Search PubMed⌕ Search

Biomedical subjects

S Leoni

Publications and source records attributed to S Leoni.

At least 55 records · Page 3Linked to original sources
PubMed1992

Amino acid uptake regulation by cell growth in cultured hepatocytes isolated from fetal and adult rats.

Amino acid uptake mediated by system A was studied in cultured fetal and adult hepatocytes, subjected to growth stimulation by EGF and insulin, or to growth inhibition by high cell density. The mitogenic stimulation induced a strong transport increase only in fetal cells, while the cell density-dependent growth inhibition, probably mediated by molecules present on adult hepatocyte membranes, provoked the decrease of amino acid uptake only in the adult cells. The results indicate that the different modulation of amino acid transport by cell growth is dependent on the age and the differentiation stage of hepatocytes.

Age Factors↗
PubMed1991

Seasonal pattern of glycosylation in frog liver.

The circannual behaviour of glycosylation and protein synthesis in frog liver slices was studied following the incorporation of 3H-galactose and 14C-glucosamine into glycolipids and glycoproteins and 3H-leucine into proteins. The activity of two enzymes the galactosyl-transferase and the N-acetyl-glucosaminyl-1-P-transferase was determined. The incorporations of both sugars into the soluble fraction and into the lipid extract present a maximum during the spring-summer period. The incorporation into the protein fraction displays a different pattern: 14C-Glucosamine and 3H-leucine incorporation increases from winter to a maximum in autumn; the incorporation of 3H-Galactose has a sharp peak during spring. The pattern of glycosyltransferase activities is similar to the pattern of incorporation of the two saccharides into proteins, indicating these enzymes as important control points for glycosylation in Anurae.

Animals↗
PubMed1990

Variations of hepatic dolichols during rat development.

The content and the percent distribution of dolichol and dolichyl phosphate homologues were measured by high-performance liquid chromatography in perinatal rat livers. Short dolichol chains and no dolichyl phosphate are detectable in the liver at foetal stages; dolichol content progressively increases during liver development. A good correlation is observable between the changes of the dolichol, dolichyl phosphate and the activity of dolichyl-phosphate phosphatase.

Animals↗
PubMed1990

Age-related changes of glycosylation pattern in isolated rat hepatocytes.

The glycosylation pattern in isolated rat hepatocytes during pre- and post-natal development and senescence has been studied by following: the [14C]glucosamine and [3H]galactose incorporation into cellular glycoproteins and glycolipids and the activity of two microsomal enzymes, N-acetyl-glucosaminyl-1-P transferase and galactosyl transferase. The data show a lowered precursor incorporation into lipids and proteins in the fetus, newborn and old rats versus the adult. Only the galactosyl transferase activity is enhanced on the 19th and 22nd day of fetal life. The glucosamine and N-acetyl-glucosamine content in both soluble and protein bound fractions was increased, while the galactose content in lipids and proteins decreased in the fetal stage. The different sugar composition of the proteins, and the decreased glucosamine and galactose incorporation into the proteins, observed in the fetus, newborn and old rat, suggest a post-translational modification which may cause alterations in functions usually mediated by glycoproteins.

Aging↗
PubMed1989

Changes in lipoprotein binding and uptake by hepatocytes during rat liver regeneration.

The binding and uptake of cholesterol enriched lipoproteins by isolated hepatocytes was decreased at 16 hours after partial hepatectomy, with a tendency to return to control values as the regeneration proceeds. The number of lipoprotein binding sites of total cellular membranes remained similar to control at 16 and 24 hours. The plasma lipoprotein pattern, determined by electrophoretic analysis, showed a lower per cent of very low density lipoproteins (VLDL) and a higher per cent of low density lipoproteins (LDL) at 16 and 24 hours post-partial hepatectomy. At these times, plasma lecithin: cholesterol acyltransferase (LCAT) activity was decreased. It is intriguing to suggest that the regenerating liver could regulate the blood lipoprotein pattern and the uptake of lipoproteins by modulating the surface expression of the receptors.

Animals↗
PubMed1989

Some aspects of glycosylation in rat liver during pregnancy.

The aim of the present report was to analyze the pattern of glycoprotein synthesis in rat liver on 19th and 22nd day of pregnancy by following the incorporation of 14C-glucosamine and 3H-galactose into isolated rat hepatocytes, the N-acetylglucosaminyl-1-P and galactosyl transferase activities, and the liver content of dolichol and dolichyl-phosphate. The data obtained show a decrease of precursor incorporation into glycoproteins during the last period of pregnancy; this decrease is independent of enzyme activities. The dolichol content increases and the dolichyl-phosphate content, usually considered as rate limiting for glycosylation, decreases. These results, present in other conditions of proliferation and differentiation of rat liver, could explain the differences in membrane organization, the increase of hepatic proteolysis and the alteration in secretory activity during the last phase of gestation.

Animals↗
PubMed1988

Changes in parameters of lipoprotein metabolism during rat hepatic development.

Maintenance of whole body cholesterol homeostasis is determined in part by the liver. Thus, changes in expression of hepatic parameters important in the regulation of cholesterol metabolism may play key roles in determining how homeostasis is maintained. The expression of hepatic lipoprotein uptake systems was studied during development using as a ligand very-low density lipoproteins rich in apolipoprotein E that had been obtained from hypercholesterolemic adult rats. These lipoproteins can serve as ligands for cell surface receptors recognizing apolipoproteins B and/or E. Uptake was lowest in freshly isolated fetal rat hepatocytes, increased substantially in hepatocytes from neonates and was intermediate in those from adults. Binding of these lipoproteins to liver membranes prepared from fetal, neonatal, suckling, weaned and adult rats was lowest in fetal preparations, while those from suckling, weaned and adult livers behaved similarly. Numbers of binding sites in neonatal liver membranes were similar to those in adult, but showed a different affinity. On the basis of this data, the ability of hepatocytes to recognize and remove apolipoprotein B/E-containing lipoproteins from the plasma appears to be a function of the differential expression or regulation of lipoprotein-uptake systems during development.

Animals↗
PubMed1988

Regulation of amino acid transport in hepatocytes isolated from adult and old rats.

The 2-aminoisobutyric acid transport in hepatocytes isolated from 3- and 24-month-old rats was studied and some age-related differences were observed. The basal uptake appeared to be almost constant in cells from old animals during the incubation time, while, in the cells from adults, it showed a progressive increase, interpreted as being due to a derepression mechanism. Epinephrine and glucagon increased the transport in hepatocytes from animals of both ages, even if with a slightly different pattern; the hormones increased the Vmax, while the Km was unchanged at each age tested. However, the glucagon-induced increase in Vmax was lower in the older animals. The mechanism of hormonal action appeared to be similar in adult and old rats. In fact the uptake stimulation by glucagon and epinephrine showed a dependence on protein synthesis. The epinephrine effect was mediated by alpha-adrenergic receptors. No effect was exerted by extracellular amino acids on hepatocytes from 24-month-old animals, suggesting a loss of adaptative regulation mechanism with aging. This behaviour was reflected in the kinetic parameters; in fact the Vmax was not modified by extracellular amino acids at 24 months of age, while it appeared to be strongly decreased in the adult.

Aging↗
PubMed1988

Frog liver dolichols: separation and quantitative determination related to seasonality.

1. The liver of female frogs shows a significantly higher dolichol content in May (134 micrograms/g) than in November (90 micrograms/g). The male frog liver (134 micrograms/g May; 119 micrograms/g November) does not show any significant change. 2. The rat liver does not show any significant change in dolichol content from May to November (30 micrograms/g). 3. The dolichyl-phosphate level was the same in male and female frog livers and in the rat liver. 4. Data is given of the distribution of dolichols according to the number of their isoprene residues.

Animals↗
PubMed1987

Regulation of amino acid transport in isolated rat hepatocytes during development.

The effect of amino acid depletion or supplementation and the effect of glucagon and insulin on the amino acid transport mediated by system A were investigated by determining the uptake of either 2-amino [1-14C]isobutyric acid (AIB) or N-methyl 2-amino [1-14C]isobutyric acid (MeAIB) in rat hepatocytes, freshly isolated at different stages of pre- and postnatal development. The data obtained show that the Na+-dependent uptake was higher at the earliest developmental stages, and steadily decreased until the adult level. The hormones increased AlB and MeAIB uptake enhancing the Vmax, while the Km was unchanged. This effect was evident in cells from adult and 18-20-day-old fetuses, while no response was present before the 18th day of fetal life and in the perinatal period. Actinomycin D or cycloheximide abolished this hormone-dependent increase. A decrease in AlB and MeAIB transport after incubation in an amino acid-rich medium was demonstrated at all ages tested, but was particularly evident in the prenatal life. The increase in the activity of the system following amino acid starvation was shown to be mostly dependent from de novo protein synthesis in the fetal life; on the contrary in the adult the increase appeared to be more linked to the release from transinhibition of the transport.

Aging↗
PubMed1987

Inverted papilloma of the ureter: two cases of conservative therapy.

We report 2 cases of inverted urothelial papilloma of the ureter. The second case demonstrates inverted papilloma and papillary transitional cell carcinoma in a single polypoid lesion. Conservative therapy was performed and a follow-up 12 months later shows no evidence of recurrences.

Carcinoma, Transitional Cell↗
PubMed1986

Enhanced production of dolichol, but not dolichyl phosphate, in the earliest stages of rat liver regeneration.

The regenerating liver presents a changed ability to use mevalonate 16 hr after partial hepatectomy. The dolichol content and its synthesis from mevalonate is increased, while no variation of dolichyl-P and ubiquinone parameters are detectable. The greater amount of mevalonate utilized to form dolichol, but not dolichyl-P, in this proliferating system, raises some questions about the physiological significance of these isoprenoid compounds and about their biosynthetic sequence.

Animals↗