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Biomedical subjects

J Stevens

Publications and source records attributed to J Stevens.

At least 289 records · Page 16Linked to original sources
PubMed1986

Nucleotide sequence and analysis of the 58.3 to 65.5-kb early region of bacteriophage T4.

The complete 7.2-kb nucleotide sequence from the 58.3 to 65.5-kb early region of bacteriophage T4 has been determined by Maxam and Gilbert sequencing. Computer analysis revealed at least 20 open reading frames (ORFs) within this sequence. All major ORFs are transcribed from the left strand, suggesting that they are expressed early during infection. Among the ORFs, we have identified the ipIII, ipII, denV and tk genes. The ORFs are very tightly spaced, even overlapping in some instances, and when ORF interspacing occurs, promoter-like sequences can be implicated. Several of the sequences preceding the ORFs, in particular those at ipIII, ipII, denV, and orf61.9, can potentially form stable stem-loop structures.

Amino Acid Sequence↗
PubMed1986

The role of glutathione conjugate metabolism and cysteine conjugate beta-lyase in the mechanism of S-cysteine conjugate toxicity in LLC-PK1 cells.

A cell line derived from pig kidney, LLC-PK1, was grown in a culture system in which the cells express morphological and biochemical characteristics of the proximal tubule. This model was used to investigate the mechanism of S-cysteine conjugate toxicity and the role of glutathione conjugate metabolism. LLC-PK1 cells have the degradative enzymes of the mercapturate pathway, and S-(1,2-dichlorovinyl)-L-cysteine and S-(1,2-dichlorovinyl)-L-glutathione are toxic. S-(1,2-Dichlorovinyl)-L-glutathione is not toxic when the cells are pretreated with AT-125, an inhibitor of gamma-glutamyl transpeptidase. The cells respond to a variety of toxic cysteine conjugates. Cysteine conjugate beta-lyase activity is not detectable by standard assays, but can be measured using radiolabeled S-(1,2-dichlorovinyl)-L-cysteine. Pyruvate stimulates the beta-elimination reaction with S-(1,2-dichlorovinyl)-L-cysteine as substrate 2-3-fold. The data suggest that a side transamination reaction regulates the flux of substrate through the beta-elimination pathway; therefore, cysteine conjugate beta-lyase in LLC-PK1 cells may be regulated by transamination, and measurement of lyase activity in some systems may require the presence of alpha-ketoacids. Aminoxyacetic acid blocks both the metabolism of S-(1,2-dichlorovinyl)-L-cysteine to a reactive species which covalently binds to cellular macromolecules and toxicity. Glutathione inhibits the binding of the sulfur containing cleavage fragment to acid insoluble material in vitro. The data provide direct evidence that S-(1,2-dichlorovinyl)-L-cysteine is metabolized to a reactive species which covalently binds to cellular macromolecules, and the binding is proportional to toxicity.

Acetylcysteine↗
PubMed1986

Conversion of angiotensin-1 to angiotensin-2 by a latent endothelial cell peptidyl dipeptidase that is not angiotensin-converting enzyme.

Cultured bovine pulmonary artery endothelial cells contain a second peptidyl dipeptidase, distinct from angiotensin-converting enzyme, present in an inactive form associated with a non-dialyzable inhibitor. Partial purification by glycine affinity chromatography separates enzyme from inhibitor to yield a preparation which hydrolyzes angiotensin-1, bradykinin, substance P, atriopeptin-2, enkephalin and Hip-His-Leu. This enzyme is resistant to inhibition by lisinopril, captopril, thiorphan, phosphoramidon, soybean trypsin inhibitor, PMSF and aminopeptidase and carboxypeptidase inhibitors, but is inhibited by EDTA.

Angiotensin I↗
PubMed1986

Long-term results of total ankle replacement.

The results are reported of 19 total ankle replacements in 18 patients with rheumatoid or other inflammatory arthritis. After a mean follow-up period of 54.4 months (minimum, 24 months), three arthroplasties had failed, all because of loosening. Although all of the remaining patients were improved in terms of pain and function, there was radiographic evidence of loosening in a further eight patients. Indications for the operation are discussed.

Adult↗
PubMed1986

Captopril antagonizes the hypotensive action of atrial natriuretic peptide in the anaesthetized rat.

Atrial natriuretic peptide (8-33; ANP) caused a prolonged hypotensive response following intravenous injection in anaesthetized rats. This response was abolished by captopril treatment and restored by concomitant angiotensin II infusion. These results suggest that ANP exerts its hypotensive action in the anaesthetized rat by the antagonism of the vasoconstrictor action of endogenous angiotensin II.

Anesthesia↗
PubMed1986

Specificity and sensitivity of methacholine challenge test in children with normal and hyperreactive airways.

To assess the ability of the methacholine challenge test for separation between normals and patients with clinically apparent mild airway hyperreactivity, the provocative dose of inhaled methacholine required to cause a 20% drop in the forced expiratory volume in one second was evaluated in two selected pediatric populations. On the basis of a standardized respiratory questionnaire, 70 subjects, 4-16 years of age were identified. Included were 49 normal individuals, and 21 individuals with mild airway hyperreactivity who responded to bronchodilators. Methacholine inhalation challenges were performed by use of a standard inhalation procedure. Forty-seven percent of the normals (23/49) had a positive methacholine challenge test while 24% (5/21) of the patients with hyperreactive airways had a negative test by the standard criteria. A wide spectrum of specificity and sensitivity of methacholine challenge was obtained at different doses of methacholine. The greater the sensitivity, the lower the specificity. Therefore, we postulate that the methacholine challenge test can be helpful in making the clinical diagnosis but it does not allow a clear and perfect separation between normal and clinically apparent mildly airway reactive patients in a pediatric age population.

Adolescent↗
PubMed1986

The heterotopically transplanted rat urinary bladder as a model for detection of tumor-promoting urinary growth factor(s).

The heterotopically transplanted rat urinary bladder (HTB) was developed in our laboratory as a model to study the role of urine in urinary bladder carcinogenesis. With this model, normal urine was found to enhance urinary bladder carcinogenesis initiated by N-methyl-N-nitrosourea or N-butyl-N-(4-hydroxybutyl)nitrosamine. Two crude urinary components (Fractions I and II) were obtained by gel filtration chromatography; they stimulated ornithine decarboxylase (ODC) in a test bladder carcinoma cell line 804G, and promoted carcinogenesis in the HTB system. Fraction I was found to stimulate growth of 804G cells in vitro. Preliminary data indicate that Fraction I contains at least one, and possibly two heat-stable ODC-inducible and mitogenic components. Further characterization of these components is in progress. The HTB system has been demonstrated to be useful for other investigations; for example, alpha-difluoromethylornithine, an enzyme-activated irreversible inhibitor of ODC, when instilled repeatedly to the bladder lumen, inhibited tumorigenesis in HTBs.

Animals↗
PubMed1985

Angiotensin-converting enzyme from human tissues. Physicochemical, catalytic, and immunological properties.

Angiotensin-converting enzyme was purified from human lung, kidney, testis, blood plasma, and seminal plasma using a facile two-step protocol which included affinity chromatography on Sepharose-bound lisinopril followed by either gel filtration or hydroxylapatite chromatography. Molecular mass for converting enzyme from all sources except testis was 140 kDa. That from testis consisted of both a 90- and a 140-kDa form in a 4:1 ratio. Detergent-extracted membrane-bound converting enzyme aggregated on gel filtration chromatography, while trypsin-extracted and soluble converting enzyme did not. Comparison of detergent-extracted and trypsin-extracted membrane-bound converting enzyme by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing indicated that the membrane binding sequence contributed minimally to the size and charge of the enzyme. Catalytic and kinetic properties assessed by interaction with substrates, inhibitors, and anti-converting enzyme immunoglobulin were similar for all forms and sources of converting enzyme. Enzyme-linked immunosorbent assay revealed only partial homology between the 90- and 140-kDa forms of the enzyme.

Chromatography, Gel↗
PubMed1985

Human testicular angiotensin-converting enzyme is a mixture of two molecular weight forms. Only one is similar to the seminal plasma enzyme.

Two molecular weight (Mr) forms of angiotensin-converting enzyme are present in human testis. Both the high Mr 140,000 form and the low Mr 90,000 form are catalytically similar but immunologically distinct. After isoelectric focusing, the profile of sialylated Mr 140,000 isozymes resembled that of seminal plasma converting enzyme, whereas the nonsialylated Mr 90,000 isozymes were distinct. These data suggest that the Mr 140,000 testicular converting enzyme may be a source of converting enzyme in seminal plasma.

Humans↗
PubMed1984

Activities of the initial enzymes of glycerolipid and sphingolipid synthesis in lung microsomes from rats exposed to air or 85% oxygen.

Lungs of adult rats exposed to 85% oxygen undergo extensive cellular reorganization; therefore, to investigate changes in lipid metabolism the initial enzymes of glycerolipid and sphingolipid synthesis were measured in lung microsomes. After 1 week of O2 treatment, the specific activity of the glycerol 3-phosphate acyltransferase increased to nearly twice that of the controls and remained elevated for the 3 weeks of study. Serine palmitoyl-transferase activities were approximately the same for both groups. These results suggest that in addition to cellular proliferation caused by hyperoxia there are also selective changes in glycerolipid synthesis, which may explain the decreased sphingomyelin content of lung and lamellar bodies.

Acyltransferases↗
PubMed1984

Interpersonal aggression and the type A coronary-prone behavior pattern: a theoretical distinction and practical implications.

Past research suggests that Type As are more aggressive than Type Bs. However, little is known about the nature of that aggression. The present two studies investigated the theoretical distinction between hostile aggression and instrumental aggression and examined the practical implications of this distinction. Study 1 used a modified version of the Buss teacher-learner procedure that allowed the isolation of hostile from instrumental acts. Results indicated that a prior task frustration produced greater aggression by Type As than Type Bs but only under conditions where the aggressive act could not affect a confederate's immediate performance (i.e., hostile aggression). Study 2 examined the representation of Type As and Type Bs among perpetrators of intrafamily violence. Results indicated that Type As were more likely than Type Bs to exhibit the extreme hostility found in child abuse. Both studies suggest that a lack of control may underlie the greater aggression displayed by Type As than Type Bs.

Adult↗
PubMed1984

The kinematics of hip joints: normal functioning.

This paper describes the use of an electrogoniometer to measure angular movements of the hip joints of a large number of 'normal' people. The object of the study was to establish a statistically significant data base for the movements of the hip joints during functional activities against which the movements of pathological hips could be compared. The measurement and the analysis used to establish 'normality' in males and females over a wide age range are introduced. The data are examined for the existence of any sex or age related gait variations, and the conclusion is that there are only minor variations. Comparison with pathological hips will be reported later.

Adolescent↗