Oxidation of fatty acids by different zones of the rat kidney

Molecular signaling mechanisms of renal gluconeogenesis in nondiabetic and diabetic conditions

The kidneys are as involved as the liver in gluconeogenesis which can significantly contribute to hyperglycemia in the diabetic condition. Substantial evidence has demonstrated the overexpression of rate-limiting gluconeogenic enzymes, especially phosphoenolpyruvate carboxykinase and glucose 6 phosphatase, and the accelerated glucose release both in the isolated proximal tubular cells and in the kidneys of diabetic animal models and diabetic patients. The aim of this review is to provide an insight into the mechanisms that accelerate renal gluconeogenesis in the diabetic conditions and the therapeutic approaches that could affect this process in the kidney. Increase in gluconeogenic substrates, reduced insulin concentration or insulin resistance, downregulation of insulin receptors and insulin signaling, oxidative stress, and inappropriate activation of the renin-angiotensin system are likely to participate in enhancing renal gluconeogenesis in the diabetic milieu. Several studies have suggested that controlling glucose metabolism at the renal level favors effective overall glycemic control in both type 1 and type 2 diabetes. Therefore, renal gluconeogenesis may be a promising target for effective glycemic control as a therapeutic strategy in diabetes.

Mass spectrometric imaging of metabolites in kidney tissues from rats treated with furosemide

In the kidney, metabolic processes are different among the cortex (COR), outer medulla (OM), and inner medulla (IM). Using matrix-assisted laser desorption/ionization (MALDI) and imaging mass spectrometry (IMS), we examined the change of metabolites in the COR, OM, and IM of the rat kidney after furosemide treatment compared with vehicle-treated controls. Osmotic minipumps were implanted in male Sprague-Dawley rats to deliver 12 mg·day(-1)·rat(-1) of furosemide. Vehicle-treated (n = 14) and furosemide-treated (furosemide rats, n = 15) rats in metabolic cages received a fixed amount of rat chow (15 g·220 g body wt(-1)·day(-1) for each rat) with free access to water intake for 6 days. At day 6, higher urine output (32 ± 4 vs. 9 ± 1 ml/day) and lower urine osmolality (546 ± 44 vs. 1,677 ± 104 mosmol/kgH2O) were observed in furosemide rats. Extracts of COR, OM, and IM were analyzed by ultraperformance liquid chromatography coupled with quadrupole time-of-flight (TOF) mass spectrometry, where multivariate analysis revealed significant differences between the two groups. Several metabolites, including acetylcarnitine, betaine, carnitine, choline, and glycerophosphorylcholine (GPC), were significantly changed. The changes of metabolites were further identified by MALDI-TOF/TOF and IMS. Their spatial distribution and relative quantitation in the kidneys were analyzed by IMS. Carnitine compounds were increased in COR and IM, whereas carnitine and acetylcarnitine were decreased in OM. Choline compounds were increased in COR and OM but decreased in IM from furosemide rats. Betaine and GPC were decreased in OM and IM. Taken together, MALDI-TOF/TOF and IMS successfully provide the spatial distribution and relative quantitation of metabolites in the kidney.

Oxidation of fatty acids by kidney microsomes of musk shrew (Suncus murinus)

Substrate specificity and other properties of a fatty acid monooxygenase system in kidney microsomes of the Japanese house musk shrew (Suncus murinus) were examined. The suncus kidney microsomes catalyzed the hydroxylation of various saturated and unsaturated fatty acids to the omega- and (omega-1)-hydroxy derivatives. Laurate was most effectively hydroxylated among saturated and unsaturated fatty acids. The specific activity (53.79 +/- 5.59 [mean +/- SD, n = 6] nmol/nmol cytochrome P450/min) of laurate in suncus kidney microsomes was very high compared with that in liver and kidney microsomes of other species. C18 unsaturated fatty acids were converted to epoxides by a cytochrome P450-dependent fatty acid monooxygenase system in suncus kidney microsomes, in addition to omega- and (omega-1)-hydroxylation products. The monooxygenase system metabolized arachidonic acid only to omega- and (omega-1)-hydroxylation products, not to epoxidation products.

Mechanism of decreased arachidonic acid in the renal cortex of rats with diabetes mellitus

The purpose of this study was to investigate the roles of decreased synthesis and increased consumption in the depression of arachidonic acid levels in renal cortex and glomeruli of rats with streptozotocin-induced diabetes mellitus. In diabetic rats, arachidonic acid was depressed 33.2% in renal cortex, 47.4% in liver and 66.1% in heart compared to values of control rats. delta 6 Desaturase activity was depressed in renal cortex, liver and heart of diabetic rats to 53.3, 55.5 and 63.7%, respectively, of control values. delta 5 Desaturase activity was also depressed 43.7, 55.5 and 47.6% in renal cortex, liver and heart of diabetic rats, respectively. In other rats the activities of five enzymes involved in the synthesis and esterification of arachidonic acid were measured in renal cortex and in isolated glomeruli. Both tissues from diabetic rats showed depressed activities of delta 5 and delta 6 desaturases, increased activities of long-chain acyl-CoA synthetase and 1-acyl-sn-glycero-3-phosphocholine acyltransferase and no change in the activity of elongase as compared to those in control tissues. Malondialdehyde, an end product of lipid peroxidation, was lower in the renal cortex of diabetic rats than in control rats, whereas beta-oxidation of linoleic acid and arachidonic acid were similar in diabetic and in control rats. Basal and stimulated prostaglandin E2 synthesis were significantly higher in isolated glomeruli from diabetic rats compared to those in control rats. In isolated tubules, prostaglandin E2 synthesis was similarly low in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose metabolism in renal tubular function

Heterogeneity of metabolic activity along the nephron points to a very varied relationship between glucose metabolism and ion transport. Glycolysis is linked closely to free-water clearance and possibly to sodium, potassium, and hydrogen ion transport. Glucose oxidation, while not the major source of renal energy, is crucial in sodium, potassium, and phosphate reabsorption. Gluconeogenesis recovers carbon compounds generated during the process of renal ammoniagenesis. Glucose synthesis and active sodium transport appear to compete for renal ATP, although no regulatory function for this competition has been identified. Glucose formed in the proximal tubule may support free-water clearance in adjacent distal tubule, but is not thought to contribute to any medullary function. The complex network of biosynthetic and catabolic pathways of glucose metabolism may have evolved in the kidney to protect the organism against wide variations in glucose demand which would otherwise be unavoidable during the course of rapidly fluctuating renal electrolyte loads.

Chemically induced renal papillary necrosis and upper urothelial carcinoma. Part 1

In the past, renal papillary necrosis (RPN) has been commonly associated with long-term abusive analgesic intake, but over recent years a wide variety of industrially and therapeutically used chemicals have been shown to induce this lesion experimentally or in man. Destruction of the renal papilla may result in: (1) secondary degenerative cortical changes which precede chronic renal failure or (2) a rapidly metastasizing upper urothelial carcinoma, which has a very poor prognosis. This article will briefly review the published data on the morphology, function, and biochemistry of the normal renal medulla and the pathology associated with RPN, together with the secondary changes which give rise to cortical degeneration or epithelial carcinoma. It will then examine in detail those chemicals which have been reported to cause RPN in an attempt to delineate structure-activity relationships. Finally, the many different theories that have been proposed to explain the pathophysiology of RPN will be examined and an hypothesis will be put forward to explain the primary pathogenesis of the lesion and its secondary consequences.

Chemically induced renal papillary necrosis and upper urothelial carcinoma. Part 2

In the past, renal papillary necrosis (RPN) has been commonly associated with long-term abusive analgesic intake, but over recent years a wide variety of industrially and therapeutically used chemicals have been shown to induce this lesion experimentally or in man. Destruction of the renal papilla may result in: (1) secondary degenerative cortical changes which precede chronic renal failure or (2) a rapidly metastasizing upper urothelial carcinoma, which has a very poor prognosis. This article will briefly review the published data on the morphology, function, and biochemistry of the normal renal medulla and the pathology associated with RPN, together with the secondary changes which give rise to cortical degeneration or epithelial carcinoma. It will then examine in detail those chemicals which have been reported to cause RPN in an attempt to delineate structure-activity relationships. Finally, the many different theories that have been proposed to explain the pathophysiology of RPN will be examined and an hypothesis will be put forward to explain the primary pathogenesis of the lesion and its secondary consequences.

Properties of carnitine transport in rat kidney cortex slices

The properties of carnitine transport were studied in rat kidney cortex slices. Tissue:medium concentration gradients of 7.9 for L-[methyl-14C]carnitine were attained after 60-min incubation at 37 degrees C in 40 microM substrate. L- and D-carnitine uptake showed saturability. The concentration curves appeared to consist of (1) a high-affinity component, and (2) a lower affinity site. When corrected for the latter components, the estimated Km for L-carnitine was 90 microM and V = 22 nmol/min per ml intracellular fluid; for D-carnitine, Km = 166 microM and V = 15 nmol/min per ml intracellular fluid. The system was stereospecific for L-carnitine. The uptake of L-carnitine was inhibited by (1) D-carnitine, gamma-butyrobetaine, and (2) acetyl-L-carnitine. gamma-Butyrobetaine and acetyl-L-carnitine were competitive inhibitors of L-carnitine uptake. Carnitine transport was not significantly reduced by choline, betaine, lysine or gamma-aminobutyric acid. Carnitine uptake was inhibited by 2,4-dinitrophenol, carbonyl cyanide m-chlorophenyl-hydrazone, N2 atmosphere, KCN, N -ethylmaleimide, low temperature (4 degrees C) and ouabain. Complete replacement of Na+ in the medium by Li+ reduced L- and D-carnitine uptake by 75 and 60%, respectively. Complete replacement of K+ or Ca2+ in the medium also significantly reduces carnitien uptake. Two roles for the carnitine transport system in kidney are proposed: (1) a renal tubule reabsorption system for the steady-state maintenance of plasma carnitine; and (2) maintenance of normal carnitine levels in kidney cells, which is required for fatty acid oxidation.

Effects of 4-pentenoic acid and furosemide on renal functions and renal uptake of individual free fatty acids

1. Effects of 4-pentenoic acid (4-PA), an inhibitor of fatty acid oxidation, on renal fatty acids (FFA) were investigated using mongrel dogs, and the results compared with findings in the case of furosemide. 2. Continuous infusion of 4-PA at a rate of 0.66 mumoles/kg.min into the renal artery resulted in a marked reduction of glomerular filtration rate after 45 min. Sodium reabsorption rate tended to decrease at 30 min and a significant decrease was seen after 45 min. With decrease in the renal sodium reabsorption rate, the urine flow increased about 3 times, and there was a marked natriuresis. 3. Concentrations of individual FFA in the arterial and renal venous plasma were determined by gas-liquid chromatographic analysis. In the control period, data from 25 dogs showed renal uptake of palmitic, stearic, oleic, and linoleic acids to be approximately 40, 15, 25, and 10 nmoles/g.min, respectively, and the uptake of palmitic and oleic acids was depressed during the natriuresis following administration of 4-PA and furosemide. 4. These results suggest that fatty acids play an important role in the energy supply in renal tubular sodium transport.

[On the effect of cadmium on tissue respiration and gluconeogenesis in rat kidney cortex (author's transl)]

Oxygen consumption (QO2), respiratory quotient (RQ) and gluconeogenesis of rat kidney cortex slices were determined (Warburg technique). QO2 was not influenced by 0.01 mM CdCl2 in the incubation medium (no exogenous substrate added), 0.1 mM, 1mM and 10 mM, respectively, reduced QO2 by 43%, 45% and 68%. In the presence of 8 mM glucose, 10 mM acetate or 5 mM butyrate, 1 mM Cd resulted in a decrease in QO2 by about 50% each. Addition of 20 g/l albumine to the medium abolished this effect of cadmium. RQ was not influenced by a mM Cd, both without and with 8 mM glucose in the medium. Glucose production from 7 mM pyruvate or 5 mM glutaminate in slices from fed and starving rats was reduced by 1 mM Cd to half the value found in controls.