Estrogen-induced modification of uterine RNA polymerase activity depends on localization of the estrogen receptor

The aim of this study was to examine the effects of estradiol (E2) on activity of RNA polymerase I and RNA polymerase II in uterine nuclei of ovariectomized (OVX) female rats. The obtained results show that estrogen-receptor (E-R) complexes in 30 min induced an increase of polymerase II activity. A second increase of polymerase II activity was observed after 3 h-incubation of nuclei with the E-R complex formed in the cytosol fraction. However, activity of polymerase I was increased 2 h after the start of incubation, with highest activity detected at 3 h in nuclei incubated with E-R complexes. On the contrary, no stimulatory effect on either polymerase I or polymerase II activity was observed in nuclei incubated with E2 alone. These results indicate that E2 stimulates the cytosolic estrogen receptor (ER), which in turn causes uterotrophic responses in OVX rats. In addition, they suggest that in order to provoke uterotrophic responses E-R complexes formed in the cytosol need to be retained in the nucleus for a longer period of time

Regulation of cardiac nitric oxide synthase in acute type I diabetes: Modulation of L-arginine availability and arginase activity

The aim of our study was to characterize the acute effects of streptozotocin-induced diabetes on the regulation of cardiac endothelial and inducibile nitric oxide synthase and related signaling pathways. Over the past decade, it has become increasing apparent that competition between the nitric oxide synthase and arginase pathways for L-arginin limits nitric oxid production. Imbalance between these pathways may contribute to heart disfunction especially in diabetes. To evaluate the role of insulin in regulation of endothelial and inducible nitric oxide synthase through phosphatidylinositol 3-kinase/protein kinase B and extracellular signaling-regulated kinase 1 and 2 signaling pathways, male Wistar rats were injected with streptozotocin (65 mg/kg i.p.). Diabetic animals were either maintained untreated for 2 weeks or treated with insulin (3 IU/animal s.c.) for seven days. The arginase activity in diabetic rat heart was augmented, followed by reduction of L-arginine. Insulin treatment significantly decreased arginase activity in heart but it still remained high compare to control rats. Diabetes and insulin treatment did not change endothelial nitric oxide synthase protein and mRNA expression in the heart. In contrast, phosphorylation of endothelial nitric oxide synthase was decreased in diabetic rats and insulin restored it to the control level. Insulin treatment caused increase in inducibile nitric oxide synthase mRNA content. Protein and mRNA expression of cardiac protein kinase B were not altered in diabetic and insulin treated rats, but protein kinase B phosphorylation was lower in diabetes and restored after insulin administration. In addition, insulin deficiency significantly decreases extracellular signaling-regulated kinase 1 and 2 phosphorylation in the heart and insulin treatment partially ameliorates this decline. These data suggest that in the early stage of diabetes arginase is markedly induced in heart and increased arginase activity preceded alterations of inducibile nitric oxide synthase expression/activity

Insulin modulates rat liver glucocorticoid receptor

This investigation used cytosol fraction of rat liver to examine the effects of insulin (INS) on functional properties of glucocorticoid receptor (GR). Male Wistar rats (220–250 g b.wt.) were injected with INS (50 μ g/200 g b.wt, i.p.) and 18 h after INS administration used for experiments. INS-stimulated dissoci- ation of G-R complexes was significantly increased by 133% compared to control level. However, INS treatment significantly stimulated stability of GR protein by 138% above control value. Furthermore, results show that INS stimulated activation of formed cytosol [ 3 H] TA-R complexes by 143% in respect to control. [ 3 H]TA-R complexes from INS treated animals could be activated and accumulated at higher rate in cell nuclei of control animals. The physiological relevance of the data was confirmed by INS- related stimulation of Tryptophan oxigenase (TO) activity. It was observed that INS stimulated TO activ- ity while INS injected to adrenalectomized rats, exhibited less effects compared to control. The results indicate that a glucocorticoid hormone (CORT) enhances INS induced stimulation of TO activity, as evi- denced by enhanced enzyme activity. Presented data suggest: that INS treatment leads to modifications of the GR protein and the nuclear components and that INS activates the rat liver CORT signaling path- way which mediates, in part, the activity of TO

Effects of dexamethasone on insulin receptor in aging

The aim of this study was to examine the effects of dexamethasone (Dex) on functional properties of the rat insulin receptor (IR). Male Mill Hill hooded rats, 3, 6, 12, 18 and 21 months old, were injected with Dex (4 mg/kg) and rat liver and erythrocytes were used for experiments 18 h after Dex administration. Treatment with Dex lowered the specific binding (SB) of insulin (INS) in the liver of 3- and 18-month- old rats and concentration of INS binding sites (N 1 , N 2 ) and the dissociation constant of low-affinity binding sites (Kd 2 ) in the liver of 6- and 18-month-old rats. In addition, Dex treatment lowered the liver IR protein level in all analyzed groups, except 21-month-old rats where it remained unchanged, but raised the IR mRNA level in 18-month-old rats. In erythrocytes, treatment with Dex decreased SB and Kd 2 (in animals 3 and 6 months old) and N 1 (in ones 3 and 18 months old). Following Dex treatment, the INS plasma level increased (in rats 3, 18 and 21 months old), while glucose (Glu) concentration increased in 3 and 12 months old, but decreased in 6- and 21-month-old rats. In summary, Dex exerts the strongest effect on the erythrocyte IR of 3- and 6-month-old rats and the hepatic IR of 18-month-old rats. IR in both tissues is almost insensitive to Dex in 12- and 21-month-old rats. The pattern of age-related changes of IR induced by Dex does not correlate with changes of plasma Glu and INS

Gender modulates development of the metabolic syndrome phenotype in fructose-fed rats

We analyzed the effects of a fructose-rich diet (FRD) to test the assumption that the expression of metabolic syndrome phenotype is different in male and female rats. Two-way ANOVA revealed a significant effect of FRD on feeding behavior and carbohydrate/lipid metabolism. The increased caloric intake in FRD rats of both sexes was followed by a cluster of gender-specific changes typical for the metabolic syndrome. Female rats were characterized by decreased glycemia, increased triglycerides, enlarged visceral adipose tissue and increased absolute mass of liver, without changes in systolic blood pressure and insulin sensitivity. In contrast, male rats developed less disturbances in physical and biochemical characteristics, but blood pressure and insulin sensitivity were impaired by FRD. The results emphasize the detrimental effects of fructose consumption on cardiovascular risk and insulin action in males, whereas females are affected by other metabolic disturbances. These results support the idea of gender-dependent differences in the expression of the metabolic syndrome phenotype

Cardiac Nitric Oxide Synthases and Na+/K+-ATPase in the Rat Model of Polycystic Ovary Syndrome Induced by Dihydrotestosterone

Nitric oxide synthases (NOSs) and Na+/K+-ATPase are enzymes essential for regular functioning of the heart. Since both enzymes are under insulin and androgen regulation and since insulin action and androgen level were disturbed in polycystic ovary syndrome (PCOS), we hypothesized that cardiac nitric oxide (NO) production and sodium/potassium transport would be deteriorated in PCOS. To test our hypothesis we introduced animal model of PCOS based on dihydrotestosterone (DHT) treatment of female Wistar rats and analyzed protein expression, phosphorylation or subcellular localization of endothelial NOS (eNOS), inducible NOS (iNOS) and alpha subunits of Na+/K+-ATPase in the heart. Obtained results indicate that DHT treatment significantly decreased cardiac eNOS protein level and activating phosphorylation at serine 1177, while inhibitory phosphorylation at threonine 495 was increased. In contrast to expression of eNOS, iNOS protein level in the heart of DHT-treated rats was significantly elevated. Furthermore, cardiac protein level of alpha 1 subunit of the ATPase, as well as its plasma membrane content, were decreased in rats with PCOS. In line with this, alpha 2 subunit protein level in fraction of plasma membranes was also significantly below control level. In conclusion, DHT treatment impaired effectiveness of NOSs and Na+/K+-ATPase in the female rat heart. Regarding the importance of NO production and sodium/potassium transport in the cardiac contraction and blood flow regulation, it implicates strong consequences of PCOS for heart functioning.Ministry of Education, Science and Technological Development, Republic of Serbia {[}III41009