The aim of the experiment was to investigate the mechanism of harmful alloxan action in vivo. 75 mg/kg b.w. of this diabetogenic agent were administered to fasting rats. Two minutes later the animals were decapitated. It was observed that alloxan caused a distinct rise in blood insulin and glucose levels with a concomitant drop of free fatty acids. The amount of sulfhydryl groups in the liver of alloxan-treated rats was decreased and glutathione peroxidase activity was substantially higher. These results indicate that some changes observed in alloxan-induced diabetes can not only be the consequence of B cells damage by alloxan but may also be the result of its direct influence on other tissues. It was also observed that glucose given 20 min before alloxan injection only partially protected against the deleterious effects of alloxan.
Adenosine is known to influence different kinds of cells, including β-cells of the pancreas. However, the role of this nucleoside in the regulation of insulin secretion is not fully elucidated. In the present study, the effects of adenosine A1 receptor antagonism on insulin secretion from isolated rat pancreatic islets were tested using DPCPX, a selective adenosine A1 receptor antagonist. It was demonstrated that pancreatic islets stimulated with 6.7 and 16.7 mM glucose and exposed to DPCPX released significantly more insulin compared with islets incubated with glucose alone. The insulin-secretory response to glucose and low forskolin appeared to be substantially pote ntiated by DPCPX, but DPCPX was ineffective in the presence of glucose and high forskolin. Moreover, DPCPX failed to change insulin secretion stimulated by the combination of glucose and dibutyryl-cAMP, a non-hydrolysable cAMP analogue. Studies on pancreatic islets also revealed that the potentiating effect of DPCPX on glucose-induced insulin secretion was attenuated by H-89, a selective inhibitor of protein kinase A. It was also demonstrated that fo rmazan formation, reflecting metabolic activity of cells, was enhanced in islets exposed to DPCPX. Moreover, DPCPX was found to increase islet cAMP content, whereas ATP was not significantly changed. These results indicate that adenosine A1 receptor blockade in rat pancreatic islets potentiates insulin secretion induced by both physiological and supraphysiological glucose concentrations. This effect is proposed to be due to increased metabolic activity of cells and increased cAMP content., A. Zywert, K. Szkudelska, T. Szkudelski., and Obsahuje bibliografii a bibliografické odkazy
Adenosine is secreted from adipocytes, binds to adenosine A1 receptor and modulates various functions of these cells. In the present study, the effects of an adenosine A1 receptor antagonist (DPCPX; 0.01, 0.1 and 1 μM) on lipogenesis, glucose transport, lipolysis and the antilipolytic action of insulin were tested in rat adipocytes. DPCPX had a very weak effect on lipogenesis and did not significantly affect glucose uptake. In adipocytes incubated with 1 μM DPCPX, lipolysis increased. This effect was blunted by insulin and by a direct inhibitor of protein kinase A. Moreover, 0.1 μM DPCPX substantially enhanced the lipolytic response to epinephrine and increased cAMP in adipocytes. However, DPCPX was ineffective when lipolysis was stimulated by direct activation of protein kinase A. Adipocyte exposure to epinephrine and insulin with or without 0.1 μM DPCPX demonstrated that this antagonist increased the release of glycerol. However, despite the presence of DPCPX, insulin was able to reduce lipolysis. It is concluded that DPCPX had a weak effect on lipogenesis, whereas lipolysis was significantly affected. The partial antagonism of adenosine A1 receptor increased lipolysis in cells incubated with epinephrine alone and epinephrine with insulin due to the synergistic action of 0.1 μM DPCPX and epinephrine., T. Szkudelski, K. Szkudelska, L. Nogowski., and Obsahuje seznam literatury
In order to elucidate the direct effect of glucose on lipolysis in isolated rat adipocytes, cells were incubated in a buffer with different concentrations of this sugar: 2, 8 or 16 mmol/l. The increase in glucose concentration from 2 mmol/l to 8 or 16 mmol/l enhanced basal lipolysis by 30% and 47 %, respectively. Epinephrine-induced lipolysis (1 m mol/l) was also increased by 31 % and 32 %, when glucose concentration was increased from 2 mmol/l to 8 or 16 mmol/l, respectively. The rise in lipolysis caused by glucose was restricted by H-89 (an inhibitor of protein kinase A, 30 µmol/l), but insulin (1 nmol/l) had no inhibitory action. The augmentation of lipolysis by glucose did not require its metabolism (as demonstrated using 2-deoxyglucose) and was due to the action of this sugar on the final steps of the lipolytic cascade, particularly on protein kinase A. However, short-term exposure of adipocytes to higher glucose concentrations did not restrict the inhibitory action of insulin on lipolysis induced by epinephrine., T. Szkudelski, K. Szkudelska., and Obsahuje bibliografii
Leptin is an adipocyte-derived hormone participating in the regulation of food intake and energy balance. Its secretion from fat cells is potentiated by insulin and by substrates providing ATP, whereas factors increasing cAMP level attenuate hormone release stimulated by insulin and glucose. The present experiments were aimed to determine the
effect of cAMP on leptin secretion stimulated by glucose, alanine or leucine in the presence of insulin. Moreover, the effect of protein kinase A inhibition on leptin secretion was tested. To stimulate leptin secretion, isolated rat adipocytes were incubated for 2 h in the buffer containing 5 mmol/l glucose, 10 mmol/l alanine or 10 mmol/l leucine, all in the presence of 10 nmol/l insulin. Inhibition of protein kinase A (PKA) by H-89 (50 μmol/l) slightly enhanced leptin release stimulated by glucose and leucine but not by alanine. Activation of this enzyme by dibutyryl-cAMP (1 mmol/l)
substantially restricted leptin secretion stimulated by glucose, alanine and leucine. The inhibitory influence of dibutyryl-cAMP on leptin secretion was totally (in the case of stimulation induced by glucose) or partially (in the case of stimulation by alanine and leucine) suppressed by H-89. These results demonstrate that leptin secretion induced by glucose, alanine and leucine is profoundly attenuated by cAMP in PKA-dependent manner. Therefore, the action of different stimulators of leptin secretion may be restricted by agents increasing the cAMP content in adipocytes. Moreover, it has also been shown that inhibition of PKA evokes the opposite effect and enhances leptin release.
b1_Rats with diabetes induced by streptozotocin (STZ) and nicotinamide (NA) are often used in animal studies concerning various aspects of diabetes. In this experimental model, the severity of diabetes is different depending on doses of STZ and NA. Moreover, diabetic changes in rats with STZ-NA-induced diabetes are not fully characte rized. In our present study, metabolic changes and insulin secretion were investigated in rats with diabetes induced by administration of 60 mg of STZ and 90 mg of NA per kg body weight. Four to six weeks after diabetes induction, insulin, glucagon and some metabolic parameters were determined to evaluate the severity of diabetes. Moreover, insulin secretory capacity of pancreatic islets isolated from control and diabetic rats was compared. It was demonstrated that admi nistration of 60 mg of STZ and 90 mg of NA per kg body weight induced relatively mild diabetes, since insulin, glucagon an d other analyzed parameters were only slightly affected in diabetic rats compared with control animals. In vitro studies revealed that insulin secretory response was preserved in pancreatic islets of diabetic rats, however, was lower than in islets of control animals. This effect was observed in the presence of different stimuli. Insulin secretion induced by 6.7 and 16.7 mmol/l glucose was moderately reduced in islets of diabetic rats compared with control islets. In the presence of leucine with glutamine, insulin secretion appeared to be also decreased in islets of rats with STZ-NA-induced diabetes. Insulinotropic action of 6.7 mmol/l glucose with forskolin was also deteriorated in diabetic islets. Moreover, it was demonstrated that at a non-stimulatory glucose, pharmacological depolarization of plasma membrane with a concomit ant activation of protein kinase C evoked significant rise in insulin release in islets of control and diabetic rats., b2_However, in diabetic islets, this effect was attenuated. These results indicate that impairment in insulin secretion in pancreatic islets of rats with mild diabetes induced by STZ and NA result s from both metabolic and nonmetabolic disturbances in these islets., T. Szkudelski, A. Zywert, K. Szkudelska., and Obsahuje bibliografii a bibliografické odkazy
Resveratrol is a polyphenol found in different plant species and having numerous health-promoting properties in animals and humans. However, its protective action against deleterious effects of ethanol is poo rly elucidated. In the present study, the influence of resveratrol (10 mg/kg/day) on some hormones and metabolic parameters was determined in rats ingesting 10 % ethanol solution for two weeks. Blood levels of insulin, glucagon and adiponectin were affecte d by ethanol, however, resveratrol partially ameliorated these changes. Moreover, in ethanol drinking rats, liver lipid accumulation was increased, whereas resveratrol was capable of reducing liver lipid content, probably due to decrease in fatty acid synt hesis. Resveratrol decreased also blood levels of triglycerides and free fatty acids and reduced γ-glutamyl transferase activity in animals ingesting ethanol. These results show that resveratrol, already at low dose, alleviates hormonal and metabolic changes induced by ethanol in the rat and may be useful in preventing and treating some consequences o f alcohol consumption., K. Szkudelska, M. Deniziak, P. Roś, K. Gwóźdź, T. Szkudelski., and Obsahuje bibliografii
Adiponectin belongs to the group of biologically active substances secreted by adipocytes and referred to as adipokines. Disturbances in its secretion an d/or action are thought to be involved in the pathogenesis of some metabolic diseases. However, regulation of adiponectin secretion is poorly elucidated. In the present study, short-term regulation of adiponectin secretion in primary rat adipocytes was investigated. Isolated rat adipocytes were incubated in Krebs-Ringer buffer containing 5 mM glucose and insulin alone or in the combination with epinephrine, dibutyryl-cAMP, adenosine A 1 receptor antagonist (DPCPX), palmitate, 2-bromopalmitate or inhibitor of mitochondrial electron transport (rotenone). Adipocyte exposure for 2 h to insulin (1-100 nM) significantly increased secretion of adiponectin compared with secretion observed without insulin. Furthermore, secretion of adipon ectin from adipocytes incubated with glucose and insulin was reduced by 1 and 2 μ M epinephrine, but not by 0.25 and 0.5 μ M epinephrine. Under similar conditions, 1 and 2 mM dibutyryl-cAMP substantially diminished secretion of adiponectin, whereas 0.5 mM dibutyryl-cAMP was ineffective. Secretion of adiponectin was found to be effectively decreased by DPCPX. Moreover, ad ipocyte exposure to rotenone also resulted in a substantial diminution of secretory response of adipocytes incubated for 2 h with glucose and insulin. It was also demonstrated that palmitate an d 2-bromopalmitate (0.06-0.5 mM) failed to affect secretion of leptin. The obtained results indicated that in short-term regulation of adiponectin secretion, insulin and epinephrine exert the opposite effects. These effects appeared as early as after 2 h of exposure. Moreover, deprivation of energy or blockade of adenosine action substantially decreased secretion of adiponectin., T. Szkudelski, L. Nogowski, K. Szkudelska., and Obsahuje bibliografii a bibliografické odkazy
Streptozotocin (STZ) is used to induce experimental diabetes in animals and is also applied for the treatment of patients with insulinoma. The aim of the present work was to investigate the direct effect of STZ on lipolysis in isolated rat adipocytes. After the isolation, the cells were incubated in a Krebs-Ringer buffer of pH 7.4, at the temperature 37 °C for 90 min with different concentrations of STZ: 0.5, 1 or 2 mmol/l. STZ caused a significant rise in basal values (99 %, 199 %, and 377 %, respectively) and epinephrine-stimulated (1 µmol/l) lipolysis (15 %, 24 % and 46 %, respectively). Augmentation of basal lipolysis by STZ was neither restricted by insulin (1 nmol/l) nor by H-89 (an inhibitor of protein kinase A, 50 µmol/l). These results indicate the stimulatory influence of STZ on the action of hormone-sensitive lipase in isolated cells of white adipose tissue. The obtained outcomes suggest that in studies employing STZ, it is necessary to consider its direct effect upon lipolysis in adipocytes., T. Szkudelski, K. Szkudelska., and Obsahuje bibliografii