Studies on the distribution of O6-methylguanine-DNA methyltransferase in rat.

O6-Methylguanine-DNA methyltransferase, a DNA repair enzyme which transfers the methyl group of O6-methylguanine residue to a cysteinyl residue in the methyltransferase itself, was examined in rat organs by quantifying the S-methylcysteine formed in the methyl acceptor protein. Among the various organs examined, the spleen exhibited the highest enzyme specific activity followed by the thymus, liver, lung and testis. Brain had the lowest activity.

Comparison of the acute toxicity of N-nitrosocimetidine with three structurally related carcinogens in the rat.

The acute toxicity of N-nitrosocimetidine, the nitrosated derivative of the histamine H2-receptor blocking agent cimetidine, was compared with the toxicities of three structurally related nitroso compounds known to be potent carcinogens, namely N-methyl-N'-nitro-N-nitrosoguanidine, N-methyl-N-nitrosourea, and N-methyl-N-nitrosourethane, and also with the parent drug cimetidine. The acute toxicity of each compound was investigated in 6-week-old female Fischer-344 rats by estimating the median lethal doses via three different routes of administration, and by assessing the sequence of histopathological alterations induced. According to median lethalities, all three known carcinogens were substantially more toxic than nitrosocimetidine whether administered by the intravenous, intraperitoneal, or oral routes.

Bypass grafting to the right coronary artery with and without endarterectomy: patency at one year.

Between January 1979 and December 1981, 142 patients undergoing surgery to the right coronary artery agreed to have repeat coronary arteriography one year later. Thirty patients underwent combined endarterectomy and bypass grafting to the right coronary artery. The patency of these grafts was compared with that of grafts in 69 patients undergoing direct grafting to the right coronary artery and in 43 with grafting to the posterior descending coronary artery.

Genetic evidence for role of extracellular proteinase in virulence of Candida albicans.

The relationship between extracellular proteinase and the virulence for mice in Candida albicans was studied by using a set of three isolates. The set included a proteinase-producing parent (C9), a proteinase-deficient mutant derived from C9 by nitrous acid treatment (C9M1), and a spontaneous revertant (C9M1M) obtained by mouse passage of C9M1. The morphological markers and the carbon assimilation pattern were identical in these isolates.

Reoperation for angina after previous aortocoronary bypass surgery.

A retrospective study was carried out of the outcome of 102 patients who underwent a second operation for myocardial revascularisation, necessitated by persistence or recurrence of intractable angina after their first coronary bypass procedures. Operative mortality was 2%. During follow up of the survivors (mean interval 36.

Factors influencing the activity of dimethylnitrosamine demethylase in hamster, rat and chicken liver microsomes.

In vitro metabolism of dimethylnitrosamine (DMN) by liver microsomal fractions of hamster, rat and chicken revealed that the three species under certain assay conditions, were capable of metabolizing DMN at different rates (hamster greater than rat greater than chicken). The magnitude of the demethylase activity was found to be dependent on the nature of the buffer, the concentration of cytochrome P-450 (P-450) and the concentration of the substrate DMN. Enzyme activity was higher in Hepes buffer than in the phosphate buffer.

Randomised placebo controlled trial of aspirin and dipyridamole in the prevention of coronary vein graft occlusion.

Treatment with the combination of aspirin and dipyridamole is believed to reduce the incidence of coronary vein graft occlusion. A double blind randomised controlled trial was carried out in which aspirin 990 mg and dipyridamole 225 mg daily or placebo were added to the routine postoperative management (warfarin for three months) of 320 patients undergoing coronary bypass grafting. The trial treatment was given for 12 months, after which the results were assessed by coronary and graft angiography.

Sporulation-regulated genes of Saccharomyces cerevisiae.

We have characterized 46 hybrid phage which hybridize preferentially to mRNA from sporulating cells. Cross-hybridization experiments demonstrate that 27 distinct SPR (Sporulation regulated) sequences are represented among these phage. The SPR genes can be grouped into three classes: early, middle, and late.

Alkylation of protein by methyl methanesulfonate and 1-methyl-1-nitrosourea in vitro.

Methylation of horse heart cytochrome c has been examined in vitro with [methyl-14C]methanesulfonate (MMS) and [1-methyl-14C]-1-nitrosourea (MNU) as alkylating agents. Analysis of protein hydrolyzates by an automatic amino acid analyzer indicates that, at pH 9.0 with MMS, epsilon-N-monomethyl-lysine is found to be the only major methylated basic amino acid.

Protein synthesis in germinating Saccharomyces cerevisiae ascospores.

The uptake and incorporation of macromolecular precursors in germinating Saccharomyces cerevisiae ascospores were investigated. Addition of cycloheximide at various times during germination revealed that protein synthesis can occur within 20 min after the spores are shifted to glucose-containing media. The time of initiation of uptake and incorporation of several amino acids differed; this can be attributed to differing amino acid pool levels in the spores, as well as differing transport activities.

The metabolism of N-nitrosomethylaniline.

The distribution in the body, rate of disappearance from organs, tissues, and blood, and excretion in the urine of N-nitrosomethylaniline (NMA, N-nitrosophenylmethylamine) was investigated after various single doses given IP to rats. The compound was distributed fairly evenly throughout the body with no preferential concentration in the esophagus, its target organ for carcinogenicity. The high lipid solubility of NMA did not lead to any increased accumulation in adipose tissue.

Inhibition of 1,2-dimethylhydrazine-induced colon tumorigenesis in Balb/c mice by dehydroepiandrosterone.

Long-term administration of dehydroepiandrosterone (DHEA) to Balb/c mice significantly inhibits the rate of appearance of 1,2-dimethylhydrazine (DMH)-induced macroscopic colon and anal tumors and microscopic precursor and malignant lesions. The steroid, which has previously been shown to inhibit spontaneous breast cancer and chemically induced lung tumors in mice, may find application as a chemopreventive in individuals at high risk for developing colon cancer.

Measurement of 7-methylguanine as an estimate of the amount of dimethylnitrosamine formed following administration of aminopyrine and nitrite to rats.

We have demonstrated that there is a dose-related increase in the excretion of 7-[methyl-14C]methylguanine ( [14C]m7Gua) following p.o. administration of di[methyl-14C]methylnitrosamine to rats.

5-Methylcytosine depletion during tumour development: an extension of the miscoding concept.

We propose a general model for neoplastic development which postulates that the loss of methyl groups from 5-methylcytosines (5-mC) involved in the control of gene expression may initiate neoplastic transformation and give rise to the aberrant phenotype of the transformed cell. Interference with normal patterns of methylation can be envisioned to occur by a number of mechanisms: as a result of carcinogen-induced G:C leads to A:T transition leading to a loss of potentially methylatable cytosines; by mutations or chromosome rearrangement which disrupt the integrity of active DNA methylase genes; by separating methylated repressor regions of the genome from the genes they control; by direct interference with DNA methylation, as proposed for ethionine and 5-azacytidine; by spontaneous deamination of 5-mC to thymine, leading to accumulation of 5-mC:G leads to T:A transitions, by virus-induced perturbations in host cell methylation patterns; and by activation of DNA demethylases.

S-adenosylmethionine metabolism and DNA methylation in hydrazine-treated rats.

The treatment of rats with hepatotoxic doses of hydrazine (NH2-NH2) induces the rapid formation of 7-methylguanine and O6-methylguanine in liver DNA. The methyl moiety in these reactions might be derived from the cellular S-adenosylmethionine pool because radioactivity administered to these rats as methionine rapidly appears in the DNA as methylated guanine. An increased incorporation of radioactivity into 5-methylcytosine was previously reported followed by subsequent suppression.

A genetic analysis of Candida albicans: isolation of a wide variety of auxotrophs and demonstration of linkage and complementation.

Naturally occurring strains of Candida albicans appear to be diploid and heterozygous for a limited number of nutritional markers. Additional heterozygosity can be induced by treatment with mutagens; nitrous acid alone or in combination with UV is a potent mutagen in terms of both efficacy and efficiency in the production of a wide variety of mutations. Spheroplast fusion followed by regeneration on selective media revealed complementation among four histidine-requiring mutants analyzed.

Construction of a new yeast cloning vector containing autonomous replication sequences from Candida utilis.

DNA sequences from the Candida utilis genome which, when cloned into a yeast integration plasmid (YIp5), confer on YIp5 the ability to replicate autonomously in Saccharomyces cerevisiae are described. Several recombinant plasmids which transform S. cerevisiae YNN27 to Ura3+ with an efficiency of 2 X 10(3) transformants per microgram of DNA were obtained.

Isolation of genes expressed preferentially during sporulation in the yeast Saccharomyces cerevisiae.

A library of Saccharomyces cerevisiae DNA in the vector lambda Charon 28 was probed for sequences complementary to cDNA made from poly(A)+ RNA isolated from the well-sporulating yeast strain AP1 a/alpha. The RNA was isolated from cells that had been incubated 7, 9, 11, and 13 hr in sporulation medium. DNA complementary to poly(A)+ RNA from alpha/alpha(nonsporulating) AP1 was used as a control, and 46 bacteriophage that gave a stronger response with a/alpha cDNA than with alpha/alpha cDNA were obtained in a screening of three yeast genomes worth of DNA.

Mutation, DNA labeling, and transformation of BHK-21/CL 13 cells by MNNG, and nitrosocimetidine.

N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG) has been reported to induce BHK-21/Cl 13 cell growth in agar suspension. To determine if MNNG was also mutagenic to BHK cells, an ouabain-resistance mutation assay was established using these cells. In this system MNNG was compared to nitrosocimetidine (NC).

Genetic analysis of Candida albicans: identification of different isoleucine-valine, methionine, and arginine alleles by complementation.

By using the spheroplast fusion technique as a tool for genetic analysis, we have demonstrated complementation among three of four isoleucine-valine mutants, two of three methionine mutants, and two arginine mutants of independent origin from two different Candida albicans isolates. The two adenine mutants derived from the same parent strain did not complement. Complementation resulted predominantly from heterokaryon formation and, in some cases, from heterozygote formation.

Comparison of intravenous nitroglycerin and sodium nitroprusside for treatment of acute hypertension developing after coronary artery bypass surgery.

The present study was designed to test the hypothesis that i.v. nitroglycerin is as effective as sodium nitroprusside for managing acute hypertension early after coronary artery bypass surgery.

DNA-methylation by nitrosocimetidine and N-methyl-N-nitro-N-nitrosoguanidine in the intact rat.

The ability of the nitroso derivative of the drug cimetidine to interact with cellular macromolecules in the intact rat was investigated. Radio-labelled nitrosocimetidine (NC) was shown to methylate DNA in a variety of tissues in the rat after oral administration. Radioactivity was also detected in the RNA and protein extracted from these same tissues.

Metabolism of [14C]trichloroethylene to 14CO2 and interaction of a metabolite with liver DNA in rats and mice.

Male Sprague-Dawley rats and male B6C3F1 mice excreted 5-15% of a tracer dose of [14C]trichloroethylene as 14CO2 within 24 h after ip injection of a single dose in a corn-oil vehicle. The proportion of the dose excreted as CO2 was greater in mice than in rats, but increased in the rats after starvation or pretreatment with phenobarbital. As the dose was increased toward the LD50 level, the proportion excreted as 14CO2 decreased slightly, but this was largely due to increased loss of unchanged trichloroethylene.