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Biomedical subjects

H C Pitot

Publications and source records attributed to H C Pitot.

At least 325 records · Page 18Linked to original sources
PubMed1978

Reversal by aminoguanidine of the inhibition of proliferation of human fibroblasts by spermidine and spermine.

The inhibitory effect of the polyamines, spermidine and spermine, on the proliferation of human fibroblasts in culture was found to be reversed by the addition of aminoguanidine (AM), a specific and highly effective inhibitor of diamine oxidase (DAO) present in fetal calf serum (FCS). Aminoguanidine itself in concentration as high as 10(-3) M exhibited no effect upon cell proliferation nor did putrescine at similar concentrations. However, at higher concentrations of putrescine, cell proliferation was inhibited and this inhibition was unaffected by the addition of mM concentrations of AM. These studies support earlier hypotheses on the mechanisms of the toxic effects of polyamines on cell proliferation and establish further that the diamine oxidase-catalyzed metabolism of spermine and spermidine is necessary for their toxic effects in cell culture.

Amine Oxidase (Copper-Containing)↗
PubMed1978

Protein degradation in normal and beige (Chediak-Higashi) mice,.

The beige mouse, C57BL/6 (bg/bg), is an animal model for the Chediak-Higashi syndrome in man, a disease characterized morphologically by giant lysosomes in most cell types. Half-lives for the turnover of [(14)C]bicarbonate-labeled total soluble liver protein were determined in normal and beige mice. No significant differences were observed between the normal and mutant strain for both rapidly and slowly turning-over classes of proteins. Glucagon treatment during the time-course of protein degradation had similar effects on both normal and mutant strains and led to the conclusion that the rate of turnover of endogenous intracellular protein in the beige mouse liver does not differ from normal. The rates of uptake and degradation of an exogenous protein were determined in normal and beige mice by intravenously injecting (125)I-bovine serum albumin and following, in peripheral blood, the loss with time of phosphotungstic acid-insoluble bovine serum albumin and the parallel appearance of phosphotungstic acid-soluble (degraded) material. No significant differences were observed between beige and normal mice in the uptake by liver lysosomes of (125)I-bovine serum albumin (t((1/2)) = 3.9 and 2.8 h, respectively). However, it was found that lysosomes from livers of beige mice released phosphotungstic acid-soluble radioactivity at a rate significantly slower than normal (t((1/2)) = 6.8 and 3.1 h, respectively). This defect in beige mice could be corrected by chronic administration of carbamyl choline (t((1/2)) = 3.5 h), a cholinergic agonist which raises intracellular cyclic GMP levels. However, no significant differences between normal and beige mice were observed either in the ability of soluble extracts of liver and kidney to bind [(3)H]cyclic GMP in vitro or in the basal levels of cyclic AMP in both tissues. The relevance of these observations to the presumed biochemical defect underlying the Chediak-Higashi syndrome is discussed.

Animals↗
PubMed1978

A comparison of polysomal messenger ribonucleoprotein particles from normal and neoplastic rat liver.

Free polysomes were isolated from normal and regenerating rat liver and from Morris hepatomas 7777, 7800, 5123C and 9618A. Sucrose gradient analysis ruled out the possibility of any significant messenger RNA degradation in these polysome preparations. The ethylenediaminetetraacetate-disrupted polysomes were fractionated on oligodeoxythymidylic acid-cellulose columns. The column-bound polyriboadenylic acid-containing messenger ribonucleoprotein particles were eluted with a formamide buffer, precipitated with ethanol, and subjected to polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The messenger RNA-associated proteins from the different tissues were qualitatively similar, but two proteins with molecular weights of 66,000 and 109,000 found as minor proteins in normal liver appeared on gels as major protein bands when hepatoma messenger ribonucleoprotein particles were examined. The 66,000- and 109,000-molecular-weight proteins in these particles from regenerating liver appeared quantitatively similar to those isolated from normal liver.

Animals↗
PubMed1978

Hormonal regulation and the effects of glucose on tyrosine aminotransferase activity in adult rat hepatocytes cultured on floating collagen membranes.

Adult rat parenchymal hepatocytes can be maintained in primary culture on floating collagen membranes of prolonged periods of time. In this system the enzyme tyrosine aminotransferase is induced by glucagon, (10(-6) to 10(-8) M) hydrocortisone (10(-5) to 10(-8) M), and cyclic adenosine 3':5'-monophosphate (cAMP) (10(-4) to 10(-5) M). Epinephrine (10(-4) M) induces the enzyme only in the presence of hydrocortisone. Addition of actinomycin D inhibited the induction of tyrosine aminotransferase by hydrocortisone and cAMP. Maintenance of the cultured hepatocytes in the presence of glucose (3g/liter) results in partial suppression of the inducing effects of glucagon and cAMP. Cyclic quanosine 3':5'-monophosphate does not mimic the effects of glucose. These results demonstrate that the phenomenon of glucose repression of enzyme induction, demonstrated in vivo in mammalian liver, is independent of changes in levels of serum hormones, which occur in vivo as a result of glucose administration. This study also demonstrates that glucose repression is not mediated by changes in intracellular levels of cAMP and cyclic quanosine 3':5'-monophosphate.

Animals↗
PubMed1978

Ultrastructure of adult rat hepatocytes cultured on floating collagen membranes.

The ultrastructure of primary hepatocytes cultured for 2 to 17 days on floating collagen membrane was evaluated. A pellet of the hepatic cell suspension used to inoculate the collagen membranes contained some single cells and many aggregates of two, three, or four cells. Desmosomes were split during the perfusion, but tight junctions and gap junctions remained intact. By 2 days in culture, the hepatocytes had formed a monolayer of cells of polygonal shape with newly synthesized desmosomes between cells. Since the flexible floating collagen membrane decreases in size as the monolayer forms, the hepatocytes do not flatten out, as is characteristic of cells cultured on a rigid substrate. Hepatocytes in culture for 10 days or less exhibited large lamellar arrays of rough endoplasmic reticulum, well developed Golgi complexes, and structures resembling bile canaliculi, which possess tight junctions and desmosomes separating them from the intercellular space. Microfilaments oriented parallel to the plasma membranes of adjoining cells and in an intermeshed network at the edge of the monolayer and beneath the plasma membrane bordering the medium increased in size and number in older cultures. After 17 days in culture, the cells maintained tight junctions, desmosomes, Golgi complexes, and rough endoplasmic reticulum in small lamellar stacks and in small vesicles. Since hepatocytes on the floating collagen membrane retain most of the subcellular structural elements characteristic of normally functioning hepatocytes for 2.5 weeks, this system may be valuable for future experiments involving drug metabolism and carcinogenesis in vitro.

Animals↗
PubMed1978

Unscheduled DNA synthesis induced by procarcinogens in suspensions and primary cultures of hepatocytes on collagen membranes.

Unscheduled DNA synthesis was induced by procarcinogens in freshly isolated suspensions and primary cultures (6 days old) of hepatocytes on collagen membranes. Incorporation of [3H]thymidine in the presence of hydroxyurea was used to measure unscheduled DNA synthesis. When hepatocellular DNA was isolated on cesium chloride gradients, significant levels of unscheduled DNA synthesis were measured. Similar concentrations of procarcinogens elicited higher levels of unscheduled DNA synthesis in hepatocellular suspensions than in primary cultures. The results demonstrate that hepatocytes cultured on collagen membranes can metabolize chemical carcinogens. Suspensions of freshly isolated hepatocytes, however, are more active in procarcinogen metabolism than are those of primary cultures. The selective advantages of the two systems of hepatocytes can be utilized for the establishment of short-term in vitro screening systems of mutagens and carcinogens.

2-Acetylaminofluorene↗
PubMed1977

Isolation and characterization of rat liver free and membrane-bound polysomal messenger ribonucleoprotein particles.

Rat liver mRNA-labeled free and membrane-bound polysomes uncontaminated with nuclear or cytoplasmic ribonucleoprotein particles were dissociated with EDTA and the released messenger ribonucleoprotein particles isolated using an oligo(dT)-cellulose column. Seventy percent of the labeled mRNA applied bound to the column. Binding of mRNP was dependent on the presence of a poly(A) segment in the RNA. The nonbound material contained most of the ribosomal subunits and also messenger-sized poly(A-)RNA molecules associated with protein. The free mRNP fraction bound to the column, washed with 250 mM NaCl, and subsequently eluted contained seven proteins ranging in molecular weight from 52 000 to 138 000 only one of which was found in the fraction not bound to the column. Furthermore, these proteins were shown to have a higher affinity for poly(A+)RNA as compared with rRNA. The membrane-bound mRNP contained five proteins, four of which were identical with those associated with free mRNP. Membrane-bound mRNP were disrupted at a lower salt concentration than the free. The proteins found associated with free and membrane-bound polysomal mRNP appeared to be clustered in the poly(A) region of the molecule. The implications of these findings are discussed.

Animals↗
PubMed1977

The stability of events in the natural history of neoplasia.

Previous studies on the natural history of neoplasia, utilizing mouse skin as a model, have demonstrated that the process of epidermal carcinogenesis may be separated into at least two different phases. The first of these, termed "initiation," is essentially irreversible; the second phase, that of promotion, may be modulated or reversed by a variety of environmental conditions. More recently, similar stages have been demonstrated for other organ systems during carcinogenesis, in particular that of murine liver. At the same time, investigations of a variety of systems including those in plants, amphibians, and, most recently, in mammals have demonstrated that the initiation process of neoplasia may not be as irreversible as previously considered, but in several of these systems, including those in plants and in the mouse teratoma, the neoplastic process appears to be reversible from its initial stages under appropriate conditions. A proposed scheme is presented which takes into account the reversibility of the process of initiation in the natural history of neoplasia.

Animals↗
PubMed1977

The natural history of neoplasia. Newer insights into an old problem.

The stages of initiation and promotion in the natural history of epidermal carcinogenesis have been known for many years. Recently, experimental systems other than skin have been shown to exhibit similar, if not completely analogous, stages in the natural history of neoplasia. In particular, the demonstration by Peraino and his associates that phenobarbital may enhance the production of hepatomas by a relatively subcarcinogenic dose of acetylaminofluorene was one of the first demonstrations of stages occurring in an extraepidermal neoplasm. Studies reported in this paper have demonstrated that administration of phenobarbital (0.05% in the diet) for 6 months following a single dose of diethylnitrosamine (5 to 10 mg/kg) given within 24 hours after partial hepatectomy resulted in a marked increase in the number of enzyme-altered foci in the liver as well as in the production of hepatocellular carcinomas. This was compared to animals receiving only a single dose of diethylnitrosamine following partial hepatectomy with no further treatment, in which only a relatively small number of foci were evident in the absence of phenobarbital feeding. Using three different enzyme markers, a distinct degree of phenotypic heterogeneity of the enzyme-altered foci in liver was demonstrated. These studies have shown that liver carcinogensis can be readily divided into two stages: a) initiation by a single dose of diethylnitrosamine following partial hepatectomy and b) promotion by the continuous feeding of phenobarbital. Furthermore, the immediate progeny of the initiated cells, the enzyme-altered focus, may be recognized by suitable microscopic means prior to the formation of gross lesions as required in the skin system. These initiated cell populations exhibit a degree of biochemical heterogeneity which reflects that seen in fully developed hepatic neoplasms, suggesting that promotion and progression in this system does not significantly alter the basic biochemical characteristics of the initiated cell.

Adenosine Triphosphatases↗
PubMed1976

Cytochrome P-450 induction by phenobarbital and 3-methylcholanthrene in primary cultures of hepatocytes.

The characteristic hepatocellular changes resulting from phenobarbital administration in vivo, namely an increase in the levels of cytochrome P-450 and proliferation of membranes of the smooth endoplasmic reticulum, have been demonstrated in primary cultures of nonreplicating hepatocytes on floating collagen membranes. Addition of methylcholanthrene to the medium resulted in an increase in cytochrome P-448 within 48 hours, whereas the phenobarbital induction of P-450 required 5 days. These results demonstrate that responses induced in adult liver cells in vivo by phenobarbital can be reporoduced in cultured hepatocytes, contrary to previous reports.

Cells, Cultured↗