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Effect of acute uremia on triglyceride kinetics in the rat.

Plasma triglyceride (TG) levesl were elevated 24 hr after the production of acute uremia in rats. The effect of acute uremia on TG production rate was estimated by determining the rate of TG accumulation following Triton WR 1339 inhibition of lipoprotein removal, by measuring hepatic TG secretion rate during in situ liver perfusion, and by quantifying hepatocyte very low density lipoprotein content with the electron microscope. The results of all three of these approaches indicated that TG synthesis and secretion were decreased in acute uremia, suggesting that the associated increase in plasma TG levels had to result from a removal defect. This hypothesis was tested directly by injecting pre-labeled very low density lipoprotein TG into acutely uremic and control rats, and measuring its rate of disappearance from plasma. The t1/2 of removal in acutely uremic rats was found to be approximately twice that of control, confirming the hypothesis that the rise in plasma TG levels in acute uremia is due to a defect in removal of TG from plasma.

Acute Disease↗

Uremia-induced disturbances in hepatic carbohydrate metabolism: enhancement by sucrose feeding.

A high-sucrose (S) diet accentuates anorexia and stunts growth in uremic (U) rats, and an oral S load induces a greater hyperfructosemia in U rats than in control (C) rats. Four studies were performed to determine the roles of S feeding and an acute S load on liver carbohydrate (CHO) metabolism in U and C rats (eight to 10 rats per group). We also examined the plasma responses to either water or a S load. Levels of the main metabolites of glycolysis, gluconeogenesis, and glycogenesis were measured under basal conditions (7 hours' postmeal) in U and C rats fed either a cornstarch diet (study I) or S diet (study II) and at 30 and 60 minutes after an intragastric S load (studies III and IV) in s-fed U and C rats. The weight gain, food intake, and plasma creatinine and urea levels of the rats in the four studies were comparable. Weight gain and liver weight (g/100 g body weight) were lower in U than in C rats. In the plasma, baseline levels of lactate were decreased by uremia and S feeding and those of glucose (G) were increased by S feeding. The increases in plasma G and fructose (F) levels after a S load were greater in U rats than in C rats, whereas those of plasma lactate were comparable. In the liver under basal conditions, uremia markedly decreased levels of glycogen, F-1,6-diphosphate (F-1,6-diP), F-2,6-diP, 3-glycero-phosphate (3-glycero-P), dihydroxyacetone phosphate (DHAP), pyruvate, lactate, and adenosine triphosphate (ATP), and the phosphorylation state (ATP/adenosine diphosphate [ADP] x inorganic phosphorus [PI]), increased phosphoenolpyruvate (PEP), ADP, and Pi levels, but did not affect the cytosolic redox state (pyruvate/lactate). In addition to uremia, S feeding further decreased levels of glycogen, F-2,6-diP, 3-glycero-P, and ATP. After S loading, liver F levels increased more in U than in C rats, but glycogen and 3-glycero-P levels increased less in U than in C rats. Liver lactate and pyruvate levels increased more in U than in C rats, and the pyruvate/lactate and DHAP/3-glycero-P ratios were higher in U than in C rats after a S load. The ATP level and the phosphorylation state in U rats increased 30 minutes later in U than in C rats. Our findings indicate that uremia causes a depletion in liver glycogen, which is enhanced by S feeding and could be partially attributed to decreased glycogen synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

The effects of uremia and dietary phosphorus on the bone of rats.

In order to evaluate the effects of uremia and low levels of dietary phosphorus on bone, male Sprague-Dawley rats weighing 320 +/- 20 g (12 weeks old) were subjected to either a two-step, subtotal nephrectomy or sham-operation (SO), and then fed a custom diet with either normal calcium (0.5%) and normal phosphorus (0.3%) (NCNP), or normal calcium and low phosphorus (0.03%). When compared to the NCNP SO group after seven days, only uremic rats fed low phosphorus diets developed osteomalacia characterized by an increase in the osteoid thickness, surface and volume, a prolonged osteoid maturation time, and a decreased bone formation rate. No other groups developed these changes. This osteomalacia was also associated with hypophosphatemia, a reduced serum PTH and an elevation in the serum 1,25(OH)2D3. It was concluded that while neither this degree of uremia nor the low phosphorus diets alone had any significant effect, the combination of uremia and low dietary phosphorus resulted in the initiation of osteomalacia. This animal model should prove useful in investigations dealing with the influence of uremia on the mineralization process.

Animals↗

Effect of chronic uremia on fructose 2,6-bisphosphate glycolytic and gluconeogenic enzymes in rat liver.

The level of fructose 2,6-bisphosphate and the maximal activities of key gluconeogenic and glycolytic enzymes were determined in the liver of a rat model of chronic uremia and in ad libitum-fed control and pair-fed control animals. Fructose 2,6-bisphosphate was decreased in uremia and its level negatively correlated with the concentration of blood urea nitrogen. The changes in gluconeogenic enzymes in uremic rats were not different from those in the pair-fed controls. However, pyruvate kinase was decreased in uremia when compared to both controls. These studies offer a possible mechanism for the role of the liver in the carbohydrate intolerance of uremia.

Animals↗

Effects of diabetes and uremia on mesenteric vascular reactivity.

BACKGROUND: Diabetes and uremia are comorbid conditions that have significant effects on cardiovascular physiology. These studies were designed to examine the effects of diabetes and uremia on vascular reactivity. METHODS: Sprague-Dawley rats were divided into control (C), diabetic (D), uremic (U), and diabetic/uremic (D + U) groups. Diabetes (D, D + U groups) was induced with an injection of streptozotocin. Uremic (U, D + U groups) was produced by seven-eighths nephrectomy. Serum glucose, blood urea nitrogen, creatinine, creatinine clearance, and protein excretion were measured at baseline and before microvascular studies at 4 or 8 weeks after injection. Vascular reactivity was studied in isolated, pressurized, and superfused segments of mesenteric arterioles (300 microns). Changes in internal vessel diameter were measured in response to phenylephrine (10(-8) to 10(-4) mol/L), acetylcholine (10(-9) to 10(-5) mol/L), and nitroprusside (10(-9) to 10(-2) mol/L). RESULTS: Results at 4 and 8 weeks were similar in all groups. Vasoconstrictor responses to phenylephrine and endothelium-independent vasodilator responses to nitroprusside were not altered in any experimental group. Endothelium-dependent vasodilator responses to acetylcholine were significantly depressed in both diabetic groups (D and D + U, p < 0.01 versus control), and there were no differences between the two diabetic groups. CONCLUSIONS: Streptozotocin-induced diabetes results in impairment of endothelial-dependent (nitric oxide mediated) vasodilator responses in mesenteric resistance vessels, which are unaffected by coexisting uremia. Uremia has little effect on mesenteric vascular reactivity in this model.

Acetylcholine↗

Absence of somatic RET gene mutation in sporadic parathyroid tumors and hyperplasia secondary to uremia, and absence of somatic Men1 gene mutation in MEN2A-associated hyperplasia.

Germline mutations of the MEN1 gene are found in more than 85% of multiple endocrine neoplasia type 1 (MEN 1) patients, and germline mutations of the RET gene are found in more than 95% of multiple endocrine neoplasia type 2 (MEN2) patients. Parathyroid hyperplasia is seen in more than 90% of MEN 1 and about 15% of MEN2A patients. To date, somatic MEN1 mutations are reported in about 20% of sporadic parathyroid tumors. To elucidate the genetic basis of parathyroid tumor development, we examined somatic RET gene mutations in sporadic parathyroid tumors and hyperplasia secondary to uremia, and somatic MEN1 gene mutations in parathyroid hyperplasia from MEN2A patients. A total of 145 parathyroid tumors comprising 129 sporadic parathyroid tumors, 14 hyperplastic lesions secondary to uremia, and two hyperplastic lesions from MEN2A patients were examined. DNA was extracted from fresh frozen parathyroid tissue. Exons 2-10 of the MEN1 gene and exons 10 and 11 of the RET gene were sequenced. No somatic RET gene mutations were found in the 129 sporadic parathyroid tumors or 14 parathyroid hyperplastic lesions secondary to uremia. No somatic MEN1 gene mutations were found in the two parathyroid hyperplasia from MEN2A patients. These data suggest that RET gene mutation may not be involved in the development of sporadic parathyroid tumors and hyperplasia secondary to uremia and that MEN1 gene mutation may not be or is rarely associated with development of parathyroid hyperplasia in MEN2A patients.

Aged↗

Host immune status in uremia. IV. Phagocytosis and inflammatory response in vivo.

Infection is a frequent complication and cause of death in renal failure, but the association between uremia, depressed immune status, and susceptibility to infection is far from proven. In the present studies, the effect of uremia on the inflammatory response and phagocytic ability was investigated in an animal model. The inflammatory response, as measured by the ability of leukocytes to mobilize into subcutaneous implanted sponges, was impaired at 6 hr but was normal 24 hr after implantation. The peripheral blood response of uremic animals to the leukocytosis promoting protein from Bordetella pertussis was similar to that of control animals. Reticuloendothelial clearance of labelled albumin was unimpaired but catabolism of this substance was reduced significantly in uremic animals. The ability of the uremic host to clear an intravenous challenge of virus was also depressed. Phagocytic and bactericidal capability of polymorphonuclear (PMN) leukocytes, measured in vitro by latex ingestion and phagocytosis and killing of Staphylococcus aureus, was normal. PMN phagocytic function in vivo was determined by the clearance of viable Escherichia coli from subcutaneously implanted sponges and no significant difference between control and uremic groups was found. These studies have further defined the effect of uremia on immune mechanisms and support our contention that uremia per se is not a major factor contributing to the compromised immune status in this host.

Animals↗

Work-induced changes in skeletal muscle IGF-1 and myostatin gene expression in uremia.

Resistance to growth hormone (GH)-induced insulin-like growth factor-1 (IGF-1) gene expression contributes to uremic muscle wasting. Since exercise stimulates muscle IGF-1 expression independent of GH, we tested whether work overload (WO) could increase skeletal muscle IGF-1 expression in uremia and thus bypass the defective GH action. Furthermore, to provide insight into the mechanism of uremic wasting and the response to exercise we examined myostatin expression. Unilateral plantaris muscle WO was initiated in uremic and pairfed (PF) normal rats by ablation of a gastrocnemius tendon and adjoining part of this muscle with the contralateral plantaris as a control. Some rats were GH treated for 7 days. WO led to similar gains in plantaris weight in both groups and corrected the uremic muscle atrophy. GH increased plantaris IGF-1 mRNA >twofold in PF rats but the response in uremia was severely attenuated. WO increased the IGF-1 mRNA levels significantly in both uremic and PF groups, albeit less brisk in uremia; however, after 7 days IGF-1 mRNA levels were elevated similarly, >2-fold, in both groups. In the atrophied uremic plantaris muscle basal myostatin mRNA levels were increased significantly and normalized after an increase in WO suggesting a myostatin role in the wasting process. In the hypertrophied uremic left ventricle the basal myostatin mRNA levels were reduced and likely favor the cardiac hypertrophy. Together the findings provide insight into the mechanisms of skeletal muscle wasting in uremia and the hypertrophic response to exercise, and suggest that alterations in the balance between IGF-1 and myostatin play an important role in these processes.

Animals↗

Autoxidation products of both carbohydrates and lipids are increased in uremic plasma: is there oxidative stress in uremia?

BACKGROUND: Advanced glycation end products (AGEs), formed by non-enzymatic glycation and oxidation (glycoxidation) reactions, have been implicated in the pathogenesis of several diseases, including normoglycemic uremia. AGE research in uremia has focused on the accumulation of carbohydrate-derived adducts generated by the Maillard reaction. Recent studies, however, have demonstrated that one AGE, the glycoxidation product carboxymethyllysine (CML), could be derived not only from carbohydrates but also from oxidation of polyunsaturated fatty acids in vitro, raising the possibility that both carbohydrate and lipid autoxidation might be increased in uremia. METHODS: To address this hypothesis, we applied gas chromatography-mass spectrometry and high performance liquid chromatography to measure protein adducts formed in uremic plasma by reactions between carbonyl compounds and protein amino groups: pentosidine derived from carbohydrate-derived carbonyls, malondialdehyde (MDA)-lysine derived from lipid-derived carbonyls, and CML originating possibly from both sources. RESULTS: All three adducts were elevated in uremic plasma. Plasma CML levels were mainly (>95%) albumin bound. Their levels were not correlated with fructoselysine levels and were similar in diabetic and non-diabetic patients on hemodialysis, indicating that their increase was not driven by glucose. Pentosidine and MDA-lysine were also increased in plasma to the same extent in diabetic and non-diabetic hemodialysis patients. Statistical analysis indicated that plasma levels of CML correlated weakly (P < 0.05) with those of pentosidine and MDA-lysine, but that pentosidine and MDA-lysine varied independently (P > 0.5). CONCLUSIONS: These data suggest that the increased levels of AGEs in blood, and probably in tissues, reported in uremia implicate a broad derangement in non-enzymatic biochemistry involving alterations in autoxidation of both carbohydrates and lipids.

Adult↗

Alterations in nonenzymatic biochemistry in uremia: origin and significance of "carbonyl stress" in long-term uremic complications.

Advanced glycation end products (AGEs), formed during Maillard or browning reactions by nonenzymatic glycation and oxidation (glycoxidation) of proteins, have been implicated in the pathogenesis of several diseases, including diabetes and uremia. AGEs, such as pentosidine and carboxymethyllysine, are markedly elevated in both plasma proteins and skin collagen of uremic patients, irrespective of the presence of diabetes. The increased chemical modification of proteins is not limited to AGEs, because increased levels of advanced lipoxidation end products (ALEs), such as malondialdehydelysine, are also detected in plasma proteins in uremia. The accumulation of AGEs and ALEs in uremic plasma proteins is not correlated with increased blood glucose or triglycerides, nor is it determined by a decreased removal of chemically modified proteins by glomerular filtration. It more likely results from increased plasma concentrations of small, reactive carbonyl precursors of AGEs and ALEs, such as glyoxal, methylglyoxal, 3-deoxyglucosone, dehydroascorbate, and malondialdehyde. Thus, uremia may be described as a state of carbonyl overload or "carbonyl stress" resulting from either increased oxidation of carbohydrates and lipids (oxidative stress) or inadequate detoxification or inactivation of reactive carbonyl compounds derived from both carbohydrates and lipids by oxidative and nonoxidative chemistry. Carbonyl stress in uremia may contribute to the long-term complications associated with chronic renal failure and dialysis, such as dialysis-related amyloidosis and accelerated atherosclerosis. The increased levels of AGEs and ALEs in uremic blood and tissue proteins suggest a broad derangement in the nonenzymatic biochemistry of both carbohydrates and lipids.

Chronic Disease↗

Central nervous dysfunction in uremia.

The mechanisms of central nervous system dysfunction in uremia are multifactorial and only partially characterized. Studies using sealed presynaptic nerve terminals (synaptosomes) for in vitro ion transport and metabolism of neurotransmitter in chronic renal failure (CRF) neuronal cell culture and in vivo brain structure microdialysis generated significant new information. An increase in total calcium content of the cerebral cortex accompanied by increased levels of cytosolic calcium ([Ca(2+)]i) in synaptosomes are common findings in rats with CRF. Mechanisms leading to the increase in [Ca(2+)]i include increased calcium uptake mediated by parathyroid hormone and decreased activity of Na(+),K(+)-adenosine triphosphatase (ATPase) and Ca(2+)-ATPase of synaptosomes in CRF rats. Moreover, these synaptosomes respond inappropriately to depolarization, which can impair neurotransmitter metabolism. Brain gamma-aminobutyric acid content, norepinephrine, and acetylcholine release uptake and degradation are affected by uremia. These may lead to certain somatic, behavioral, and motor dysfunctions in uremia. Many derangements of the central nervous system in uremia appear to be mediated by secondary hyperparathyroidism of CRF because parathyroidectomy of animals with CRF prevented the increase in basal levels of [Ca(2+)]i and derangements in neurotransmitter metabolism. The role of other neurotoxins, such as guanidinosuccinic acid, are also reviewed.

Adenosine Triphosphate↗

Zinc and the sodium pump in uremia.

A defect in sodium transport is known to exist in the leucocytes of uremic patients. Recent work has shown changes in cation flux rates associated with alterations of extracellular zinc concentration. As plasma zinc is known to be low in uremia, the possibility that this might be the cause of the defect in membrane transport was investigated. Plasma zinc was shown to be lower in uremic patients than in normal controls but this was not matched by alterations in leucocyte zinc content. Leucocytes from normal subjects and from patients with uremia have similar increases in the sodium efflux rate constant when exposed to elevated extracellular zinc concentrations. However, the abnormality in leucocyte sodium transport in uremia was not completely corrected by elevation of the extracellular zinc, when compared with normal cells in the same zinc concentrations. Although extracellular zinc is a factor that must be controlled in studies of cellular membrane transport, a low plasma zinc is not the explanation for the defect of sodium transport seen in uremia.

Biological Transport↗

Serum lipid and lipoprotein concentrations in chronic uremia.

The concentrations of triglycerides and cholesterol have been determined in total serum and in the three major serum lipoprotein classes--very low (VLDL), low (LDL) and high (HDL) density lipoproteins-after an overnight fast in 39 patients with chronic uremia of more than 2 years' duration and with serum creatinine above 350 mumol/l. The values were compared with data from healthy male and female controls. The findings were similar for male and female uremics. Hypertriglyceridemia was common while serum cholesterol tended to be normal or subnormal. With the conventional typing system for hyperlipidemia, types II A, III and IV were present in 6,9 and 30%,respectively. The tryglyceride and cholesterol concentrations in VLDL were increased, while their normal relation for this lipoprotein class was maintained. In LDL the concentration of tryglycerides was increased, while that of cholesterol was low. The LDL composition, therefore, was changed to be more triglyceride-rich than normal. The changes in concentration and composition of LDL indicated that the levels of LDL 1 were raised and of LDL 2 decreased in chronic uremia. Increased levels of LDL tryglycerides occurred more frequently (40%) than increased levels of VLDL triglycerides (33%). The most striking and consistent lipoprotein abnormality was a low HDL cholesterol, which was not related to high VLDL levels. The HDL tryglycerides, on the other hand, tended to be somewhat high. The importance of the raised levels of the triglyceride-rich VLDL and LDL 1 and the decreased levels of HLD cholesterol for the rapid development of atherosclerotic vascular diseases which occur in chronic uremia is discussed. It is of interest in this context that both total cholesterol and LDL cholesterol were low. The possible mechanisms underlying the lipoprotein abnormalities in chronic uremia are discussed and it is suggested that they are complex.

Adult↗

Uremia causes endothelial progenitor cell deficiency.

BACKGROUND: Circulating bone marrow-derived endothelial progenitor cells (EPCs) promote vascular repair. Their number in peripheral blood correlates with endothelial function and cardiovascular risk in humans. We explored whether uremia influences the number of EPCs. METHODS: We assessed circulating CD34+ hematopoietic progenitor cells in whole blood using flow cytometry and EPCs (in vitro assay) in 46 patients with advanced renal failure and in 46 age- and gender-matched healthy subjects. Further, the effect of uremia on EPC differentiation was studied in vitro and in vivo. RESULTS: Both in renal patients (r= 0.34, P < 0.02) and in healthy subjects (r= 0.32, P= 0.04) the number of EPCs was significantly correlated to the absolute number of CD34+ hematopoietic progenitor cells. Renal patients had significantly fewer EPCs than healthy subjects, however (167 +/- 15 cells/high power field vs. 235 +/- 17 cells/high power field; P < 0.05). Uremic serum significantly (P < 0.05) inhibited EPC differentiation and functional activity in vitro. Amelioration of uremia after institution of renal replacement therapy in patients with terminal renal failure also significantly (P < 0.05) increased the number of EPCs. CONCLUSION: Uremia inhibits differentiation of EPCs. This may impair cardiovascular repair mechanisms in patients with renal failure.

Cell Count↗

Toxicity of parathyroid hormone in uremia.

The most significant complication of elevated parathyroid hormone (PTH) levels in uremia is the development of osteitis fibrosa cystica. The hormone also appears to play a role in soft-tissue and organ calcification, metabolic abnormalities (glucose, lipids), and electroencephalographic changes seen in uremic patients. Its role in the hematological abnormalities of uremia (anemia, bleeding) is controversial. A role for PTH in heart and skeletal muscle dysfunction in uremia has not been clearly established. Further studies are required to establish PTH as a "universal" toxin in uremia.

Anemia↗

Nitric oxide/L-arginine in uremia.

Nitric oxide (NO), a gaseous free radical derived from L-arginine, is a potent modulator of vascular tone and platelet functions. A number of recent studies, both in the experimental model of renal mass reduction (RMR) in rats and in uremic patients, have raised the hypothesis that abnormalities of NO synthetic pathway could have a key role in mediating the complex hemodynamic and hemostatic disorders associated to the progression of renal disease. Thus, kidneys from rats with RMR produce less NO than normal rats and NO generation negatively correlates with markers of renal damage. The abnormality is due to a strong defect of inducible NO synthase (iNOS) content in the kidney. Recent in vitro and in vivo data have raised the possibility that excessive renal synthesis of the potent vasoconstrictor and promitogenic peptide endothelin-1 (ET-1) is a major determinant for progressive iNOS loss in the kidney of RMR rats. In contrast, uremia is associated with excessive systemic NO release, both in experimental model and in human beings. In the systemic circulation of uremic rats, as well as uremic patients, NO is formed in excessive amounts. Possible cause of the increased NO levels is higher release from systemic vessels due to the augmented expression of both iNOS and endothelial NOS. A putative cause for excessive NO production in uremia can be guanidinosuccinate, an uremic toxin that accumulates in the circulation of uremic patients and upregulates NO synthesis from cultured endothelial cells. Upregulation of systemic NO synthesis might be a defense mechanism against hypertension of uremia. On the other hand, more NO available to circulating cells may sustain the bleeding tendency, a well-known complication of uremia.

Animals↗

Effect of prolonged uremia on insulin-like growth factor-I receptor autophosphorylation and tyrosine kinase activity in kidney and muscle.

Recently, based on a study in rats with chronic renal failure (CRF), it has been suggested that IGF-I resistance in uremia may be caused in part by defective IGF-I receptor autophosphorylation and tyrosine kinase activity. Thus if such a defect were to develop in prolonged acute renal failure (ARF), this may explain why IGF-I therapy, effective in rats, has failed to promote recovery from ARF in patients. Accordingly, we examined IGF-I receptor function in rats with uremia of increasing duration and in pair-fed sham-operated controls. After 6 days of prolonged ARF, kidney IGF-I receptor binding increased twofold, while IGF-I stimulated receptor phosphorylation and tyrosine kinase activity were unchanged. Muscle receptor binding, autophosphorylation and tyrosin kinase activity were similar to control values after 6 or even 21 days of uremia. Taking all these findings together it appears that IGF-I resistance in uremia cannot be attributed to a receptor defect. This in turn argues against altered receptor function as a cause of the failure of IGF-I to modify clinical ARF.

Acute Kidney Injury↗

The sink action of cerebrospinal fluid in uremia.

The distribution of water, electrolytes and non-electrolytes in various compartments of the central nervous system was analyzed in rats subjected to various stages of uremia. After bilateral nephrectomy for various periods of time ranging from 1 to 18 h, there is a progressive hyperkalemia, hyponatremia and metabolic acidosis. Although the cerebrospinal fluid (CSF) [K] progressively increases to a concentration of 6 mmol/l at 48 h post-nephrectomy, the ratio of CSF [K]/plasma [K] remains relatively constant throughout the duration of the uremic challenge; on the other hand, the concentration gradient for Na (CSF to plasma) markedly increases with progression of uremia. The steady rise in cellular [K] in both the choroid plexus and in at least one compartment of the cerebral cortex is presumably a reflection of stimulattion of the Na-K pump caused by a build-up in [K] in the extracellular fluids of the brain. The blood-brain and blood-CSF barrier systems to both 14C-urea and 131I remain intact 24--48 h after nephrectomy; and there is not any evidence of cerebral edema at any stage of uremia. Thus, several lines of evidence indicate that the CSF-sink effect is maintained even in advanced uremia.

Acid-Base Equilibrium↗