Search PubMed⌕ Search

Biomedical subjects

G McMahon

Publications and source records attributed to G McMahon.

72 records · Page 4Linked to original sources
PubMed1990

Characterization of c-Ki-ras and N-ras oncogenes in aflatoxin B1-induced rat liver tumors.

c-Ki-ras and N-ras oncogenes have been characterized in aflatoxin B1-induced hepatocellular carcinomas. Detection of different protooncogene and oncogene sequences and estimation of their frequency distribution were accomplished by polymerase chain reaction, cloning, and plaque screening methods. Two c-Ki-ras oncogene sequences were identified in DNA from liver tumors that contained nucleotide changes absent in DNA from livers of untreated control rats. Sequence changes involving G.C to T.A or G.C to A.T nucleotide substitutions in codon 12 were scored in three of eight tumor-bearing animals. Distributions of c-Ki-ras sequences in tumors and normal liver DNA indicated that the observed nucleotide changes were consistent with those expected to result from direct mutagenesis of the germ-line protooncogene by aflatoxin B1. N-ras oncogene sequences were identified in DNA from two of eight tumors. Three N-ras gene regions were identified, one of which was shown to be associated with an oncogene containing a putative activating amino acid residing at codon 13. All three N-ras sequences, including the region detected in N-ras oncogenes, were present at similar frequencies in DNA samples from control livers as well as liver tumors. The presence of a potential germ-line oncogene may be related to the sensitivity of the Fischer rat strain to liver carcinogenesis by aflatoxin B1 and other chemical carcinogens.

Aflatoxin B1↗
PubMed1989

Monoexponential analysis of plasma disappearance of 99mTc-DTPA and 131I-iodohippurate: a reliable method for measuring changes of renal function.

Glomerular filtration rate and effective renal plasma flow were measured in 170 subjects using monoexponential analysis of plasma disappearance curves for 99mTc-DTPA and 131I-iodohippurate after single injection. In the current study population, glomerular filtration rate and effective renal plasma flow decreased with increasing age, were less in females than in males, and were less in hypertensives than in normotensives. Differences in glomerular filtration rate according to age and sex in the current study were similar to those reported using traditional creatinine clearance methodology. Monoexponential treatment of plasma isotope disappearance gave reproducible values for both glomerular filtration rate and effective renal plasma flow when measured either during the day or on a daily basis. Intraindividual coefficient of variation was less than 10% for both 99mTc-DTPA and 131I-iodohippurate clearances derived from monoexponential analysis. These results demonstrate that monoexponential analysis of plasma disappearance curves for 99mTc-DTPA and 131I-iodohippurate after a single injection is a useful method for evaluating changes in renal hemodynamics either during chronic drug therapy or acutely after single dose administration.

Adult↗
PubMed1989

The effects of enoximone on renal function in patients with congestive heart failure.

Enoximone is an investigational cardiotonic agent with positive inotropic and vasodilatory properties. In this protocol the effects of enoximone on parameters of renal function in patients (n = 14) with New York Heart Association class II or III congestive heart failure were determined after intravenous (IV) treatment (2 mg/kg) and after chronic oral administration (150 mg t.i.d.), either alone or with added furosemide (40 mg b.i.d.). Glomerular filtration rate (GFR), effective renal plasma flow (ERPF), filtration fraction, mean arterial pressure (MAP), renal blood flow (RBF), and renal vascular resistance (RVR) were determined each time. Plasma volume (PV) was determined at baseline and after oral enoximone and after oral enoximone plus furosemide. Significant reductions in GFR (18%) and ERPF (20%) were observed after IV treatment but not after oral treatment with or without furosemide. MAP also was lowered significantly by 14% after IV administration but not after oral treatments. PV after oral enoximone plus furosemide was reduced significantly (31%) compared with baseline. These results demonstrate that enoximone produces acute reductions in GFR and ERPF when given intravenously but has no effect on parameters of renal function when given orally, either alone or with furosemide.

Adult↗
PubMed1987

Characterization of c-Ki-ras oncogene alleles by direct sequencing of enzymatically amplified DNA from carcinogen-induced tumors.

Activated c-Ki-ras genes in liver tumors from rats exposed to the potent hepatocarcinogen aflatoxin B1 were analyzed to determine the nature of their activation by characterization of two c-Ki-ras alleles present in tumor-derived NIH 3T3 mouse transformants. Using selective hybridization of synthetic oligonucleotides to transformant DNA, we have determined that a single G X C to A X T base transition in either the first or second position of the 12th codon is associated with activation of the gene. Such mutations would lead to amino acid substitutions of aspartate or serine for glycine in the mutant proteins. To confirm these findings, we applied a technique for direct sequence analysis of a 90-base-pair region of the rat c-Ki-ras gene produced by primer-directed enzymatic amplification. Findings produced by this approach, which provides a convenient method to characterize mutations in multiple alleles without the necessity to clone individual genes, confirmed the presence and identity of the 12th codon mutations in the activated oncogene, as initially determined by the oligonucleotide hybridization technique.

Aflatoxin B1↗
PubMed1987

Fate of the DNA in plasmid-containing Escherichia coli minicells ingested by human neutrophils.

Escherichia coli minicells containing the plasmid pSC101 (approximately 10 kb) or pBR322 (approximately 4 kb) were opsonized and incubated with human neutrophils. The neutrophils responded to the minicells as they would to native E coli: they ingested the minicells, discharged their granule contents into the minicell-containing phagosomes, and expressed a respiratory burst. After one hour of incubation, the fate of the ingested plasmid DNA was examined. No DNA degradation was detected by trichloroacetic acid precipitation or agarose gel electrophoresis. Moreover, when pBR322 recovered from ingested minicells was transformed into E coli, no mutations in either of the antibiotic resistance genes carried by the plasmid were detected out of many thousand transformants screened. These findings confirm the surprisingly limited effect of neutrophils on ingested DNA.

Blood Bactericidal Activity↗
PubMed1986

Evaluation of an enkephalin analog in men with castor oil-induced diarrhea.

This study was a parallel, double-blind, placebo-controlled evaluation of acute doses of nifalatide, an enkephalin analog, in subjects with castor oil-induced diarrhea. Seventy-two subjects completed the study. The time to first stool after castor oil administration was significantly greater after the 16 and 48 mg doses of nifalatide as compared with placebo dosing. The same doses of nifalatide also decreased the overall stool frequency, the frequency of abdominal cramping, and the incidence of nausea and vomiting. There were no clinically significant, drug-related changes in the physical examination results, ECG, vital signs, or clinical laboratory parameters. The only increased adverse experiences that appeared to be related to the drug were dizziness and mild dry mouth.

Administration, Oral↗
PubMed1986

Identification of an activated c-Ki-ras oncogene in rat liver tumors induced by aflatoxin B1.

Weanling male Fischer rats were administered 40 intraperitoneal injections of aflatoxin B1 (25 micrograms per animal per day) over a 2-month period. This chronic dosing regimen resulted in the sequential formation of hyperplastic foci, preneoplastic nodules, and hepatocellular carcinomas in all of the animals treated. The presence of transforming DNA sequences was detected by formation of anchorage-independent foci after transfection of tumor-derived DNA in NIH 3T3 mouse fibroblasts. Transfection of genomic DNA isolated from individual tumors from eight animals resulted in specific transforming activities ranging from 0.05 to 0.2 foci per micrograms of DNA. Primary transfectant DNAs were analyzed by Southern blot hybridization with DNA probes homologous to c-Ha-ras, c-Ki-ras, and N-ras oncogenes. A highly amplified c-Ki-ras oncogene of rat origin was detected in transformants derived from tumors in two of the eight animals tested. There was no evidence to suggest the presence of c-Ha-ras or N-ras sequences in any of the transformants. Analysis of primary liver tumor DNA showed no Ki-ras DNA amplification when compared to control liver DNA samples. Increased levels of c-Ki-ras p21 proteins were detected in 3T3 transformants containing activated rat c-Ki-ras genes. The presence of c-Ki-ras sequences of rat origin capable of inducing transformed foci can be taken as evidence that the c-Ki-ras gene has been activated in the primary liver tumors.

Aflatoxin B1↗
PubMed1985

Ca2+, Mg2+-dependent endonuclease activity in different subpopulations of spleen cells from normal and erythroleukemic mice.

We have detected Ca2+, Mg2+-dependent endonuclease activity in spleen cells of normal, Friend erythroleukemic, and phenylhydrazine-treated mice. When nuclei were isolated and incubated in the presence of Ca2+ and Mg2+ ions, the activity resulted in the production of 3'-OH termini in the cellular DNA and the release of chromatin due to internucleosomal DNA fragmentation. This enzyme activity was chromatin-bound and could be extracted from chromatin in an active form in 0.35 M KCl. The majority of endonuclease activity from erythroleukemic spleens was present in nuclei of precursor erythroid cells of low buoyant density (1.025-1.05 g/ml). Uninfected normal splenic tissue contained an endonuclease activity which was almost entirely confined to a B-lymphocyte population of high buoyant density (greater than 1.07 g/ml). Erythroid cell-enriched spleens from phenylhydrazine-treated mice exhibited a distribution of endonuclease activity in cells at low and high densities reflecting a mixture of erythroid and lymphoid cells. Cloned erythroleukemic cell lines propagated in vitro lacked cells of low density and showed no detectable endonuclease activity. However, nuclei from these cell lines were susceptible to exogenously added endonuclease extracted from erythroleukemic spleen cells. These same cell lines propagated as subcutaneous tumors contained endonuclease activity and a morphologically-similar low-density cell population which accounted for the endonuclease activity in these tumors. Nuclei from cloned lymphoid cell lines, representing different B-lymphocyte phenotypes, showed differences in the presence of endonuclease activity. Among the cell lines tested, only those expressing late B-cell markers showed detectable endonuclease activity.

Animals↗
PubMed1984

Induction of a Ca2+, Mg2+-dependent endonuclease activity during the early stages of murine erythroleukemic cell differentiation.

A Ca2+, Mg2+-dependent endonuclease activity was detected in erythroleukemic cells undergoing differentiation in vitro in response to induction by dimethyl sulfoxide (Me2SO) or hexamethylene-bis-acetamide (HMBA). The endonuclease activity was demonstrated in isolated nuclei within 6 hr after the addition of inducer, reached maximum levels between 24 and 48 hr, and returned to control levels within 72 hr. The activity caused single strand breaks in high molecular weight native DNA, which could be labeled at exposed 3'-OH termini with Escherichia coli DNA polymerase I and radiolabeled nucleotides. Alkaline elution studies revealed DNA fragmentation that appeared coincident with the presence of the endonuclease activity. The detection and levels of single strand DNA breakage correlated with induction of terminal differentiation by Me2SO or HMBA. Induction of the endonuclease activity was reversible: depletion of Me2SO from the growth medium after treatment for 6 and 18 hr led to a rapid decrease in the level of activity. Removal of the inducer prevented terminal differentiation, a finding that strongly suggests the endonuclease activity is present during the precommitment phase of differentiation. DNA fragmentation was not observed in cells incubated with hemin, which has been shown previously to increase the cytoplasmic level of globin mRNA without causing commitment to terminal maturation. Me2SO did not induce the endonuclease activity or DNA fragmentation in an uninducible Friend cell line.

Animals↗
PubMed1983

Effect of hydrostatic pressure on translational fidelity.

We have used the application of hydrostatic pressure to modify the misreading of polyuridylate template. Pressure was used to test ribosomes isolated from Escherichia coli strains containing mutations in the S12 ribosomal protein which lead to streptomycin-resistance and -dependence. The incorporation of phenylalanine into polypeptide, at a given pressure, was found to vary with the source of ribosomes and was found to correlate with S12-dependent changes in rates of incorporation suggesting a role of the S12 ribosomal protein in the pressure effect. Streptomycin partially alleviated the increased pressure-resistance in those cases where control rates of incorporation were found to be stimulated by the addition of streptomycin. In contrast, the misincorporation of isoleucine was substantially more sensitive to pressure application, regardless of ribosome source or the presence of streptomycin. These results suggest that the application of hydrostatic pressure affects at least two distinct ribosomal reactions important to the discrimination of these two amino acids.

Escherichia coli↗
PubMed1982

Light and electron microscopy of liver in hyperlipoproteinemic patients under long-term gemfibrozil treatment.

The effects of long-term gemfibrozil (Lopid) therapy on human liver structure are not known. Studies of this nature are becoming essential in determining the risk/benefit ratio since gemfibrozil is an effective agent for the control of hyperlipoproteinemia types IIa, IIb, and IV. Particularly, gemfibrozil is effective when dietary management or available therapeutic control fail to reduce serum cholesterol and triglycerides as well as normalizing the lipoprotein pattern. Percutaneous liver biopsies of 9 patients on long-term gemfibrozil therapy were evaluated by light microscopy, interference contrast optics and transmission electron microscopy. The distribution of patients according to lipoprotein phenotype was 3 Type IIa, 3 Type IIb, and 3 Type IV. Their lipoprotein patterns approached normal and the serum lipids were controlled during gemfibrozil therapy. By light microscopy, the lobular architecture and other parameters were within normal limits. Varying degrees of fatty change were found as would be expected. No preferential lobular disposition of the fat globules was evident. Coalescence of fat droplets, nuclear displacement and fatty cysts were noted. Differential interference contrast microscopy revealed several degrees of contrast amplitude in these droplets suggesting a heterogeneous lipid deposition in hepatocytes. The subcellular analysis revealed a moderate degree of glycogen deposition, absence of nuclear abnormalities and unremarkable mitochondria; the rough endoplasmic reticulum was not significantly altered and smooth surfaced membranes appeared proliferated. Detailed analysis of the peroxisome population showed matrix rarefaction, marginal plate formation and spurious densities though no significant proliferation occurred. Distribution of peroxisomes in hepatocytes varied widely from cell to cell and in different lobular areas. This study confirmed the association of hepatic fatty change with hyperlipoproteinemia irrespective of the pattern observed in circulating lipoproteins. Peroxisome proliferation, as seen in rodents when receiving gemfibrozil, did not occur and the structure of these subcellular organelles was not compromised. It was concluded that the long-term administration of this compound did not show adverse effects on the hepatocyte in hyperlipoproteinemia.

Gemfibrozil↗
PubMed1982

Effect of S12 ribosomal mutations on peptide chain elongation in Escherichia coli: a hydrostatic pressure study.

Protein synthesis in Escherichia coli mutants that differ from one another in mutations which impart streptomycin resistance was investigated by the application of hydrostatic pressure. Increased pressure resistance was only observed in mutants which exhibited reduced rates of peptide chain elongation. These findings indicate that the major effect of pressure on protein synthesis in E. coli may involve the S12 ribosomal protein.

Escherichia coli↗
PubMedDate not supplied

Fibroblast growth factor receptors regulate the ability for hindlimb regeneration in Xenopus laevis.

During outgrowth of the developing limb, signals from the apical ectodermal ridge, such as fibroblast growth factors, are paramount for limb patterning. Similarly, fibroblast growth factor molecules and their receptors are synthesized in the wound epithelium of the regenerating limb blastema, implicating an analogous function to limb development. To address this issue further and to understand the role of fibroblast growth factor receptor signaling in limb regeneration, we have examined the expression patterns of x-fibroblast growth factor receptors-1, -2, -3, -4a, and -4b in Xenopus laevis. This amphibian model provides a system in which both regenerating (premetamorphic; tadpole or larva stage) and nonregenerating (postmetamorphic; froglet stage) hindlimbs can be studied. In premetamorphic hindlimbs (stage 53), all of the receptors were expressed in the wound epithelium and the underlying mesenchyme. In postmetamorphic limbs (stage 61), however, transcripts for x-fibroblast growth factor receptors-1 and -2 were absent from the wound epithelium. The expression results for x-fibroblast growth factor receptors-1 and -2 were corroborated at the protein level by employing specific antibodies. Thus, it appears that expression of both fibroblast growth factor receptors-1 and -2 is associated with the ability for limb regeneration. The role of these receptors in regeneration was further investigated by using specific inhibitors to fibroblast growth factor receptors during premetamorphic hindlimb regeneration. These compounds inhibited the normal limb outgrowth and resulted, in the majority of the cases, in outgrowths of cones or spikes reminiscent of growth that is seen in amputated postmetamorphic limbs. Thus, fibroblast growth factor receptors-1 and -2 expression and function should be regarded as paramount for the ability of limb regeneration in Xenopus.

Amputation, Surgical↗