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Biomedical subjects

R A Preston

Publications and source records attributed to R A Preston.

83 records · Page 5Linked to original sources
PubMed1979

Protein synthesizing systems from spores and vegetative cells of Bacillus cereus.

A system of polyphenylalanine synthesis was optimized for a comparison of the polymerizing activities of ribosomes from spores and vegetative cells of Bacillus cereus T. Ribosomes of both types react similarly, showing a magnesium optimum of about 6mM and spermidine optima of about 5mM and 4mM for vegative and spore ribosomes, respectively. These lead to optimum mono- to multivalent cation rations of 9 and 10 respectively at 100 mM ammonium ion. A comparison of the response of these ribosomes to suboptimal concentrations of magnesium and spermidine show that they differ qualitatively from each other, suggesting that they possess different structure, macromolecular or ionic components.

Bacillus cereus↗
PubMed1978

Isolation of stable ribosomal subunits from spores of Bacillus cereus.

Analyses of ribosomes extracted from spores of Bacillus cereus T by a dryspore disruption technique indicated that previously reported defects in ribosomes from spores may arise during the ribosome extraction process. The population of ribosomes from spores is shown to cotain a variable quantity of free 50S subunits which are unstable, giving rise to slowly sedimenting particles in low-Mg2+ sucrose gradients and showing extremely low activity in in vitro protein synthesis. The majority of the ribosomal subunits in spores, obtained by dissociation of 70S ribosomes and polysomes, are shown to be as stable as subunits from vegetative cells, though the activity of spore polysomes was lower than that of vegetative ribosomes. In spite of the instability and inactivity of a fraction of the spore's ribosomal subunits, the activity of the total population obtained from spores by the dry disruption technique was 32% of vegetative ribosome activity, fivefold higher than previously obtained with this species. The improvement in activity and the observed variability of subunit destabilization are taken as evidence for partial degradation of spore ribosomes during extraction.

Bacillus cereus↗
PubMed1976

Cytoplasmic fibrils in plasma cell leukemia.

In a patient with plasma cell leukemia, associated with pleural effusion, ultrastructural studies of the peripheral blood plasma cells showed an abundance of cytoplasmic fibrils. The nature of fibrils was not clarified, but they were not amyloid fibrils. This finding, coupled with a liaterature review, suggests that the cytoplasmic fibrils in plasma cells may be an additional cytological feature of this rare form of leukemia.

Cytoplasm↗
PubMedDate not supplied

The effects of dopamine agonists on fixed interval schedule-controlled behavior are selectively altered by low-level lead exposure.

A previous report of differential effects of catecholaminergic compounds, but not other classes of compounds, on FI (fixed interval) response rates of lead (Pb)-treated pigeons suggests that catecholamine system disturbances might play a role in lead (Pb)-induced changes in FI performance. The current study sought to extend those findings using more selective dopaminergic (DA) D1 and D2-like receptor agonists, Pb-treated rats, and additional classes of compounds. Drug-induced changes in FI performance of rats exposed chronically from weaning to 0, 50, or 150 ppm Pb acetate in drinking water were compared following the administration of drugs known to impact various neurotransmitter systems altered by Pb exposure, including the selective D2-like agonist quinpirole, the D1 agonists SKF38393 and SKF82958, the mu-opioid agonist morphine, the muscarinic cholinergic agonist arecoline, the glutamate agonist NMDA, and the noncompetitive NMDA antagonist MK-801. All drugs except NMDA significantly altered FI performance, but only the effects of DA agonists differed in control and Pb-exposed rats. Pb exposure attenuated the decrements in rates produced by D1 agonists and at 150 ppm modestly altered the rate changes associated with low doses of quinpirole. These data demonstrate functional DA alterations in response to Pb exposure and provide further evidence for the selective involvement of such effects in FI performance.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMedDate not supplied

Involvement of kallikrein in the antihypertensive response to furosemide in essential hypertension.

Twelve white men with essential hypertension were treated for 1 month in randomized order with either placebo or low-dose furosemide (40 mg/day) and compared to 22 race-, age-, and diet-matched normal controls. Furosemide therapy significantly reduced mean arterial pressure (108.6 +/- 2.4 vs. 101.0 +/- 2.7 mm Hg, p < 0.02) in association with a significant increase in 24 hr urinary kallikrein activity (7.9 +/- 1.8 vs. 13.4 +/- 2.8 esterase units/24 hr, p < 0.02). Normal controls on no therapy excreted 19.4 +/- 2.6 esterase units/24 hr of urinary kallikrein activity, significantly greater than hypertensives on placebo (p < 0.01) but not hypertensives on furosemide (p > 0.1). A significant (p < 0.05) inverse correlation between mean arterial pressure and urinary kallikrein activity suggests a possible role for the kallikrein-kinin system in the antihypertensive mechanism of furosemide.

Aldosterone↗
PubMedDate not supplied

Urinary kallikrein activity and renal vascular resistance in the antihypertensive response to thiazide diuretics.

To evaluate the mechanism of chronic thiazide diuretic action in hypertension, we treated 19 essential hypertensive white men for 1-month periods on placebo alone and hydrochlorothiazide alone. During therapy, mean arterial pressure (MAP) fell, but radioisotopically determined intravascular volume remained unchanged, suggesting other mechanisms of thiazide action upon blood pressure. In the renal circulation, thiazides did not change renal plasma flow or glomerular filtration rate, but renovascular resistance was diminished, probably at the afferent arteriole. Concomitant with the decline in blood pressure and renovascular resistance, urinary kallikrein excretion increased, from subnormal (hypertensive) levels back into the normal range. The kallikrein increase did not correlate with changes in plasma aldosterone. In addition, patients with blood pressure responses (reduction greater than or equal to 10%) to thiazides (n = 12) had greater increases in kallikrein excretion than those without such a blood pressure decrement (n = 7), suggesting a role for renal kallikrein in the hypotensive response to thiazide diuretics.

Aldosterone↗
PubMedDate not supplied

Molecular analysis of bacterial pathogens in otitis media with effusion.

OBJECTIVE: To determine if the polymerase chain reaction (PCR) can detect bacterial DNA in pediatric middle ear effusions that are sterile by standard cultural methods. DESIGN: Single-center, blinded, comparative study of diagnostic assays. The PCR-based detection systems for Moraxella catarrhalis, Haemophilus influenzae, and Streptococcus pneumoniae were designed and validated using a battery of DNAs obtained from cultured bacteria. Chronic middle ear effusion specimens were collected and comparatively analyzed by culture and the PCR. SETTING: Tertiary care pediatric hospital. PATIENTS: A total of 97 middle ear effusions were collected from pediatric outpatients at Children's Hospital of Pittsburgh (Pa) during myringotomy and tube placement for chronic otitis media with effusion (duration > 3 months). All patients had failed multiple courses of antimicrobial therapy and were diagnosed by a combination of validated otoscopy and tympanograms. MAIN OUTCOME MEASURE: Differences in the percentage of positive test results between PCR-based assays and culture for M catarrhalis, H influenzae, and S pneumoniae. RESULTS: Of the 97 specimens of otitis media with effusion, 28 (28.9%) tested positive by both culture and PCR for M catarrhalis, H influenzae, or S pneumoniae. An additional 47 specimens (48%) were PCR positive/culture negative for these three bacterial species. Thus, 75 (77.3%) of the 97 specimens tested PCR positive for one or more of the three test organisms. The minimum number of bacterial genomic equivalents present in the average culture-negative ear was estimated to be greater than 10(4) based on dilutional experiments. CONCLUSIONS: The PCR-based assay systems can detect the presence of bacterial DNA in a significant percentage of culturally sterile middle ear effusions. While this finding is not proof of an active bacterial infectious process, the large number of bacterial genomic equivalents present in the ears is suggestive of an active process.

Bacteriological Techniques↗
PubMedDate not supplied

Prazosin and renal hemodynamics: arteriolar vasodilation during therapy of essential hypertension in man.

Renal hemodynamic effects of chronic prazosin therapy were studied in 10 men and with essential hypertension. Successful antihypertensive therapy was accompanied by diminution in total renovascular resistance, probably at the level of the afferent arteriole. The resistance change was unexplained by alterations in intravascular volume, the vasodilatory renal kallikrein-kinin system, or sympathetic nervous system activity, but was associated with a diminution in plasma renin activity. Potential mechanisms for the resistance decrement are discussed, including renal perfusion autoregulation, diminished activity of the vasoconstrictive renin-angiotensin system, and direct intrarenal afferent arteriolar alpha adrenergic blockade.

Adult↗
PubMedDate not supplied

Renal perfusion changes during treatment of essential hypertension: prazosin versus propranolol.

To evaluate renal hemodynamic changes during therapy of essential hypertension, we treated 12 essential hypertensives in crossover fashion, with 1 month each of placebo, prazosin, and propranolol alone. During prazosin treatment, blood pressure was normalized with preservation of glomerular filtration rate, renal plasma flow, and renal blood flow. Propranolol, however, normalized blood pressure with an associated significant decline in glomerular filtration rate, renal plasma flow, and renal blood flow. The potential mechanisms are discussed.

Adult↗