Aims/hypothesis. Augmented formation of reactive oxygen species (ROS) induced by hyperglycaemia has been suggested to contribute to the development of diabetic nephropathy. This study was designed to evaluate the influence of streptozotocin (STZ)-induced diabetes mellitus, as well as the effects of preventing excessive ROS formation by α-tocopherol treatment, on regional renal blood flow, oxygen tension and oxygen consumption in anaesthetized Wistar Furth rats. Methods. Non-diabetic and STZ-diabetic rats were investigated after 4 weeks with or without dietary treatment with the radical scavenger DL-α-tocopherol (vitamin E, 5%). A laser-Doppler technique was used to measure regional renal blood flow, whilst oxygen tension and consumption were measured using Clarktype microelectrodes. Results. Renal oxygen tension, but not renal blood flow, was lower throughout the renal parenchyma of diabetic rats when compared to non-diabetic control rats. The decrease in oxygen tension was most pronounced in the renal medulla. Renal cellular oxygen consumption was markedly increased in diabetic rats, predominantly in the medullary region. Diabetes increased lipid peroxidation and protein carbonylation in the renal medulla. Treatment with α-tocopherol throughout the course of diabetes prevented diabetesinduced disturbances in oxidative stress, oxygen tension and consumption. The diabetic animals had a renal hypertrophy and a glomerular hyperfiltration, which were unaffected by α-tocopherol treatment. Conclusions/interpretation. We conclude that oxidative stress occurs in kidneys of diabetic rats predominantly in the medullary region and relates to augmented oxygen consumption and impaired oxygen tension in the tissue. [Diabetologia (2003[Diabetologia ( ) 46:1153[Diabetologia ( -1160

In this study, we syngeneically transplanted islets to three different implantation sites of diabetic and nondiabetic rats, then 9 -12 weeks later we measured the blood perfusion and compared the tissue partial pressure of oxygen (PO 2 ) levels of these transplanted islets to endogenous islets. Modified Clark microelectrodes (outer tip diameter 2-6 m) were used for the oxygen tension measurements, and islet transplant blood perfusion was recorded by laser-Doppler flowmetry (probe diameter 0.45 mm). The islet graft blood perfusion was similar in all islet grafts, irrespective of the implantation site. In comparison, the three implantation organs (the kidney cortex, liver, and spleen) differed markedly in their blood perfusion. There were no differences in islet graft blood perfusion between diabetic and nondiabetic recipients. Within native pancreatic islets, the mean PO 2 was ϳ40 mmHg; however, all transplanted islets had a mean PO 2 of ϳ5 mmHg. The oxygen tension of the grafts did not differ among the implantation sites. In diabetic recipients, an even lower PO 2 level was recorded in the islet transplants. We conclude that the choice of implantation site seems less important than intrinsic properties of the transplanted islets with regard to the degree of revascularization and concomitant blood perfusion. Furthermore, the mean PO 2 level in islets implanted to the kidney, liver, and spleen was markedly decreased at all three implantation sites when compared with native islets, especially in diabetic recipients. These results are suggestive of an insufficient oxygenization of revascularized transplanted islets, irrespective of the implantation site. Diabetes 50: -495, 2001A factor of potential importance in the failure of islet grafts is poor or inadequate engraftment of the islets in the implantation organ. Normally, pancreatic islets have a dense glomerular-like capillary network in which the capillaries course through the islet in a tortuous fashion that is ideal for the delivery of oxygen and nutrients to the islet cells and for the dispersal of the secreted hormones to the target organs (1,2). This pancreatic islet angioarchitecture entails a blood perfusion of the pancreatic islets that is 10 times higher than that in the exocrine pancreas and similar to that seen in the renal cortex (ϳ5-7 ml ⅐ min Ϫ1 ⅐ g -1 ) (3-6). However, during the process of isolation and in vitro culture of pancreatic islets preceding transplantation, the islet vasculature dedifferentiates or degenerates (7,8). Therefore, immediately after transplantation, the pancreatic islets are supplied with oxygen and nutrients solely by diffusion from the surrounding tissues. The revascularization process is initiated within a few days, and the islets are generally thought to be fully revascularized by 1 month posttransplantation (9,10). We had previously observed markedly decreased oxygen tension in islets transplanted beneath the renal capsule at 1 month posttransplantation, a decrease that was even more pronounced in diabetic animals (11)....

Palm F, Onozato ML, Luo Z, Wilcox CS. Dimethylarginine dimethylaminohydrolase (DDAH): expression, regulation, and function in the cardiovascular and renal systems. Am J Physiol Heart Circ Physiol 293: H3227-H3245, 2007. First published October 12, 2007; doi:10.1152 doi:10. /ajpheart.00998.2007 )-dimethylarginine (ADMA) inhibits nitric oxide (NO) synthases (NOS). ADMA is a risk factor for endothelial dysfunction, cardiovascular mortality, and progression of chronic kidney disease. Two isoforms of dimethylarginine dimethylaminohydrolase (DDAH) metabolize ADMA. DDAH-1 is the predominant isoform in the proximal tubules of the kidney and in the liver. These organs extract ADMA from the circulation. DDAH-2 is the predominant isoform in the vasculature, where it is found in endothelial cells adjacent to the cell membrane and in intracellular vesicles and in vascular smooth muscle cells among the myofibrils and the nuclear envelope. In vivo gene silencing of DDAH-1 in the rat and DDAH ϩ/Ϫ mice both have increased circulating ADMA, whereas gene silencing of DDAH-2 reduces vascular NO generation and endothelium-derived relaxation factor responses. DDAH-2 also is expressed in the kidney in the macula densa and distal nephron. Angiotensin type 1 receptor activation in kidneys reduces the expression of DDAH-1 but increases the expression of DDAH-2. This rapidly evolving evidence of isoform-specific distribution and regulation of DDAH expression in the kidney and blood vessels provides potential mechanisms for nephron site-specific regulation of NO production. In this review, the recent advances in the regulation and function of DDAH enzymes, their roles in the regulation of NO generation, and their possible contribution to endothelial dysfunction in patients with cardiovascular and kidney diseases are discussed. nitric oxide synthase; hypertension; diabetes mellitus; chronic kidney disease; asymmetric dimethylarginineis an endogenous methylated amino acid that inhibits the constitutive endothelial (e) or type III and neuronal (n) or type I isoforms of nitric oxide (NO) synthase (NOS) (49,91,103,199). It is a less potent inhibitor of the inducible (i) or type II NOS isoform (41,191,213). Proteins are subject to methylation of arginine residues by protein arginine methyltransferase (PRMT). S-adenosylmethionine, which is synthesized from methionine and ATP, serves as the methyl donor and, in the process, is converted to S-adenosylhomocysteine, which itself can be hydrolyzed to homocysteine. Remethylation of homocysteine in the "remethylation pathway" regenerates methionine (14,179). ADMA is released by protein hydrolysis and exported from the cell and taken up by other cells via system y ϩ carriers of the cationic amino acid (CAT) family (14,196,212). ADMA is eliminated both by renal excretion and metabolic degradation. Its metabolism is facilitated by dimethylarginine dimethylaminohydrolases (DDAHs), which are expressed as type 1 and 2 isoforms. Recent studies have shown differential sites of expression of DDAH-1 and -2 in blo...

Bacteria co-ordinate expression of virulence determinants in response to localised microenvironments in their hosts. Here we show that Shigella flexneri, which causes dysentery, encounters varying oxygen concentrations in the gastrointestinal (GI) tract, which govern activity of its type three secretion system (T3SS); the T3SS is essential for cell invasion and virulence 1 . In anaerobic environments (e.g. the GI tract lumen), Shigella expresses extended T3SS needles while reducing Ipa (Invasion plasmid antigen) effector secretion. This is mediated by FNR, a regulator of anaerobic metabolism that represses transcription of spa32 and spa33, virulence genes that the switch in secretion through the T3SS. We demonstrate there is a zone of relative oxygenation adjacent to the GI tract mucosa, caused by diffusing from the capillary network at the tips of villi. This would reverse the anaerobic block of Ipa secretion, allowing T3SS activation at its precise site of action, enhancing invasion and virulence.Shigella virulence depends on its ability to enter epithelial cells by delivering Ipa effectors via its T3SS into the host cell cytoplasm 1 . Secretion through T3SSs is highly regulated.Initially, T3SS needle components are secreted until it reaches a pre-defined length 23 . In inducing conditions, a switch then occurs allowing Ipa secretion through needles, mediating bacterial entry 4 .

SUMMARY The high renal oxygen (O2) demand is associated primarily with tubular O2 consumption (QO2) necessary for solute reabsorption. Increasing O2 delivery relative to demand via increased blood flow results in augmented tubular electrolyte load following elevated glomerular filtration, which, in turn, increases metabolic demand. Consequently, elevated kidney metabolism results in decreased tissue oxygen tension.The metabolic efficiency for solute transport (QO2/TNa) varies not only between different nephron sites, but also under different conditions of fluid homeostasis and disease. Contributing mechanisms include the presence of different Na+ transporters, different levels of oxidative stress and segmental tubular dysfunction.Sustained hyperglycaemia results in increased kidney QO2, partly due to mitochondrial dysfunction and reduced electrolyte transport efficiency. This results in intrarenal tissue hypoxia because the increased QO2 is not matched by a similar increase in O2 delivery.Hypertension leads to renal hypoxia, mediated by increased angiotensin receptor tonus and oxidative stress. Reduced uptake in the proximal tubule increases load to the thick ascending limb. There, the increased load is reabsorbed, but at greater O2 cost. The combination of hypertension, angiotensin II and oxidative stress initiates events leading to renal damage and reduced function.Tissue hypoxia is now recognized as a unifying pathway to chronic kidney disease. We have gained good knowledge about major changes in O2 metabolism occurring in diabetic and hypertensive kidneys. However, further efforts are needed to elucidate how these alterations can be prevented or reversed before translation into clinical practice.