Direct effects of iodothyronines on excess fat storage in rat hepatocytes.

Background & Aims: Previous studies have demonstrated that 3,5-L-diiodothyronine (T(2)) is able to prevent lipid accumulation in the liver of rats fed a high-fat diet. Whether this effect is due to a direct action of T(2) on the liver has not been elucidated. In this study, we investigated the ability of T(2) to reduce the excess lipids in isolated hepatocytes treated with fatty acids (FFAs).

PAT protein mRNA expression in primary rat hepatocytes: Effects of exposure to fatty acids.

Excess energy is stored as neutral lipids in lipid droplets (LDs) whose surface is coated by PAT proteins, each playing a distinct cellular function. The adipocyte differentiation-related protein (ADRP) and tail-interacting protein (TIP47) are expressed almost ubiquitously, whereas the oxidative tissue-enriched PAT protein (OXPAT) is expressed in specific tissues, such as the liver. In rat liver, only ADRP expression has been documented.

Effects of 3,5-diiodo-L-thyronine administration on the liver of high fat diet-fed rats.

In rats fed a high fat diet (HFD), long-term administration of 3,5-diiodo-L-thyronine (T2), a naturally occurring iodothyronine, was shown to reduce body-weight gain, fat mass, and hepatic lipid accumulation. This work was aimed at investigating the mechanisms of T2 action in the liver of HFD rats. The results show that HFD induces liver lipid peroxidation and stimulates the activity of enzymes involved in hydrogen peroxide (H2O2) metabolism, catalase in particular.

Uncoupling protein-2 induction in rat hepatocytes after acute carbon tetrachloride liver injury.

This study is focused on the role of UCP-2 in hepatic oxidative metabolism following acute CCl(4) administration to rats. UCP-2 mRNA, almost undetectable in the liver of controls, was significantly increased 24 h after CCl(4) administration, peaked at 72 h and then tended to disappear. UCP-2 protein, undetectable in controls, increased 48-72 h after CCl(4) treatment.

Combined effects of high-fat diet and ethanol induce oxidative stress in rat liver.

Individuals affected by liver steatosis seldom have symptoms of liver injury, but may be particularly vulnerable to oxidative insults. In this study, we evaluated liver redox alterations produced by acute ethanol administration to rats that were fed a high-fat diet (HFD). Adult male Wistar rats were fed HFD or standard diet (controls) for 1 month; a group of animals from each condition were gavaged with 35% (vol/vol) ethanol every 12h for the last 3 days of the experiment.

Is the platelet serotonin transporter different in venous vs. arterial blood?

The binding of labelled paroxetine to the serotonin transporter (SERT) of platelet membranes has been studied in both venous and mixed venous/arterial blood of the rat. In addition, we studied the inhibition of paroxetine binding to SERT by quipazine and N-methyl-quipazine (NMQ). The results indicate differences in affinity for the two test drugs, quipazine and NMQ, in venous vs.

Thyroid status affects rat liver regeneration after partial hepatectomy by regulating cell cycle and apoptosis.

In rats, various growth factors and hormones, as well as partial hepatectomy (PH) are able to trigger the proliferative response of hepatocytes. Although recent evidence highlights the important role of thyroid hormones and thyroid status in regulating the growth of liver cells in vitro and in vivo models, the mechanism involved in the pro-proliferative effects of thyroid hormones is still unclear. Here we have investigated how in rats made hypo- and hyperthyroid after prolonged treatment respectively with propylthiouracil (PTU) and triiodothyronine (T3), the thyroid status affects liver regeneration after PH by regulating cell cycle and apoptosis proteins.

3,5-diiodothyronine mimics the effect of triiodothyronine on insulin-like growth factor binding protein-4 expression in cultured rat hepatocytes.

We have previously demonstrated that triiodothyronine (T(3)) stimulates hepatic IGFBP-4 expression in rats. Since there is evidence that some of the genes whose expression is regulated by T(3) are also sensitive to 3,5-diiodothyronine (T(2)), we used the adult rat hepatocyte model in primary cultures directly exposed to T(2) to evaluate insulin-like growth factor binding protein-4 (IGFBP-4) expression by Northern and Ligand blot analyses in this study. Our results demonstrate that T(2), like T(3), is able to enhance IGFBP-4 mRNA and protein after 12-24 h of incubation.

Retinoic acid increases insulin-like growth factor-binding protein-4 expression in cultured rat hepatocytes.

Hepatic insulin-like growth factor binding protein (IGFBP) expression is controlled by diverse factors including thyroid hormone, which enhances IGFBP-4 production in hepatocytes. In the present work, we have investigated whether hepatic IGFBP-4 expression is regulated by retinoic acid (RA), which acts via nuclear receptors belonging to the steroid/thyroid hormone receptor superfamily. Primary cultures of adult rat hepatocytes were incubated with two natural stereoisomers of RA, all-trans RA and 9-cis RA (atRA and 9cRA), and with the synthetic RA receptor (RAR)-selective agonist TTNPB.

Effect of simulated microgravity conditions on poly(ADP-ribose) polymerase activity in primary cultures of adult rat hepatocytes.

The possible involvement of poly(ADP-ribose) polymerase [PARP; E.C. 2.

Uncoupling protein 2 mRNA expression and respiratory parameters in Kupffer cells isolated from euthyroid and hyperthyroid rat livers.

Objective: The levels of uncoupling protein 2 (UCP2) mRNA and determinants of respiration (ATP synthesis, proton leak and non-mitochondrial respiration) were evaluated in Kupffer cells isolated from the livers of normal euthyroid, acute hyperthyroid and chronic hyperthyroid rats.

Methods: After liver perfusion, Kupffer cells were purified by density-gradient centrifugation followed by counterflow centrifugal elutriation. UCP2 mRNA levels were measured by Northern blot and respiratory parameters by polarographic method.

Regulation of renal growth and IGFBP-4 expression by triiodothyronine during rat development.

The insulin-like growth factors (IGFs) and insulin-like growth factor binding proteins (IGFBPs), which regulate IGF activity, play a fundamental role in renal cell proliferation and differentiation. The thyroid hormone is considered to be required for kidney development; excess induces local hypertrophy and hyperplasia. The aim of the present study was to investigate the possible involvement of the IGF/IGFBP system in thyroid hormone-induced renal growth during the development of the rat.

Poly(ADP-ribose) polymerase is affected early by thyroid state during liver regeneration in rats.

Poly(ADP-ribose) polymerase (PARP), a nuclear enzyme involved in DNA synthesis, DNA repair, and cell replication and transformation, also plays a role in the early steps of liver regeneration induced by partial hepatectomy (PH). PARP and DNA topoisomerase I (Topo I) activities and de novo DNA synthesis were studied during liver regeneration in rats with altered thyroid state. Hepatic PARP activity, evaluated as [(32)P]NAD incorporated into isolated liver nuclei, was inhibited in hyperthyroid rats and increased in hypothyroid animals.

Metabolic effects of L-carnitine on prepubertal rat Sertoli cells.

The role of carnitine on Sertoli cell metabolism was investigated. Carnitine effects on Sertoli cell lipid metabolism were evaluated by measuring the intracellular levels of non-esterified fatty acids (NEFA) and ketone bodies. The concentration of NEFA in Sertoli cell cultured in the presence of carnitine is significantly reduced as compared to control, while, no significant changes were observed in the concentration of ketone bodies.

Increased insulin-like growth factor binding protein-4 expression after partial hepatectomy in the rat.

The insulin-like growth factor (IGF) binding proteins (IGFBPs) are important regulators of cell growth produced by different tissues. The IGFBPs regulate cell growth by modulating the activity and bioavailability of IGFs. The evidence that IGFBP-1 is a liver-specific immediate-early gene highly induced after 70% partial hepatectomy (PHx) suggests a role for the IGF-IGFBP system in hepatic regeneration.

Tri-iodothyronine increases insulin-like growth factor binding protein-2 expression in cultured hepatocytes from hypothyroid rats.

Previous evidence suggests the existence of a thyroid hormone-IGF axis in the liver and changes in hepatic insulin-like growth factor binding protein (IGFBP) expression in rats with altered thyroid status have been previously reported. The aim of this study was to check if the higher IGFBP-2 mRNA levels observed in liver of hypothyroid rats could be due to a direct effect of thyroid hormone on the IGFBP-2 gene. In our experiments, cultured hepatocytes isolated from normal and hypothyroid adult rats were used.

Direct stimulatory effects of insulin-like growth factor-I (IGF-I) on nuclear RNA polymerase II activity and overall protein synthesis in immature rat Sertoli cells.

A large body of evidence support the existence of an intratesticular Insulin-like Growth Factor I (IGF-I) system that can be viewed as a positive regulator of testicular functions. IGF-I may act at the testis level as a paracrine and autocrine differentiating factor. In the present study the role of IGF-I on Sertoli cell protein synthesis at transcriptional level has been investigated by evaluating the effect of IGF-I on nuclear RNA polymerase II activity as well as on total protein synthesis.

Effect of the somatostatin analog, octreotide, and of other hormones on the release of the acid-labile subunit of the 150 kDa complex by rat hepatocyte in primary culture.

Objective: In normal subjects, the major form of circulating IGF is the GH-dependent 150 kDa complex. The liver appears to be the main source of the three components of the 150 kDa complex and, in particular, hepatocytes synthesize the insulin-like growth factor (IGF) peptide and the acid-labile subunit (ALS), whereas Kupffer and sinusoidal endothelial cells produce IGF-binding protein-3 (IGFBG-3). We have studied the effects of the somatostatin analog octreotide, IGF-II des(1-3)IGF-I, transforming growth factor (TGF)-beta 1 and tri-iodothyronine (T3) on ALS secretion into the medium conditioned by rat hepatocytes in primary culture.

Tri-iodothyronine increases insulin-like growth factor binding protein-4 expression in rat hepatocytes.

Previous in vivo studies demonstrated significant variations in insulin-like growth factor binding protein-1 (IGFBP-1), IGFBP-2 and IGFBP-4 hepatic mRNAs and/or serum levels depending on the rat thyroid status. In this study we employed cultured hepatocytes from adult rats to demonstrate a possible direct regulation of these genes by tri-iodothyronine (T3). Northern blot analysis revealed that IGFBP-1 and -4 messages were clearly expressed, whereas IGFBP-2 signal was barely detectable.

Regulation of IGFBP-1 and -4 expression by triiodothyronine (T3) in cultured hepatocytes is cell- and gene-specific.

Evidence suggests that thyroid hormone plays a role in the regulation of hepatic IGF/IGFBP expression both in human and rats. In this study we compared the effect of T3 on IGFBP-1 and -4 expression in rat hepatocyte primary cultures and in the human hepatoma cell line HepG2. Northern blot analysis revealed that IGFBP-1 mRNA levels were not affected by T3 in cultured rat hepatocytes, whereas a net increase of IGFBP-1 transcript abundance was induced by the hormone in HepG2 cells.

Influence of thyroid hormone on Sertoli cell protein metabolism in the prepubertal pig.

In order to better understand the role of thyroid hormones in testis development, the influence of tri-iodothyronine on protein metabolism of immature pig Sertoli cells has been investigated. Sertoli cells were isolated enzymatically from 2- to 3-week-old piglet testes and cultured in the presence or absence of tri-iodothyronine. Protein labelling was evaluated in Sertoli cell monolayers incubated in medium containing a tracer dose of [3H]leucine.

Thyroid hormone affects rat uterine expression of IGF-I and IGFBP-4.

The rat uterus has been shown to be a site of production of insulin-like growth factor-I (IGF-I) and multiple IGF-binding proteins (IGFBP-2, -3, -4, -5, -6) which are involved in estrogen-induced uterine proliferation. The presence of T3-receptors in rat uterus suggests a role of thyroid hormone in the regulation of uterus responses to estradiol. In this study IGF-I and IGFBP-4 mRNAs in uterus, oviduct and cervix from euthyroid, hypothyroid and T3-treated rats were quantified by Northern blot analysis.

Effect of triiodothyronine administration on estrogen receptor contents in peripuberal Sertoli cells.

The effects of thyroid hormone on androgen metabolism in peripuberal Sertoli cells through the inhibition of estradiol production have been reported previously. It was our intention to investigate further the possible role of thyroid hormone on the interaction between testicular steroids and Sertoli cells by analyzing the effects of triiodothyronine (T3) on estrogen receptor content in 2-, 3- and 4- week-old euthyroid rats. Triiodothyronine treatment (3 micrograms/100 body wt per day) given during the last week prior to sacrifice resulted in reduced testicular growth in 2-week-old animals.

Thyroid hormone modulates androgen and oestrogen receptor content in the Sertoli cells of peripubertal rats.

A possible role of tri-iodothyronine (T3) on the interplay between testicular steroids and Sertoli cells has been investigated on the basis of previous findings demonstrating a direct inhibitory influence of T3 on aromatase activity and oestradiol production in peripuberal Sertoli cells. In this context, the present study was focused on the effects of T3 on oestrogen receptor (ER) and androgen receptor (AR) contents in the cytosol and nucleus of Sertoli cells isolated from 2-, 3- and 4-week-old euthyroid, hypothyroid and hypothyroid treated rats. Hypothyroidism was induced by the oral administration of 0.

Triiodothyronine decreases gammaglutamyltranspeptidase expression in cultured rat hepatocytes.

Recently, an increase in gammaglutamyltranspeptidase (GGT) activity and mRNA in liver of hypothyroid rats has been reported. The aim of this study was to verify if triiodothyronine (T3) can directly affect GGT expression in primary cultures of rat hepatocytes. Results obtained from adult rat hepatocytes cultured in serum-free medium demonstrate: 1) a rise in GGT mRNA level magnified by dexamethasone during the maintenance of hepatocytes in culture which parallels the stimulation of GGT activity; 2) a negative effect of T3 on GGT activity of cultured hepatocytes which reflects a specific inhibition of GGT gene expression.