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Biomedical subjects

H C Pitot

Publications and source records attributed to H C Pitot.

At least 307 records · Page 17Linked to original sources
PubMed1980

Use of primary cultures of adult rat hepatocytes on collagen gel-nylon mesh to evaluate carcinogen-induced unscheduled DNA synthesis.

The procarcinogen, 2-acetylaminofluorene, the direct-acting carcinogen, methyl methanesulfonate, and two other hepatocarcinogens, thioacetamide and urethan, were tested for their ability to elicit unscheduled DNA synthesis in adult rat hepatocytes maintained in primary culture on collagen gel-nylon mesh. The carcinogens, dissolved in dimethyl sulfoxide were added to 6-hr or to 28-hr cultures along with [methyl-3H]thymidine (1 muCi/ml medium) in the presence of 10 mM hydroxyurea. Twelve hr later, the hepatocytes were harvested from the cultures with collagenase, and their DNA was purified on CsCl isopyknic gradients. Unscheduled DNA synthesis was measured as the increase in [methyl-3H]thymidine radioactivity incorporated per microgram DNA of the carcinogen-treated cultures as compared with that of control cultures. Both 2-acetylaminofluorene and methyl methanesulfonate demonstrated a concentration-dependent stimulation of unscheduled DNA synthesis in the 6-hr hepatocyte cultures. However, the response of the 28-hr cultures to these two carcinogens was absent unless the hepatocytes were preincubated for 22 hr in culture medium supplemented with 10(-5) M dexamethasone and 10(-6) M glucagon or in a more complete hormone-supplemented medium. Thioacetamide and urethan, on the other hand, failed to elicit a concentration-dependent unscheduled DNA synthesis under these conditions. The results obtained with this culture system are similar to those of other short-term tests for chemical carcinogenicity and support the potential use of the collagen gel-nylon mesh-hepatocyte primary culture as an in vitro screen for chemical carcinogens. Furthermore, this study suggests the importance of specific hormones in maintaining the capability for repair of DNA damage produced by carcinogenic and mutagenic chemicals in cultured hepatocytes.

2-Acetylaminofluorene↗
PubMed1979

Characterization of a proteolipid complex of aminoacyl-tRNA synthetases and transfer RNA from rat liver.

A high molecular weight complex containing aminoacyl-tRNA synthetases, peptidyl acetyltransferase, lipids and tRNA has been isolated from the 250,000 x g postmitochondrial supernatant from rat liver cells. Aminoacyl-tRNA synthetase activity directed towards arginine, aspartate, glutamine, glutamate, glycine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, and tyrosine is present. An endogenous pool of aminoacyladenylates is indicated by an ATP-32PPi exchange catalyzed by the native complex, which shows a dramatic increase after addition of ATP. Lysine is the only amino acid which greatly increases the exchange rate catalyzed by the native complex in vitro, whereas components of the denatured complex activate all the 13 amino acids in the presence of ATP. Six of the eight lipid fractions were glycolipids; cholesterol and cholesterol esters were absent. The extracted RNA has many characteristics of tRNA. These findings provide evidence for the organization of aminoacyl-tRNA synthetases in a complex with peptidyl acetyltransferase that also contains lipids and tRNA and that can be readily isolated from the cytosol of rat liver cells.

Adenosine Triphosphate↗
PubMed1979

Putrescine-oxidase activity in adult bovine serum and fetal bovine serum.

Putrescine-oxidase activity was found in fetal bovine serum (FBS) with a pH optimum of 8.0 and in adult bovine serum (ABS) with a pH optimum of 9.8. The crude FBS enzyme had a KM for putrescine of 2.58 x 10(-6) M and a Vmax of 0.53 nmol per hr per 50 microliter serum. Aminoguanidine competitively inhibited the enzyme with a KI of 1.8 x 10(-8) M. Spermidine and spermine proved competitive inhibitors of putrescine for both the FBS and the crude ABS putrescine oxidases. The Vmax for the ABS putrescine oxidase was 2.10 nmol per hr per 50 microliter serum, and the KM for putrescine, 50.3 x 10(-6) M. The K1 of the ABS putrescine oxidase for aminoguanidine was 41 x 10(-6) M. On the basis of both the KM and KI values, the adult serum enzyme, at its optimal pH of 9.8, bound spermidine and spermine more avidly than the smaller putrescine and aminoguanidine; whereas the FBS enzyme, at pH 8.0, bound aminoguanidine and putrescine more tightly than the larger polyamines. Each of the enzymes retained over 80% of its activity after heating at 56 degrees C for 30 min. Applications of these data to the study of polyamines in tissue culture and to the purification of diamine oxidases are discussed.

Animals↗
PubMed1979

Fetal phenotypic expression by adult rat hepatocytes on collagen gel/nylon meshes.

Hepatocytes from adult rats were maintained in primary culture for up to 10-13 days on nylon meshes coated with a thin layer of rat tail collagen gel. Their ultrastructure closely resembled that of the liver parenchymal cell in vivo, but hepatocytes in late culture exhibited a pronounced buildup of microfilaments beneath their apical cell surface. Hepatocytes in early and late cultures secreted albumin, transferrin, and alpha1-acid glycoprotein into the medium; they exhibited a 7- to 10-fold induction of tyrosine aminotransferase activity by dexamethasone; and they expressed an alkaline phosphatase that was similar to that of normal rat liver with respect to its inhibition by the liver enzyme inhibitor L-homoarginine. In addition, the hepatocytes in culture demonstrated phenotypic changes characteristic of fetal liver parenchymal cells. These changes, which paralleled an increase in DNA synthesis, included the expression of and linear increase in the activity of the fetal liver cell enzyme gamma-glutamyl transpeptidase, an increased production of alpha1-fetoprotein, and a change in the substrate specificity of fructose-bisphosphate aldolase to that of the fetal liver isozyme.

Animals↗
PubMed1979

Promotion by dietary phenobarbital of hepatocarcinogenesis by 2-methyl-N,N-dimethyl-4-aminoazobenzene in the rat.

The hepatocarcinogenicity of 2-methyl-N,N-dimethyl-4-aminoazobenzene, previously shown to be noncarcinogenic in adult rats in the absence of further treatment, was observed by following a 1- to 6-week period of feeding this dye to weanling rats with the dietary administration of 0.05% phenobarbital for up to 70 weeks. Many large hepatocellular carcinomas developed in the phenobarbital-treated animals by 72 weeks, whereas a very small number of tiny neoplastic nodules, including one carcinoma, were seen in the rats not given this drug. This study suggests that the use of promoting agents, following the short-term administration of weak carcinogens for the liver, can be useful in demonstrating the initiating activity of such compounds. This system may be useful in the identification of such agents in the environment.

Animals↗
PubMed1979

The N-hydroxy metabolites of N-methyl-4-aminoazobenzene and related dyes as proximate carcinogens in the rat and mouse.

The carcinogenicities for rats and mice of N-methyl-4-aminoazobenzene (MAB) and its hepatic microsomal metabolite N-hydroxy-N-methyl-4-aminoazobenzene (N-hydroxy-MAB) were compared under several conditions. N-Ethyl-4-aminoazobenzene, 4-aminoazobenzene, and their N-hydroxy derivatives were also included in some of the assays. About 25% of the rats given MAB or N-hydroxy-MAB (3 to 5 mmol/kg body weight) by stomach tube over a 5-week period developed hepatic tumors by 18 to 22 months. Similarly treated rats subsequently given phenobarbital in the drinking water until the termination of the experiment developed about twice as many hepatic tumors. N-Hydroxy-MAB, administered p.o., but not MAB, also induced multiple papillomas and extensive carcinomas of the forestomach in approximately 50% of the rats. Only low incidence of hepatocellular carcinomas occurred in partially hepatectomized rats given a single i.p. injection of 180 mumol/kg body weight of MAB or N-hydroxy-MAB with or without subsequent administration of phenobarbital. Although repeated s.c. doses of N-benzoyloxy-N-methyl-4-aminoazobenzene induced sarcomas at the injection site in 90% of the rats, only 3 of 20 rats developed sarcomas at the site of s.c. injections of N-hydroxy-MAB. N-Ethyl-4-aminoazobenzene, 4-aminoazobenzene, and their N-hydroxy derivatives did not induce significant numbers of tumors in any of the above assay systems. Administration to preweaning male mice of MAB, N-hydroxy-MAB, N-hydroxy-N-ethyl-4-aminoazobenzene, and N-hydroxy-4-aminoazobenzene resulted in high incidences and high multiplicities of hepatic tumors (averages of 5 to 7 tumors/mouse) within 1 year. N-Ethyl-4-aminoazobenzene and 4-aminoazobenzene also induced hepatic tumors under the same conditions, but they were less active. These data support the conclusion that the N-hydroxy metabolites of these aminoazo dyes are proximate carcinogens.

Age Factors↗