Uremic Group Research Articles

Circulating platelet-derived microparticles with procoagulant activity may be a potential cause of thrombosis in uremic patients

Clinical experience indicates that bleeding and thrombotic tendencies co-exist in uremic patients. Numerous studies have shown that platelet functional defects contribute to the bleeding tendency in uremic patients. In contrast, there are no solid studies clarifying the pathogenesis of the prothrombotic state in uremic patients. Platelet-derived microparticles (PMPs), which are small vesicles with procoagulant activity released from activated platelets, are thought to be involved in clinical thrombogenesis. This study addressed the question of why uremic patients are thrombophilic even though they have a bleeding tendency, focusing on the clinical significance of PMPs. The subjects were pre-dialyzed patients, patients under hemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD) therapy, and age-matched healthy controls. Analyses of PMPs were performed using a flow cytometer. Annexin V was used to probe procoagulant activity of PMPs. The impacts of the HD procedure, arteriovenous (AV) fistula, and recombinant human erythropoietin (rHuEPO) treatment on the release of PMPs were additionally assessed. Major results are: (1) PMP counts were significantly greater in each uremic group than in controls. The PMP counts were not different among three types of uremic groups; (2) PMP counts were significantly higher in uremic patients with thrombotic events than in those without thrombotic events; and (3) the HD procedure and existence of AV fistula did not affect PMP counts, but rHuEPO treatment possibly enhanced the PMP release in these patients. Elevated PMP counts may trigger thrombosis in uremic patients. The primary cause of PMP elevation in uremia was not clarified in this study.

Altered L-arginine metabolism results in increased nitric oxide release from uraemic endothelial cells.

Results regarding the nitric oxide (NO) system in uraemia are contradictory. L-arginine, the precursor of NO, is also metabolized by arginase to form ornithine and urea. In the present study, endothelial NO production and arginine metabolism in uraemia were assessed. In addition an in vivo model was used to examine excess consumption of NO in uraemia. NO and amino acid measurements were made from basal and stimulated (by bradykinin) uraemic and control endothelial cells. Reverse-transcriptase PCR was used to assess endothelial NO synthase (eNOS) and inducible NOS (iNOS) expression. Finally, aortae of uraemic rats were stained for nitrotyrosine (a marker of peroxynitrite). Basal uraemic cells produced more NO than the control cells. L-arginine levels were greater in uraemic (supernatants/cells), but ornithine levels were higher in control (supernatants/cells). Following stimulation, NO levels in supernatants were similar, but the rise in NO production was greater in control compared with uraemic cells; l-arginine levels still remained higher in uraemic supernatants/cells. Differences in ornithine concentration (supernatants/cells) disappeared following bradykinin stimulation, due to a rise in ornithine levels in the uraemic group. There was no difference in eNOS expression, nor was iNOS detected in either group. Only aortae from uraemic rats showed evidence for nitrotyrosine staining. These studies demonstrated increased basal NO release in uraemic endothelial cells, perhaps by inhibition of arginase and hence diversion of arginine to the NO pathway. The increased NO produced under basal conditions may be inactive due to excessive consumption, resulting in peroxynitrite formation. Interestingly, bradykinin appears to restore arginase activity in uraemia, resulting in normalization of NO production.

Hyperplasia of the parathyroid gland without secondary hyperparathyroidism

Low dietary phosphorus (P) prevents parathyroid gland (PTG) hyperplasia and the development of secondary hyperparathyroidism (SH) in uremic rats. The present study explores the effects of P restriction on parathyroid hormone (PTH) synthesis and secretion and PT cell growth in rats with established SH and PTG hyperplasia. Normal and 5/6 nephrectomized rats were fed a high P (0.8%) diet. After two weeks, the normal rats and half of the uremic rats were sacrificed (U-HP) while the remaining uremic rats were switched to a low P (0.2%) diet (U-HP-LP). High dietary P induced a significant increase in serum P, PTH, and PTG weight, but not ionized calcium compared to normal animals fed the same diet (N-HP). P restriction returned serum P and PTH to normal levels by one week. In contrast, PTG size did not regress and glands remained enlarged for up to eight weeks with no evidence of apoptosis. Ribonuclease protection assay and metabolic labeling studies demonstrated similar PTH/actin mRNA ratios and 35S-labeled PTH among the three groups. Intracellular intact PTH was higher in U-HP and U-HP-LP rats compared to N-HP animals with no differences between the two uremic groups. PTG-PTH content correlated only with PTG weight, and serum PTH only with serum P. The PTG secretory response to calcium remained intact. In established chief-cell hyperplasia, P restriction restores normal serum PTH levels without affecting PTG hyperplasia, PTH synthesis, PTG cytosolic PTH or the PTH secretory response to calcium, suggesting an impaired exocytosis of PTH.

Nitric oxide generation by peripheral blood cells in chronic renal failure

Nitric oxide (NO), a labile free radical synthesised from L-arginine by the action of nitric oxide synthase (NOS), is said to be implicated in uraemic complications, such as infection and a tendency to bleed. In this study of NO production by peripheral blood cells, an increased level is seen in platelets from uraemic patients (both non-dialysed and haemodialysed) and a decreased level in leucocytes (neutrophils and monocytes). A negative correlation was noted between blood urea level and inducible NO in neutrophils and monocytes in uraemic patients not on dialysis. In contrast, haemodialysis appears to lead to an increase in inducible NO production in neutrophils and monocytes. Plasma NO levels were significantly increased in uraemic patients, compared with normal controls, and hemodialysis led to further increases. Superoxide dismutase (SOD) activity was significantly reduced in platelets, neutrophils and monocytes in the uraemic group. It is concluded that increased NO production by platelets may contribute to the bleeding tendency observed in uraemia, and high urea concentrations may contribute to the regulation of inducible NO production in leucocytes.

The Effect of Renal Transplantation on Pulmonary Function

In patients with chronic renal failure, mechanical and hemodynamic changes could occur in the lungs without obvious pulmonary symptoms and findings and their effects could pave the way to pulmonary functional disorders. In this study, pulmonary functional disorders and especially alveolocapillary defects, which are frequently seen in uremia, were determined in renal transplanted patients. Pulmonary functions and diffusion capacity were assessed in uremic patients (n = 20) and in successfully transplanted patients (n = 20) without any lung disease or pulmonary edema symptoms and findings. Patients were selected randomly among outpatients who were followed up in a Nephrology and Transplantation Unit. Forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), and peak expiratory flow (PEF_25–75) were measured. Single breath carbon monoxide diffusion test and diffusion lung capacity adjusted for hemoglobin concentration (DLAdj) were done. The means of the spirometric values such as FVC, FEV₁ and FEV₁/FVC were normal in the nondialyzed uremic group, but the PEF_25–75 value (68.7%) and diffusion capacity (DLAdj 72.7%) were found to be slightly low. There were 2 patients with normal values and 18 patients with some functional abnormalities in this nondialyzed uremic group. The means of all spirometric parameters and diffusion capacities were found to be normal in the transplanted group. There were 7 patients with normal function and 13 patients with some functional abnormalities in this transplanted group. When the nondialyzed uremic group and the transplanted group were compared statistically, significant differences were found between their spirometric values (except for FVC) and their diffusion capacities. Even though the uremic patients did not show any symptoms, their pulmonary function tests, especially diffusion capacity, were found to be disturbed. Although the transplanted patients as a group had normal mean spirometric values and diffusion capacity there were nevertheless many individual transplanted patients with defective diffusion capacity and abnormal spirometric values.

An oral sorbent reduces overload of indoxyl sulphate and gene expression of TGF-beta1 in uraemic rat kidneys.

An oral adsorbent (AST-120) delays the progression of chronic renal failure (CRF). The aims of the present study are to determine the effects of AST-120 on the localization of indoxyl sulphate in uraemic rat kidneys, and to examine whether AST-120 reduces the renal cortical gene expression of transforming growth factor (TGF)-beta1, tissue inhibitor of metalloproteinase (TIMP)-1 and pro-alpha1(I)collagen, and ameliorates glomerular and tubulointerstitial injuries in uraemic rats. Two weeks after 5/6-nephrectomy, 10 rats were divided into pairs such that both rats in each pair exhibited almost the same levels of serum creatinine, blood urea nitrogen and creatinine clearance. One rat from each pair was assigned to a control uraemic group, the other to a uraemic group which received AST-120 everyday for 11 weeks. The localization of indoxyl sulphate was studied by immunohistochemistry using a monoclonal anti-indoxyl sulphate antibody we had developed. The renal cortical gene expression was studied by using northern blotting. Rats treated with AST-120 showed decreased levels of serum creatinine, blood urea nitrogen and urinary protein as well as increased levels of creatinine clearance as compared with control uraemic rats. AST-120 markedly decreased indoxyl sulphate levels in both serum and urine. Immunohistochemistry demonstrated that indoxyl sulphate was localized in the renal proximal tubular epithelial cells, especially of dilated tubules, and that AST-120 markedly reduced the tubular staining of indoxyl sulphate. AST-120 attenuated interstitial fibrosis, tubular injury as well as glomerular sclerosis, and reduced the renal gene expression of TGF-beta1, TIMP-1 and pro-alpha1(I)collagen. AST-120 reduces the gene expression of TGF-beta1, TIMP-1 and pro-alpha1(I)collagen in the kidneys, and delays the progression of CRF, at least in part, by alleviating the overload of indoxyl sulphate on remnant proximal tubular epithelial cells.

Ramipril prevents basal arterial constriction and enhanced myogenic tone in the femoral artery in mildly uraemic normotensive rats

Some aspects of vascular reactivity are altered in mild experimental uraemia, as shown by increased myogenic tone and a reduced lumen diameter in the femoral artery. This study was conducted to investigate the prevention of these uraemia-induced vascular abnormalities by the angiotensin-converting enzyme inhibitor (ACE-I) Ramipril. Ten male Wistar rats were rendered uraemic (U) by 5/6th nephrectomy, and 10 control (C) rats were concurrently sham-operated. After 4 weeks, both groups were given daily subcutaneous injections of 3 microg of Ramipril for a further 4 weeks. Tail-cuff systolic blood pressure was then recorded and the rat was killed. Isolated femoral arteries were mounted on a pressure myograph and pressurized at 40 mmHg for baseline measurements of the lumen internal diameter. Myogenic tone was then assessed over a range of intravascular pressures from 40 to 160 mmHg. Biochemically, serum urea and creatinine were significantly higher in the uraemic (U) group [urea: U, 23+/-3 mmol/l; C, 6+/-1 mmol/l (P<0.001); creatinine: U, 147+/-17 mmol/l, C, 72+/-11 mmol/l (P<0.01)]. Systolic blood pressure was the same in both groups (U, 127+/-7 mmHg; C, 127+/-3 mmHg). The mean baseline internal diameter was the same in both groups (U, 756+/-22 microm; C, 721+/-34 microm, not significant), as was mean myogenic tone (U, 4.7+/-1%; C, 3.4+/-1%). In conclusion, there were no differences in baseline lumen diameter or myogenic tone in uraemic compared with control femoral arteries of rats treated with Ramipril, which suggests that Ramipril may prevent the development of elevated myogenic tone and decreased lumen diameter previously observed in this model of uraemia. These results suggest that these specific vascular abnormalities in uraemia may be mediated by renin or bradykinin, or by the direct action of angiotensin II on vascular smooth muscle.

Effects of parathyroid hormone infusion on glucose tolerance and glucose-stimulated insulin secretion in normal and uremic rats

We used thyroparathyroidectomized (TPTX) rats with hypocalcemia to evaluate the effects of parathyroid hormone (PTH) infusion on glucose tolerance and glucose-stimulated insulin secretion in normal and uremic rats. Animals were subjected to oral glucose tolerance test (OGTT) and glucose-stimulated insulin secretion before and after TPTX or after their plasma calcium level was normalized by PTH infusion, vitamin D injection or calcium load. In both normal and uremic groups, TPTX produced a significant increase in area under the cure (AUC) of plasma glucose from 0 to 6 h in response to an oral glucose challenge and decrease plasma insulin level in response to glucose-stimulated insulin secretion. Before TPTX, uremic animals have a normal basal plasma insulin level (29±3 versus 31±2 μU/ml) and a normal glucose-stimulated insulin secretion, but significantly increase plasma glucose AUC in response to OGTT as compared with normal rats. TPTX worsen the response of glucose intolerance in uremic rats. After PTH infusion, vitamin D injection or calcium load, all rats in the response of OGTT and glucose-stimulated insulin secretion are recovered to the level before TPTX including normal and uremic rats, but uremic rats still have an abnormal glucose tolerance in response to OGTT. Uremic rats have a low basal plasma glucose level as compared with normal rats. TPTX significantly increase basal plasma glucose level in normal and uremic rats, but the uremic rats with TPTX have been found to elevate basal plasma glucose level to the range of normal rats. The basal plasma glucose level of normal rats with TPTX was recovered to the range before TPTX by PTH infusion, vitamin D injection or calcium load, but PTH infusion, vitamin D injection or calcium load did not decrease the level of basal plasma glucose in uremic rats with TPTX. All TPTX rats, including intact kidney or five-sixths Nx rats, were treated three times weekly by subcutaneous injection of 8 μg/kg l-thyroxin. These results indicate that uremia may produce thyroid dysfunction and PTH infusion did not affect the glucose tolerance in OGTT and glucose-stimulated insulin secretion in normal and uremic rats. In addition to PTH, other uremic toxins may be responsible for the glucose intolerance of uremia.

Perioperative hypercoagulability in uremic patients: A viscoelastic study

Study Objective: To examine whole blood coagulation in uremic patients presenting for surgery with the thromboelastogram and the Sonoclot analyzer. Design: Prospective, observational study. Setting: Operating rooms of a university-affiliated hospital. Patients: 30 ASA physical status II and III patients with chronic renal failure, and 30 age-matched and gender-matched patients with normal renal function, presenting for elective surgery. Interventions: Blood sampling for thromboelastograph and Sonoclot analysis immediately after anesthetic induction, prior to surgical incision. Measurements and Main Results: Thromboelastographic indices of coagulation, reflecting coagulation factor function (R time), fibrinogen-platelet interaction (K time and alpha angle), and qualitative platelet function (maximum amplitude) were hypercoagulable in the uremic group compared with the control group ( p < 0.05). Fibrinolysis (%) was decreased in the uremic group ( p < 0.05). Fibrin formation (initial slope) and platelet function (time to peak) of the Sonoclot trace also were hypercoagulable in the uremic group ( p < 0.05). Conclusions: The high incidence of arteriovenous graft and fistulae thromboses in uremic patients belies in vitro laboratory evidence of platelet dysfunction. We have demonstrated perioperative hypercoagulability in uremic patients with viscoelastic measures of whole blood coagulation. These data suggest that traditional concern for coagulopathy and platelet dysfunction in uremic patients may require re-assessment in light of this “pro-thrombotic” state.

Alloantigen-blocking antibodies in sera from highly sensitized uremic patients: antibody class and relationship with lymphocytotoxins.

Previously, we identified an antimitogenic IgG antibody separated from sera of patients with known kidney transplant chronic rejection. This antibody inhibits individual patients' own unprimed T helper cell responses to alloantigens as well as a third-party mixed lymphocyte response, but does not inhibit autologous unprimed T helper cell proliferation to adherent anti-CD3 antibody. We suggest that the mechanism of inhibitory action is allogeneic-dependent. We used a series of similar experimental designs to test the presence of this antibody in uremic, sensitized patients and have studied its relationship to sensitization as defined by the presence of lymphocytotoxins in four uremic groups: highly sensitized with or without previous graft loss, moderately sensitized with or without graft loss, nonsensitized without previous graft loss, and nonsensitized with graft loss. (1) Sensitization is associated with the presence of a potent antibody that blocks primary mixed lymphocyte response. Primed cells are less susceptible to its antimitogenic action. (2) The blocking antibody activity is present only in sensitized patients who have IgG lymphocytotoxic activity against the same HLA class I antigens. (3) The blocking activity is unequal in the following order: IgG 3 > IgG 1 > IgG 2. (4) Although IgG 1 and 2 fractions contain lymphocytotoxic activity against HLA class I antigens, the IgG 3 fraction does not. The differential effect of IgG antibodies on naive and memory T cells may explain why humeral responses to alloantigens can be maintained in the presence of blocking antibodies.

Uremia Enhances the Blood Pressure Response to Erythropoietin

To investigate the role of uremia in the development of human recombinant erythropoietin (r-HuEPO)-induced hypertension, Wistar rats were divided into a uremic (subtotal nephrectomy) and a control group. After three weeks, both groups were again divided and each subgroup received either r-HuEPO (100 u/kg s.c., 3 times weekly) or the vehicle for a further 3 weeks. Hematocrit, blood pressure and blood chemistry were measured prior to surgery, before either vehicle or r-HuEPO treatment and before euthanasia. The uremic group developed anemia, hypertension and all the biochemical features observed in humans with end-stage renal disease. r-HuEPO therapy increased hematocrit from 29 ± 2.5% to 46 ± 2% (p < 0.01) in the uremic rats. The mean baseline blood pressure was 119 ± 10 mmHg. At week 3, mean blood pressure was unchanged in control rats, but it was increased to 151 & 5 mmHg (p CO.01) in the nephrectomized group. At week 6, mean blood pressure in the untreated uremic rats remained unchanged from week 3, but blood pressure in the uremic animals treated with r-HuEPO increased significantly to 187 & 8 mmHg (p CO.01). There was no significant correlation between hematocrit and blood pressure in the r-HuEPO treated uremic group (r=0.01, NS). r-HuEPO had no effect on blood pressure in control rats despite a significant increase in hematocrit. These results indicate that the blood pressure response to r-HuEPO is enhanced in rats with chronic renal failure.

Vitamin D metabolites and growth hormone therapy in uraemic rats: the short‐term effect on growth failure and hyperparathyroidism

Summary: The aim of our study was to evaluate the effect of 1,25 dihydroxyvitamin D3 (D), 22‐oxacalcitriol (O) or recombinant human growth hormone (GH) on growth failure and hyperparathyroidism in 5/6 nephrectomized uraemic (Ur) rats. Seven groups of rats were studied: (i) sham controls (SC; n=6); (ii) Ur controls (UrC;n=8); (iii) Ur treated either with D (UrD; n=7); (iv) O (UrO, n=8); (v) GH (UrGH; n=7); (vi) D+GH (UrDGH; n=9); or (vii) O+GH (UrOGH; n=7). For 14 days, D and O were administered intraperitoneally daily at 30 ng/kg per day and GH subcutaneously daily at 1.3 i.u./day. Four weeks after 5/6 nephrectomy, plasma creatinine (Cr), plasma and urine calcium (Ca), plasma phosphate (P), ratio of urine Ca/urine Cr, amino‐terminal parathyroid hormone (PTH; pg/mL) and Ca/dry bone weight in the left femur (mg/g) were measured. Uraemic controls, UrD, UrO and UrDGH rats were lower in weight gain than SC rats over the study period, but linear growth was not retarded in any uraemic group. Plasma Cr was greatly increased in any Ur group as compared with SC group. Plasma Ca and P concentrations did not differ among each group. the ratio of urine Ca/urine Cr in UrD and UrDGH groups was higher than SC, UrCand UrGH groups. the use of Dor D+GH suppressed PTH, returning the level in these rats to the normal level of the SC rats, while the PTH concentrations in the UrO and UrOGH rats were less decreased. Bone Ca content was enhanced by D+GH and O+GH administration in comparison with UrC rats, but there was no difference in the bone Ca content between UrD and UrDGH rats, and between UrO and UrOGH rats. In conclusion, growth failure in weight was shown in uraemia, but linear growth was not retarded in any uraemic group. 1.25 dihydroxyvitamin D3 and D plus GH successfully suppressed secondary hyperparathyroidism. Further studies are needed in order to elucidate the interactions on bone between vitamin D rnctabolites and GH.

Serum tumour markers in renal failure.

In order to assess the clinical value of six tumour markers in pre-dialysis patients with chronic renal failure as well as in patients on regular haemodialysis, we studied these markers in 35 predialysis patients, 35 patients on chronic haemodialysis and 35 healthy controls. Serum squamous cell antigen (SCC), CA 19.9, and CA 125 levels were found to be elevated in the uraemic groups as compared to the normal controls. Carcinoembryonic antigen (CEA), alpha foetoprotein (AFP), and prostate-specific antigen (PSA) levels were within normal limits in all groups.

Relationship Between Susceptibility to Apoptosis and Fas Expression in Peripheral Blood T Cells from Uremic Patients: A Possible Mechanism for Lymphopenia in Chronic Renal Failure

Chronic renal failure (CRF) is often complicated by lymphopenia, which may be partly responsible for immune deficiency. We hypothesized that lymphopenia in CRF might result from apoptosis of T cells in vivo. To elucidate the involvement of Fas antigen which mediates apoptosis, we analyzed Fas expression on peripheral blood T cells in uremic non-dialyzed (non-HD) patients and hemodialysis (HD) patients. T cells from both uremic groups expressed Fas with higher intensity than control T cells. When two uremic groups were compared, Fas intensity on T cells was significantly higher in non-HD patients than in patients on HD. Moreover, uremic T cells were shown to undergo accelerated apoptosis when cultured in vitro, in correlation with Fas expression. Our results suggest that T cells in CRF may undergo apoptosis by the Fas system and that hemodialysis treatment has beneficial effects in the light of the inhibition of T cell apoptosis.

Activities of hepatic vitamin B 6 metabolizing enzymes and concentrations of vitamin B 6 vitamers in tissues of chronically azotemic rats

The activities of hepatic vitamin B 6 metabolizing enzymes and the concentrations of vitamin B 6 vitamers in plasma and liver were studied in uremic rats. The uremic group of rats was prepared by a two-stage surgical procedure. Food intake of the control and uremic groups was not significantly different. The loss of renal function of the uremic rats was evident by the significantly decreased creatinine clearance value as well as the elevated serum urea levels. Concentrations of each liver B 6 vitamer and plasma total vitamin B 6 were not significantly different between the control and uremic groups. Plasma pyridoxal 5′-phosphate concentrations were 31% ( P P 6 in the uremic rats resulted from the significantly elevated plasma pyridoxal levels. Based on the results of this study, plasma total vitamin B 6 would apparently not be an appropriate biochemical index for assessing vitamin B 6 status in chronic renal disease.

Lack of enhanced T-helper cell function in uremic patients with circulating alloreactive antibodies.

Some uremic patients with a history of blood transfusion, pregnancy, and previous transplantation maintain high levels of alloreactive cytotoxic antibodies in the absence of continuous exogenous allogenic stimuli and are thus considered sensitized to the major histocompatibility proteins. To differentiate into antibody-producing cells, B lymphocytes must interact with T-helper (CD4+) cells. Whether ongoing help from these cells is necessary for the B cells to continue producing cytotoxic alloreactive antibodies in these sensitized uremic patients is unknown. To gain insight into the cellular mechanisms that are associated with sustained alloantibody production, T cell activation markers were measured and specific and nonspecific T-helper cell function was studied in three uremic groups with different levels of panel reactive antibodies: 10 patients whose sera reacted to more than 80% of a panel of normal lymphocytes for at least 6 months before the study were highly sensitized, 20 patients whose sera reacted to less than 80% of the panel were moderately sensitized, and 10 nonsensitized patients whose sera did not react to any cell on the panel. The number of total and activated T-helper cells was similar in the highly sensitized and nonsensitized patients. Peripheral blood lymphocyte proliferation in response to plant lectins, soluble OKT3, or alloantigens was similar in the three uremic groups. The spontaneous proliferation of pure T-helper cells and proliferative responses to immobilized OKT3 or alloantigens were also similar in highly sensitized and nonsensitized patients. Alloreactive interleukin-2-producing cell frequencies with pure CD4+ cells as responding cells were 771 +/- 77.9/10(6) cells in highly sensitized, 945 +/- 252/10(6) cells in nonsensitized, and 973 +/- 114/10(6) cells in controls (P = not significant). Panel reactive antibody levels did not correlate with any of the measures of T helper responses. There was a significant decrease of peripheral blood lymphocyte responses to alloantigens and anti-CD3 antibody in all uremic patients as compared with normals, suggesting a dysfunction in accessory cells that was quantitatively similar in sensitized and nonsensitized patients. In spite of the continuous production of alloantibodies by B cells, there is no evidence of either specific or nonspecific enhancement of T-helper cell function in sensitized patients. The absence of T cell immunity to alloantigens suggests that sustained activation of T-helper cells with subsequent interleukin-2 production is not necessary to maintain alloreactive B cell function.

Haemodynamic and catecholamine responses to induction of anaesthesia and tracheal intubation in diabetic and non-diabetic uraemic patients

We have studied cardiovascular and catecholamine responses to induction of anaesthesia and tracheal intubation in 13 patients with diabetic nephropathy, in 12 patients with uraemia of other origin and in 12 ASA I control patients. All uraemic patients were undergoing renal transplantation. Cardiovascular autonomic function tests indicated that severe autonomic neuropathy was common in the diabetic patients; less severe impairment of autonomic function was found in the non-diabetic uraemic patients. The systolic pressor response to intubation was greater in diabetic uraemic patients than in the other groups (P < 0.05). Both uraemic groups had higher plasma catecholamine concentrations than the ASA I patients both before and after induction of anaesthesia. The increased plasma concentrations of catecholamines in the uraemic patients may be a result of impaired clearance of catecholamines and higher sympathoadrenal activity needed to maintain cardiac function. The normal systolic pressor response to tracheal intubation in the uraemic patients indicates that the capacity of the cardiovascular system to respond to a stressful stimulus was preserved in these patients also, in spite of autonomic neuropathy. The greater response in the diabetic group may be caused by increased sensitivity to catecholamines and loss of autonomic control.

Potentiated 1,25(OH)2D3-induced 24-hydroxylase gene expression in uremic rat intestine

24-Hydroxylase has been considered a major enzyme regulating metabolism of circulating 1 alpha, 25-dihydroxyvitamin D3 [1,25(OH)2D3]. To understand the metabolism of 1,25(OH)2D3 in chronic renal failure, we examined 1,25(OH)2D3-induced 25-hydroxyvitamin D3-24-hydroxylase (24-hydroxylase) gene expression in the intestine of uremic rats. Northern blot and dot blot analyses showed that the induction of duodenal 24-hydroxylase gene expression was 2.0- to 3.8-fold greater in uremic rats than in sham-operated rats (P < 0.05, Student's t-test) at 6 h after 1,25(OH)2D3 administration. Gene induction of calbindin D9k by 1,25(OH)2D3 was not augmented in uremic group. In situ hybridization analysis revealed that the induction of 24-hydroxylase mRNA by 1,25(OH)2D3 was observed exclusively in the columnar epithelium of the crypt and the lower part of the villi, suggesting that the stage of epithelial cell differentiation is a major determinant of 1,25(OH)2D3-induced 24-hydroxylase gene expression. In uremia, 1,25(OH)2D3-induced 24-hydroxylase gene expression was accelerated selectively, possibly because of poorly differentiated epithelial cells.

Low Nitrogen Diets Preserve Nutritional Status but Not Residual Renal Function in Rats with Severe Renal Failure

The effects of low nitrogen diets (oral and parenteral) on nutritional status and residual renal function were evaluated in rats with experimentally induced severe renal failure (partial nephrectomy) and compared with the effects of a normal protein diet. Non-uremic rats were used as controls. Muscle protein synthesis was significantly lower in uremic rats fed a normal protein diet than in those fed low protein diets. Values for serum insulin-like growth factor 1 (IGF-1) were significantly lower than for controls in all uremic groups as were the wet and dry weights of skeletal muscle. The glomerular filtration rate was studied after 3 wk of nutritional intervention. Serum creatinine concentration was lower and creatinine clearance greater in uremic rats given the low nitrogen dietary treatments (both oral and parenteral) compared with those fed the normal protein diet. However, the glomerular filtration rate determined with 51Cr-EDTA clearance did not differ between uremic rats with normal and low protein intake. Thus, a low nitrogen diet had positive effects on uremic toxicity and did not compromise nutritional status. The results do not, however, establish a favorable influence on residual renal function and emphasize the need for reliable methods for studying dietary effects on renal function in uremia.

Vitamin B-6 metabolism is altered in chronic renal failure rats

Effect of chronic renal failure on plasma pyridoxal phosphate and total vitamin B-6 concentrations and the activation coefficients of erythrocyte aminotransferases in rats were studied. The uremia was induced by two-stage five–sixths nephrectomy. Urine and blood samples were collected eight weeks after the surgery. Serum urea levels were significantly greater in uremic animals. Creatinine clearance of uremic group was 30% of the control value. Food intake of the control and uremic groups did not significantly differ. The levels of plasma pyridoxal phosphate of the uremic group were 43% lower than those of the control group, but the concentrations of plasma total vitamin B-6 were not significantly different between the control and uremic groups. No differences were observed in activation coefficients of erythrocyte aspartate aminotransferase and alanine aminotransferase between the control and uremic groups. Results of this study indicated that vitamin B-6 metabolism was altered in chronic renal failure animals. More than one biochemical index for assessing vitamin B-6 status should be employed in chronic renal failure. The serum alkaline phosphatase activity was comparable between the control and uremic groups, indicating that serum alkaline phosphatase was not involved in lowering plasma PLP of chronic renal failure animals.