Genetic deletion of Mas receptor in FVB/N mice impairs cardiac use of glucose and lipids.

Angiotensin-(1-7) is a biologically active product of the renin-angiotensin system cascade and exerts inhibitory effects on inflammation, vascular and cellular growth mechanisms signaling through the G protein-coupled Mas receptor. The major purpose of the present study was to investigate the use of glucose and fatty acids by cardiac tissue in Mas knockout mice models. Serum levels of glucose, lipids, and insulin were measured in Mas-deficient and wild-type FVB/N mice. To investigate the cardiac use of lipids, the lipoprotein lipase, the gene expression of peroxisome proliferator-activated receptor alpha; carnitine palmitoyltransferase I and acyl-CoA oxidase were evaluated. To investigate the cardiac use of glucose, the insulin signaling through Akt/GLUT4 pathway, glucose-6-phosphate (G-6-P) and fructose-6-phosphate (F-6-P) glycolytic intermediates, in addition to ATP, lactate and the glycogen content were measured. Despite normal body weight, cholesterol and insulin, Mas-Knockout mice presented hyperglycemia and hypertriglyceridemia, impaired insulin signaling, through reduced phosphorylation of AKT and decreased translocation of GLUT4 in response to insulin, with subsequent decrease of the cardiac G-6-P and F-6-P. Lactate production and glycogen content were not altered in Mas-KO hearts. Mas-KO presented reduced cardiac lipoprotein lipase activity and decreased translocation of CD36 in response to insulin. The expression of peroxisome proliferator-activated receptor alpha and carnitine palmitoyltransferase I genes were lower in Mas-KO animals compared to wild-type animals. The ATP content of Mas-KO hearts was smaller than in wild-type. The present results suggest that genetic deletion of Mas produced a devastating effect on cardiac use of glucose and lipids, leading to lower energy efficiency in the heart.

Carbohydrate-enriched diet impairs cardiac performance by decreasing the utilization of fatty acid and glucose.

AIMS: We hypothesized that a high-carbohydrate diet affects the cardiac performance by interfering in the metabolic steps involved in energy transfer in this organ. To verify this, we investigated the myocardial utilization of different substrates and contractile function in rats fed a high-carbohydrate diet, under normal flow and ischemia. METHODS: and RESULTS: Male Wistar rats were fed over 9 days with standard (39.5% carbohydrate, 8% fiber) or high-carbohydrate diet (58% carbohydrate) and, afterwards, their cardiac function was examined using isolated heart preparations. The high-carbohydrate diet decreased the activity of the lipoprotein lipase, utilization of fatty acids, expression of the gene of peroxisome proliferator-activated receptor α and its target enzymes. In addition, decreased GLUT4 mass, glucose uptake, glycogen content and glycolytic intermediates were also observed. High-carbohydrate hearts displayed weaker activation of the glycolytic pathway during ischemia, according to minor production of lactate, in relation to control hearts. The functional impairment caused by high-carbohydrate diet shown by the decrease in the ventricular systolic strength, +dT/dt and -dT/dt was, at least in part, due to the low availability of adenosine triphosphate (ATP). CONCLUSION: Our data suggest that a high-carbohydrate diet can damage myocardial contractile function by decreasing the cardiac utilization of glucose and fatty acids and, consequently, the ATP pool.

Investigation of the acute effect of leptin on the inhibition of glycogen catabolism by insulin in rat liver perfused in situ.

Leptin, a cytokine secreted by adipose tissue, has been implicated in the insulin resistance associated with obesity. Here we examined the acute influence of leptin at physiological (10 ng/ml) and supraphysiological (50 ng/ml and 100 ng/ml) concentrations on the inhibition of glycogen catabolism promoted by insulin in rat liver perfusion experiments. Perfusion of the liver with insulin (20 microU/ml) decreased the activation of glucose production (p < 0.05) and glycogenolysis by cAMP (3 microM). However, the infusion of leptin, at concentrations similar to those found in non-obese (10 ng/ml), obese (50 ng/ml), and morbidly obese (100 ng/ml) individuals did not influence the acute inhibitory effect of insulin (20 microU/ml) on glucose production and glycogenolysis stimulated by cAMP (p > 0.05).We conclude that neither physiological nor supraphysiological concentrations of leptin directly influence the inhibition of glycogen catabolism promoted by insulin in rat liver perfused in situ.

Central role of cAMP in the inhibition of glycogen breakdown and gluconeogenesis promoted by leptin and insulin in perfused rat liver.

Leptin showed less prominent inhibiting effect on the activation of hepatic glycogen breakdown and gluconeogenesis promoted by cAMP. The role of cAMP in the inhibition of glycogen breakdown and gluconeogenesis induced by physiological levels of leptin (10 ng/ml) and insulin (20 microU/ml) in the perfused liver was investigated. Insulin but not leptin inhibited (p < 0.05) the activation of glycogen breakdown promoted by cAMP (3 microM). Contrary to cAMP, the activation of glycogen catabolism promoted by 8-Br-cAMP (0.3 microM), a cAMP analogue more resistant to hydrolysis by phosphodiesterase 3B (PD3B), was inhibited (p < 0.05) not only by insulin (20 microU/ml) but also by leptin (10 ng/ml). The effect of leptin, however, was less intense than that of insulin. To verify the participation of the intracellular levels of cAMP, the experiments were repeated with N(6)-monobutyryl-cAMP (N(6)-MB-cAMP), a cAMP analogue, which is not metabolized by PD3B. The activation of glycogen breakdown promoted by N(6)-MB-cAMP (0.3 microM) was not affected by leptin or insulin. In agreement with the results regarding glycogen catabolism, insulin and leptin at 50 ng/ml but not leptin at 10 ng/ml inhibited (p < 0.05) the activation of gluconeogenesis promoted by cAMP (7.5 microM). Taken together, these results led us to postulate that the convergent signaling pathways of these two hormones causing the inhibition of glycogen catabolism and gluconeogenesis involve a reduction of intracellular cAMP. Thus, cAMP levels may play an important role in the cross talk between both hormones and for the insulin-like effects of leptin.