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R Dixon

Publications and source records attributed to R Dixon.

At least 145 records · Page 8Linked to original sources
PubMed1984

Tandem promoters determine regulation of the Klebsiella pneumoniae glutamine synthetase (glnA) gene.

Transcription of the structural gene for glutamine synthetase (glnA) in Klebsiella pneumoniae is controlled by the nitrogen regulatory genes ntrA, ntrB and ntrC. The nucleotide sequence of the regulatory region upstream of the glnA gene is reported here. High resolution S1 mapping of in vivo transcripts indicates that the regulatory region contains tandem promoters separated by 100 nucleotides. Measurements of beta-galactosidase activities determined in vivo from glnA-lac fusions suggest that the upstream promoter (for RNA2) is negatively regulated by the ntrBC gene products whereas transcription from the downstream promoter (for RNA1) is positively activated by the ntrA gene product in the presence of either the ntrBC or the nifA genes. The nucleotide sequence of the upstream promoter resembles the consensus sequence for E. coli promoters, whereas the downstream promoter shows homology with the nitrogen fixation (nif) promoters of K. pneumoniae.

Base Sequence↗
PubMed1984

Positive and negative control of the glnA ntrBC regulon in Klebsiella pneumoniae.

The nitrogen regulation system of Klebsiella pneumoniae comprises three genes ntrA, ntrB and ntrC. We have found that the glnA ntrBC regulon in K. pneumoniae has a similar structure, P1 glnA P2 ntrBC, to that in other enterobacteria. We have constructed plasmids with glnA and ntrB translational lacZ fusions and measured expression from P1 and/or P2 in a K. pneumoniae delta (glnA ntrBC) background with different plasmids which provided the ntrB, ntrC or nifA products in trans. These studies demonstrate that, as in other enterobacteria, transcription of ntrBC is from P1 under nitrogen deficiency and from P2 under nitrogen excess. The P1 promoter can be regulated both positively and negatively; activation requires both ntrB and ntrC products but the ntrC product is sufficient to repress. The P2 promoter is negatively controlled by the ntrC product. Comparison of the modes of regulation of P1 and P2 with regulation of the promoter of the nifLA operon leads us to suggest that these may represent three different classes of ntr-regulated promoters. Although previous studies have shown that the nifA product can substitute for the ntrC product as a positive activator of transcription for a number of promoters, we find that nifA product cannot substitute for ntrC product as a negative regulator at P1 or P2.

Gene Expression Regulation↗
PubMed1984

Nalmefene: radioimmunoassay for a new opioid antagonist.

A specific radioimmunoassay (RIA) has been developed for the quantitation of a new opioid antagonist, nalmefene, in human plasma. The method employs a rabbit antiserum to an albumin conjugate of naltrexone-6-(O-carboxymethyl)oxime and [3H]naltrexone as the radioligand. Assay specificity was achieved by extraction of nalmefene from plasma at pH 9 into ether prior to RIA. The procedure has a limit of sensitivity of 0.2 ng/mL of nalmefene using a 0.5-mL sample of plasma for analysis. The intra- and interassay coefficients of variation did not exceed 5.6 and 11%, respectively. The specificity of the RIA was established by demonstrating excellent agreement (r = 0.99) with a less sensitive and more time consuming HPLC procedure in the analysis of clinical plasma samples. The use of the RIA for the pharmacokinetic evaluation of nalmefene is illustrated with plasma concentration profiles of the drug in humans following intravenous and oral administration.

Humans↗
PubMed1984

Rat hepatic cytochrome P-450 isozyme specificity for the metabolism of the steroid sulfate, 5 alpha-androstane-3 alpha, 17 beta-diol-3,17-disulfate.

Nine rat hepatic microsomal cytochromes P-450 (P-450a-P-450i) have been purified to electrophoretic homogeneity and assayed as potential catalysts of 15 beta-hydroxylation of 5 alpha-androstane-3 alpha,17 beta-diol-3,17-disulfate in a reconstituted system containing NADPH-cytochrome c reductase and dilauroylphosphatidylcholine. Of the nine isozymes, only cytochrome P-450i, which is present in adult female but not adult male rats, catalyzes the hydroxylation of 5 alpha-androstane-3 alpha,17 beta-diol-3,17-disulfate. The reaction has an absolute requirement for cytochrome P-450i, NADPH-cytochrome c reductase, and NADPH, as well as a marked dependence on dilauroylphosphatidylcholine. Under optimal conditions, the Km,app was 69 microM, and the Vmax was 7.8 nmol min-1 nmol cytochrome P-450i-1. The affinity of cytochrome P-450i for the substrate, as expressed by the apparent spectral dissociation constant (Ks,app), was 20 microM. This female-specific isozyme had very low catalytic activity toward testosterone, and the metabolite profile from testosterone was distinct compared to the profiles obtained with the other eight isozymes. The results with androstane disulfate indicated that cytochrome P-450i is responsible for the sex-specific microsomal 15 beta-hydroxylase system in adult female rat liver, originally described by Gustafsson and Ingelman-Sundberg [(1974) J. Biol. Chem. 249: 1940-1945].

Aging↗
PubMed1984

Diazepam and desmethyldiazepam plasma concentrations in chronic anxious outpatients.

Within the framework of a large-scale clinical study on the effect of diazepam in chronic anxiety, diazepam (D) and desmethyldiazepam (DD) plasma concentrations were determined frequently. Significant relationships were found between the clinical effect and the plasma concentrations of D and DD, respectively; a curvilinear relationship resulted if the dosage was disregarded, but within the individual dosage groups the relationship was found to be linear. For these computations, the daily diazepam dose was treated as a covariable in a factorial analysis of variance approach. It was found, in addition, that the daily diazepam dose was one of the most significant predictors of the plasma concentration of D or DD, respectively. The steady state plasma concentrations were highest in patients experiencing an exacerbation of their conditions of anxiety if they were returned to placebo after 14 to 22 weeks of diazepam medication. The lowest steady state concentrations were found with those patients who showed withdrawal symptoms under these conditions.

Adult↗
PubMed1983

Positive control and autogenous regulation of the nifLA promoter in Klebsiella pneumoniae.

The nitrogen fixation (nif) genes of Klebsiella pneumoniae are specifically regulated by the products of the nifLA operon. We have located the promoter of this operon, and identified sequences required for nifLA transcription. Transcription from this promoter is shown to be positively regulated by the ntrC gene product (which coordinates the expression of many operons required for nitrogen assimilation) and also autogenously by the product of the nifA gene.

Base Sequence↗
PubMed1983

Corynebacterium parvum versus BCG adjuvant immunotherapy in human malignant melanoma.

One-hundred and sixteen patients with Stage I and Stage II malignant melanoma were randomized to treatment with either Bacillus Calmette-Guerin (BCG) (Tice) or subcutaneous Corynebacterium parvum (Burroughs-Wellcome). Life table analysis failed to reveal a difference between these two forms of treatment in 68 Stage I patients. The relapse rate was significantly reduced in Stage II patients treated with C. parvum.

BCG Vaccine↗
PubMed1983

In vitro exposure of male and female mice gametes to cadmium chloride during the fertilization process, and its effects on pregnancy outcome.

The effect of cadmium chloride (Cd) on gamete fusion in vitro was evaluated, with further observations of the embryonic development and assessment of the pregnancy outcome of the in vitro fertilized mice. Oocytes were recovered from superovulated B6C3F1 females. Of 1210 control oocytes, 53.2% cleaved into two-cell stage embryos. Of these, 46.6% developed into blastocyst stage embryos which were then surgically transferred to pseudopregnant female CD-1 mice. Of a total of 63 implanted embryos, 8 (12.7%) developed in utero to live fetuses. Teratological examinations of these "test-tube" mice revealed no signs of abnormalities caused by in vitro culture. Male and female gametes were exposed to 0.4, 0.8, or 1.6 microM of Cd and a decrease in sperm motility was noted in the 1.6 microM group. Nevertheless, even in the highest concentration used, 56.4% of the ova cleaved into the two-cell stage, thus indicating no effect of Cd on initial gamete interaction. Gametes that had been treated with 0.4 and 0.8 microM Cd developed to blastocysts at rates comparable to that of the controls. In the 1.6 microM group, however, only one (3.2%) of the two-cell embryos developed to the blastocyst stage. Blastocysts from 0.4 microM Cd-treated gametes were then transferred to surrogate dams. Statistically significant blastocyst losses were recorded during the implantation period, whereas the pregnancy rate and the numbers of resorbed and live fetuses, were comparable to those of the controls. The offspring exhibited no malformations, and their body weights remained within the control values.

Animals↗
PubMed1983

Levorphanol: pharmacokinetics and steady-state plasma concentrations in patients with pain.

Plasma concentrations of the narcotic analgesic, levorphanol, have been determined following i.v., i.m. and oral administration of therapeutic doses of the drug to patients with pain. In two patients who received single i.v. doses of levorphanol the plasma concentration-time profile in each subject was best described by a triexponential decline of the concentrations with terminal half-lives (t 1/2) of about 11 hr. Following i.m. and oral administrations, peak plasma concentrations of intact drug were generally reached after about 0.5 and 1 hr, respectively. Conjugated (beta-glucuronidase labile) levorphanol appeared rapidly in plasma following all routes of administration and quickly reached concentrations which were 5 to 10 fold higher than the intact drug. Effective analgesic steady-state concentrations of levorphanol in patients receiving a wide range of chronic oral and i.m. dosages of the drug ranged from about 10 to 100 ng/ml and these concentrations showed no apparent correlation with either the dose or the subjective analgesic response achieved. The latter observations are probably a reflection of extensive and variable inter-subject "first-pass" metabolism of the drug combined with different degrees of pharmacologic tolerance at the receptor level. However, in the non-tolerant patient it appears that a plasma concentration of about 10 ng/ml is associated with a positive analgesic effect. Furthermore it seems that analgesia is often maintained within a narrow plasma concentration range for each subject in that relatively small decreases in plasma concentration in some patients may be associated with either mild or severe pain. Plasma protein binding at steady-state in 10 patients averaged 40 +/- 2.6%. Concentrations of the drug in the cerebrospinal fluid of 2 patients studied were 60 to 70% of the corresponding plasma levels of the drug.

Humans↗
PubMed1983

Nalmefene: quantitation of a new narcotic antagonist in human plasma using high performance-liquid chromatography with electrochemical detection.

A high performance-liquid chromatographic procedure employing electrochemical detection (LCEC) has been developed for the quantitation of a new narcotic antagonist, nalmefene, in human plasma. Following extraction of the plasma at pH9, the extract was chromatographed on a reverse-phase C18 column using naltrexone as an internal standard. An electrochemical detector equipped with a glassy carbon electrode monitored the elution of nalmefene and the internal standard. The method had a limit of sensitivity of 3 ng/ml of nalmefene using a 1 ml sample of plasma and the calibration curve was linear over a range of 3-200 ng/ml. The intra- and inter-assay coefficients of variation did not exceed 6 and 12% respectively over the entire range of the calibration curve. The LCEC method has been used to quantitate the plasma concentrations of nalmefene in man following oral administration of 64 mg of the drug. In one subject, a peak plasma concentration of 58 ng/ml occurred 2 hr after drug administration and declined to 5 ng/ml after 24 hr.

Chromatography, High Pressure Liquid↗
PubMed1982

Cloning of the glnA, ntrB and ntrC genes of Klebsiella pneumoniae and studies of their role in regulation of the nitrogen fixation (nif) gene cluster.

The glnA, ntrB and ntrC genes of Klebsiella pneumoniae have been cloned, on a 12 kb HindIII fragment, into the plasmid pACYC184. In a coupled in vitro transcription/translation system the resultant plasmid, pGE100, directed synthesis of five polypeptides (molecular weights 73, 53, 51, 39, 36 kd) from the cloned fragment. A number of plasmids were derived from pGE100 and studied by complementation analysis and in vitro transcription/translation in order to locate particular genes and identify their products. On the basis of the results presented here, together with previous genetic and physical characterisation of the glnA gene and its product in other enteric bacteria, we propose that the 53 kd polypeptide is the glnA gene product (glutamine synthetase monomer). Two polypeptides (36 kd and 51 kd) were synthesised from a 3 kb region previously defined as glnR. In E. coli and S. typhimurium this region comprises two genes ntrB and ntrC with products of 36 kd and 54 kd respectively. This analogy supports the idea that the 36 kd and 51 kd polypeptides are the products of the K. pneumoniae ntrB and ntrC genes respectively. Comparison of these assignments with the physical map of the region indicates a gene order glnA, ntrB, ntrC. Assessment of the Nif phenotype of a glnA-ntrC deletion strain carrying various clones from pGE100 demonstrated that glnA is not required for expression of the nif regulon and that of the three genes cloned, ntrC alone is sufficient for nif expression.

Cloning, Molecular↗
PubMed1982

The surgical management of thyroid-related upper eyelid retraction.

Excision of Müller's muscle can usually correct thyroid-related upper eyelid retraction. A transcutaneous approach to Müller's muscle was used in 22 eyelids. The findings at surgery included diffuse eyelid scarring, disinsertion of the levator aponeurosis, fat herniation, and changes resembling dermatochalasis. Identification and correction of these factors, complemented anterior resection of Müller's muscle and influenced final eyelid position and cosmesis.

Adult↗
PubMed1982

Adjuvant antiplatelet therapy with aspirin in colo-rectal cancer.

Sixty-six patients with Duke's B2 or C colon or rectal cancer were randomized for treatment with aspirin (ASA), 600 mg, p.o., twice daily x 2 years or placebo (P). Compliance was checked in both groups by random measurement of blood salicylate levels. Fifty-seven patients are currently evaluable. No difference in disease-free (p = .66) or overall survival (p = .90) is present between ASA and P groups. The time at which ASA therapy is started (within 2 or within 4 weeks) following surgery does not affect these results. Aspirin at conventional dosage is ineffective in preventing the appearance of metastases in patients with colo-rectal cancer.

Actuarial Analysis↗
PubMed1982

Randomized trial of aminoglutethimide versus tamoxifen in metastatic breast cancer.

We compared antiestrogen therapy (tamoxifen) with an estrogen suppression regimen (aminoglutethimide-hydrocortisone) in postmenopausal women with metastatic breast carcinoma. Fifteen of 39 patients (38%) who received tamoxifen experienced an objective tumor regression (3 complete, 12 partial remissions), whereas 13 of 36 women (36%) receiving aminoglutethimide responded (one complete remission, 12 partial remissions). The median duration of response was similar. The site of tumor involvement appears to be important in choosing between these hormonal treatments. Aminoglutethimide appears to offer a greater chance of response in patients with bone involvement.

Aminoglutethimide↗