients with untreated borderline to mild hypertension, mean age 44 years. MAIN OUTCOME MEASURES: The intraclass correlation coefficient (RI) and standard deviation of the difference (SDD) between visits. MAIN RESULTS: The mean blood pressures and left ventricular mass did not differ between visits. Concordance between visits reached RI = 0.86 systolic/0.66 diastolic for ambulatory blood pressure and RI = 0.85 systolic/0.64 diastolic for nurse-measured random-zero sphygmomanometer resting blood pressure. The respective variabilities were SDD = 9/8 and 8/8 mmHg. Submaximal exercise systolic blood pressure (SBP) and echo left ventricular mass showed excellent reliability. Echo left ventricular mass and resting SBP or ambulatory SBP were significantly more reproducible than resting diastolic blood pressure (DBP) or ambulatory DBP. CONCLUSIONS: Despite averaging many readings within each day, clinically important between-visit variations in ambulatory blood pressure remained. The between-visit variability of daytime ambulatory blood pressure was similar to that of resting blood pressure when carefully measured by a research nurse. The echo left ventricular mass appears to be more reproducible over the short term than the current diagnostic standard for hypertension, the resting DBP.

Adult↗
PubMed1991

White coat phenomenon in patients receiving antihypertensive therapy.

The occurrence of the white coat phenomenon in hypertensive patients receiving drug therapy was determined in a consecutive series of 71 patients undergoing ambulatory blood pressure (ABP) recordings because of suspected differences between office and ambulatory values. Overall mean (+/- SEM) office blood pressure (BP) was 166 +/- 2/95 +/- 1 v awake ABP 139 +/- 2/86 +/- 1 mm Hg. The white coat phenomenon [(office BP - ABP) greater than or equal to 20/10 mm Hg] was present in 52 of 71 patients: office BP 170 +/- 3/96 +/- 2 v ABP 135 +/- 2/83 +/- 1 mm Hg. A marked white coat effect [(office BP - ABP) greater than or equal to 40/20 mm Hg] was seen in 22 patients with office BP being 178 +/- 4/98 +/- 3 v ABP 131 +/- 3/79 +/- 2 mm Hg. The frequent occurrence of white coat phenomenon in these patients suggests that office BP readings may not always represent usual ABP in patients receiving chronic antihypertensive therapy.

Antihypertensive Agents↗
PubMed1991

The effect of caffeine on daytime ambulatory blood pressure.

Caffeine produces an acute increase in blood pressure in the research laboratory, but its effect on the ambulatory blood pressure during normal daily activities is unknown. In 25 normotensive, caffeine-naive subjects, daily administration of 400 mg caffeine produced a small increase (+3/+3 mm Hg, P less than .001) in ambulatory daytime blood pressure on the first day, with values returning to baseline by the third day. The initial rise in blood pressure was associated with a fall in heart rate (-3 beats/min, P less than .02). Readings taken the morning following the first day of caffeine ingestion did not show any persistent effect of caffeine on blood pressure. A 400 mg dose of caffeine causes a small increase in daytime ambulatory blood pressure, but tolerance develops with daily caffeine consumption. Infrequent ingestion of caffeine may cause a transient rise in blood pressure which is unlikely to be harmful to an individual but might influence the diagnosis of hypertension in a patient with a borderline elevated blood pressure.

Adult↗
PubMed1991

Patient and environmental factors affecting ambulatory blood pressure monitoring.

Several patient and environmental factors may limit the applicability of ambulatory BP monitoring. In children and in elderly patients, erroneous readings may occur more frequently. Comparison of 25 elderly (greater than 65 yr) vs 25 young subjects recently monitored for clinical reasons in our hypertension clinic showed slightly higher error rates (19% vs 15% of readings) in the elderly but similar willingness to undergo monitoring again (96% vs 84% of subjects, respectively). The technique has not been well validated in obesity. Arrhythmias may prevent currently available ambulatory BP machines from obtaining usable readings. Monitoring may prove unsatisfactory for patients engaged in physically active occupations, travelling in automobiles, or in environments where the noise of the ambulatory BP machine would be disruptive. Portable automatic monitors can detect abnormally elevated average BP during sleep but the diagnostic value of this pattern remains unknown. It is concluded that ambulatory BP monitoring may be successfully performed in most patients.

Age Factors↗
PubMed1991

A review of the stability of ambulatory blood pressure: implications for diagnosis of hypertension.

Ambulatory BP monitoring by obtaining many measurements on one day might eliminate the need for multiple visits on different days to diagnose hypertension. However, review of the published literature shows the stability of ambulatory BP as assessed by test-retest correlation between days to be similar to that of office BP in research settings: r = 0.87/0.70 vs 0.79/0.71 (systolic/diastolic). Between-day standard deviations of the difference are also similar: 8/7 mmHg vs 9/7 mmHg, respectively. The reproducibility of within-day fluctuation in BP is poor (r = 0.28/0.11) and may account for some of the difficulty in showing correlations between BP variability and target organ damage. Evidence to date suggests that ambulatory BP monitoring will not reduce observed between-day differences in BP. Diagnosis of elevated BP will require repeated visits whether office or ambulatory BP measurement is employed.

Blood Pressure Determination↗
PubMed1989

Beta-blockade disappearance rate predicts beta-adrenergic hypersensitivity.

We determined whether the beta-blockade disappearance rate would determine the degree of subsequent transient beta-adrenoceptor hyperresponsiveness after abrupt withdrawal of a beta-adrenoceptor drug. In a single-blind randomized study, 10 healthy men took a placebo for 1 week and then took nadolol one time a day (t1/2, 18 to 24 hours) or propranolol three times a day (t1/2, 4 to 6 hours) in doses that were increased weekly for 4 weeks to reach 240 mg per day. beta-Receptor responsiveness was assessed before and repeatedly after abrupt drug withdrawal by infusion of isoproterenol and epinephrine and by ergometer exercise. In the 13 days after drug discontinuation, peak beta-receptor sensitivity correlated (p less than 0.05) with the disappearance rate of beta-blockade as assessed by heart rate responses to isoproterenol (r = 0.68) and to submaximal exercise (r = 0.62) and by diastolic blood pressure responses to isoproterenol (r = 0.86) and epinephrine (r = 0.86). Plasma catecholamine levels and renin activity showed no overshoot. beta-Blockers with long plasma t1/2 values may prevent beta-blocker withdrawal syndromes by means of "self-tapering."

Adult↗