Biomedical subjects

I Fabregat

Publications and source records attributed to I Fabregat.

At least 37 records · Page 2Linked to original sources

PubMed1994

Hepatocyte growth factor up-regulates met expression in rat fetal hepatocytes in primary culture.

Hepatocyte growth factor (HGF) is a potent mitogen for primary cultured fetal hepatocytes. In the present study, we have analyzed the c-met/HGF receptor expression in fetal hepatocytes and its modulation by growth factors and hormones. 20-day old fetal liver showed a barely expression of c-met mRNA levels. However, when fetal hepatocytes were incubated in the presence of HGF, a 10-fold increase in c-met mRNA levels was observed 30 min after addition of the factor. This HGF-induced effect on c-met expression was transient, losing its up-regulatory effect after 24 hours and returning to the initial levels at 48 hours. Transforming growth factor-beta, a negative regulator of fetal liver growth, increased c-met mRNA levels 48 hours after the addition of the factor, whereas glucocorticoids had a negative effect.

Animals↗

PubMed1994

Noradrenergic modulation of albumin expression in growth-stimulated adult rat hepatocytes in primary culture.

Serum albumin is the most abundant protein synthesized by liver cells, and its production is a reliable indicator of the differentiated state of hepatocytes. We have recently shown that fetal rat hepatocytes cultured under proliferative conditions, i.e., in the presence of EGF, responded to glucagon and noradrenaline increasing albumin protein and mRNA levels (de Juan et al., 1992. J. Cell. Physiol., 152:95-101). This effect was mimicked by agents that increase cyclic AMP levels. In this report, we show that in regenerating liver, noradrenaline modulation of albumin expression seems to be different. Hepatocytes from hepatectomized rats were cultured at low cell density and in the presence of EGF. Under these conditions, noradrenaline, which acted synergistically with EGF increasing DNA synthesis (de Juan et al., 1992. Exp. Cell. Res., 202:495-500), produced a decrease in albumin mRNA levels. This effect was dose-dependent, being maximum at 1 microM noradrenaline. Noradrenergic effect seemed to be mediated by alpha 1-receptors, because it was blocked by prazosin, but not by propranolol. Other Ca(2+)-increasing agents, as vasopressin, angiotensin II, or ATP, did not produce any effect. However, albumin mRNA levels decreased when the cells were incubated in the presence of tetradecanoyl phorbol-13-acetate (TPA). In addition, noradrenergic modulation of albumin expression was blocked by staurosporine, a protein kinase inhibitor with relative specificity for protein kinase C. Thus we can conclude that the role of noradrenaline on the regulation of liver growth and differentiation changes from fetal to adult life. This change is probably due to its action on different receptors: beta-receptors in fetal hepatocytes and alpha 1-receptors in the adult liver.

Adenosine Triphosphate↗

PubMed1992

Growth stimulation of rat fetal hepatocytes in response to hepatocyte growth factor: modulation of c-myc and c-fos expression.

Hepatocyte growth factor, which is a potent growth factor for primary cultured adult hepatocytes, strongly stimulated DNA synthesis of rat fetal (20-day of gestation) hepatocytes. Its mitogenic capacity, measured as (3H)-thymidine incorporation into acid precipitable material was dose dependent, being detectable at 1 ng/ml and maximal at 5 ng/ml. Over 15% of the cells entered into S-phase and mitosis as judged by flow cytometric analysis of the cell cycle. HGF had additive effects with transforming growth factor-alpha, whereas transforming growth factor-beta strongly inhibited DNA synthesis of fetal hepatocytes stimulated by HGF. HGF induced c-fos and c-myc expression in a time-dependent manner, with a maximum at 30 min for c-fos and 8 h for c-myc. These results suggest that HGF may act as a proliferative factor during fetal liver growth.

Animals↗

PubMed1992

Regulation of albumin expression in fetal rat hepatocytes cultured under proliferative conditions: role of epidermal growth factor and hormones.

Sustained production of plasma proteins, notably albumin, is a reliable indicator of the differentiated state of hepatocytes. In this work, we have developed a fetal hepatocyte culture system where studying the regulation of albumin expression in proliferating liver cells. Our results show that under proliferative conditions (i.e., in the presence of EGF) fetal hepatocytes maintain albumin production above control quiescent non-treated cells. Glucagon and noradrenaline have no effect on the proliferation induced by EGF in cultured fetal hepatocytes; however, they act synergistically with the growth factor, increasing intracellular albumin levels. The maximum response is obtained by treatment of cells with EGF and noradrenaline. The stimulatory noradrenergic effect is mimicked by agents that increase cyclic AMP levels (forskolin plus IBMX). However, vasopressin or phorbol esters have no effect on albumin production, neither alone nor in combination with EGF. Dexamethasone, which does not alter the proliferative induction of EGF, increases albumin content. This effect is independent of the proliferative status of the cells and is not enhanced by glucagon, noradrenaline, or cyclic AMP increasing agents. The hormonal changes observed in albumin production partially correlate with changes in mRNA levels. This is the first time that cyclic AMP increasing agents are shown to act synergistically with EGF, increasing the expression of this liver specific gene.

1-Methyl-3-isobutylxanthine↗

PubMed1992

Differential proliferative response of cultured fetal and regenerating hepatocytes to growth factors and hormones.

Upon epidermal growth factor (EGF) stimulation, fetal (20 days of gestation) and regenerating (44-48 h after partial hepatectomy) rat hepatocytes, isolated and cultured under identical conditions, increased DNA synthesis and entered into S-phase and mitosis, measured as [3H]thymidine incorporation and DNA content per nucleus in a flow cytometer, respectively. Fetal hepatocytes consisted of a homogeneous population of diploid (2C) cells. Two different populations of cells were present in regenerating liver, diploid (2C) and tetraploid (4C) cells, that responded to EGF. Glucagon or norepinephrine did not affect EGF stimulation of DNA synthesis in fetal liver cells, but they potentiated EGF response in regenerating hepatocyte cultures. Glucocorticoid hormones (dexamethasone) inhibited DNA synthesis in fetal hepatocyte cultures, an effect potentiated by the presence of glucagon or norepinephrine. In contrast, in regenerating hepatocytes, dexamethasone increased EGF-induced proliferation. EGF-dependent DNA synthesis was inhibited by TGF-beta in both fetal and regenerating cultured hepatocytes. TGF-beta action was partially suppressed by norepinephrine in regenerating hepatocytes, but was without effect in fetal hepatocyte cultures, whereas a synergistic action between TGF-beta and dexamethasone inhibiting growth in fetal but not in regenerating hepatocytes was found. Taken together, these results may suggest that there are significant differences between fetal and regenerating hepatocyte growth in their response to various hormones.

Animals↗

PubMed1991

The role of NADPH in the regulation of glucose-6-phosphate and 6-phosphogluconate dehydrogenases in rat adipose tissue.

Previous studies examining the regulation of the synthesis of G6PDH and 6PGDH in rat liver and adipose tissue have focused on the induction of these enzymes by different diets and some hormones. In rat liver these enzymatic activities seem to be regulated by a mechanism involving changes in the NADPH requirements. In this paper we have studied the effect of changes in the flux through different NADPH-consuming pathways on G6PDH and 6PGDH levels in adipose tissue and on the NADPH/NADP ratio. The results show that: I) an increase in the consumption of NADPH, caused by the activation of either fatty acid synthesis or detoxification systems which consume NADPH, is paralleled by an increase in the levels of these enzymes; II) when the increase in consumption of NADPH is prevented, the G6PDH and 6PGDH levels do not change.

Adipose Tissue↗

PubMed1990

Possible involvement of NADPH requirement in regulation of glucose-6-phosphate and 6-phosphogluconate dehydrogenase levels in rat liver.

Previous studies examining regulation of synthesis of Glucose-6-Phosphate and 6-Phosphogluconate dehydrogenase in rat liver have focussed on the induction of these enzymes by different diets and some hormones. However, the precise mechanism regulating increases in the activities of these enzymes is unknown and the factors involved remain unidentified. Considering that many of these metabolic conditions occur simultaneously with the increase of some NADPH consuming pathway, in particular fatty acid synthesis, we suggest that the activities of Glucose-6-Phosphate and 6-Phosphogluconate dehydrogenase could be regulated through a mechanism involving changes in the NADPH requirement. Here, we have studied the effect of changes in the flux through different NADPH consuming pathways on the NADPH/NADP ratio and on Glucose-6-Phosphate and 6-Phosphogluconate levels. The results show that: i) an increase in consumption of NADPH, caused by activation of fatty acid synthesis or the detoxification system which consumes NADPH, is paralleled by an increase in levels of these enzymes; ii) when increase in consumption of NADPH is prevented, Glucose-6-Phosphate and 6-Phosphogluconate dehydrogenase levels do not change.

Animals↗

PubMed1990

Solubilization of the bombesin receptor from Swiss 3T3 cell membranes. Functional association to a guanine nucleotide regulatory protein.

Bombesin and structurally related peptides including gastrin releasing peptide (GRP) are potent mitogens for Swiss 3T3 cells. Here we attempted to solubilize bombesin receptors under conditions in which the ligand (125I-labelled GRP) was prebound to the receptor prior to detergent extraction. We found that 125I-GRP-receptor complexes were solubilized from Swiss 3T3 cell membranes by using the detergents taurodeoxycholate or deoxycholate. These detergents promoted ligand-receptor solubilization in a dose-dependent manner. In contrast, a variety of other detergents including Triton X-100, octylglycoside, CHAPS, digitonin, cholic acid and n-dodecyl-beta-D-maltoside, were much less effective. Addition of guanosine 5'-[gamma-thio]triphosphate (GTP gamma S) to ligand-receptor complexes isolated by gel filtration enhanced the rate of ligand dissociation in a concentration-dependent and nucleotide-specific manner. Our results demonstrate for the first time the successful solubilization of 125I-GRP-receptor complexes from Swiss 3T3 cell membranes and provide evidence for the physical association between the ligand-receptor complex and a guanine nucleotide binding protein(s).

Animals↗

PubMed1990

Vasoactive intestinal contractor, a novel peptide, shares a common receptor with endothelin-1 and stimulates Ca2+ mobilization and DNA synthesis in Swiss 3T3 cells.

Vasoactive intestinal contractor peptide (VIC), a novel member of the endothelin family, stimulated a rapid increase in the intracellular Ca2+ concentration in fura-2-loaded Swiss 3T3 cells. Sequential addition of VIC and endothelin-1 (ET1) demonstrated the induction of both homologous and heterologous desensitization. VIC was as potent as ET1 in displacing the binding of 125I-ET1 and in stimulating mitogenesis in Swiss 3T3 cells. These findings suggest that VIC and ET1 share a common receptor in Swiss 3T3 cells.

Animals↗

PubMed1990

[D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P, a neuropeptide antagonist, blocks binding, Ca2(+)-mobilizing, and mitogenic effects of endothelin and vasoactive intestinal contractor in mouse 3T3 cells.

Endothelin (ET1) and vasoactive intestinal contractor (VIC) stimulate quiescent Swiss 3T3 cells to resume DNA synthesis acting synergistically with epidermal growth factors (EGF) and other mitogens. The peptide [D-Arg1,D-Phe5,D-Trp7,9,Leu11] substance P has been identified as a broad spectrum neuropeptide antagonist which blocks the binding and biological effects of the Ca2(+)-mobilizing neuropeptides bombesin, vasopressin, and bradykinin. In the present study we show that [D-Arg1,D-Phe5,D-Trp7,9,Leu11] substance P also acts as an ET1/VIC antagonist as judged by the following criteria: a) inhibition of specific 125I-labelled ET1 binding to a ET1/VIC receptor in a competitive and dose-dependent manner; b) blocking of the rapid increase in the cytosolic Ca2+ concentration promoted by ET1 or VIC; and c) inhibition of DNA synthesis stimulated by VIC in the presence of EGF. The inhibitory effects of [D-Arg1,D-Phe5,D-Trp7,9,Leu 11] substance P on Ca2+ mobilization and DNA synthesis were reversed by increasing the concentration of VIC. This is the first time that a peptide structurally unrelated to ET1 or VIC is shown to block the binding and mitogenic effects of peptides of the endothelin family.

Animals↗

PubMed1990

Mitogenic signalling through the bombesin receptor: role of a guanine nucleotide regulatory protein.

Bombesin and structurally related peptides including gastrin releasing peptide (GRP) are potent mitogens for Swiss 3T3 cells. The early cellular and molecular responses elicited by bombesin and structurally related peptides have been elucidated in detail. Further understanding of the molecular basis of the potent mitogenic response initiated by bombesin is required in order to elucidate the mechanism by which the occupied receptor communicates with effector molecules in the cell. Transmembrane signalling mechanisms involving either a tyrosine kinase or a guanine nucleotide-binding regulatory protein (G protein) have been proposed. Here we summarize our experimental evidence indicating that a G protein(s) is involved in the coupling of the bombesin receptor to the generation of intracellular signals related to mitogenesis. Evidence for the role of G proteins in bombesin signal transduction pathways has been obtained by assessing the effects of guanine nucleotide analogues on both receptor-mediated responses in permeabilized cells and ligand binding in membrane preparations. We found that [125I]GRP-receptor complexes were solubilized from Swiss 3T3 cell membranes by using the detergents taurodeoxycholate or deoxycholate. Addition of guanosine 5-[gamma-thio]triphosphate (GTP gamma S) to ligand-receptor complexes isolated by gel filtration enhanced the rate of ligand dissociation in a concentration-dependent and nucleotide-specific manner. These results demonstrate the successful solubilization of [125I]GRP-receptor complexes from Swiss 3T3 cell membranes and provide evidence for the physical association between the ligand-receptor complex and a guanine nucleotide binding protein(s).

Animals↗

PubMed1989

Hormonal regulation of malic enzyme expression in primary cultures of foetal brown adipocytes.

Insulin increased malic enzyme activity and protein content in foetal brown adipocyte primary cultures through a two fold increase in the rates of enzyme synthesis. Conversely, noradrenaline prevented the induction caused by insulin on enzyme expression through an accelerate rate of malic enzyme degradation. Tri-iodothyronine had no effect on the expression of malic enzyme in cultured foetal brown adipocytes.

Adipose Tissue, Brown↗

PubMed1989

Rates of lipogenesis in fetal hepatocytes in suspension and in primary culture: hormonal effects.

Lipogenesis in isolated fetal hepatocytes in suspension for 3 h was modulated by insulin depending on substrates utilization, but was inhibited by glucagon and noradrenaline from all substrates studied. After primary culture for 5 days in the presence of glucose, the lipogenic response to insulin increased, the glucagon response decreased and noradrenaline produced the same degree of inhibition at 3 h. At 24 h, insulin produced an even higher increase on lipogenesis parallel to an increase in fatty acid synthase activity. Dexamethasone increased lipogenesis, but progesterone had no effect. Both hormones, in the presence of insulin, increased lipogenesis and fatty acid synthase activity. Triiodothyronine, alone or in the presence of insulin, increased lipogenesis and fatty acid synthase activity.

Animals↗

PubMed1989

Inhibition of fatty acid biosynthesis by bezafibrate in different rat cells.

Bezafibrate is one of the main drugs used in the treatment of human hyperlipemic diseases. Its action on the biosynthesis of fatty acids has been studied and the following conclusions have been drawn: (1) Lipogenesis from glucose is inhibited in hepatocytes and adipocytes isolated from "refed" rats previously treated with bezafibrate. (2) Lipogenesis from glucose is inhibited by bezafibrate in hepatocytes and adipocytes isolated from "refed" rats. (3) Lipogenesis from glucose is also inhibited by bezafibrate in acini isolated from lactating rats. These results show that bezafibrate is an inhibitor of fatty acid synthesis.

Adipose Tissue↗

PubMed1989

Precocious induction of malic enzyme by nutritional and hormonal factors in rat foetal hepatocyte primary cultures.

Rat foetal hepatocytes in primary cultures were used as a model for the study of malic enzyme gene expression. Carbohydrates and glycolytic metabolites produced the precocious induction of the malic enzyme in foetal hepatocytes cultured in the absence of serum and hormones. Palmitate prevented this induction. Insulin and triiodothyronine produced a significant increase in the malic enzyme specific activity in all the conditions studied. A synergistic effect between the two hormones is observed only when high concentrations of glucose are present. Glucagon prevents partially the induction produced by insulin plus triiodothyronine. Both carbohydrate and hormonal inductions of malic enzyme activity are related to parallel increases in its expression, and are prevented by protein synthesis inhibitors.

Animals↗

PubMed1988

Hormonal regulation of rat foetal lipogenesis in brown-adipocyte primary cultures.

Insulin stimulates lipogenesis by 100% for 5 h by a covalent modulation of acetyl-CoA carboxylase, and by 200% for 24 h by increasing malic enzyme and fatty acid synthase enzymic activities in brown-adipocyte primary cultures. At short times, noradrenaline and isoprenaline decrease lipogenesis. However, phenylephrine and glucagon have no effect. At long times, dexamethasone inhibits lipogenesis. This effect is precluded in the presence of insulin. Progesterone and tri-iodothyronine, alone or in the presence of insulin, produce a stimulation of the rates of lipogenesis.

Adipose Tissue, Brown↗

PubMed1987

Short-term control of the pentose phosphate cycle by insulin could be modulated by the NADPH/NADP ratio in rat adipocytes and hepatocytes.

The short-term activation of the pentose phosphate cycle by insulin in rat adipocytes and hepatocytes has been studied. This NADPH-producing pathway is regulated by the activation or inhibition of different NADPH-consuming pathways. The stimulation of the fatty acid synthesis by insulin produced an increase in the flux through the pentose phosphate cycle. Kynurenate produced a decrease in the fatty acid synthesis and, consequently a diminution in the flux through the pentose phosphate cycle. Incubation of adipocytes and hepatocytes in presence of kynurenate (10 mM and 3 mM respectively) and insulin (5 nM), prevents both insulin activation on fatty acid synthesis and pentose phosphate cycle. These results suggest that insulin activates the pentose phosphate cycle through the activation of fatty acid synthesis.

Adipose Tissue↗

PubMed1987

The NADPH consumption regulates the NADPH-producing pathways (pentose phosphate cycle and malic enzyme) in rat adipocytes.

The changes in the activity of the pentose phosphate cycle and the malic enzyme produced by the activation or inhibition of different NADPH-consuming pathways have been studied. The inhibition of the fatty acid synthesis by kynurenate produced a decrease in the flux through the pentose phosphate cycle and a diminution in the malic enzyme pathway. The incubation of the adipocytes in the presence of ter-butyl-hydroperoxide, a compound which is metabolized via a NADPH-consuming pathway, produced a big increase in the pentose phosphate cycle and the malic enzyme activities. The regulation of these NADPH-producing pathways by the NADPH/NADP ratio is discussed.

Adipose Tissue↗