Effects of ischaemia on content of metabolites in rat liver and kidney in vivo.
TL;DR: The regulatory role of glycogen phosphorylase, pyruvate kinase and phosphofructokinase is discussed in relation to the observed changes in the concentrations of the glycolytic intermediates.
Abstract: 1. The time-course of changes in content of intermediates of glycolysis in rat liver and kidney cortex after severance of blood supply was investigated. 2. The decline in content of ATP was more rapid in kidney (1.7–0.5μmol/g in 30s) than in liver (2.7–1.6μmol/g in 60s). In both tissues AMP and Pi accumulated. 3. Net formation of lactate was 1.7μmol/g during the second minute of ischaemia in liver from well-fed rats, 1.1μmol/g in liver from 48h-starved rats, and about 1.0μmol/g during the first 30s of ischaemia in kidney. Net formation of α-glycerophosphate was rapid, especially in liver. 4. In kidney the concentration of β-hydroxybutyrate rose, but that of α-oxoglutarate and acetoacetate decreased. 5. In both organs the concentrations of fructose diphosphate and triose phosphates increased during ischaemia and those of other phosphorylated C3 intermediates decreased. 6. The concentration of the hexose 6-phosphates rose rapidly during the first minute of ischaemia in liver, but decreased during renal ischaemia. 7. In kidney the content of glutamine fell after 2min of ischaemia, and that of ammonia and glutamate rose. 8. The redox states of the cytoplasmic and mitochondrial NAD couple in kidney cortex were similar to those in liver. 9. The regulatory role of glycogen phosphorylase, pyruvate kinase and phosphofructokinase is discussed in relation to the observed changes in the concentrations of the glycolytic intermediates.
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TL;DR: The oxygen free radical scavengers SOD and DMTU, and allopurinol, which inhibits free radical generation, protected renal function after ischemia, and restoration of oxygen supply to ischemic kidney results in the production of oxygen free radicals, which causes renal injury by lipid peroxidation.
Abstract: During renal ischemia, ATP is degraded to hypoxanthine. When xanthine oxidase converts hypoxanthine to xanthine in the presence of molecular oxygen, superoxide radical (O-2) is generated. We studied the role of O-2 and its reduction product OH X in mediating renal injury after ischemia. Male Sprague-Dawley rats underwent right nephrectomy followed by 60 min of occlusion of the left renal artery. The O-2 scavenger superoxide dismutase (SOD) was given 8 min before clamping and before release of the renal artery clamp. Control rats received 5% dextrose instead. Plasma creatinine was lower in SOD treated rats: 1.5, 1.0, and 0.8 mg/dl vs. 2.5, 2.5, and 2.1 mg/dl at 24, 48, and 72 h postischemia. 24 h after ischemia inulin clearance was higher in SOD treated rats than in controls (399 vs. 185 microliter/min). Renal blood flow, measured after ischemia plus 15 min of reflow, was also greater in SOD treated than in control rats. Furthermore, tubular injury, judged histologically in perfusion fixed specimens, was less in SOD treated rats. Rats given SOD inactivated by prior incubation with diethyldithiocarbamate had plasma creatinine values no different from those of control rats. The OH X scavenger dimethylthiourea (DMTU) was given before renal artery occlusion. DMTU treated rats had lower plasma creatinine than did controls: 1.7, 1.7, and 1.3 mg/dl vs. 3.2, 2.2, and 2.4 mg/dl at 24, 48, and 72 h postischemia. Neither SOD nor DMTU caused an increase in renal blood flow, urine flow rate, or solute excretion in normal rats. The xanthine oxidase inhibitor allopurinol was given before ischemia to prevent the generation of oxygen free radicals. Plasma creatinine was lower in allopurinol treated rats: 2.7, 2.2, and 1.4 mg/dl vs. 3.6, 3.5, and 2.3 mg/dl at 24, 48, and 72 h postischemia. Catalase treatment did not protect against renal ischemia, perhaps because its large size limits glomerular filtration and access to the tubular lumen. Superoxide-mediated lipid peroxidation was studied after renal ischemia. 60 min of ischemia did not increase the renal content of the lipid peroxide malondialdehyde, whereas ischemia plus 15 min reflow resulted in a large increase in kidney lipid peroxides. Treatment with SOD before renal ischemia prevented the reflow-induced increase in lipid peroxidation in renal cortical mitochondria but not in crude cortical homogenates. In summary, the oxygen free radical scavengers SOD and DMTU, and allopurinol, which inhibits free radical generation, protected renal function after ischemia. Reperfusion after ischemia resulted in lipid peroxidation; SOD decreased lipid peroxidation in cortical mitochondria after renal ischemia and reflow. We concluded that restoration of oxygen supply to ischemic kidney results in the production of oxygen free radicals, which causes renal injury by lipid peroxidation.
978 citations
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...On the other hand, the administration of adenine nucleotides could potentially be harmful if the administered ATP, like endogenous ATP, were degraded during ischemia with the production of greater amounts of hypoxanthine and, therefore, increased generation of oxygen free radicals when perfusion was reestablished....
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...Renal ischemia results in a rapid decrease in tissue ATP (2) and a rise in the ATP degradation products adenosine, 1156 M. S. Paller, J. R. Hoidal, and T. F. Ferris J. Clin....
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...Perhaps the simultaneous administration of ATP and free radical scavengers would provide more complete protection than that seen with either alone....
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...Although these studies were undertaken to increase ATP in renal tissue, tissue levels of ATP after allopurinol administration were not measured....
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...During renal ischemia, ATP is degraded to hypoxanthine....
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TL;DR: How ketones serve discrete fine-tuning metabolic roles that optimize organ and organism performance in varying nutrient states and protect from inflammation and injury in multiple organ systems is discussed.
820 citations
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...…100 mM to 2 mM with 24 hr fasting (Figure 2B), while renal steady-state bOHB concentrations approximate 100 mM in the fed state and only 1 mM in the 24 hr fasted state (Figures 2C–2E), observations that are consistent with concentrations quantified more than 45 years ago (Hems and Brosnan, 1970)....
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TL;DR: By acting as ligands for GPCRs, succinate and α-ketoglutarate are found to have unexpected signalling functions beyond their traditional roles and it is shown that succinate increases blood pressure in animals.
Abstract: The citric acid cycle is central to the regulation of energy homeostasis and cell metabolism. Mutations in enzymes that catalyse steps in the citric acid cycle result in human diseases with various clinical presentations. The intermediates of the citric acid cycle are present at micromolar concentration in blood and are regulated by respiration, metabolism and renal reabsorption/extrusion. Here we show that GPR91 (ref. 3), a previously orphan G-protein-coupled receptor (GPCR), functions as a receptor for the citric acid cycle intermediate succinate. We also report that GPR99 (ref. 4), a close relative of GPR91, responds to alpha-ketoglutarate, another intermediate in the citric acid cycle. Thus by acting as ligands for GPCRs, succinate and alpha-ketoglutarate are found to have unexpected signalling functions beyond their traditional roles. Furthermore, we show that succinate increases blood pressure in animals. The succinate-induced hypertensive effect involves the renin-angiotensin system and is abolished in GPR91-deficient mice. Our results indicate a possible role for GPR91 in renovascular hypertension, a disease closely linked to atherosclerosis, diabetes and renal failure.
745 citations
TL;DR: It is shown here that AQP0 from the lens core, containing some carboxy-terminally cleaved AQP1, forms double-layered crystals that recapitulate in vivo junctions, which may be responsible for pore gating.
Abstract: The lens-specific water pore aquaporin-0 (AQP0) is the only aquaporin known to form membrane junctions in vivo. We show here that AQP0 from the lens core, containing some carboxy-terminally cleaved AQP0, forms double-layered crystals that recapitulate in vivo junctions. We present the structure of the AQP0 membrane junction as determined by electron crystallography. The junction is formed by three localized interactions between AQP0 molecules in adjoining membranes, mainly mediated by proline residues conserved in AQP0s from different species but not present in most other aquaporins. Whereas all previously determined aquaporin structures show the pore in an open conformation, the water pore is closed in AQP0 junctions. The water pathway in AQP0 also contains an additional pore constriction, not seen in other known aquaporin structures, which may be responsible for pore gating.
375 citations
TL;DR: It is implied that there is little or no free [Mg2+] gradient between intracellular and extracellular fluids in spite of very different total magnesium concentrations between tissue and Extracellular fluid.
365 citations