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H L Leffert

Publications and source records attributed to H L Leffert.

At least 73 records · Page 4Linked to original sources
PubMed1978

Hepatocyte growth control: in vitro approach to problems of liver regeneration and function.

Primary monolayer fetal and adult rat hepatocyte culture systems, which are being used to help analyze in vivo mechanisms controlling liver regeneration, proliferation, and differentiation are described. With results from animal studies of normal or genetically altered rats subjected to partial hepatectomy, to chemical infusions, or to specific dietary deficiency regimens, an apparently complex growth regulatory pattern has emerged. The data suggest a working hypothesis postulating interactions among hormone, nutritional, lipoprotein, and novel nucleotide factors at multiple regulatory sites. These findings may provide some conceptual and experimental basis for future research regarding the development of hepatic cancer, as it may arise spontaneously or from exposure to environmental carcinogens.

Animals↗
PubMed1977

Proliferation of hepatocytes.

Hepatocyte proliferation may be controlled by reversible patterns of endocrine changes, monitored by the liver, involving known hormones and their receptors. A two-programme model of related interactions among nutrients, specific lipoproteins, and highly phosphorylated nucleotides is postulated. This hypothesis stems from in vitro studies of rat hepatocyte proliferation under chemically defined conditions and from in vivo studies using partially hepatectomized, hormone-infused, developing and lipotrope-deficient rats. Certain findings are discussed with regard to receptor systems which show negatively cooperative properties; to problems of proliferative specificity; and to novel approaches for defined studies of chemical hepatocarcinogenesis.

2-Acetylaminofluorene↗
PubMed1976

Growth control of differentiated fetal rat hepatocytes in primary monolayer culture. IX. Specific inhibition of DNA synthesis initiation by very low density lipoprotein and possible significance to the problem of liver regeneration.

Rat serum very low density lipoprotein (VLDL) inhibits initiation of DNA synthesis in fetal rat hepatocyte cultures; cells engaged in synthesizing DNA resist inhibition. VLDL action is specific and apparently blocks prereplicative protein synthesis. These and other results, from studies of altered blood VLDL levels and [3H] thymidine incorporation into isolated liver nuclei in 70% hepatectomized normal and mutant hyperlipoproteinemic rats, as well as from infusion studies with a "mitogenic" hormone solution, suggest that hepatic VLDL metabolism is linked to the suppression of hepatocyte proliferation.

Amino Acids↗
PubMed1976

Thyroid hormone metabolism during liver regeneration in rats.

The metabolism of thyroid hormones was studied during the prereplicative period of liver regeneration. After partial hepatectomy, serum thyroxine (T4) and triiodothyronine (T3) levles progressively fell, and reached a nadir at 12 h proportional to the quantity of liver tissue exised. The diminution (60-80%) in serum iodothyronines was related specifically to partial hepatectomy because laparotomy, ether anesthesia, and other stressful surgical procedures did not induce similar changes. At least 3 phenomena appear to be involved: 1) increased utilization and turnover of thyroid hormone by the regenerating liver remmant. 2) diminished hormone secretion by the thyroid gland between 6-12 h after surgery, and 3) a slightly reduced concentration of serum iodothyronine carrier proteins. The results support the concept that the liver participates in the metabolic regulation of T2 and T4 which in turn, control hepatocellular growth. It is suggested, however, that additional unknown factors control increased hepatic thyroid hormone turnover after partial hepatectomy.

Animals↗
PubMed1976

Expression of an oncodevelopmental gene product (alpha-fetoprotein) during fetal development and adult oncogenesis.

The expression of an "oncodevelopmental" protein, alpha-fetoprotein (AFP), has been systematically studied in rats during normal development and during regeneration of the liver by fetal rat hepatocytes in vitro, in rats bearing transplantable hepatomas, in rats fed chemical carcinogens, and in mice that spontaneously develop hematomas. AFP is a serum protein made normally during fetal and neonatal stages by liver and yolk sac cells. In newborn rats at approximately 4 weeks of age, the production of AFP is abruptly terminated, a process which is closely associated with cessation of liver cell proliferation. In adult rats, AFP production recurs following the reinitiation of hepatic DNA synthesis induced by partial hepatectomy or by the administration of heaptotoxic chemicals. Detailed metabolic and direct labeling studies of fetal rat hepatocytes in vitro also demonstrate a kinetically similar pattern of hepatocyte DNA synthesis and AFP production. In vitro studies utilizing combined autoradiography for DNA-synthesizing cells and immunofluorescence for AFP-containing cells demonstrates that replicating hepatocytes produce AFP, however, available data do not yet permit a distinction between G1 (pre- or postmitotic) and/or G2 production. During growth of an AFP- producing tumor, the serum concentration of AFP may be used as a accurate index of tumor growth, and, if a transplanted tumor is removed, as a marker for metastatic growth of the tumor. Using this model, we have shown that radiation to the lung at the time of surgical removal of a growing tumor in the leg will prevent establishment and growth of pulmonary metastases and that anti-AFP serum treatment may inhibit growth of a transplantable hepatoma that produces AFP. The exposure of rats to chemical hepatocarcinogens results in the appearance of evaluated serum AFP concentration as early as within 1 week of feeding; noncarcinogenic chemical analogs do not cause an elevation. AFP elevation also occurs with low doses of the hepatocarcinogen in the absence of detectable cell injury (by morphological examination of serum enzyme levels) or any other known morphological or biochemical change. This may represent a highly selective derepression of protein synthesis that occurs following the formation of a complex between the metabolites of the carcinogen and specific chromatin loci. Although every rat so far treated with even subcarcinogenic doses of hepatocarcinogens has elevated serum AFP concentrations, many primary carcinogen-induced hepatomas do not produce detectable AFP. Either there is a subsequent change in the preneoplastic AFP-producing cell that occurs prior to irreversible neoplastic alteration, or the hepatocytes originally influenced by the carcinogens to produce AFP are not necessarily the same cells that are the progenitors of the hepatoma produced by more prolonged exposure...

2-Acetylaminofluorene↗
PubMed1975

Relationship of the biosynthesis of alpha-fetoprotein, albumin, hemopexin, and haptoglobin to the growth state of fetal rat hepatocyte cultures.

AFP and albumin are produced by arginine-synthesizing fetal rat hepatocytes in vitro. AFP and hemopexin production are coupled to hepatocellular proliferation, whereas albumin and haptoglobin production are not. During the cell cycle, AFP is synthesized prior to S and released prior to M. AFP may play a role in regulation of hepatocellular growth through estradiol binding and modulation of the intracellular concentration of lipoprotein (VLDL).

Albumins↗
PubMed1974

Growth control of differentiated fetal rat hepatocytes in primary monolayer culture. V. Occurrence in dialyzed fetal bovine serum of macromolecules having both positive and negative growth regulatory functions.

Dialyzed fetal bovine serum contains two distinct growth-controlling macromolecular fractions: one stimulates and the other inhibits proliferation of primary cultured differentiated fetal rat hepatocytes. Both fractions are precipitated by ammonium sulfate (50% saturation, pH 7.4, 4 degrees C). Serum fraction I (SFI, mol wt >/= 120,000 daltons estimated by gel filtration with Bio-gel P200) appears to contain at least two factors which function, respectively, to initiate DNA synthesis (activity pH 4-10 stable) and to increase the rate at which initiated cells traverse the cell cycle (activity pH 4 and pH 10 labile). Intraperitoneal injections of SFI into adult rats have produced detectable stimulation of hepatic but not renal DNA synthesis. Serum fraction II (SFII, mol wt 40,000-80,000 daltons) suppresses in vitro incorporation of CH(3)-[(3)H]thymidine into DNA under conditions which diminish neither cell viability nor cell attachment. Mixing experiments indicate that SFI and SFII mutually antagonize each other with respect to DNA synthesis and cell multiplication. Thus, both the relative and absolute serum levels of multiple factors control in vitro fetal hepatocyte proliferation.

Animals↗
PubMed1974

Growth control of differentiated fetal rat hepatocytes in primary monolayer culture. VI. Studies with conditioned medium and its functional interactions with serum factors.

Serum-deficient </=0.00003% vol/vol) conditioned medium (CM) obtained from primary cultures of fetal rat hepatocytes initiates DNA synthesis and mitosis in homologous quiescent cultures. CM similarly prepared from 3T3 fibroblast cultures is inactive. At least two conditioning factors are involved in initiating DNA synthesis. The first of these, arginine, is obligatory, synthesized by the cells, and released into the culture medium. The second, a lipid or lipid-containing material, is stable to pH extremes (pH 2, pH 10) and chromatographs with an apparent R(1) approximately 0.5 on silica gel thin-layer plates using hexane-ether (4: 1) as the solvent system. It is suggested that these cultured hepatocytes enter or leave the G(0) or early G(1) phase of the cell cycle as determined in part by their capacity to use available conditioning factor and nutrient components of the medium, in particular, arginine. Serum factors including serum fraction I (4), insulin, and possibly, lipid-like conditioning material appear to initiate DNA synthesis by controlling cellular processes involved with the enhanced utilization and synthesis of growth-limiting nutrients.

Animals↗
PubMed1974

Growth control of differentiated fetal rat hepatocytes in primary monolayer culture. VII. Hormonal control of DNA synthesis and its possible significance to the problem of liver regeneration.

The initiation of DNA synthesis has been studied in quiescent primary cultures of fetal rat hepatocytes using defined hormones and chemically defined medium. Preparations of crystalline insulin (0.01-10 microg/ml) or 20,000-fold purified somatomedin (0.01-1 microg/ml) are stimulatory. Growth hormone (0.025 microg/ml) and hydroxycortisone (0.025 microg/ml), 3':5'-GMP! (10(-5) M) fail by themselves to initiate DNA synthesis but added together with insulin, enhance the stimulatory response by 50-100%. Thyroid hormones (L-T(3), L-T(4), 7.5-30 ng/ml) are by themselves without effect, but when they are added to thyroid hormone-depleted serum, the reconstituted mixtures show an enhanced capacity to initiate DNA synthesis. In contrast, glucagon (0.01 microg/ml) inhibits the insulin-stimulated response by about 50% without reducing basal DNA synthesis rates. The results described here and in the accompanying two reports indicate that environmental control over the initiation of DNA synthesis is complex, and can involve the participation of many factors. The in vitro findings are consistent with the concept that liver regeneration is hormonally controlled and raise the possibility that alterations of the intrahepatic ratio of insulin to glucagon are growth regulatory.

Animals↗
PubMed1972

Studies on primary cultures of differentiated fetal liver cells.

A method for culturing non- or slowly growing, differentiated fetal rat liver cells is described. It involves the use of collagenase as a digesting agent and of a selective medium deficient in arginine which suppresses the growth of nonparenchymal liver cells. Evidence is presented that surviving cells (a) retain liver-specific urea cycle functions measured by their capacity to transform ornithine into arginine, (b) synthesize DNA in glucose-deficient medium, and (c) synthesize and secrete albumin. This primary cell culture responds to partially hepatectomized rat serum and may be an appropriate assay system for the study of mechanisms which regulate liver regeneration.

Animals↗