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      Nitric Oxide Synthetic Capacity in Relation to Dialysate Temperature

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          Background: During hemodialysis, vascular reactivity is impaired, which can be corrected by lowering dialysate temperature. It has also been shown that nitric oxide (NO) is related to intradialytic hypotension. As NO synthesis may be temperature-dependent, this study addressed the influence of dialysate temperature on the NO synthetic capacity of plasma. Methods: NO synthetic capacity was studied during hemodialysis with a dialysate temperature of 37.5°C (dialysis-37.5°C) and programmed extracorporeal blood cooling (cool dialysis; Blood Temperature Monitor; Fresenius C) in 12 stable patients. NO synthetic capacity was assessed ex vivo by [<sup>3</sup>H] L-citrulline formation from [<sup>3</sup>H] L-arginine in cultured endothelial cells after incubation with plasma samples obtained during the respective sessions. Results: Core temperature decreased (–0.32 ± 0.10°C) and energy transfer rate was significantly lower (–27.5 ± 2.8 W; p < 0.05) during cool dialysis compared to dialysis-37.5°C (0.19 ± 0.06°C and –0.8 ± 1.2 W respectively; p < 0.05). Systolic blood pressure decreased during dialysis-37.5°C (–19 ± 4 mm Hg; p < 0.05), but not during cool dialysis (–6 ± 5 mm Hg). NO synthetic capacity increased during dialysis-37.5°C (55.5 ± 9.3 to 73.5 ± 10.2 pmol/10<sup>5</sup> cells; p < 0.05), in contrast to cool dialysis (67.3 ± 11.1 to 66.2 ± 10.8 pmol/10<sup>5</sup> cells). Conclusion: The stimulatory effect of uremic plasma on endothelial NO synthesis was augmented during dialysis-37.5°C but not during cool dialysis.

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          Most cited references 12

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          Hemodynamic changes during hemodialysis: role of nitric oxide and endothelin.

          Etiology of dialysis induced hypotension and hypertension remains speculative. There is mounting evidence that nitric oxide (NO) and endothelin (ET-1) may play a vital role in these hemodynamic changes. We examined the intradialytic dynamic changes in NO and ET-1 levels and their role in the pathogenesis of hypotension and rebound hypertension during hemodialysis (HD). The serum nitrate + nitrite (NT), fractional exhaled NO concentration (FENO), L-arginine (L-Arg), NGNG-dimethyl-L-arginine (ADMA) and endothelin (ET-1) profiles were studied in 27 end-stage renal disease (ESRD) patients on HD and 6 matched controls. The ESRD patients were grouped according to their hemodynamic profile; Group I patients had stable BP throughout HD, Group II had dialysis-induced hypotension, and Group III had intradialytic rebound hypertension. Pre-dialysis FENO was significantly lower in the dialysis patients compared to controls (19.3 +/- 6.3 vs. 28.6 +/- 3.4 ppb, P < 0.002). Between the experimental groups, pre-dialysis FENO was significantly higher in Group II (24.1 +/- 6.7 ppb) compared to Group I (17.8 +/- 5.6 ppb) and Group III (16.1 +/- 4.2 ppb; P < 0.05). Post-dialysis, FENO increased significantly from the pre-dialysis values (19.3 +/- 6.3 vs. 22.6 +/- 7.9 ppb; P=0.001). Pre-dialysis NT (34.4 +/- 28.2 micromol/L/L) level was not significantly different from that of controls (30.2 +/- 12.3 micromol/L/L). Serum NT decreased from 34.4 +/- 28.2 micromol/L/L at initiation of dialysis to 10.0 +/- 7.4 micormol/L/L at end of dialysis (P < 0.001). NT concentration was comparable in all the three groups at all time points. Pre-dialysis L-Arg (105.3 +/- 25.2 vs. 93.7 +/- 6.0 micromol/L/L; P < 0.05) and ADMA levels were significantly higher in ESRD patients (4.0 +/- 1.8 vs. 0.9 +/- 0.2 micromol/L/L; P < 0.001) compared to controls. Dialysis resulted in significant reduction in L-Arg (105.3 +/- 25.2 vs. 86.8 +/- 19.8 micromol/L/L; P < 0.005) and ADMA (4.0 +/- 1.8 vs. 1.6 +/- 0.7 micromol/L/L; P < 0.001) concentrations. Pre-dialysis ET-1 levels were significantly higher in ESRD patients compared to the controls (8.0 +/- 1.9 vs. 12.7 +/- 4.1 pg/mL; P < 0.002), but were comparable in the three study groups. Post-dialysis ET-1 levels did not change significantly in Group I compared to pre-dialysis values (14.3 +/- 4.3 vs.15.0 +/- 2.4 pg/mL, P=NS). However, while the ET-1 concentration decreased significantly in Group II (12.0 +/- 4.0 vs. 8.7 +/- 1.8 pg/mL, P < 0.05), it increased in Group III from pre-dialysis levels (12.8 +/- 3.8 vs. 16.7 +/- 4.5 pg/mL, P=0.06). Pre-dialysis FENO is elevated in patients with dialysis-induced hypotension and may be a more reliable than NT as a marker for endogenous NO activity in dialysis patients. Altered NO/ET-1 balance may be involved in the pathogenesis of rebound hypertension and hypotension during dialysis.
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            The effects of control of thermal balance on vascular stability in hemodialysis patients: results of the European randomized clinical trial.

            Many reports note that the use of cool dialysate has a protective effect on blood pressure during hemodialysis (HD) treatments. However, formal clinical trials in which dialysate temperature is tailored to the body temperature of appropriately selected hypotension-prone patients are lacking. We investigated the effect of thermal control of dialysate on hemodynamic stability in hypotension-prone patients selected from 27 centers in nine European countries. Patients were eligible for the study if they had symptomatic hypotensive episodes in 25% or more of their HD sessions, assessed during a prospective screening phase over 1 month. The study is designed as a randomized crossover trial with two phases and two treatment arms, each phase lasting 4 weeks. We used a device allowing the regulation of thermal balance (Blood Temperature Monitor; Fresenius Medical Care, Bad Homberg, Germany), by which we compared a procedure aimed at preventing any transfer of thermal energy between dialysate and extracorporeal blood (thermoneutral dialysis) with a procedure aimed at keeping body temperature unchanged (isothermic dialysis). One hundred sixteen HD patients were enrolled, and 95 patients completed the study. During thermoneutral dialysis (energy flow rate: DeltaE = -0.22 +/- 0.29 kJ/kg x h), 6 of 12 treatments (median) were complicated by hypotension, whereas during isothermic dialysis (energy flow rate: DeltaE = -0.90 +/- 0.35 kJ/kg x h), the median decreased to 3 of 12 treatments (P < 0.001). Systolic and diastolic blood pressures and heart rate were more stable during the latter procedure. Isothermic dialysis was well tolerated by patients. Results show that active control of body temperature can significantly improve intradialytic tolerance in hypotension-prone patients. Copyright 2002 by the National Kidney Foundation, Inc.
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              Role of nitric oxide, endothelin-1, and inflammatory cytokines in blood pressure regulation in hemodialysis patients.

              Altered regulation of blood pressure (BP) in hemodialysis patients is associated with increased morbidity and mortality. Regulation of BP is dependent in part on such vasoactive agents as nitric oxide (NO) and endothelin-1 (ET-1). Cytokine-mediated NO synthase activation during dialysis previously has been reported. The purpose of this study is to investigate the relationship between cytokine-mediated activation of the NO and ET-1 systems and BP regulation in hemodialysis patients. Nine patients with chronic hypotension (predialysis systolic BP 1 month), nine patients with hypertension (predialysis systolic BP > or = 180 mm Hg), and nine age- and sex-matched normotensive controls were enrolled. Predialysis NO end product levels in the hypotensive group were greater than in controls (17.63 +/- 5.9 versus 11.06 +/- 2.12 microm/mL; P = 0.01), whereas the hypertensive group showed lower levels (4.76 +/- 2.33 microm/mL; P < 0.01). The hypotensive group had low postdialysis levels (3.45 +/- 1.11 microm/mL; P = 0.01). Predialysis ET-1 levels in the hypotensive and hypertensive groups were greater in comparison to the normotensive group (7.54 +/- 4.52 and 8.95 +/- 3.52 versus 4.41 +/- 0.6 pg/mL; P < 0.01). Postdialysis endothelin levels increased in both the control and hypertensive groups (P < 0.01). Interleukin-1 and tumor necrosis factor-alpha levels increased postdialysis in all groups, but not significantly. High levels of NO end products in hypotensive patients and low levels in hypertensive patients suggest a critical influence of NO in BP control. In addition, elevated ET-1 levels in hypertensive patients may contribute to systemic vasoconstriction and may suggest vascular dysfunction in this patient population. Copyright 2002 by the National Kidney Foundation, Inc.

                Author and article information

                Blood Purif
                Blood Purification
                S. Karger AG
                July 2004
                30 March 2004
                : 22
                : 2
                : 203-209
                Departments of aInternal Medicine and bClinical Chemistry, University Hospital Maastricht, Maastricht, TheNetherlands; cMario Negri Institute for Pharmacological Research, Bergamo, Italy
                76854 Blood Purif 2004;22:203–209
                © 2004 S. Karger AG, Basel

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                Figures: 1, Tables: 2, References: 31, Pages: 7
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