Chronic Streptozotocin-diabetic Rats Research Articles

Ameliorative effect of Withania coagulans on hyperglycaemia and oxidative stress

Introduction: Management of diabetes mellitus always begins with improving glycaemic control by modification of diet, use of oral hypoglycaemic agents and insulin supplementation. However, owing to a steady increase in the dosage of treatment with time and adverse side-effects, there is a demand for new compounds to manage diabetes mellitus. Withania coagulans is a natural product with folkloric medicinal use for chronic disorders of liver, dyspepsia, flatulent coli, intestinal infections, ulcers, rheumatism, bronchitis and degenerative diseases. However, there is lack of information regarding its effect on chronic diabetes mellitus. Objectives: We aimed to evaluate the antihyperglycaemic effect of aqueous W. coagulans extract on hepatic glucose-6-phosphate dehydrogenase (G6PDH) activity and oxidative stress in acute and chronic diabetic models. Materials and methods: The screening of the most effective dose of W. coagulans was determined by postprandial glucose test in streptozotocin (STZ) diabetic rats. The beneficial effects of administration of W. coagulans (10mg/kg) for 21 days on body weight, blood glucose, hepatic G6PDH activity, reduced glutathione (GSH) and malondialdehyde (MDA) were investigated in acute and chronic STZ diabetic rats. Results: W. coagulans (10mg/kg) significantly inhibited the postprandial rise in blood glucose level after food administration at 60, 120 and 240 minutes in STZ rats, compared with control. Twenty-one-day treatment with W. coagulans resulted in significant improvements in body weight and glycaemic control in both acute and chronic diabetic groups. The levels and activities of hepatic G6DPH activity, GSH and MDA were either significantly increased or near normal due to treatment. Conclusions: W. coagulans demonstrated antihyperglycaemic activity in diabetic rats. The beneficial effect was associated with increased hepatic glucose uptake and decrease in oxidative stress, which may attenuate diabetic complications. These data suggest that the dietary intake of W. coagulans may reinforce the effect of existing treatments for diabetes mellitus.

Influence of nitric oxide synthase and kinin antagonists on metabolic parameters in chronic streptozotocin-induced diabetes mellitus.

In vivo administration of HOE 140 (a new bradykinin receptor antagonist) and L-NAME (nitric oxide synthase inhibitor) was performed in chronic streptozotocin-diabetic rats. Basal increases (in umol.g dw-1) in liver (45.0 +/- 3.4.1) and uterine (40.0 +/- 2.95) triglyceride levels in diabetic animals vs control (liver: 34.0 +/- 3.87; uterus: 30.2 +/- 4.01) were partially prevented by L-NAME (p < 0.01), HOE 140 (p < 0.01) and L-NAME + HOE 140 (p < 0.01). High glycogen levels (in mg.g dw-1) observed in diabetic uterine tissue (3.07 +/- 0.90), and decreased glycogen content detected in diabetic liver (11.64 +/- 1.50) vs. control (uterus: 1.59 +/- 0.15, liver: 17.25 +/- 0.87) were unaffected. Uterine 14CO2 production from 14C-U-Glucose (in uCi.mg dw), which is lower in diabetic (35.0 +/- 5.12) than in control (50.12 +/- 4.54) tissues, was improved by HOE 140 (p < 0.05) and L-NAME+HOE 140 (p < 0.05), while hepatic glucose oxidation was not increased by the drugs. Glycemia levels were decreased in diabetic rats injected with L-NAME and L-NAME plus HOE 140. Pancreatic 6-Keto-prostaglandin F1 alpha to Thromboxane B2 ratio was lower in diabetic animals than in controls, and L-NAME and/or HOE 140 treatment prevented the decrement. These findings suggest that vasoactive compounds might prevent streptozotocin-induced damage in pancreatic tissue from chronic diabetic rats.

Influence of Nitric Oxide Synthase and Kinin Antagonists on Metabolic Parameters in Chronic Streptozotocin-Induced Diabetes Mellitus

In vivo administration of HOE 140 (a new bradykinin receptor antagonist) and L-NAME (Nitric oxide synthase inhibitor) was performed in chronic streptozotocin-diabetic rats. Basal increases (in umol.g dw −1) in liver (45.0 ± 3.4.1) and uterine (40.0 ± 2.95) triglyceride levels in diabetic animals vs control (liver: 34.0 ± 3.87; uterus: 30.2 ± 4.01) were partially prevented by L-NAME (p < 0.01), HOE 140 (p < 0.01) and L-NAME + HOE 140 (p < 0.01). High glycogen levels (in mg.g dw −1) observed in diabetic uterine tissue (3.07 ± 0.90), and decreased glycogen content detected in diabetic liver (11.64 ± 1.50) vs. control (uterus: 1.59 ± 0.15; liver: 17.25 ± 0.87) were unaffected. Uterine 14CO 2 production from 14C-U-Glucose (in uCi.mg dw), which is lower in diabetic (35.0 ± 5.12) than in control (50.12 ± 4.54) tissues, was improved by HOE 140 (p < 0.05) and L-NAME + HOE 140 (p < 0.05), while hepatic glucose oxidation was not increased by the drugs. Glycemia levels were decreased in diabetic rats injected with L-NAME and L-NAME plus HOE 140. Pancreatic 6-Keto-prostaglandin F 1alpha to Thromboxane B 2 ratio was lower in diabetic animals than in controls, and L-NAME and/or HOE 140 treatment prevented the decrement. These findings suggest that vasoactive compounds might prevent streptozotocin-induced damage in pancreatic tissue from chronic diabetic rats.

Impaired contraction and relaxation in aorta from streptozotocin-diabetic rats: role of polyol pathway.

The effects of 3 months streptozotocin-induced diabetes mellitus on contraction and relaxation of aorta were examined in vitro. A further diabetic group was treated with a novel sulphonylnitromethane-based aldose reductase inhibitor for 3 months following diabetes induction. Diabetes resulted in reduced maximal tension production, particularly for responses to phenylephrine (p < 0.001) and serotonin (p < 0.001). However, with aldose reductase inhibitor treatment, responses were in the non-diabetic range. The ratio of maximum contractions to noradrenaline and phenylephrine were 28% elevated by diabetes (p < 0.01), which may suggest increased alpha 2-adrenoreceptor-mediated responses. Endothelium-independent relaxation to glyceryl trinitrate was unaffected by diabetes or treatment. By contrast, there were 38% deficits in endothelium-dependent relaxation to acetylcholine (p < 0.001) and Ca2+ ionophore A23187 (p < 0.001) with diabetes which were prevented by aldose reductase inhibitor treatment (p < 0.001). A 121% shift in the concentration giving a 50% maximum effect for acetylcholine towards lower sensitivity with diabetes (p < 0.001) was also largely corrected by treatment (p < 0.001). A non-diabetic group treated with aldose reductase inhibitor showed a 30% decrease in the 50% effective concentration for acetylcholine (p < 0.05). A 15% deficit in maximum relaxation to the ATP-sensitive K+ channel opener cromakalim for the diabetic group (p < 0.001) was prevented by aldose reductase inhibitor treatment (p < 0.01). We conclude that there are polyol pathway related abnormalities for contraction, some aspects of endothelium-independent relaxation, but particularly for endothelium-dependent relaxation in aorta from chronic streptozotocin-diabetic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of arachidonic acid metabolites on cardiac alpha 1-adrenoceptor responses in diabetic rats.

There is evidence that one or more metabolites of arachidonic acid can produce positive inotropic effects and may also be implicated in the enhanced alpha 1-adrenoceptor responses in hearts from diabetic rats. We therefore carried out a study to investigate the possibility that arachidonic acid metabolites could be involved in the altered cardiac alpha 1-effect of norepinephrine (in the presence of propranolol) in chronic streptozotocin-diabetic rats. Our results have shown that in the presence of the cyclooxygenase inhibitor indomethacin or the thromboxane synthetase inhibitor imidazole, the norepinephrine-stimulated positive inotropic effect and the formation of inositol 1,4,5-trisphosphate were significantly increased in control hearts but were unaltered in hearts from diabetic rats. The addition of the prostacyclin synthetase inhibitor tranylcypromine reduced the norepinephrine-stimulated positive inotropic effect and inositol 1,4,5-trisphosphate formation only in diabetic hearts and had no effect in the controls. The nature and physiological significance of the enhanced positive inotropic effect and inositol 1,4,5-trisphosphate formation in the control heart with the addition of indomethacin and imidazole are still unclear. The effect of tranylcypromine may indicate the participation of prostacyclin in mediating the enhanced alpha 1-inotropic effect of norepinephrine in the chronic diabetic heart.

Enhanced arterial contractility to noradrenaline in diabetic rats is associated with increased phosphoinositide metabolism.

The purpose of this study was to investigate whether the increased contractile responsiveness of aortae from male rats with 12-14 week streptozotocin-induced diabetes to noradrenaline is associated with alterations in phosphoinositide metabolism. The contractile response to noradrenaline (10 microM) in both the presence and absence of extracellular calcium was significantly enhanced in aortae from diabetic rats. No significant differences were found between control and diabetic arteries in the basal incorporation of 32P and [3H]myo-inositol into phosphoinositides, or in the basal accumulation of [32P]phosphatidic acid and [3H]inositol phosphates. However, noradrenaline (10 microM) caused significantly greater breakdown of [32P]phosphatidylinositol 4,5-bisphosphate and formation of [32P]phosphatidic acid and [3H]inositol phosphates in diabetic aortae than in control preparations. The production of [3H]inositol phosphates induced by noradrenaline was selectively reduced by the alpha 1-adrenoceptor antagonist, prazosin, in both control and diabetic tissues. These results indicate that phosphoinositide metabolism in response to noradrenaline via stimulation of alpha 1-adrenoceptors is enhanced in aortae from chronic streptozotocin-diabetic rats. The increase in inositol 1,4,5-trisphosphate and 1,2-diacylglycerol production that presumably results could be responsible, at least in part, for the enhanced contractile response of aortae from diabetic rats to noradrenaline.

Effects of experimental diabetes on spontaneous contractions, on the output of prostaglandins and on the metabolism of labelled arachidonic acid, in uteri isolated from ovariectomized rats. Influences of estradiol

Spontaneous changes in isometric developed tension (IDT) as a function of time after isolation (contractile constancy) in uteri from control-castrated and castrated chronic streptozotocin-diabetic rats, were explored. The effects of injecting 17-beta estradiol (E 0) were also studied. No differences in the minor changes of contractile constancy, between control and diabetic preparations, during a period of 60 min, were detected, whereas uteri from non-diabetic E O injected animals (0.5+1.0 ug, prior to sacrifice), exhibited a profound reduction of IDT, significantly greater than in tissues obtained from E 0 injected-diabetic rats. Moreover, basal generation and outputs into the suspending solution of prostaglandins (PGs) E 1, E 2 and F 2α, were explored in the same groups, at 60 min following tissue isolation. The basal outputs of these three PGs were similar in castrated control rats, but preparations from castrated-diabetics released significantly more PGE 1. The administration of E 0 to castrated-diabetics, failed to alter the releases of the three PGs explored. In addition, the metabolism of labelled arachidonic acid (AA) into different prostanoids (6-keto-PGF 1, PGF 2, PGE 2 and thromboxane B 2-TXB 2), was also investigated. The non-diabetic spayed rat uterus converted AA into these four prostanoids, the transformation into 6-keto-PGF 1α (as an index of PGI 2 formation) being the most prominent. In preparations from diabetic rats the formation) being the most prominent. In preparations from diabetic rats the formation of 6-keto-PGF 1α, PGF 2α and PGE 2, was significantly smaller than in controls, whereas a greater % of TXB 2 formation (as an index of TXA 2), was detected. On the other hand uterine preparations from non-diabetic spayed rats injected with E 0 formed less 6- keto-PGF 1α and PGE 2 and similar amounts of PGF 2α or of TXB 2 from AA, than E 0 injected controls, whereas uteri from castrated diabetic animals injected with E 0, formed a similar % of 6-keto-PGF 1α, PGF 2α and PGE 2 from AA, than tissue preparations from non-estrogenized controls. However, the enhanced transformation of the labelled fatty acid precursor (AA) into TXB 2 in the diabetic group, was significantly reduced by the steroid. The role of the augmented generation and release of PGE 1 in uteri from diabetic rats is discussed in terms of precedents indicating the relevance of PGs type E supporting rat uterine motility. In addition the influence of E 0 is attractive, because its reducing effect on TX production, in diabetes, a disease known to be accompanied by enhanced synthesis of vasoconstrictor and platelet aggregation TXA 2, and by frequent obstructive circulatory problems.

Hyperalgesia in spontaneous and experimental animal models of diabetic neuropathy.

Hyperactivity of nociceptive C-fibers has been recently described in diabetic BB/Wistar rats. This study assesses the association of hyperalgesia, using an analgesy-meter, with elevated glycosylated haemoglobin levels in three animal models of diabetic and nutritional neuropathies: Psammomys obesus (sand rat), streptozotocin-treated and galactose-fed rats. Pain threshold measurements (paw pressure test) and motor nerve conduction velocities were recorded in controls (n = 75), hyperinsulinaemic (n = 16), insulin-deficient (n = 46) und galactosaemic (n = 12) animals. The reproducibility of the paw pressure test, evaluated by a correlation coefficient, was statistically significant (p less than 0.001). When compared with their controls (396 +/- 18 g), the average pain threshold in young diabetic sand rats (309 +/- 17 g) was found to be markedly reduced and to correlate inversely (p less than 0.001) with their respective HbA1c levels (mean 4.9 versus 7.4%). Acute, subacute and chronic streptozotocin-diabetic rats displayed a reduction of pain threshold (p less than 0.001) associated with slowed motor nerve conduction velocities (p less than 0.001). Similarly, galactose-feeding over 4 weeks resulted in an elevation of glycosylated haemoglobin levels with significant (p less than 0.001) reductions of pain threshold and motor nerve conduction velocity. It is concluded that hyperalgesia is a constant feature of sensory dysfunction in spontaneous and experimental models of diabetic neuropathy.

The effects of a high fat diet on chronic streptozotocin-diabetic rats.

The effects of a high fat diet (30% (w/w) corn oil) on chronic streptozotocin-diabetic rats were investigated at the whole body level and at the enzyme level. The diet caused significant decreases in the extent of polydipsia (66% decrease), polyphagia (49%), polyuria (67%) and glycosuria (70%). The activities of selected hepatic enzymes from the glycolytic, gluconeogenic, ureogenic and lipogenic clusters were determined. The fat diet caused significant decreases (range: 47 to 54%) in the activity of the ureogenic enzymes carbamyl phosphate synthetase, ornithine transcarbamylase and arginase; had no effect on the glycolytic enzymes glucokinase, hexokinase and pyruvate kinase; partially decreased the diabetes-induced elevated activities of the gluconeogenic enzymes phosphoenolpyruvate carboxykinase (63% decrease), serine dehydratase (90%), alanine aminotransferase (31%) and aspartate aminotransferase (65%), and partially reversed the activity of one lipogenic enzyme, ATP citrate lyase.

Effects of increased heart work on glycolysis and adenine nucleotides in the perfused heart of normal and diabetic rats.

1. In the isolated perfused rat heart, the contractile activity and the oxygen uptake were varied by altering the aortic perfusion pressure, or by the atrial perfusion technique (;working heart'). 2. The maximum increase in the contractile activity brought about an eightfold increase in the oxygen uptake. The rate of glycolytic flux rose, while tissue contents of hexose monophosphates, citrate, ATP and creatine phosphate decreased, and contents of ADP and AMP rose. 3. The changes in tissue contents of adenine nucleotides during increased heart work were time-dependent. The ATP content fell temporarily (30s and 2min) after the start of left-atrial perfusion; at 5 and 10min values were normal; and at 30 and 60min values were decreased. ADP and AMP values were increased in the first 15min, but were at control values 30 or 60min after the onset of increased heart work. 4. During increased heart work changes in the tissue contents of adenine nucleotide and of citrate appeared to play a role in altered regulation of glycolysis at the level of phosphofructokinase activity. 5. In recirculation experiments increased heart work for 30min was associated with increased entry of [(14)C]glucose (11.1mm) and glycogen into glycolysis and a comparable increase in formation of products of glycolysis (lactate, pyruvate and (14)CO(2)). There was no major accumulation of intermediates. Glycogen was not a major fuel for respiration. 6. Increased glycolytic flux in Langendorff perfused and working hearts was obtained by the addition of insulin to the perfusion medium. The concomitant increases in the tissue values of hexose phosphates and of citrate contrasted with the decreased values of hexose monophosphates and of citrate during increased glycolytic flux obtained by increased heart work. 7. Decreased glycolytic flux in Langendorff perfused hearts was obtained by using acute alloxan-diabetic and chronic streptozotocin-diabetic rats; in the latter condition there were decreased tissue contents of hexose phosphates and of citrate. There were similar findings when working hearts from streptozotocin-diabetic rats with insulin added to the medium were compared with normal hearts. 8. The effects of insulin addition or of the chronic diabetic state could be explained in terms of an action of insulin on glucose transport. Increased heart work also acted at this site, but in addition there was evidence for altered regulation of glycolysis mediated by changes in tissue contents of adenine nucleotides or of citrate.