Reduced coronary NO production in conscious dogs after the development of alloxan-induced diabetes.
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The role of nitric oxide (NO) in the control of coronary blood flow (CBF) during the development of diabetes is unknown. To study this, mongrel dogs were chronically instrumented using sterile techniques for measurements of systemic hemodynamics and CBF. With heart rate controlled (150 beats/min), veratrine (1-10 micrograms/kg) caused dose-dependent increases in CBF; e.g., 5 mirograms/kg of veratrine increased CBF by 57 +/- 7% from 41 +/- 1.3 ml/min (P < 0.05). The dogs developed diabetes 4-5 wk after injection of alloxan (40-60 mg/kg iv, blood glucose levels were 384 +/- 18 mg/dl). After diabetes the same doses of veratrine caused smaller increases in CBF; i.e., 5 micrograms/kg of veratrine increased CBF by 32 +/- 2% (P < 0.05 compared with control) from 28 +/- 4 ml/min. ACh- and adenosine-induced coronary vasodilation were reduced after diabetes as well. In anesthetized dogs after diabetes, vagal stimulation caused smaller increases in CBF. ACh and bradykinin caused smaller increases in NO(-)(2) production in coronary microvessels from diabetic dogs. Furthermore, despite the fact that mRNA for endothelial cell NO synthase from the aorta was increased twofold with the use of Northern blotting, the protein for aortic endothelial constitutive NO synthase was reduced by 66% after diabetes, as determined by Western blotting. Our results indicate that the NO-dependent coronary vasodilation by the Bezold-Jarisch reflex is impaired in conscious dogs after diabetes. The mechanism responsible for the impaired endothelium-dependent coronary vasodilation is most likely the decreased release of NO from the endothelium. (+info)
Reperfusion-induced oxidative stress in diabetes: cellular and enzymatic sources.
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Reactive oxygen metabolites (ROMs) have been implicated in the pathogenesis of the inflammatory response to ischemia/reperfusion (I/R), which is exacerbated in diabetes. This study revealed an increased (P < 0.01) ROMs production in mesenteric tissue (measured using the oxidant-sensitive fluorochrome dihydrorhodamine 123) after I/R in control and diabetic rats, with larger increments (P <0.0001) observed in the latter group, that was associated with an increased inflammatory response measured by intravital microscopy. Either xanthine oxidase inhibition, superoxide scavenging, ICAM-1 immunoneutralization, or blockade of platelet-activating factor or leukotrienes effectively reduced leukocyte recruitment and ROMs production in control and diabetic rats. Moreover, neutrophils from diabetic rats showed an enhanced production of ROMs in vitro in basal and stimulated conditions. We conclude that the oxidative stress during reperfusion is markedly enhanced in diabetes and this appears to result from increased leukocyte recruitment and a higher capacity of diabetic leukocytes to generate ROMs in response to stimulation. (+info)
Increased bradykinin and "normal" angiotensin peptide levels in diabetic Sprague-Dawley and transgenic (mRen-2)27 rats.
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BACKGROUND: The transgenic (mRen-2)27 rat (TGR) is a high tissue renin, high angiotensin (Ang) II model of hypertension. When administered streptozotocin (STZ), TGRs develop a rapidly progressive diabetic nephropathy with renal failure over 12 weeks. Bradykinin (BK) and Ang II are potent vasoactive peptides that may participate in the vascular and metabolic abnormalities of diabetes. METHODS: TGR and Sprague-Dawley (SD) rats were administered STZ (diabetic) or citrate buffer (nondiabetic) at six weeks of age. Diabetic rats received daily ultralente insulin to maintain moderate hyperglycemia ( approximately 18 mM). Rats were sacrificed four- and eight-weeks post-STZ or vehicle. RESULTS: Diabetes did not modify the blood pressure of either SD rats or TGRs. Diabetes increased levels of BK-(1-9) and its metabolite BK-(1-7) in kidney, aorta, and heart of both SD rats and TGRs. Diabetes did not influence Ang II levels in plasma, kidney, aorta, heart, or adrenal gland of SD rats, but reduced to normal the elevated Ang II levels in plasma, kidney, aorta, and adrenal gland of TGRs. CONCLUSIONS: STZ-induced diabetes was associated with elevated tissue levels of BK-(1-9) and "normal" circulating and tissue levels of Ang II. The increased BK-(1-9) levels were consistent with the participation of this peptide in the vascular and metabolic abnormalities of diabetes. However, the rapidly progressive nephropathy of diabetic TGRs was not associated with BK-(1-9) and Ang II levels in target organs that differed from those of diabetic SD rats. (+info)
Effect of partial pancreatectomy on diabetic status in BALB/c mice.
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Pancreatic regeneration after pancreatectomy has been well documented in animal models. However, the phenomenon of pancreatic regeneration in diabetes has not been exploited as yet. We report here the restoration of euglycaemic status in streptozotocin (STZ)-induced diabetic BALB/c mice, after 50% pancreatectomy. We observed that, after pancreatectomy, STZ-diabetic mice showed a rapid improvement in glycaemic status, starting from the 8th postoperative day, and remained normoglycaemic throughout a 90-day follow-up study. STZ-induced diabetic and control non-diabetic BALB/c mice underwent pancreatectomy and were monitored regularly for changes in body weight, plasma glucose and serum insulin concentrations and histological status of the pancreas. All the pancreatectomised animals showed euglycaemic status from about 20 days after operation, whereas a majority (around 70%) of the diabetic, sham-operated animals died of sustained hyperglycaemia by 20-30 days after operation. Examination of the regenerating pancreas indicated nesidioblastotic activity and supported the theory of a ductal origin of islet stem cells. Islets isolated from the regenerating pancreas showed a progressive increase in islet area (1227.9+/-173.2 micrometer(2) on day 5 compared with 2473.8+/-242.0 micrometer(2) by day 20). The increment in insulin concentrations and subsequent decrement in glycaemia of the diabetic pancreatectomised animals indicate islet neogenesis occurring after the operative insult, leading to a normoglycaemic status, probably recapitulating ontogeny. We have shown that induction of a regenerative stimulus (pancreatectomy) in conditions of STZ-induced diabetes may trigger pancreatic regenerative processes, thereby restoring a functional pancreas, in STZ-diabetic mice. (+info)
Enhanced proteolytic activity directed against the N-terminal of IGF-I in diabetic rats.
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We have recently identified in serum an acid protease which is capable of generating des(1-3)IGF-I from intact IGF-I. Here we have utilized a synthetic substrate with the sequence, biotin-G-P-E-T-L-C-BSA which contains the N-terminal sequence of IGF-I, to investigate the levels of this protease activity in streptozotocin-diabetic rats. Protease activity, quantified in terms of the amount of the biotin label lost, was determined in serum and hepatic extracts from normal control rats, diabetic rats and insulin-treated diabetic rats. Both the serum protease activity and protease activity in hepatic extracts were significantly increased in diabetic rats compared with control rats (P<0.02 and P<0.005). Following acute administration of insulin, a rapid and marked reduction in serum protease activity was observed; with an approximately 50% reduction apparent at 30 min (P<0.001). Chronic insulin treatment of diabetic rats also significantly reduced the serum and hepatic protease activity to the levels seen in control rats. A positive correlation between protease activity and serum glucose level was observed (r=0.58, P<0.005). The abundance of Spi 2.1 mRNA, a serine protease inhibitor, capable of inhibiting the IGF-I protease activity in vitro, was significantly decreased in the liver of diabetic rats and insulin treatment of diabetic rats did not normalize Spi 2.1 mRNA levels. These data suggest that the conversion of IGF-I to the more active des(1-3)IGF-I variant may be enhanced in diabetic animals. Since serum IGF-I levels are reduced in diabetic rats, increased des(1-3)IGF-I-generating protease activity would enhance the functional activity of the circulating IGF-I. (+info)
Cellular immune response to phogrin in the NOD mouse: cloned T-cells cause destruction of islet transplants.
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The ability of nonobese diabetic (NOD) mice to mount a cellular immune response to the secretory granule protein tyrosine phosphatase (PTP), phogrin was evaluated by immunization of 8- to 12-week-old animals with recombinant phogrin in complete Freund's adjuvant. Draining lymph nodes displayed a robust proliferative response to the protein, as did derived T-cell lines and clones. Ten clones obtained by limiting dilution were all CD4+ and of a T-helper-1-like phenotype, but showed variation in their Vbeta usage. Of the 10 clones, 3 responded to endogenous antigens in rat islets. Two of these caused the destruction of rat islets that had been transplanted under the kidney capsule of streptozotocin-treated NOD scid mice without affecting adjacent thyroid implants. The results demonstrate the feasibility of generating antigen-specific diabetes-inducing CD4+ cells by direct immunization of NOD mice and their potential use for further studies of the antigenic epitopes in the PTP family members. The conclusion, based on serological studies, that PTP members do not play a role in the pathogenesis of type 1 diabetes in rodent models needs reevaluation in light of these findings. (+info)
Mechanism responsible for inactivation of skeletal muscle pyruvate dehydrogenase complex in starvation and diabetes.
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Regulation of the activity of the pyruvate dehydrogenase complex in skeletal muscle plays an important role in fuel selection and glucose homeostasis. Activation of the complex promotes disposal of glucose, whereas inactivation conserves substrates for hepatic glucose production. Starvation and diabetes induce a stable increase in pyruvate dehydrogenase kinase activity in skeletal muscle mitochondria that promotes phosphorylation and inactivation of the complex. The present study shows that these metabolic conditions induce a large increase in the expression of PDK4, one of four pyruvate dehydrogenase kinase isoenzymes expressed in mammalian tissues, in the mitochondria of gastrocnemius muscle. Refeeding starved rats and insulin treatment of diabetic rats decreased pyruvate dehydrogenase kinase activity and also reversed the increase in PDK4 protein in gastrocnemius muscle mitochondria. Starvation and diabetes also increased the abundance of PDK4 mRNA in gastrocnemius muscle, and refeeding and insulin treatment again reversed the effects of starvation and diabetes. These findings suggest that an increase in amount of this enzyme contributes to hyperphosphorylation and inactivation of the pyruvate dehydrogenase complex in these metabolic conditions. It was further found that feeding rats WY-14,643, a selective agonist for the peroxisome proliferator-activated receptor-alpha (PPAR-alpha), also induced large increases in pyruvate dehydrogenase kinase activity, PDK4 protein, and PDK4 mRNA in gastrocnemius muscle. Since long-chain fatty acids activate PPAR-alpha endogenously, increased levels of these compounds in starvation and diabetes may signal increased expression of PDK4 in skeletal muscle. (+info)
TGF-beta receptor expression and binding in rat mesangial cells: modulation by glucose and cyclic mechanical strain.
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BACKGROUND: Transforming growth factor-beta (TGF-beta) is a causal factor in experimental glomerulosclerosis, and it mediates the increased extracellular matrix (ECM) accumulation that occurs in cultured mesangial cells (MCs) exposed to high glucose concentrations and cyclic mechanical strain. This change is associated with increased levels of TGF-beta, but may also involve alterations in receptor expression and binding. METHODS: Rat MCs cultured in media containing either 8 or 35 mM glucose were seeded into culture plates with elastin-coated flexible bottoms. Thereafter, they were subjected to cyclic stretch or static conditions and then examined for 125I-TGF-beta1 binding and expression of TGF-beta receptors at the gene and protein levels. RESULTS: Kinetic studies showed that MCs bound TGF-beta1 in a time- and concentration-dependent manner, expressing 6800 high-affinity receptors per cell, with an apparent dissociation constant (Kd) of 15.4 pM, while cross-linking analysis identified three TGF-beta receptors (betaR) corresponding to betaRI, betaRII, and betaRIII of 54, 73, and 200 kDa, respectively. Immunocytochemical studies of betaRI and betaRII protein revealed MC expression in a homogeneous, punctate distribution, whereas Northern analysis demonstrated the presence of the corresponding mRNAs. Exposure to cyclic stretching significantly increased (10%) the overall number of TGF-beta receptors, whereas ligands associated with betaRs I, II, and III also increased (25 to 50%). The finding of increased (30 to 40%) betaRI and betaRII transcript levels and immunoreactive protein (163 and 59%, respectively) in the absence of significant changes in the apparent Kd indicated that stretch-induced binding was the result of increased receptor synthesis and expression and not due to a change in binding affinity. In a similar, but more dramatic fashion, exposure to high glucose also elevated (50%) the receptor number, as well as the amount of ligands associated with betaRs I, II, and III (100 to 250%). This same treatment also increased the levels of betaRI and betaRII mRNA (30 to 40%) and the immunoreactive protein (82 and 82%, respectively), without significantly altering the binding affinity of the receptor. A concerted or synergistic effect of both stimuli was not evidenced. CONCLUSION: These results suggest that the modulation of TGF-beta receptors may be an additional control point in mediating the glucose- and mechanical force-induced increase in ECM deposition by MCs. (+info)