Functional interaction of AT1 and AT2 receptors in fructose-induced insulin resistance and hypertension in rats

The present study was performed to evaluate the potential role and functional interaction of angiotensin II AT1 and AT2 receptors (AT1R and AT2R) in the regulation of blood pressure and glucose homeostasis in fructose-induced insulin-resistant, hypertensive rats. Male Sprague-Dawley rats on fructose-enriched or regular diets for 4 weeks were subjected to 2-step euglycemic euinsulinemic (EEI) and euglycemic hyperinsulinemic (EHI) clamp studies with [3-3H]glucose infusion. After a 40-minute basal period, selective AT1R and AT2R antagonists, losartan (LOS, 10 mg/kg IV bolus) and PD123319 (PD, 50 microg/kg/min), alone or in combination were separately given to control and fructose-fed groups in the 2 clamp periods. The results showed that during the EEI period, LOS significantly reduced the elevated blood pressure in fructose-fed rats, whereas PD further increased fructose-induced high blood pressure. Coadministration of LOS and PD did not alter the elevated blood pressure in fructose-fed rats. Administration of LOS and/or PD failed to change the blood pressure in control rats. During the EHI period, blockade of both AT1R and AT2R eliminated the insulin-induced blood pressure elevation in control and fructose-fed rats. Hepatic glucose production (HGP) did not alter among groups in the basal and EEI periods. Insulin infusion (EHI period) markedly suppressed HGP in control rats, but this suppressive effect was significantly attenuated in fructose-fed rats. LOS administration further reduced the insulin-induced suppression of HGP in fructose-fed rats. The whole-body glucose uptakes (rates of glucose disappearance, Rd) during the basal and EEI periods were similar among groups. During the EHI period, Rd was markedly increased in all groups and the magnitude of increase was significantly greater in control rats than in fructose-fed rats except those with LOS treatment. LOS treatment also redirected Rd in favor of glycolysis in fructose rats, but not in control rats, during the EEI and EHI periods. The effects of LOS on glycolysis during the 2 clamp periods and on HGP during the EHI period were reversed when PD was concomitantly administered, but PD alone did not alter glucose metabolism throughout the experiment in fructose-fed rats. Administration of LOS and/or PD did not change the glucose metabolism in control rats. Our data suggest that AT2R can counterbalance the AT1R-mediated effects on blood pressure and glucose metabolism in fructose-induced insulin-resistant, hypertensive rats. Furthermore, AT1R- and AT2R-mediated effects on blood pressure are disassociated with their actions on glucose metabolism in this hypertensive model.     

Impact of liver diseases on the development of type 2 diabetes mellitus

The prevalence of type 2 diabetes mellitus (T2DM) is higher in patients who have liver diseases such as nonalcoholic fatty liver disease, chronic viral hepatitis, hemochromatosis, alcoholic liver disease and cirrhosis. It is suggested that there is a pathogenic link between the presence of T2DM and the severity of liver injury. However, evidence related to the impact of hepatic inflammation on the development of T2DM has not yet emerged. This article provides an overview of the evidence for an increased pre...     

Lipoic acid suppresses portal endotoxemia-induced steatohepatitis and pancreatic inflammation in rats

AIM: To examine the effect of α-lipoic acid (LA) on mild portal endotoxemia-induced steatohepatitis and associated pancreatic abnormalities in fructose-fed rats. METHODS: Rats were randomly assigned into two groups with a regular or 60% fructose-enriched diet for 8 wk. After fructose feeding for 4 wk, rats were further divided into four subgroups: with intraportal saline (F PV ), with intraportal saline plus administration of LA (F PV + LA ), with lipopolysaccharide (LPS) infusion (F PLPS ), and with LPS infusion plus administration of LA (F PLPS + LA ). Rats were treated with LPS using intraportal infusion while LA was administered orally. Metabolite levels, superoxide levels, inflammatory markers, malondialdehyde content, glutathione content and toll-like receptor 4 (TLR4 ) gene expression were all measured using standard biochemical techniques. Pancreatic insulin secretion was evaluated by a hyperglycemic clamp technique. Histology of liver and pancreas tissues were evaluated using hematoxylin and eosin staining and immunohistochemistry. RESULTS: Fructose-induced elevation in plasma C-reactive protein, amylase, superoxide, white blood cell count as well as in hepatic and pancreatic contents of malondialdehyde, tumor necrosis factor alpha and interleukin-6 were increased in animals treated with LPS and reversed with LA administration. The augmented hepatic gene expression of TLR4 in fructose-fed rats was further increased in those with intraportal LPS infusion, which was partially reversed by LA administration. Pathological examination showed inflammatory changes and leukocyte infiltration in hepatic and pancreatic islets of animals treated with LPS but were rarely observed in those with LA treatment. In addition to affects on the liver, impaired pancreatic insulin secretion seen in fructose-fed rats was deteriorated in with LPS treatment and partially reversed with LA administration. CONCLUSION: These data suggest LA could significantly suppress mild portal-endotoxemia but not fructoseinduced liver and pancr     

Expression of cortactin and survivin in renal cell carcinoma associated with tumor aggressiveness

Purpose  We tested the hypothesis that the expression of cortactin and survivin in renal cell carcinomas (RCCs) correlates with more advanced stages of the disease. Methods  Immunohistochemical analysis of cortactin and survivin expression (scored on a scale of 0–400) was performed in 124 renal cell carcinomas including clear cell renal cell carcinoma (CRCC), papillary RCC (PRCC), CRCC with sarcomatoid differentiation (SRCC), chromophobe RCC (ChRCC), and CRCC with granular cell differentiation (GRCC). Results  Higher cortactin scores in CRCC were significantly correlated with higher T (p = 0.021) and N stages (p = 0.036), and nuclear grade (p = 0.012). Higher cortactin immunostaining scores were associated with higher mortality (p = 0.035). In addition, the survivin scores were significantly higher in the more aggressive GRCC and SRCC than in CRCC, suggesting a significant role of survivin expression in transformation of tumor cells to a more malignant phenotype. Conclusions  Higher expression of cortactin and survivin significantly correlated with advanced clinicopathological stage. Our findings support the potential targeting of survivin and cortactin for the development of novel therapeutic strategies for renal cell carcinoma.     

Hyperinsulinemia instead of insulin resistance induces baroreflex dysfunction in chronic insulin-infused rats

BACKGROUND: The present study was undertaken to compare the effects of chronic hyperinsulinemia with or without insulin resistance on the autonomic control of heart rate (HR) in rats. METHODS: Male Sprague-Dawley rats were implanted subcutaneously with insulin (3 mU/kg x min) or vehicle-filled osmotic minipumps for 8 weeks. Insulin-infused rats were further divided into insulin resistant (IR) and insulin sensitive (IS) groups according to the results of the homeostasis model assessment method and euglycemic hyperinsulinemic clamp study. Autonomic function in HR control was indicated by arterial baroreflex sensitivity (BRS) after a bolus injection of phenylephrine or sodium nitroprusside. RESULTS: Compared with those in control group, plasma insulin levels were elevated about threefold and 1.5-fold in the IR and IS groups at the end of week 8, respectively. Blood glucose level remained basal in the IR group, but was significantly lower in the IS group. The elevated mean arterial pressure (MAP) observed in IR was not exhibited in IS. The HR and BRS in reflex tachycardia were significantly increased in the IR and IS groups, but the BRS in reflex bradycardia was not different among all rats. Propranolol eliminated the tachycardia and enhanced BRS responses in both groups. Methylatropine further accelerated tachycardia and diminished the enhanced BRS in the IR group. However, in IS, the enhanced BRS remained after methylatropine was given. The intrinsic HR was similar among all groups. The baseline MAP, HR, and BRS in reflex tachycardia were significantly correlated to plasma insulin levels but not to the Si value, an index of insulin sensitivity. CONCLUSIONS: The present results demonstrate that hyperinsulinemia but not insulin resistance is a dominant contributing factor to the development of arterial baroreflex abnormalities in this chronic hyperinsulinemic model, which may simultaneously enhance sympathetic nerve activity and possibly vagal withdrawal if insulin resistance coexisted.     

Discipline-specific insulin sensitivity in athletes

ObjectiveWeight status and abnormal liver function are the two factors that influence whole-body insulin sensitivity. The main goal of the study was to compare insulin sensitivity in athletes (n = 757) and physically active controls (n = 670) in relation to the two factors.MethodsHomeostatic metabolic assessment for insulin resistance (HOMA-IR), weight status, and abnormal liver function (alanine aminotransferase and aspartate aminotransferase) were determined from 33 sports disciplines under morning fasted condition. This study was initiated in autumn 2006 and repeated in autumn 2007 (n = 1508) to ensure consistency of all observations.ResultsIn general, HOMA-IR and blood pressure levels in athletes were significantly greater than those in physically active controls but varied widely with sport disciplines. Rowing and short-distance track athletes had significantly lower HOMA-IR values and archery and field-throwing athletes had significantly higher values than the control group. Intriguingly, athletes from 22 sports disciplines displayed significantly greater body mass index values above control values. Multiple regression analysis showed that, for non-athlete controls, body mass index was the only factor that contributed to the variations in HOMA-IR. For athletes, body mass index and alanine aminotransferase independently contributed to the variation of HOMA-IR.ConclusionThis is the first report documenting HOMA-IR values in athletes from a broad range of sport disciplines. Weight status and abnormal liver function levels appear to be the major contributors predicting insulin sensitivity for the physically active population.     

Attenuation of insulin-mediated pressor effect and nitric oxide release in rats with fructose-induced insulin resistance

Hyperinsulinemia and insulin resistance frequently coexist and have been implicated in the pathogenesis of hypertension. This study aimed to identify the specific effect of hyperinsulinemia on blood pressure and nitric oxide (NO) release in fructose-induced hyperinsulinemic, insulin-resistant rats. Male Sprague-Dawley rats were fed either standard chow or a 60% fructose-enriched diet for 8 weeks before acute study. After basal period, somatostatin (1.3 microg/kg/min) and a variable glucose infusion (to maintain euglycemia) were given intravenously to all groups of rats. In control rats (C) and fructose-fed rats (F) with insulin infusion, insulin (4 mU/kg/min) was given to create a similar hyperinsulinemic condition. In C and F without insulin infusion, a vehicle instead of insulin was infused to produce a hypoinsulinemic state. In C, somatostatin reduced plasma insulin level but did not alter mean arterial pressure (MAP) and heart rate. Insulin infusion significantly increased MAP and NOx (sum of nitrate and nitrite) levels after 90 min and thereafter the elevated MAP and NOx responses were sustained throughout the study. In the basal period, F exhibited significantly higher MAP and plasma insulin levels than C. The index of insulin sensitivity (M) was significantly lower in F than in C with insulin infusion. Somatostatin significantly reduced plasma insulin level but did not affect MAP and NOx level in F. The stimulatory effects of insulin on MAP and NO levels were significantly smaller in F than in C. In conclusion, acute insulin-induced pressor response and NO release were attenuated in rats with fructose-treated insulin resistance, suggesting that hyperinsulinemia-associated attenuation of NO production contributes, at least partly, to the development of fructose-induced hypertension in rats.