Biomedical subjects

N L Brown

Publications and source records attributed to N L Brown.

At least 19 recordsLinked to original sources

PubMed1992

The venous antithrombotic effect of LF 1351 in the rat following oral administration.

The venous antithrombotic effects of a novel chemical entity, LF 1351, were investigated in rats following single oral administration, in comparison with i.v. administered heparin. LF 1351 demonstrated a dose-related antithrombotic effect in three models of venous thrombosis. The compound was approximately equipotent in two models involving complete stasis of the vena cava and administration of factor Xa or porcine serum, giving respective ED50 values of 48.7 mg/kg and 36.7 mg/kg. LF 1351 was less effective in a model involving partial stasis in the presence of an endothelial lesion. In this case, the antithrombotic effect did not exceed 60-65%, the ED50 being 150 mg/kg. Heparin (50-300 micrograms/kg; 7.5-45.0 U/kg) was effective in all three models. At the approximate ED80 value against factor Xa-induced thrombosis (75 mg/kg) the antithrombotic effect of LF 1351 persisted for 6 h. The antithrombotic effect of LF 1351 (300 mg/kg) occurred without significant changes in APTT or thrombin time.

Administration, Oral↗

PubMed1992

Copper resistance determinants in bacteria.

Copper is an essential trace element that is utilized in a number of oxygenases and electron transport proteins, but it is also a highly toxic heavy metal, against which all organisms must protect themselves. Known bacterial determinants of copper resistance are plasmid-encoded. The mechanisms which confer resistance must be integrated with the normal metabolism of copper. Different bacteria have adopted diverse strategies for copper resistance, and this review outlines what is known about bacterial copper resistance mechanisms and their genetic regulation.

Amino Acid Sequence↗

PubMed1991

A complex family of class-II restriction endonucleases, DsaI-VI, in Dactylococcopsis salina.

A series of class-II restriction endonucleases (ENases) was discovered in the halophilic, phototrophic, gas-vacuolated cyanobacterium Dactylococcopsis salina sp. nov. The six novel enzymes are characterized by the following recognition sequences and cut positions: 5'-C decreases CRYGG-3' (DsaI); 5'-GG decreases CC-3' (DsaII); 5'-R decreases GATCY-3' (DsaIII); 5'-G decreases GWCC-3' (DsaIV); 5'-decreases CCNGG-3' (DsaV); and 5'-GTMKAC-3' (DsaVI), where W = A or T, M = A or C, K = G or T, and N = A, G, C or T. In addition, traces of further possible activity were detected. DsaI has a novel sequence specificity and DsaV is an isoschizomer of ScrFI, but with a novel cut specificity. A purification procedure was established to separate all six ENases, resulting in their isolation free of contaminating nuclease activities. DsaI cleavage is influenced by N6-methyladenine residues [derived from the Escherichia coli-encoded DNA methyltransferase (MTase) M.Eco damI] within the overlapping sequence, 5'-CCRYMGGATC-3'; DsaV hydrolysis is inhibited by a C-5-methylcytosine residue in its recognition sequence (5'-CMCNGG-3'), generated in some DsaV sites by the E. coli-encoded MTase, M.Eco dcmI.

Base Sequence↗

PubMed1991

Bacterial resistances to mercury and copper.

Heavy metals are toxic to living organisms. Some have no known beneficial biological function, while others have essential roles in physiological reactions. Mechanisms which deal with heavy metal stress must protect against the deleterious effects of heavy metals, yet avoid depleting the cell of a heavy metal which is also an essential nutrient. We describe the mechanisms of resistance in Escherichia coli to two different heavy metals, mercury and copper. Resistance of E. coli to mercury is reasonably well understood and is known to occur by transport of mercuric ions into the cytoplasmic compartment of the bacterial cell and subsequent reductive detoxification of mercuric ions. Recent mutational analysis has started to uncover the mechanistic detail of the mercuric ion transport processes, and has shown the essential nature of cysteine residues in transport of Hg(II). Resistance to copper is much less well understood, but is known to involve the increased export of copper from the bacterial cell and modification of the copper; the details of the process are still being elucidated. Expression of both metal resistance determinants is regulated by the corresponding cation. In each case the response enables the maintenance of cellular homeostasis for the metal. The conclusions drawn allow us to make testable predictions about the regulation of expression of resistance to other heavy metals.

Amino Acid Sequence↗

PubMed1991

hairy gene function in the Drosophila eye: normal expression is dispensable but ectopic expression alters cell fates.

The regulatory gene hairy is expressed and required during early embryogenesis to control segmentation gene expression properly and during larval and pupal development to control the pattern of certain adult sensory structures. We have found the hairy protein to be expressed transiently during two stages of eye imaginal disc development, including all cells immediately anterior to the morphogenetic furrow that traverses the developing eye disc, and again in the presumptive R7 photoreceptor cells of the developing ommatidia. This pattern is conserved in a significantly diverged Drosophila species. We show that, surprisingly, ommatidia formed by homozygous hairy- mutant clones are apparently normal, indicating that hairy function in the eye is dispensable. However, we do find that ectopic expression of hairy causes numerous structural abnormalities and the alteration of cell fates. Thus, proper regulation of hairy is still essential for normal eye development. We suggest that the loss of hairy function may be compensated by other regulatory proteins, as has been observed previously for several structurally and functionally related genes involved in sensory organ development. The effects of ectopic hairy expression may result from interactions with proneural genes involved in the development of the eye and other sensory organs.

Animals↗

PubMed1991

Molecular characterization of the gor gene encoding glutathione reductase from Pseudomonas aeruginosa: determinants of substrate specificity among pyridine nucleotide-disulphide oxidoreductases.

In order to investigate the basis of functional diversity among the pyridine nucleotide-oxidoreductases the gor gene from Pseudomonas aeruginosa PAO, which encodes glutathione reductase, was analysed. The P. aeruginosa gor gene was identified by hybridization with a short DNA sequence from the gene encoding mercuric reductase in transposon Tn501. The gene was cloned, sequenced and overexpressed in Escherichia coli. Expression of the gene enabled rescue of an E. coli gor- mutant, confirming the identity of the cloned gene. The predicted sequence of the gene product showed homology with other members of the pyridine nucleotide-disulphide oxidoreductase family, and allowed determination of positions that may be involved in substrate specificity. These predictions provided information on the relationship of sequence to function, independently of structural data used in previous studies.

Amino Acid Sequence↗

PubMed1991

Erdheim-Chester disease. Case report with autopsy findings.

Erdheim-Chester disease is a rare pathologic entity characterized by symmetrical radiodensities in the metaphyseal and the diaphyseal portions of the long bones. Fibrosis, osteoblastic cortical bone deposition, and fibroxanthomatous granulomas with lipid-laden macrophages and multinucleated giant cells, which have a particular tropism for connective and adipose tissues, are the pathologic hallmarks. To our knowledge, 27 cases have been reported in the literature since the entity was first described in 1930. Protean clinical features range from a focal and asymptomatic process to a multisystemic infiltrative disease. We describe the clinical course of a new case and review the extensive pathologic findings at autopsy, including those demonstrated by light and electron microscopy and cytochemical and immunocytochemical studies.

Adipose Tissue↗

PubMed1990

Site-specific insertion and deletion mutants in the mer promoter-operator region of Tn501; the nineteen base-pair spacer is essential for normal induction of the promoter by MerR.

We have made site-specific mutations in the promoter-operator region of the mercury-resistance (mer) operon of transposon Tn501. Mutations were selected to alter the spacing between the -10 and -35 promoter elements without altering the sequence of a 7 bp dyad symmetrical sequence, which is the site of binding of the regulatory protein, MerR. (MerR acts as a repressor in the absence of mercuric salts and as an inducer in their presence, and binds to the same site in each case). Transcription from the mutant promoters was measured in vivo in the presence and absence of MerR and of mercuric salts; and the relative affinities of the mutant promoters for partially purified MerR were determined in vitro by gel-shift assay in the presence and absence of mercuric salts. The 19 bp spacer was found to be essential for correct induction and repression of the operon; a spacer size of 20 or 21 bp prevents induction, and a spacer size of 18 or 17 bp causes the promoter to be highly active under all conditions. Double mutations, which alter the position of the 7 bp dyad relative to the -10 and -35 sequences without altering their spacing prevent induction by the MerR-Hg(II) complex, demonstrating the tight constraints on the positions of MerR and RNA polymerase in the transcriptional complex. The data are compatible with a model for induction of the mer promoter involving a local conformational change in the DNA structure caused by the MerR-Hg(II) complex.

Bacterial Proteins↗

PubMed1990

Cardiovascular properties of LF 2.0254, a new potent vasoselective calcium channel blocker with a slow onset of action.

The effects of LF 2.0254, a new 1,4-dihydropyridine derivative, were studied in rabbit aorta stimulated by various contractile agents and in isolated guinea pig atria. LF 2.0254 inhibited in a time-dependent fashion K(+)- and CA2(+)-induced contractions of rabbit aorta with respective IC50 of 2.7 nM and 1.7 nM. An action of LF 2.0254 at the voltage operated calcium channel was consistent with the finding that LF 2.0254 antagonized 45Ca2(+)-uptake induced by depolarisation of smooth muscle, and since contractile responses evoked by (-) norepinephrine and the calcium ionophore A23187 were insensitive to the drug. In isolated paced left atria and spontaneously beating right atria of guinea pig, LF 2.0254 added for 60 min at 1 microM only slightly decreased the contractile force and beating rate. In anesthetized open-thorax dogs, LF 2.0254 (1 to 100 micrograms/kg, iv) dose-dependently lowered systemic blood pressure and increased cardiac output with a slower onset of action than nifedipine. LF 2.0254 and nifedipine decreased total peripheral, coronary, femoral and vertebral resistance. In marked contrast to nifedipine, LF 2.0254 induced only a slight decrease in left ventricular dP/dt. In conscious hypertensive dogs LF 2.0254 (0.1 and 0.3 mg/kg per os) decreased blood pressure and concomitantly increased heart rate and plasma renin activity. It is concluded that LF 2.0254 differ markedly from nifedipine in its more gradual onset of action and greater selectivity for the vasculature with respect to the myocardium.

Anesthesia↗

PubMed1990

A prospective evaluation of a simplified captopril test for the detection of renovascular hypertension.

Renovascular hypertension is potentially curable but of low prevalence. A previous retrospective study has demonstrated the use of a potentiated increase in plasma renin activity after captopril administration as a diagnostic test for renovascular hypertension; this requires two blood samples for plasma renin activity determination and three inclusive criteria for a positive test result. We applied this test prospectively to screen 100 hypertensive patients for renovascular hypertension. We evaluated 29 patients with renovascular hypertension; the remainder were diagnosed as having essential hypertension. In our patient population, a postcaptopril plasma renin activity of 5.7 ng of angiotensin per milliliter per hour (ngAl.mL-1.h-1) or greater had a 100% sensitivity and an 80% specificity for renovascular hypertension. An absolute increase in plasma renin activity with captopril of 4.7 ngAl.mL-1.h-1 or greater had a lower sensitivity of 90% and a specificity of 87%, whereas a fractional increase in plasma renin activity after captopril of 150% or higher had the lowest sensitivity of 69% and a specificity of 86%. A subgroup analysis of 38 patients who were receiving diuretic therapy demonstrated that the test sensitivity was unchanged but the specificity was reduced. In conclusion, a single postcaptopril plasma renin activity value of 5.7 ngAl.mL-1.h-1 or greater is a simplified screening test for renovascular hypertension, with excellent sensitivity and acceptable specificity. This test is well tolerated, inexpensive, and easy to perform.

Captopril↗

PubMed1989

Regulation of transcription in Escherichia coli from the mer and merR promoters in the transposon Tn501.

We report studies on deletion mutants of the regulatory region of the mercuric ion resistance (mer) genes of transposon Tn501, isolated from Pseudomonas aeruginosa. Transcription of the mer genes in Escherichia coli from the promoter Pmer is regulated both positively (in the presence of mercuric salts) and negatively (in their absence) by the product of the merR gene. The merR gene is transcribed divergently with respect to the other mer genes, and negatively regulates its own synthesis. The experiments described here suggest that both positive and negative regulation by MerR, as well as its autoregulation, are largely mediated by MerR binding to a single site on DNA. This site contains a hyphenated dyad symmetrical sequence centred 24 base-pairs before the start of the mer transcript. Additional sites may be involved in full repression of the mer and merR promoters. Studies on deletions of the Pmer promoter show that the -35 sequence is not required for constitutive activity. An alternative -10 sequence may be used in the absence of the -35 and normal -10 sequences, but the properties of a point mutation indicate that, in the presence of the -35 sequence, the normal -10 sequence is required for promoter activity. A model for the regulation of expression of the mercury resistance genes by mercuric ions and the MerR protein is discussed.

Base Sequence↗

PubMed1989

Cardiovascular actions and tissue-converting enzyme inhibitory effects of chronic enalapril and trandolapril treatment of spontaneously hypertensive rats.

The angiotensin I-converting enzyme (CE) inhibitors, trandolapril (RU 44570) and enalapril were administered for 2 weeks to SHR at doses (3 and 10 mg/kg/day, p.o., respectively) that produced important and comparable inhibitions of plasma (84 and 88%), aorta (97 and 88%), and atrium (89 and 82%) CE activities. At these doses, the inhibitory effects of trandolapril and enalapril were nonetheless different on CE in heart ventricle (58 and 72%) and kidney (45 and 85%). In addition, although both drugs reduced blood pressure (BP) and heart hypertrophy, trandolapril was more potent despite a lower dose-ratio. All these parameters were reexamined 1, 3, and 8 days after drug withdrawal: BP returned to control levels within 3 days in enalapril-treated rats, whereas it remained low for at least 8 days in trandolapril-treated animals. The reduction of heart hypertrophy owing to trandolapril was still present 8 days after drug discontinuation. On cessation of treatment, plasma CE increased above controls, ventricle CE returned to control levels within 3 days, whereas atrial and aortic CE activities remained inhibited for 8 days in the enalapril group. In contrast, in trandolapril-treated rats, CE activities in serum and tissues were still inhibited after 8 days. These results demonstrate that at the doses used trandolapril is more potent and longer acting than enalapril.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1989

[Hypertensive myocardial hypertrophy and rhythm disorders: 2 possible origins].

It has been suggested that complex ventricular arrhythmias commonly occur in hypertensive patients with left ventricular hypertrophy. We have previously demonstrated that coronary artery ligation in anesthetized spontaneously hypertensive rats (SHR) and their normotensive controls (WKY) resulted in a significantly increased incidence and duration of ventricular fibrillation in SHR compared with WKY. The object of the present study was to characterize the structural and electrophysiological abnormalities in hypertrophied hearts, associated with the occurrence of arrhythmias. We used a double tissue bath in which a ventricular strip was exposed simultaneously to normal and to altered conditions (low pH, hypoxia and high potassium). Electrical activity recorded using standard micro-electrode techniques showed the occurrence of arrhythmias in all preparations and the development of major alterations in conduction (a conduction block appeared at 11 +/- 1 mn in SHR vs 16 +/- 1 mn in WKY, p less than 0.05), and maximal upstroke velocity (Vmax values before and 3 mn after the beginning of ischemia were 229 +/- 12 to 46 +/- 7 v/s for the SHR and 227 +/- 10 to 106 +/- 12 v/s for the WKY; p less than 0.001). These changes were associated in hypertrophied ventricles with a marked sub-endocardial collagen fibrosis as estimated by the use of automated image analysis (subendocardial collagen density = 4.39 +/- 0.34 p. 100 in SHR vs 1.66 +/- 0.15 p. 100 in WKY; p less than 0.001). Action potential duration measured using conventional glass micro-electrodes in a single chamber tissue bath revealed a highly significant difference (p less than 0.001) in APD 90 p. 100 of papillary muscles between SHR (114.7 +/- 2.8 ms) and WKY (76.9 +/- 1.7 ms). The addition of tetra-ethylammonium to block potassium channels induced triggered activity arising from early afterdepolarizations only in muscles hypertrophied SHR hearts.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1989

Lack of association between hypothyroidism and chondrocalcinosis.

The association between hypothyroidism and calcium pyrophosphate dihydrate deposition disease (CPPD) is controversial. We studied the prevalence of chondrocalcinosis, the roentgenographic marker of CPPD by obtaining anteroposterior knee roentgenograms in 49 hypothyroid patients over the age of 40 years, and compared them with knee roentgenograms in 31 euthyroid patients matched for age and sex. Only 2 hypothyroid patients and one euthyroid control had knee chondrocalcinosis. Our results indicate that hypothyroid patients have no greater prevalence of chondrocalcinosis compared to euthyroid subjects. There are also no difference in the degree and prevalence of osteoarthritis between the 2 groups, although hypothyroid patients may have a higher prevalence of periarticular osteopenia.

Adult↗

PubMed1988

Investigation of sequence homology in a group of type-II restriction/modification isoschizomers.

We have dissected the cloned PstI M and R genes to make DNA hybridization probes spanning most of the sequence. These subclones, and also the intact sequence, were used to search for nucleic acid homology by Southern blot in the DNA from twelve organisms which produce PstI isoschizomers. One of these probes, a 206-bp fragment from the N-terminal domain of the endonuclease, showed significant hybridisation in four strains (Escherichia coli strains RFL48, RFL49 and RFL83, and Streptomyces albus P). No significant hybridisation was detected with other parts of the PstI sequences. We have used computer similarity searches to look for homology between the PstI proteins and the known sequences of other type-II systems that recognise different sites. We postulate a possible recognition domain within the M.PstI methyltransferase based on similarity to the M.PaeR7 and M.TaqI methyltransferases.

Amino Acid Sequence↗

PubMed1988

Angiotensin-converting enzyme inhibition, anti-hypertensive activity and hemodynamic profile of trandolapril (RU 44570).

Trandolapril (RU 44570), a new non-sulfhydryl angiotensin-converting enzyme (ACE) inhibitor chemically related to enalapril, and its diacid (RU 44403), were investigated for their ability to inhibit angiotensin-converting enzyme. Trandolapril attenuated angiotensin I (Ang I)-induced pressor responses following i.v. administration to rats and dogs with ID50 values of 13.1 +/- 1.3 and 21.1 +/- 2.3 micrograms/kg. RU 44403 produced corresponding values of 9.9 +/- 0.7 and 7.2 +/- 2.3 micrograms/kg. Trandolapril (3-300 micrograms/kg) produced a dose-related attenuation of Ang I-induced pressor responses (ID50 30 micrograms/kg) following oral administration to rats. Oral administration of trandolapril (30-1000 micrograms/kg) to dogs inhibited Ang I pressor responses for over 6 h. The depressor action of bradykinin in the rat was potentiated by i.v. trandolapril and RU 44403 with ED50 values of 5.5 +/- 0.8 and 4.9 +/- 0.3 micrograms/kg respectively. Trandolapril was 2.3-10-fold more potent than enalapril in all experiments, depending on species or route of administration. RU 44403 and MK 422 were approximately equipotent, implying that trandolapril was more readily hydrolysed than enalapril. Trandolapril (0.3-30 mg/kg) produced dose-related, long-lasting (greater than 24 h) reductions in blood pressure (BP) in spontaneously hypertensive rats (SHR) following oral administration. The anti-hypertensive effect was potentiated significantly in hydrochlorothiazide-pretreated SHR when the plasma renin activity was increased. Enalapril was 10-fold less potent than trandolapril in reducing BP. The anti-hypertensive action of trandolapril (3 mg/kg) was abolished in SHR that were bilaterally nephrectomized 24 h beforehand, but was maintained in SHR pretreated by indomethacin (5 mg/kg p.o.). Trandolapril (1 mg/kg i.v.) produced a modest and transient reduction in BP in anesthetized dogs. Trandolapril produced dose-related (30-1000 micrograms/kg) reductions in BP, total peripheral resistance and heart work in dogs pretreated with hydrochlorothiazide to increase plasma renin activity.

Angiotensin I↗

PubMed1988

Differential effects of oral trandolapril and enalapril on rat tissue angiotensin-converting enzyme.

Trandolapril (3-100 micrograms/kg) and enalapril (10-300 micrograms/kg) were administered orally to conscious rats. Angiotensin-converting enzyme (CE) activity was inhibited in serum, heart ventricle, renal inner cortex, lung, aorta, adrenal cortex and adrenal medulla, but not in the striatum. Inhibition was maximal at 2 h and with trandolapril was maintained for 24 h. Blood pressure and heart rate were not affected by either compound. Trandolapril was 6-10-fold more potent than enalapril. Differences between trandolapril and enalapril in CE inhibition observed in heart ventricle, adrenal cortex and medulla could be due to the presence of more than one type of CE or CE-like activity.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1988

Comparison of the effects of the ace inhibitors trandolapril and enalapril on phlogogen induced foot pad oedema in the rat.

Two angiotensin converting enzyme (ACE) inhibitors, trandolapril and enalapril, were compared for their effects on rat food-pad oedema induced by carrageenin, bradykinin, dextran and platelet activating factor (PAF). Trandolapril (0.03-30.0 mg/kg, per os) potentiated carrageenin-induced oedemas. Enalapril produced the same effect at 3-10 fold higher doses (0.3-30.0 mg/kg per os). Both ACE inhibitors were equiactive in potentiating bradykinin-induced oedema. Neither compound affected dextran-induced oedema. In marked contrast PAF-induced oedema was reduced by both ACE inhibitors, trandolapril being approximately 10 fold more active than enalapril. The observed differences in potency between the two ACE inhibitors corresponded with their previously described actions on inhibition of plasma and tissue ACE and in inducing hypotension. The results suggest a crucial role of kinins in the oedemagenic response to carrageenin. The reason why the ACE inhibitors reduced PAF-induced oedema is not clear, but could involve peripheral vasodilation.

Animals↗