Cyclosporin a treatment is able to revert the decrease in circulating GH and IGF-I and the increase in IGFBPs induced by adjuvant arthritis.

The aim of this study was to find out whether cyclosporin A administration is able to revert the decrease in circulating growth hormone (GH) and insulin-like growth factor-I (IGF-I) and the increase in IGF-binding proteins (IGFBPs) levels caused by adjuvant-induced arthritis in rats. Male Sprague-Dawley rats were intradermically injected with Freund's adjuvant or vehicle. Fourteen days later, rats were randomly divided into two groups - one injected with cyclosporin (15 mg/kg) and the other with vehicle from day 16 to 23 after adjuvant injection. Arthritis decreased body weight gain and serum concentrations of GH. Cyclosporin administration to arthritic rats prevented both effects, whereas cyclosporin had no effect in control rats. Arthritis decreased serum concentrations of IGF-I (p < 0.01), but increased IGFBPs. Cyclosporin administration increased circulating IGF-I, and there was a negative correlation between circulating IGF-I and arthritis index scores in arthritic rats injected with cyclosporin (p < 0.05). Cyclosporin treatment did not alter serum IGFBPs levels in control rats, whereas cyclosporin administration normalised IGFBPs in arthritic rats. These results indicate that the effects of cyclosporin administration on the GH-IGF-IGFBPs system may partly mediate its beneficial effect on body weight in arthritic rats.     

GH administration and renal IGF-I system in arthritic rats

Experimental arthritis in rats results in a growth failure and a decrease in circulating and hepatic concentrations of insulin-like growth factor I (IGF-I). Renal damage has also been reported in arthritic rats. The aim of this study was 1) to analyse if alterations in the IGF-I system in the kidney occurs in adjuvant-induced arthritis and 2) to analyse if recombinant human GH (rhGH) administration is able to reverse these effects. Male Wistar rats were injected with complete Freund's adjuvant or vehicle and 22 days later they were killed. Arthritis increased serum creatinine levels, relative kidney weight and IGF-I concentrations in this organ. In a second experiment, arthritic and control rats received rhGH (3 UI/Kg sc) or 250 microl saline from day 14, after adjuvant or vehicle injection, until day 22. IGF-I concentrations were higher in both the renal cortex and medulla of arthritic rats. In contrast, kidney IGF-I mRNA was lower in both areas of arthritic animals. GH treatment significantly decreased serum creatinine levels and IGF-I concentrations in the kidney cortex and medulla of arthritic rats. However, the administration of rhGH to arthritic animals significantly increased the IGF-I gene expression in both the renal cortex and medulla. Serum and kidney concentrations of IGF-I binding proteins (IGFBPs) were increased in arthritic animals and they were reduced by GH administration. CONCLUSION: These data suggest that experimental arthritis causes renal dysfunction and GH treatment can ameliorate this effect.     

Experimental arthritis inhibits the insulin-like growth factor-I axis and induces muscle wasting through cyclooxygenase-2 activation

Chronic arthritis induces cachexia associated with an inhibition of the growth hormone (GH)-insulin-like growth factor-I (IGF-I) system and an activation of the E3 ubiquitin-ligating enzymes muscle atrophy F-box (MAFbx) and muscle Ring finger 1 (MuRF1) in the skeletal muscle. The aim of this work was to study the role of cyclooxygenase (COX)-2 in chronic arthritis-induced cachexia. Arthritis was induced in rats by Freund's adjuvant injection, and the effects of two COX inhibitors (indomethacin, a nonspecific inhibitor, and meloxicam, a selective COX-2 inhibitor on pituitary GH and on liver and serum IGF-I levels) were tested. Arthritis decreased body weight gain and GH and liver IGF-I gene expression. In the arthritic rats, both inhibitors, indomethacin and meloxicam, prevented the inhibitory effect of arthritis on body weight gain. Indomethacin and meloxicam administration to arthritic rats increased pituitary GH and liver IGF-I mRNA as well as serum levels of IGF-I. These data suggest that induction of COX-2 during chronic inflammation is involved in the inhibition of the GH-IGF-I axis and in the body weight loss. In the gastrocnemius muscle, arthritis increased the gene expression of tumor necrosis factor (TNF)-alpha, the E3 ubiquitin-ligating enzymes MAFbx and MuRF1, as well as of IGF-I and IGF-binding protein-5 (IGFBP-5). Inhibition of COX-2 by meloxicam administration increased gastrocnemius weight and decreased MAFbx, MuRF1, TNF-alpha, and IGFBP-5 gene expression. In summary, our data indicate that chronic arthritis-induced cachexia and muscle wasting are mediated by the COX-2 pathway resulting in a decreased GH-IGF-I secretion and increased expression of MAFbx and MuRF1 mRNA.     

Ghrelin receptor agonist GHRP-2 prevents arthritis-induced increase in E3 ubiquitin-ligating enzymes MuRF1 and MAFbx gene expression in skeletal muscle

Chronic arthritis is a catabolic state associated with an inhibition of the IGF system and a decrease in body weight. Cachexia and muscular wasting is secondary to protein degradation by the ubiquitin-proteasome pathway. The aim of this work was to analyze the effect of adjuvant-induced arthritis on the muscle-specific ubiquitin ligases muscle ring finger 1 (MuRF1) and muscle atrophy F-box (MAFbx) as well as on IGF-I and IGF-binding protein-5 (IGFBP-5) gene expression in the skeletal muscle. We also studied whether the synthetic ghrelin receptor agonist, growth hormone releasing peptide-2 (GHRP-2), was able to prevent arthritis-induced changes in the skeletal muscle. Arthritis induced an increase in MuRF1, MAFbx (P < 0.01), and tumor necrosis factor (TNF)-alpha mRNA (P < 0.05) in the skeletal muscle. Arthritis decreased the serum IGF-I and its gene expression in the liver (P < 0.01), whereas it increased IGF-I and IGFBP-5 gene expression in the skeletal muscle (P < 0.01). Administration of GHRP-2 for 8 days prevented the arthritis-induced increase in muscular MuRF1, MAFbx, and TNF-alpha gene expression. GHRP-2 treatment increased the serum concentrations of IGF-I and the IGF-I mRNA in the liver and in the cardiac muscle and decreased muscular IGFBP-5 mRNA both in control and in arthritic rats (P < 0.05). GHRP-2 treatment increased muscular IGF-I mRNA in control rats (P < 0.01), but it did not modify the muscular IGF-I gene expression in arthritic rats. These data indicate that arthritis induces an increase in the activity of the ubiquitin-proteasome proteolytic pathway that is prevented by GHRP-2 administration. The parallel changes in muscular IGFBP-5 and TNF-alpha gene expression with the ubiquitin ligases suggest that they can participate in skeletal muscle alterations during chronic arthritis.     

The effect of cyclosporine administration on growth hormone release and serum concentrations of insulin-like growth factor-I in male rats.

The aim of this work was to study the effect of cyclosporine on the somatotropic axis. Accordingly, growth hormone (GH) secretion, circulating insulin-like growth factor I (IGF-I) and IGF binding proteins (IGFBPs) in response to cyclosporin A (CsA) treatment were examined in adult male Wistar rats. Cyclosporine administration (5, 10 or 20 mg/Kg daily) over 8 days did not modify the body weight, but it did decrease serum concentration of corticosterone and increased serum IGF-I and GH levels. Rats treated with 5 and 10 mg/Kg of cyclosporine had similar levels of serum IGFBPs to control rats, but there was an increase in circulating IGFBP-3 and IGFPB-1,2 in the group treated with 20 mg/Kg of CsA. The increase in circulating GH correlates with a decrease in pituitary GH content in CsA treated rats, with no modification in hypothalamic somatostatin content, suggesting an increase in pituitary GH release. In order to test this hypothesis, anterior pituitary cell cultures were exposed to different CsA concentrations during a 4 h incubation period. Cyclosporine increased GH secretion in cultured pituitary cells (p<0.05). These data suggest that cyclosporine increases circulating IGF-I and GH by stimulating pituitary GH release.     

Liver mRNA expression of IGF-I and IGFBPs in adult undernourished diabetic rats.

To investigate the role played by factors other than GH, such as nutrients and insulin, on IGF-I secretion, adult male rats of 200 g.b.w. were food-restricted for 7 days and then made diabetic by streptozotocin administration (UD). Different groups of UD rats were submitted to the following four day treatments: left untreated (UD), refed (UD+R), treated with insulin (UD+I), or a combination of both refeeding and insulin (UD+R+I). Serum concentration of IGF-I and liver mRNA expression of IGF-I, IGF-binding proteins and GH receptor were measured. Insulin treatment alone partially recovered liver IGF-I and IGFBPs mRNA expression, while refeeding alone had no effect. Only a combination of both insulin and refeeding recovered both parameters. Contrary to the results obtained with a longer period of recovery, these experiments show that serum and mRNA expression of IGF-I and IGFBPs in adult undernourished diabetic rats can be restored by insulin and nutrients administration with no prior restoration of serum and pituitary GH to control values and no compensatory changes in GH receptor gene expression.     

Anti-inflammatory effect of the ghrelin agonist growth hormone-releasing peptide-2 (GHRP-2) in arthritic rats

Chronic arthritis induces hypermetabolism and cachexia. Ghrelin is a gastrointestinal hormone that has been proposed as a treatment to prevent cachexia. The aim of this work was to examine the effect of administration of the ghrelin agonist growth hormone-releasing peptide-2 (GHRP-2) to arthritic rats. Male Wistar rats were injected with Freund's adjuvant, and 15 days later arthritic and control rats were daily injected with GHRP-2 (100 microg/kg) or with saline for 8 days. Arthritis induced an increase in serum ghrelin (P < 0.01) and a decrease in serum concentrations of leptin (P < 0.01), whereas GHRP-2 administration increased serum concentrations of leptin. GHRP-2 increased food intake in control rats but not in arthritic rats. However, in arthritic rats GHRP-2 administration ameliorated the external symptoms of arthritis, as it decreased the arthritis score (10.4 +/- 0.8 vs. 13.42 +/- 0.47, P < 0.01) and the paw volume. In addition, circulating IL-6 and nitrites/nitrates were increased by arthritis, and GHRP-2 treatment decreased the serum IL-6 levels (P < 0.01). To elucidate whether GHRP-2 is able to modulate IL-6 release directly on immune cells, peritoneal macrophage cultures were incubated with GHRP-2 or ghrelin, the endogenous ligand of the growth hormone (GH) secretagogue receptor. Both GHRP-2 (10(-7) M) and ghrelin (10(-7) M) prevented endotoxin-induced IL-6 and decreased nitrite/nitrate release from peritoneal macrophages in vitro. These data suggest that GHRP-2 administration has an anti-inflammatory effect in arthritic rats that seems to be mediated by ghrelin receptors directly on immune cells.     

Infusion of human insulin-like growth factor I (IGF-I) into malnourished rats reduces hepatic IGF-I mRNA abundance

To determine whether the serum level of IGF-I influences its hepatic synthesis through negative feedback regulation, we infused 200 micrograms/d of human IGF-I subcutaneously into young male rats eating either an energy-restricted or ad lib diet. In energy-restricted rats, a two-fold increase in serum IGF-I concentration produced a 41% increase in growth rate at the end of one week, and a 30% decrease in steady state hepatic IGF-I mRNA and 56% drop in serum GH at the end of two weeks. In ad lib fed rats, the increased serum IGF-I concentration neither enhanced growth rate nor significantly reduced hepatic IGF-I mRNA abundance or serum GH levels. These data suggest that the abundance of hepatic IGF-I mRNA in energy-restricted rats is controlled, in part, by serum IGF-I levels via negative feedback regulation.     

The effect of hypophysectomy on pancreatic islet hormone and insulin-like growth factor I content and mRNA expression in rat

The growth arrest after hypophysectomy in rats is mainly due to growth hormone (GH) deficiency because replacement of GH or insulin-like growth factor (IGF) I, the mediator of GH action, leads to resumption of growth despite the lack of other pituitary hormones. Hypophysectomized (hypox) rats have, therefore, often been used to study metabolic consequences of GH deficiency and its effects on tissues concerned with growth. The present study was undertaken to assess the effects of hypophysectomy on the serum and pancreatic levels of the three major islet hormones insulin, glucagon, and somatostatin, as well as on IGF-I. Immunohistochemistry (IHC), in situ hybridization (ISH), radioimmunoassays (RIA), and Northern blot analysis were used to localize and quantify the hormones in the pancreas at the peptide and mRNA levels. IHC showed slightly decreased insulin levels in the cells of hypox compared with normal, age-matched rats whereas glucagon in cells and somatostatin in cells showed increase. IGF-I, which localized to cells, showed decrease. ISH detected a slightly higher expression of insulin mRNA and markedly stronger signals for glucagon and somatostatin mRNA in the islets of hypox rats. Serum glucose concentrations did not differ between the two groups although serum insulin and C-peptide were lower and serum glucagon was higher in the hypox animals. These changes were accompanied by a more than tenfold drop in serum IGF-I. The pancreatic insulin content per gram of tissue was not significantly different in hypox and normal rats. Pancreatic glucagon and somatostatin per gram of tissue were higher in the hypox animals. The pancreatic IGF-I content of hypox rats was significantly reduced. Northern blot analysis gave a 2.6-, 4.5-, and 2.2-fold increase in pancreatic insulin, glucagon, and somatostatin mRNA levels, respectively, in hypox rats, and a 2.3-fold decrease in IGF-I mRNA levels. Our results show that the fall of serum IGF-I after hypophysectomy is accompanied by a decrease in pancreatic IGF-I peptide and mRNA but by partly discordant changes in the serum concentrations of insulin and glucagon and the islet peptide and/or mRNA content of the three major islet hormones. It appears that GH deficiency resulting in a low IGF-I state affects translational efficiency of these hormones as well as their secretory responses. The maintenance of normoglycemia in the presence of reduced insulin and elevated glucagon serum levels, both of which would be expected to raise blood glucose, may result mainly from the enhanced insulin sensitivity, possibly due to GH deficiency and the subsequent decrease in IGF-I production.     

Chronic upper airway resistive loading induces growth retardation via the GH/IGF-I axis in prepubescent rats.

The effect of upper airway loading on longitudinal bone growth and various components of the growth hormone (GH)/insulin-like growth factor I (IGF-I) axis has not been fully elucidated. In the present study, the effect of chronic resistive airway loading (CAL) in a prepubescent rat model on linear bone growth and weight gain was investigated. We hypothesize that CAL induced in prepubescent rats will lead to impaired longitudinal growth due to impairment in circulating and liver GH/IGF-I parameters. The tracheae of 22-day-old rats were obstructed by tracheal banding to increase inspiratory esophageal pressure. The GH/IGF-I markers were analyzed using ELISA, RT-PCR, and Western immunoblot analysis 14 days after surgery. Animals exhibited impaired longitudinal growth as demonstrated by reduction of tibia and tail length gains by 40% (P < 0.0001) and body weight gain by 24% (P < 0.0001). No differences were seen in total body energy balance, i.e., oxygen consumption, daily food intake, or arterial blood gases. Circulating GH, IGF-I, and IGF binding protein-3 (IGFBP-3) levels were reduced by 40% (P = 0.037), 30% (P < 0.006), and 27% (P = 0.02), respectively, in the CAL group. Liver IGF-I mRNA level decreased by 20% (P < 0.0002), whereas GH receptor mRNA and protein expression were unchanged. We conclude that impaired longitudinal growth in prepubescent CAL rats is related to a decrease in GH, IGF-I, and IGFBP-3 levels.     

Fenofibrate, a PPAR{alpha} agonist, decreases atrogenes and myostatin expression and improves arthritis-induced skeletal muscle atrophy

Arthritis is a chronic inflammatory illness that induces cachexia, which has a direct impact on morbidity and mortality. Fenofibrate, a selective PPARα activator prescribed to treat human dyslipidemia, has been reported to decrease inflammation in rheumatoid arthritis patients. The aim of this study was to elucidate whether fenofibrate is able to ameliorate skeletal muscle wasting in adjuvant-induced arthritis, an experimental model of rheumatoid arthritis. On day 4 after adjuvant injection, control and arthritic rats were treated with 300 mg/kg fenofibrate until day 15, when all rats were euthanized. Fenofibrate decreased external signs of arthritis and liver TNFα and blocked arthritis-induced decreased in PPARα expression in the gastrocnemius muscle. Arthritis decreased gastrocnemius weight, which results from a decrease in cross-section area and myofiber size, whereas fenofibrate administration to arthritic rats attenuated the decrease in both gastrocnemius weight and fast myofiber size. Fenofibrate treatment prevented arthritis-induced increase in atrogin-1 and MuRF1 expression in the gastrocnemius. Neither arthritis nor fenofibrate administration modify Akt-FoxO3 signaling. Myostatin expression was not modified by arthritis, but fenofibrate decreased myostatin expression in the gastrocnemius of arthritic rats. Arthritis increased muscle expression of MyoD, PCNA, and myogenin in the rats treated with vehicle but not in those treated with fenofibrate. The results indicate that, in experimental arthritis, fenofibrate decreases skeletal muscle atrophy through inhibition of the ubiquitin-proteasome system and myostatin.     

Insights into a role of GH secretagogues in reversing the age-related decline in the GH/IGF-I axis

Growth hormone (GH) secretion and serum insulin-like growth factor-I (IGF-I) decline with aging. This study addresses the role played by the hypothalamic regulators in the aging GH decline and investigates the mechanisms through which growth hormone secretagogues (GHS) activate GH secretion in the aging rats. Two groups of male Wistar rats were studied: young-adult (3 mo) and old (24 mo). Hypothalamic growth hormone-releasing hormone (GHRH) mRNA and immunoreactive (IR) GHRH dramatically decreased (P < 0.01 and P < 0.001) in the old rats, as did median eminence IR-GHRH. Decreases of hypothalamic IR-somatostatin (SS; P < 0.001) and SS mRNA (P < 0.01), and median eminence IR-SS were found in old rats as were GHS receptor and IGF-I mRNA (P < 0.01 and P < 0.05). Hypothalamic IGF-I receptor mRNA and protein were unmodified. Both young and old pituitary cells, cultured alone or cocultured with fetal hypothalamic cells, responded to ghrelin. Only in the presence of fetal hypothalamic cells did ghrelin elevate the age-related decrease of GH secretion to within normal adult range. In old rats, growth hormone-releasing peptide-6 returned the levels of GH and IGF-I secretion and liver IGF-I mRNA, and partially restored the lower pituitary IR-GH and GH mRNA levels to those of young untreated rats. These results suggest that the aging GH decline may result from decreased GHRH function rather than from increased SS action. The reduction of hypothalamic GHS-R gene expression might impair the action of ghrelin on GH release. The role of IGF-I is not altered. The aging GH/IGF-I axis decline could be rejuvenated by GHS treatment.     

Seasonal regulation of the growth hormone-insulin-like growth factor-I axis in the American black bear (Ursus americanus)

The American black bear maintains lean body mass for months without food during winter denning. We asked whether changes in the growth hormone/insulin-like growth factor-I (GH-IGF-I) axis may contribute to this remarkable adaptation to starvation. Serum IGF-I levels were measured by radioimmunoassay, and IGF-binding proteins (IGFBPs) were analyzed by ligand blotting. Initial studies in bears living in the wild showed that IGF-I levels are highest in summer and lowest in early winter denning. Detailed studies in captive bears showed that IGF-I levels decline in autumn when bears are hyperphagic, continue to decline in early denning, and later rise above predenning levels despite continued starvation in the den. IGFBP-2 increased and IGFBP-3 decreased in early denning, and these changes were also reversed in later denning. Treatment with GH (0.1 mg·kg(-1)·day(-1) × 6 days) during early denning increased serum levels of IGF-I and IGFBP-3 and lowered levels of IGFBP-2, indicating that denning bears remain responsive to GH. GH treatment lowered blood urea nitrogen levels, reflecting effects on protein metabolism. GH also accelerated weight loss and markedly increased serum levels of free fatty acids and β-hydroxybutyrate, resulting in a ketoacidosis (bicarbonate decreased to 15 meq/l), which was reversed when GH was withdrawn. These results demonstrate seasonal regulation of GH/IGF-I axis activity in black bears. Diminished GH activity may promote fat storage in autumn in preparation for denning and prevent excessive mobilization and premature exhaustion of fat stores in early denning, whereas restoration of GH/IGF activity in later denning may prepare the bear for normal activity outside the den.     

Differential regulation of insulin-like growth factor-(IGF) I and IGF-binding protein (IGFBP) secretion by human peripheral blood mononuclear cells

BACKGROUND: Recent studies have shown that immunocompetent cells synthesize and express growth hormone (GH), growth hormone receptors (GH-R), insulin-like growth factor I (IGF-I), IGF-I receptors (IGF-I-R) and different insulin-like growth factor binding proteins (IGFBPs). The aim of the current study was to evaluate the regulation of IGFBP and IGF-I secretion from immunocompetent cells by different mitogens. METHODS/RESULTS: We studied the in vitro secretion pattern of IGFBPs and IGF-I from human peripheral blood mononuclear cells (PBMC), derived from 10 normal adults and 8 GH-deficient patients with adult onset. In serum-free conditioned medium of unstimulated PBMC, derived from normal adults, Western ligand blotting (1D-WLB) revealed a 24-kD, a 34-kD and a 39/43-kD doublet band to be most prominent. According to their molecular weight and two-dimensional Western ligand blot analysis (2D-WLB), these bands are deglycosylated IGFBP-4, IGFBP-2 and IGFBP-3, respectively. When the cells were treated with the T-cell mitogen phytohemagglutinin (PHA) (10 microg/ml), a differential stimulation of IGFBPs was found with a 2.57 +/- 0.48-fold increase of IGFBP-4 (p < 0.01), a 1.55 +/- 0.13-fold increase of IGFBP-2 (p < 0.01), and a 1.35 +/- 0.19-fold increase of IGFBP-3 (n.s.). In contrast, treatment with the B-cell mitogen pokeweed mitogen (PWM) (10 microg/ml) caused only a modest 1.40 +/- 0.07-fold increase of IGFBP-4 (p < 0.01). Treatment with rhGH (100 ng/ml) or rhIGF-I (200 ng/ml) caused no significant induction of any specific band, respectively. In contrast to the secretion pattern of IGFBPs, IGF-I secretion of the PBMC was not stimulated by either PHA or PWM, but showed a significant increase after GH incubation (p < 0.01). A similar differentiated secretion pattern of IGFBPs and IGF-I was also observed in the conditioned medium of PBMC, derived from GH-deficient patients. CONCLUSION: In summary, at least three different IGFBPs are secreted by human PBMC. Secretion of IGFBPs by PBMC is differentially regulated by different lymphocyte mitogens. Secretion of IGFBPs by PBMC is independent of GH or IGF-I, whereas the secretion of IGF-I is stimulated by GH. PBMC derived from normal adults and GH-deficient patients show similar patterns of IGF-I and IGFBPs secretion, thus indicating that the paracrine/autocrine IGF-I-IGFBPs interactions of the PBMC are not altered by pituitary GH deficiency.     

NO plays a role in LPS-induced decreases in circulating IGF-I and IGFBP-3 and their gene expression in the liver

In this study, we administered aminoguanidine, a relatively selective inducible nitric oxide synthase (iNOS) inhibitor, to study the role of nitric oxide (NO) in LPS-induced decrease in IGF-I and IGFBP-3. Adult male Wistar rats were injected intraperitoneally with LPS (100 microg/kg), aminoguanidine (100 mg/kg), LPS plus aminoguanidine, or saline. Rats were injected at 1730 and 0830 the next day and killed 4 h after the last injection. LPS administration induced an increase in serum concentrations of nitrite/nitrate (P < 0.01) and a decrease in serum concentrations of growth hormone (GH; P < 0.05) and IGF-I (P < 0.01) as well as in liver IGF-I mRNA levels (P < 0.05). The LPS-induced decrease in serum concentrations of IGF-I and liver IGF-I gene expression seems to be secondary to iNOS activation, since aminoguanidine administration prevented the effect of LPS on circulating IGF-I and its gene expression in the liver. In contrast, LPS-induced decrease in serum GH was not prevented by aminoguanidine administration. LPS injection decreased IGFBP-3 circulating levels (P < 0.05) and its hepatic gene expression (P < 0.01), but endotoxin did not modify the serum IGFBP-3 proteolysis rate. Aminoguanidine administration blocked the inhibitory effect of LPS on both IGFBP-3 serum levels and its hepatic mRNA levels. When aminoguanidine was administered alone, IGFBP-3 serum levels were increased (P < 0.05), whereas its hepatic mRNA levels were decreased. This contrast can be explained by the decrease (P < 0.05) in serum proteolysis of this binding protein caused by aminoguanidine. These data suggest that iNOS plays an important role in LPS-induced decrease in circulating IGF-I and IGFBP-3 by reducing IGF-I and IGFBP-3 gene expression in the liver.     

Cell-specific localization of insulin-like growth factor binding protein mRNAs in rat liver

The liver is a major source of circulating insulin-like growth factor I (IGF-I), and it also synthesizes several classes of IGF binding proteins (IGFBPs). Synthesis of IGF-I and IGFBPs is regulated by hormones, growth factors, and cytokines. They are nutritionally regulated and expressed in developmentally specific patterns. To gain insight into cellular regulatory mechanisms that determine hepatic synthesis of IGF-I and IGFBPs and to identify potential target cells for IGF-I within the liver, we studied the cellular sites of synthesis of IGF-I, IGF receptor, growth hormone (GH) receptor, and IGFBPs in freshly isolated rat hepatocytes, endothelial cells, and Kupffer cells. We also localized cellular sites of IGFBP synthesis by in situ hybridization histochemistry. Western ligand and immunoblot analyses were used to determine IGFBP secretion by isolated cells. Two IGF-I mRNA subtypes with different 5' ends (class 1 and class 2) were detected in all isolated liver cell preparations. Type 1 IGF receptor mRNA was detected in endothelial cells, indicating that these cells are a local target for IGF actions in liver. GH receptor was expressed in all cell preparations, consistent with GH regulation of IGF-I and IGFBP synthesis in multiple liver cell types. The IGFBPs expressed striking cell-specific expression. IGFBP-1 was synthesized only in hepatocytes, and IGFBP-3 was expressed in Kupffer and endothelial cells. IGFBP-4 was expressed at high levels in hepatocytes and at low levels in Kupffer and endothelial cells. Cell-specific expression of distinct IGFBPs in the liver provides the potential for cell-specific regulation of hepatic and endocrine actions of IGF-I.     

Vascular endothelial dysfunction associated with elevated serum homocysteine levels in rat adjuvant arthritis: effect of vitamin E administration

We aimed to study the alterations in serum homocysteine levels and endothelium-dependent and -independent vascular relaxant responses in adjuvant-induced arthritis of the rat and to determine the effects of vitamin E administration on these changes. Arthritis was induced by a single intradermal injection of Freund's complete adjuvant into the paw. 26 days after the induction of arthritis, serum homocysteine levels and relaxant responses to acetylcholine and sodiumnitroprusside in thoracic aortas were evaluated. The relaxant responses to acetylcholine were decreased in aortas from arthritic rats, whereas the responses to sodiumnitroprusside were not significantly different when compared to the aortas from control rats. A significant increase was observed in serum homocysteine levels of the arthritic rats in comparison to those of controls. Vitamin E administration (100 mg/kg/day, i.m. for 26 days) to arthritic rats resulted in a significant increase in endothelium-dependent aortic responses to acetylcholine and a significant decrease in serum homocysteine levels with respect to the non-treated arthritic rats. However, in healthy rats, vitamin E treatment significantly decreased the acetylcholine-induced relaxant responses. We conclude that adjuvant-induced arthritis in the rat is associated with increased serum homocysteine levels and this is accompanied by a reduction in endothelium-dependent vascular responses in the thoracic aortas. Vitamin E treatment leads to normalization of the increased serum homocysteine levels and improves the endothelium-dependent relaxant responses in this experimental model.     

Influence of thyroidal status on pituitary content of thyrotropin beta- and alpha-subunit, growth hormone, and prolactin messenger ribonucleic acids

Thyroidectomized rats were used to study the effects of a single injection of T3 on pituitary mRNA synthesis and hormone secretion. T3 was injected ip at doses of 0, 0.2, 1, or 5 micrograms/100 g body weight, and and animals were killed 24 h later. T3 caused a significant decrease in serum TSH, but caused no significant change in either serum GH or PRL. Pituitary mRNA was quantified by slot blot hybridization with cDNA probes specific for alpha-TSH, beta-TSH, PRL, and GH. We found that both the alpha and beta mRNA subunits decreased, that PRL mRNA remained relatively unchanged, and that GH mRNA increased with increasing T3 dose. The data show that a single dose of T3 can profoundly influence mRNA levels in the anterior pituitary; the lowest dose of T3 caused maximum inhibition of alpha-TSH mRNA while beta-TSH mRNA declined further in a dose-dependent manner.     

Estrogen induces insulin-like growth factor-I expression in the rat uterus

The inability to convincingly demonstrate a mitogenic effect of estrogen on isolated uterine cells in culture suggests that autocrine or paracrine growth factors may be important in the estrogen-induced uterine proliferative response. Here we report that uterine expression of insulin-like growth factor-I (IGF-I), an important mediator of GH action, is increased after 17 beta-estradiol (5 micrograms/100 g bw, ip) administration to ovariectomized prepubertal rats. An increase in uterine IGF-I mRNA abundance, approximately 14-fold above untreated controls, was apparent 6 h after estrogen administration and the level achieved exceeded that seen in the uterus from intact mature rats during diestrus. In contrast to the increase in IGF-I expression in the uterus, no significant change in serum IGF-I concentration or hepatic or renal IGF-I mRNA abundance was demonstrable after 17 beta-estradiol injection of ovariectomized prepubertal rats. The increase in uterine IGF-I expression, was similar in both pituitary-intact and hypophysectomized, ovariectomized rats. We believe this is the first report of induction of IGF-I expression by estrogen in vivo. As such, the finding expands the role and significance of IGF-I as a mediator of growth beyond that related to GH.