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Biomedical subjects

P Dennis

Publications and source records attributed to P Dennis.

16 recordsLinked to original sources
PubMed1992

An inter-observer and intra-observer variability study on the diagnosis of lymph node biopsy specimens.

One hundred lymph node biopsy specimens were examined on two separate occasions by seven pathologists differing in experience in lymphoreticular pathology. Neither history nor immunohistochemistry was provided and the study, therefore, focused on morphological interpretation alone. The participants evaluated each case using a constructed response form in which the confidence with which they entered each response was also entered. Agreement on various points, between pathologists, between the two rounds, and with the referring centre was assessed. Whilst there was a high level of agreement over a diagnosis of benign vs. malignant and non-Hodgkin lymphoma vs. Hodgkin's disease, there was considerably less agreement over both T vs. B cell phenotype and high vs. low grade. The lack of agreement over grade, an evaluation which is usually made independent of immunohistochemistry, is particularly important, because of the relevance to selection of treatment. Proliferation markers may be more appropriate determinants of treatment choice.

Biopsy↗
PubMed1990

Growth factor control of extracellular proteolysis.

The involvement of proteases and growth factors in angiogenesis is complex. The angiogenic factor basic fibroblast growth factor (bFGF) induces increased synthesis of both plasminogen activator and collagenase in endothelial cells. In addition, bFGF increases the number of plasminogen activator receptors on the cell surface. Increased production of plasmin may be responsible for the release of soluble complexes of heparan sulfate-bFGF which may be the active form of bFGF. The activity of a negative regulator of angiogenesis, transforming growth factor beta (TGF-beta), is also regulated by proteases since the released latent form of TGF-beta is activated by a surface proteolytic assembly plasminogen activator and plasmin. Since TGF-beta induces an inhibitor of plasminogen activator, the activation reaction is self-regulatory.

Animals↗
PubMed1986

Preservative cytotoxicity to cultured corneal epithelial cells.

Cultured human and rat corneal epithelial cells with 51Cr incorporated were used as a model to test the cytolytic action of four common preservatives. Benzalkonium chloride, chlorohexidine and thimerosol were all found to lyse greater than 40% cells when incubated for fifteen minutes at concentrations in clinical use in topical ophthalmic medications. Chlorobutanol is the only preservative tested which has a low level of cytotoxicity (10%) and which, under these conditions, can be considered a safe preservative using cytolytic activity as the means of criteria.

Animals↗
PubMed1984

Sterol carrier protein2 (SCP2)-mediated transfer of cholesterol to mitochondrial inner membranes.

Rats treated with cycloheximide accumulate cholesterol in the adrenal mitochondria. This cholesterol is largely associated with the mitochondrial outer membrane. The addition of homogeneous sterol carrier protein2 (SCP2) to these mitochondria stimulated pregnenolone production to a greater extent than with mitochondria from untreated rats. Adrenal mitochondria from cycloheximide-treated rats were incubated in the presence of aminoglutethimide and cycloheximide to prevent further utilization of cholesterol for pregnenolone synthesis. Outer and inner membrane fractions of these mitochondria incubated with and without 0.75 microM SCP2, were prepared following hypotonic disruption. Incubations of mitochondria in the presence of SCP2 caused a marked shift in cholesterol from outer to inner membrane fractions. The findings provide direct evidence for a role of SCP2 or a similar peptide in modulating transfer of cholesterol to the inner membrane site of cholesterol side chain cleavage.

Adrenal Glands↗
PubMed1983

Sterol carrier protein2. Identification of adrenal sterol carrier protein2 and site of action for mitochondrial cholesterol utilization.

Addition of homogeneous rat liver sterol carrier protein2 (SCP2) or an adrenal cytosolic fraction enhanced pregnenolone production by adrenal mitochondria. Pretreatment of SCP2 or adrenal cytosol with anti-SCP2 IgG abolished the stimulatory effect of both preparations on mitochondrial pregnenolone output. Incubation of mitochondria with aminoglutethimide, which blocks interaction of cholesterol with inner membrane cytochrome P-450scc, resulted in decreased pregnenolone production and a decreased level of mitoplast cholesterol. Addition of SCP2 to the incubation media caused an almost 2-fold increase in cholesterol associated with the mitoplast, but did not enhance mitochondrial pregnenolone production. Studies with reconstituted cytochrome P-450scc in phospholipid vesicles also suggested that SCP2 did not affect interaction of cholesterol with the hemoprotein. Treatment of rats with cycloheximide alone or with adrenocorticotropic hormone resulted in a dramatic increase in mitochondrial cholesterol. However, these mitochondria did not exhibit increased levels of pregnenolone output under control incubation conditions. When SCP2 was included in the mitochondrial incubation media, pregnenolone production was significantly increased over that observed with adrenal mitochondria from untreated or adrenocorticotropic hormone-treated rats. The results imply that SCP2 enhances mitochondrial pregnenolone production by improving transfer of mitochondrial cholesterol to cytochrome P-450scc on the inner membrane, but does not directly influence the interaction of substrate with the hemoprotein.

Adrenal Glands↗
PubMed1982

Inhibition of leucine aminopeptidase by amino acid hydroxamates.

Amino acid hydroxamates are strong competitive inhibitors of leucine aminopeptidase from porcine kidney. The side chain specificity for inhibition correlates well with substrate specificity. L-Leucine hydroxamate (Ki = 14 microM) protects the enzyme from inactivation by EDTA and is presumed to be a bidentate ligand of the zinc at the active site. A substituted beta-mercaptoketone which may bind in a similar way is also a potent inhibitor (Ki = approximately 1 microM). The binding of these inhibitors suggests a mechanism for this enzyme in which a zinc-bound hydroxide ion participates in concerted proton-transfer processes, while the coordination and charge field at the zinc atom remain unchanged.

Amino Acids↗
PubMed1982

Hypoxic cardiac hypertrophy is not inhibited by cardioselective or non-selective beta-adrenoceptor antagonists.

1. Young rabbits, eight at a time, were exposed to more than 170 hr of hypoxia (O2 at 70-80 torr) at atmospheric pressure during 9-11 days. 2. The animals were injected twice daily with doses of beta-blockers up to the highest used in human therapy, or with an equivalent volume of saline. These controls were litter mates of the treated rabbits. 3. In comparison with untreated normoxic rabbits of similar age, the hypoxia induced highly significant mean increases in right ventricular dry weight (+57%, controls; +55% treated). 4. In each group, the same degree of hypertrophy was induced in the treated and control animals, irrespective of whether the drug used was a non-selective beta-blocker (propranolol) or a cardioselective drug (atenolol). 5. The right atria were also hypertrophied, though not as much as the right ventricles. 6. In all the hypertrophied tissues the water content was increased. 7. No significant change was observed in the dry weight or water content of the left ventricles of treated or control animals.

Animals↗
PubMed1982

Insertions of transposon Tn5 into ribosomal protein PNA polymerase operons.

The genetic organization and interrelationships between the two ribosomal protein transcription units (the L11 and L10 operons) from near 89 min on the Escherichia coli chromosome were studied by using insertional mutations generated by the kanamycin-resistant transposable element Tn5. The polar effects of Tn5 insertions on the expression of the L11, L1, L10, and L12 ribosomal protein genes and the beta RNA polymerase subunit gene were examined (i) by the level of beta-galactosidase activity generated from L10-lacZ and beta-lacZ gene fusions, (ii) by direct sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the proteins specified by plasmid ribosomal protein genes in UV-irradiated maxicells, and (iii) by urea-polyacrylamide gel electrophoresis of plasmid- and chromosome-specified L12 protein. The results confirmed the organization of these genes into two transcription units as follows: PL11, rplK (L11), rplA (L1), PL10, rplJ (L10), rplL (L12), rpoB (beta). . .; they also localized the position of the PL10 promoter within an 80-nucleotide region near the end of the L1 gene. The results also support the idea that the translational regulatory proteins for the L11 and L10 operons are L1 and L10, respectively, and that the expression of the L12 gene is closely linked to L10 gene expression.

Bacterial Proteins↗