Acute Streptozotocin Diabetes Research Articles

Participation of Heart Mitochondria in Myocardial Protection Against Ischemia/Reperfusion Injury: Benefit Effects of Short-Term Adaptation Processes

Acute streptozotocin diabetes mellitus (DM) as well as remote ischemic preconditioning (RPC) has shown a favorable effect on the postischemic-reperfusion function of the myocardium. Cardioprotective mechanisms offered by these experimental models involve the mitochondria with the changes in functional properties of membrane as the end-effector. The aim was to find out whether separate effects of RPC and DM would stimulate the mechanisms of cardioprotection to a maximal level or whether RPC and DM conditions would cooperate in stimulation of cardioprotection. Experiments were performed on male Wistar rats divided into groups: control, DM, RPC and DM treated by RPC (RPC+DM). RPC protocol of 3 cycles of 5-min hind limb ischemia followed by 5-min reperfusion was used. Ischemic-reperfusion injury was induced by 30-min ischemia followed by 40-min reperfusion of the hearts in Langendorff mode. Mitochondria were isolated by differential centrifugation, infarct size assessed by staining with 1 % 2,3,5-triphenyltetrazolium chloride, mitochondrial membrane fluidity with a fluorescent probe DPH, CoQ(9) and CoQ(10) with HPLC. Results revealed that RPC as well as DM decreased the infarct size and preserved mitochondrial function by increasing the mitochondrial membrane fluidity. Both used models separately offered a sufficient protection against ischemic-reperfusion injury without an additive effect of their combination.

Effect of insulin on characteristics of contractile responses of fast and slow skeletal muscles of rats with acute streptozotocin-induced diabetes

Comparison of amplitude-time characteristics of fast (m. EDL) muscles in rats with acute model of streptozotocin diabetes (SD) (12 and 30 days after treatment with streptozotocin) did not reveal significant changes in strength of single normalized contractile responses as compared with control. In slow (m. Soleus) muscles of rats with the 30-day SD there were observed essential changes in amplitude-time characteristics of such contractile responses: a decrease of their amplitude and an increase of duration. In diabetic rats treated with a course of insulin, resistance of skeletal muscles to both types of exogenous insulin is developing. Both in control and in diabetic animals the fatiguing stimulation of m. EDL by firing from 5 impulses did not reveal significant differences at early (up to 3 min) terms of development of fatigue. Under similar conditions, fatigue of m. Soleus in rats of both diabetic groups developed significantly faster as compared with control (as early as 30 s after the beginning of stimulation). Insulin at a concentration of 5-1 nM produced a dose-dependent decrease of amplitude of single contractile responses in fast and slow muscles of rats with the acute SD model (the negative inotropic action). The same effect of insulin, but at the higher concentrations, we demonstrated earlier in health rats. Insulin at a concentration of 10 nM did not produce essential effect on the time course of depression of responses in the course of development of fatigue at tetanic stimulation of m. EDL and m. Soleus both in control and in diabetic rats, but affected essentially the time course of change in duration of the half-decline (T(hd)) of their tetanic responses. The presence of insulin in the bath solution led to stabilization of the muscle relaxation period in the course of development fatigue in all studied animal groups.

Energy transfer in rat heart mitochondria: Compensatory response to abnormal household of energy in acute streptozotocin diabetes

Energy transfer in rat heart mitochondria: Compensatory response to abnormal household of energy in acute streptozotocin diabetes

Diabetes affects phospholipid content in the nuclei of the rat liver.

The aim of the present study was to examine the effect of acute streptozotocin diabetes on the content of different phospholipids and the incorporation of blood-borne 14C-palmitic acid into the phospholipid moieties in the rat liver nuclei. Diabetes was produced by intravenous administration of streptozotocin, and determinations were carried out two and seven days thereafter. Phospholipids were extracted from isolated nuclei and separated into the following fractions: sphingomyelin, phosphatidylcholine, phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine and cardiolipin. Following that, they were quantified and radioactivity was measured. It was found that, in comparison to non-diabetic controls, two-day diabetes reduced the total content of phospholipids in the nuclei by 9.6%. The content of phospholipids in the nuclei by 9.6%. The content of phosphatidylcholine and phosphatidylserine was reduced and the content of the remaining phospholipids was stable. The specific activity of phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine and cardiolipin, based on radioactivity incorporated from 14C-palmitic acid, was elevated. Seven-day diabetes resulted in a reduction of the total phospholipid content in the nuclei by 39.4%. This was accounted for by a reduction in the content of each phospholipid fraction with the exception of cardiolipin. The specific activity of each phospholipid fraction, was elevated in this group. It is concluded that insulin is involved in the regulation of the nuclear phospholipid content.

Effect of acute streptozotocin diabetes on fatty acid content and composition in different lipid fractions of rat skeletal muscle.

The aim of the present study was to examine the effect of acute streptozotocin diabetes on long chain fatty acid content and composition in different lipid classes of particular muscle types in the rat. Two days after streptozotocin administration, rats were anesthetised, and the white and red sections of the gastrocnemius, the soleus and the blood were taken. Lipids were extracted with chloroform/methanol and separated into different fractions (phospholipids, free fatty acids, di- and triacylglycerols) by means of thin layer chromatography. Fatty acids of each fraction were identified and quantified by means of gas-liquid chromatography. The diabetes resulted in elevation of the concentration of blood glucose (over four-fold) and the plasma free fatty acid (over two-fold). Total free fatty acid content in the muscles of diabetic rats increased by 26% in the white, 24% in the red gastrocnemius and 21% in the soleus. There were also changes in the composition of that fraction in each muscle. Diacylglycerol fatty acid content was elevated in both parts of the gastrocnemius (the white part by 15%, the red part by 44%) and remained stable in the soleus of the diabetic rats. The content of triacylglycerol fatty acids was elevated only in the red gastrocnemius in the diabetic group (by 112%), but changes in fatty acid composition in this fraction occurred in each muscle. The content of phospholipid fatty acids was elevated in the white gastrocnemius (by 13%) and remained stable in other muscles. There were only minor changes in phospholipid fatty acid composition in the diabetic rats. We concluded that acute insulin deficiency changes fatty acid content and composition in skeletal muscle lipids. The changes depend both on lipid fraction and muscle type.

Effect of Acute Diabetes on Rat Hepatic Glucose-6-Phosphatase Activity and Its Messenger RNA Level

Glucose-6-phosphatase catalyzes the final step of glucose production by liver and kidney. Though its strategic position has sparked interest in its regulation, difficulty with isolating a pure, stable enzyme has slowed progress. Virtually all previous work examining the physiologic regulation of this enzyme has relied on estimates of glucose-6-phosphatase activity in crude microsome preparations. The recent cloning of human and murine glucose-6-phosphatase cDNAs has now allowed study of its mRNA expression. We studied the effect of acute, streptozotocin-induced diabetes on hepatic microsomal glucose-6-phosphatase activity and mRNA expression in young (89 ± 3 g), juvenile (304 ± 4 g) and adult (512 ± 10 g) rats. In control rats, mRNA expression and enzyme activity was similar among the three age groups. Streptozotocin-induced diabetes significantly increased the enzyme activities in both intact and triton-treated microsomes in all groups of rats (p<0.001). Glucose-6-phosphatase mRNA expression was increased in the diabetic rats as well (p<0.0001). Blood glucose concentrations correlated significantly with glucose-6-phosphatase mRNA level (p<0.005) and both intact (p<0.002) and triton-treated (p<0.001) microsomal glucose-6-phosphatase activity. Both intact and triton-treated microsomal glucose-6-phosphatase activity correlated with mRNA level (p<0.001, for each). We conclude that acute streptozotocin-diabetes increases expression of glucose-6-phosphatase mRNA and this contributes to the increased glucose-6-phosphatase activity seen with diabetes mellitus.

Parameters of the systemic hemodynamics in conscious rats with acute streptozotocin diabetes

The effect of acute streptozotocin-induced diabetes mellitus on the systemic hemodynamic parameters was studied in conscious rats by thermodilution technique. Male Wistar rats were made diabetic with a single intravenous injection of streptozotocin (STZ, 50 mg/kg). The most important finding of this work was the elucidation of the systemic vasodilation and increased cardiac index one day after STZ injection. Such alteration in hemodynamic parameters could result in the increased blood flow and capillary hypertension in some vascular beds and, therefore, be considered as a pathogenic factor in the development of diabetic microangiopathy.

Insulin stimulates renal glomerular sodium-potassium adenosine triphosphatase activity

The effect of insulin on total and ouabain-inhibited membrane-bound adenosine triphosphatase (ATPase) activity in renal glomeruli isolated from adult white rats was examined. In concentrations of 1–10 μg/ml, insulin significantly stimulated the ouabain-inhibited (Na + + K +)-ATPase activity, without affecting total (composite) ATPase activity. These results, coupled with previous findings demonstrating that glomerular (Na + + K +)-ATPase activity is reduced in acute streptozotocin diabetes, suggest that the renal glomerulus is a target tissue with respect to this biologic effect of insulin.

Proteinuria in the acutely diabetic rat and its response to insulin treatment.

The development of proteinuria and its response to insulin therapy in acute experimental diabetes was examined in 11 female rats by sequentially measuring 24 h excretion of glucose and total protein before diabetes, during 5-37 days of acute streptozotocin diabetes, during and after 7-14 days of continuous subcutaneous insulin administration. Induction of diabetes promptly resulted in marked polyuria (78 +/- 9 ml/24 h), and glycosuria (6.6 +/- 0.7 g/24 h), while proteinuria quadrupled (from 4.7 +/- 0.7 to 18.8 +/- 1.8 mg/24 h, p less than 0.001). Concurrent with amelioration of polyuria and glycosuria by insulin treatment, proteinuria decreased strikingly (8.5 +/- 1.2 mg/24 h, p less than 0.001) Polyuria and glycosuria resumed after discontinuing continuous subcutaneous insulin, and proteinuria promptly returned to pretreatment levels (19.0 +/- 2.5 mg/24 h). Similarly decreased proteinuria (8.8 +/- 0.9 mg/24 h) recurred in five rats retreated with insulin after 100 days of diabetes. Elevated proteinuria was not associated with lysozymuria or consistent changes in glomerular filtration rate. The rapid fluctuations in proteinuria attending acute diabetes and its effective treatment suggest that metabolic aberrations of diabetes may directly effect renal handling of proteins.

Increased blood somatostatin concentration in streptozotocin diabetic rats

Immunoreactive somatostatin (IRS) was measured and characterized in plasma from the abdominal portel vein (PV) and inferior vena cava (IVC) of normal and streptozotocin diabetic rats. At 1 day following the induction of diabetes, PV and IVC levels of IRS were unchanged, at 2 weeks IVC IRS but not PV IRS was increased, but at 6 months both PV and IVC levels were strikingly elevated. Measurement of the IRS content of the pancreas and gut of the 6 month diabetic group showed a significant increase in the pancreas and stomach but not in the lower gut. Gel filtration of PV plasma from control and chronic diabetic rats revealed 3 immunoreactive forms with apparent m.w. of 12–15 K, 3.6 K and 1.6 K daltons. Immunoreactive somatostatin in the IVC was composed predominantly of the 12–15 K material in normal and diabetic rats. These results suggest that chronic but not acute streptozotocin diabetes leads to increased secretion of IRS from the pancreas and upper gut and to altered peripheral metabolism of IRS. Plasma IRS is heterogeneous, the main component being a high molecular weight form, the concentration of which is markedly increased in chronic insulinopenic diabetes.

Abnormal sciatic nerve myo-inositol metabolism in the streptozotocin-diabetic rat: effect of insulin treatment.

The metabolism of myo-inositol and its hospholipids has been studied in the sciatic nerves of control, two weeks' streptozotocin-diabetic, and insulin-treated diabetic rats. The concentrations of glucose, fructose, and sorbitol were increased and the concentration of myo-inositol was decreased in the sciatic nerves of the diabetic animals; these abnormalities were only partially corrected by insulin therapy that was adequate to obviate hyperglycemia. Whereas the space of distribution of 2-3H-myo-inositol was found to exceed the total water space of the nerves of control animals, the 2-3H-myo-inositol space approximated the water space in the nerves of diabetic animals and was only slightly increased after insulin therapy. During the first 2 h after the intraperitoneal injection of 2-3H-myo-inositol, the recovery of radioactivity in nerve lipids was decreased by 69% in the untreated diabetics and by 77% in the insulin-treated diabetics. Analysis of the individual phosphoinositides revealed a proportional increase in the radioactivity recovered with phosphatidylinositol and a decrease in the recovery with triphosphatidylinositol in the diabetic nerves. CDP-diglyceride:inositol transferase activity was decreased by 44% in homogenates of sciatic nerves from untreated diabetic rats, but it was normal in nerve homogenates from insulin-treated diabetics. The pattern of incorporation of radioactivity into phospholipids after 1 h of incubation of nerve homogenates with 2-3H-myo-inositol was similar to that observed in vivo. The fractional recovery of radioactivity with phosphatidylinositol was increased, whereas the recovery of label as triphosphatidylinositol was decreased by 11% in the presence of homogenates of sciatic nerves from diabetic rats. These observations indicate that 2 wk of acute streptozotocin diabetes results in a decrease in the sciatic nerve content and space of distribution of myo-inositol and suggests that nerve myo-inositol transport may be defective in the diabetic animal. The observed abnormalities in the amount and pattern of incorporation of 2-3H-myo-inositol into diabetic nerve phospholipids could be explained, in part, by decreased activities of CDP-diglyceride:inositol transferase and phosphatidylinositol 4-phosphate kinase activities in the diabetic nerves. However, the fact that the incorporation of 2-3H-myo-inositol into phospholipids was decreased in the nerves of insulin-treated—diabetic animals despite a normal CDP-diglyceride:inositol transferase activity suggests that defective myo-inositol transport may also contribute to the abnormal neural phosphoinositide metabolism in this model. The possibility that these abnormalities are related to the development of the structural and functional changes associated with diabetic neuropathy requires further investigation.

An alteration in internodal myelin membrane structure in large sciatic nerve fibres in rats with acute streptozotocin diabetes and impaired nerve conduction velocity.

Replicas of the freeze-fracture surfaces of the internodal myelin membranes of large sciatic nerve fibres from normal and diabetic rats were compared by quantitative electron microscopy. The internodal myelin of the diabetics was examined 14 days after streptozotocin (70 mg/kg IV) induced persistent hyperglycaemia, conditions under which sciatic motor nerve conduction velocity (MNCV) is consistently decreased by 20%. The number of intramembranous particles per unit area of both the P-face and the E-face of the internodal myelin membrane was significantly decreased in the diabetics. This alteration in the structure of the internodal myelin membrane was not found in large sciatic nerve fibres from diabetic rats treated with insulin from day 3 through 14, or from diabetic rats fed a diet containing 1% myoinositol; these are conditions under which the development of decreased sciatic MNCV is prevented or ameliorated. An alteration in internodal myelin structure occurs in acute streptozotocin diabetes which may explain the associated decreased sciatic MNCV.

Effects of insulin and dietary myoinositol on impaired peripheral motor nerve conduction velocity in acute streptozotocin diabetes.

The factors influencing the development of impaired sciatic motor nerve conduction velocity (MNCV) in acute experimental diabetes were examined. Decreased MNCV developed by the 14th day after streptozotocin administration but only in rats which became hyperglycemic. Insulin treatment, begun on day 3, failed to prevent imparied MNCV in diabetic rats in which improved or normal weight gain and a decreased degree of hyperglycemia was induced. However, insulin treatment prevented the development of impaired MNCV in a group of diabetic rats in which the tail vein plasma glucose concentration was never found to exceed 160 mg/dl during days 6 through 14, andin which the mean plus or minus SEM of the average plasma glucose concentration for each animal during the same period was 75 plus or minus 18 mg/dl. In normal rats fed diets containing 0.011% or 0.069% free myoinositol (a presumably normal range), sciatic nerve free myoinositol concentrations were 90- and 60-fold higher than those in plasma. On these diets the development of impaired MNCV in the diabetics was associated with a decrease in nerve free myoinositol as compared with nerves from normals fed the same diet, despite similar plasma levels in the normals and diabetics. Plasma and nerve free myoinositol increased with increasing dietary myoinositol content in both normals and diabetics, and nerve myoinositol content could be acutely increased by an i.p. myoinositol load. By supplementing the diets with 1.0% myoinositol, the difference in nerve myoinositol in normal and diabetic rats on day 14 was abolished; on this diet the development of impaired MNCV in the diabetics was moderated or totally prevented, despite persistent hyperglycemia and elevated nerve sorbitol and fructose concentrations. Insulin treatment that prevented impaired MNCV prevented a decrease in nerve myoinositol in diabetics. These studies suggest that insulin deficiency, and possibly hyperglycemia, are primary factors in the development of imparied MNCV in acute experimental diabetes. However, the development of impaired MNCV appears to be related in some manner to a derangement in the regulation of nerve free myoinositol content, which appears to be subject to modification by increases in plasma myoinositol concentration over a critical range.

Vascular basement membrane thickness in muscle of spiny mice and activities of glycolysis and gluconeogenesis in the liver of animals with spontaneous and experimental diabetes and of untreated human diabetics.

Vascular basement membrane thickness in the muscle was measured in spiny mice according to the method of Sipersteinet al. (1968). The mean basement membrane width in spiny mice with normal glucose tolerance was 73±16 nm and in spiny mice with moderately and severely impaired glucose tolerance 75±18 and 80±18 nm respectively. In spiny mice with long lasting overt ketotic diabetes the basement membrane width was 105±9 nm. This small increase is unlikely to be related to diabetes since it is within the range of basement membrane thickness measured in normal swiss mice and far below the range described in human and experimental diabetes. — The activity of different enzymes of glycolysis and gluconeogenesis was measured in the liver of animals with experimental and spontaneous diabetes and in untreated human diabetes. The pattern of liver enzyme activity found under the different conditions could be related to the type of diabetes present. In the case of insulin deficiency (acute streptozotocin diabetes of rats, ketotic type of diabetes of spiny mice and untreated human juvenile diabetes) there is a decrease in the activity of GK, PFK and PK while FDPase and G-6-Pase activity was increased and aldolase activity unchanged. In the case of non-ketotic diabetes (mild spontaneous diabetes of spiny mice, obese hyperglycemic Bar Harbor mice, New Zealand obese mice, human maturity onset type diabetes) the activity of glucokinase was significantly increased. While the activity of gluconeogenetic enzymes increased only in the more severe states of hyperglycemia, the activity of PK increased only in the milder forms of the non-ketotik diabetes.