Methylene blue, a nitric oxide inhibitor, prevents haemodialysis hypotension.

BACKGROUND: Plasma nitric oxide (NO) levels have been found to be high in haemodialysis (HD) patients, especially in those prone to hypotension in dialysis. The aim of the study was to prevent dialysis hypotension episodes by i.v. administration of methylene blue (MB), an inhibitor of NO activity and/or production. METHODS: MB was given i.v. in 18 stable HD patients with hypotensive episodes during almost every dialysis, in 18 HD patients without hypotension during dialyses, and in five healthy controls. MB was given as a bolus of 1 mg/kg bodyweight followed by a constant infusion of 0.1 mg/kg bodyweight lasting 210 min until the end of the dialysis session and only as a bolus on a non-dialysis day. Systolic and diastolic blood pressures (BP) were measured at 10-min intervals during HD sessions with or without MB and on a non-dialysis day with MB. RESULTS: In hypotension-prone patients, MB completely prevented the hypotension during dialysis and increased both systolic and diastolic BP on non-dialysis days. In normotensive patients, MB increased BP during the first hour of dialysis and for 90 min on the non-dialysis day. The BP in the healthy controls remained unchanged. Plasma and platelet NO(2)+NO(3) (stable metabolites of NO) levels were determined. The NO(2)+NO(3) generation rate in the first post-dialysis day was calculated. The plasma and platelet NO(2)+NO(3) were higher in the hypotensive group than in the normotensive dialysis group. The generation rate of nitrates was higher (P<0.01) in the hypotensive group (1.21+/-0.13 micromol/min and 0.74+/-0.16 after MB) than in the normotensive patients (0.61+/-0.11 micromol/ min and 0.27+/-0.14 after MB). No side-effects were recorded. CONCLUSIONS: MB is an efficient therapy in the prevention of dialysis hypotension.

Down regulation of interleukin 1beta production in human osteoarthritic synovial tissue and cartilage cultures by aminoguanidine.

OBJECTIVE: To evaluate the effect of aminoguanidine (AG) on de novo interleukin 1beta (IL1beta), nitric oxide (NO), and interleukin 1 receptor antagonist (IL1ra) production by osteoarthritic human synovial tissue and articular cartilage cultures. METHODS: Synovial tissue and cartilage, obtained during surgery from 29 patients undergoing total knee or hip replacement for osteoarthritis, were cut into small pieces and cultured in the presence or absence of lipopolysaccharide (LPS) and test materials. IL1beta, IL1ra, and NO were determined in culture media. The inducible nitric oxide synthase inhibitor, AG, was added to cultures in various concentrations (0.3-3 mmol/l). RESULTS: In synovial tissue cultures AG (0.3, 1, and 3 mmol/l) decreased LPS (1 microg/ml) stimulated IL1beta and NO release in the media in a dose dependent manner (p<0.05 at 1 mmol/l and p<0.05 at 0.3 mmol/l, respectively). In articular cartilage cultures AG (0.3, 1, and 3 mmol/l) decreased LPS (1 microg/ml) stimulated IL1beta and NO release in the media in a dose dependent manner (p<0.05 at 1 mmol/l and p<0.01 at 0.3 mmol/l, respectively). Hydrocortisone (5 microg/ml) also significantly decreased LPS stimulated IL1beta release in media of synovial tissue and cartilage cultures and NO in media of synovial cultures. AG (0.3, 1, and 3 mmol/l) decreased LPS (1 microg/ml) stimulated IL1ra levels in media of synovial tissue cultures in a dose dependent manner (p<0.05 at 1 mmol/l) but increased LPS (1 microg/ml) stimulated IL1ra release in media of cartilage cultures (p<0.01 at 3 mmol/l). The NO donor, nitroprusside (10, 30, 100, and 300 microg/ml) stimulated IL1beta release in media of synovial tissue cultures in a dose dependent manner (p<0.01 at 100 microg/ml). AG and nitroprusside at the concentrations used had no toxic effect on human synovial cells. CONCLUSIONS: NO synthase inhibitors may modulate osteoarthritis and articular inflammatory processes not only by decreasing NO synthesis but also by their effects on ILbeta and IL1ra production.

Glomerular basement membrane polyanion distribution and nitric oxide in spontaneous hypertensive rats: effects of salt loading and antihypertensive therapy with propranolol.

Cationic colloidal gold (CCG), a polycationic histochemical probe, was used to analyze the distribution of glomerular basement membrane (GBM) polyanions, mainly heparan sulfate proteoglycan in spontaneous hypertensive rats (SHR) with or without salt loading and antihypertensive treatment with propranolol. The changes of mean GBM width and anionic sites distribution were assessed by electron microscopy. Plasma and urinary nitrates (NO(x)) were measured by nitrite (NO2) + nitrate (NO3), stable metabolites of NO. SHR had decreased NO production and increased GBM width (27%) compared with the control Wistar-Kyoto (WKY) rats. The chronic high dietary salt intake resulted in a significant increase in blood pressure, proteinuria, and renal function in the SHR rats. The chronic high salt dietary intake resulted in a decrease in NO in the WKY and a further reduction in NO production in the SHR. The GBM anionic sites count was similar in the SHR and WKY nonsalt-loaded groups, 13.5 +/- 0.5 and 12.8 +/- 0.4 CCG counts/microm GBM, respectively, but significantly lower in both salt-loaded SHR and WKY, 9.9 +/- 0.55 (P < .01) and 9.6 +/- 0.55 (P < .01) CCG counts/microm GBM, respectively. Antihypertensive treatment with propranolol in the salt-loaded SHR group resulted in lower blood pressure, a further decrease in NO production, but no significant changes in GBM width and anionic sites count. It is concluded that chronic high salt intake may be deleterious to the permselectivity of the GBM. A low NO production state that results from chronic salt loading in already hypertensive rats will result in more severe organ (renal) damage, most probably by the addition of the loss of GBM permselectivity to the existing pathomorphologic changes.

Low nitric oxide production in patients with chronic renal failure.

BACKGROUND: Rats with chronic renal failure have a low nitric oxide (NO) production and a diminished NO excretion. The supplementation of L-arginine has an inhibitory effect on the progression of renal insufficiency. METHODS: The present study was designed to determine whether chronic renal failure patients have a low NO production. Plasma and urine nitrate (NO3) and nitrite (NO2), stable metabolites of NO, were measured in 83 consecutive patients with chronic renal failure. The 83 chronic renal failure patients were divided into three groups: group 1, mild renal failure (creatinine clearance >60 ml/min/1.73 m2); group 2, moderate renal failure (creatinine clearance >30 <60 ml/min/1.73 m2), and group 3, severe renal failure (creatinine clearance <30 ml/min/1.73 m2). Thirty-three healthy volunteers served as controls. RESULTS: The daily urinary NO excretion was significantly lower in patients with moderate and severe renal failure as compared with those with mild renal failure and normal controls. The lowest values were found in the severe renal failure group. When the 24-hour urinary NO excretion or NO per milligram creatinine and the NO clearance were correlated with the renal function in all patients as a group, these parameters were directly correlated with the creatinine clearance and inversely correlated with the serum creatinine level. The plasma NO concentration was not different between the three chronic renal failure groups, but higher than in the controls. Plasma NO in renal failure patients was not correlated with the creatinine clearance or serum creatinine levels. CONCLUSIONS: Chronic renal failure is a state of NO deficiency. Treatment strategies to increase NO production (L-arginine supplementation or other NO compounds) may prove to be useful in maintaining the renal function and slow the progression of renal disease.

Glomerular basement membrane polyanionic sites and nitric oxide in genetically salt-sensitive and resistant hypertensive rats.

Cationic colloid gold, a polycationic histochemical probe, was used to analyze the distribution of glomerular basement membrane (GBM) polyanions, including heparan sulfate protoglycan in genetic salt-sensitive (SBH/Y) and resistant (SBN/Y) hypertensive rats, with or without high dietary salt intake. GBM morphology, renal function and nitric oxide, as measured by plasma and urine nitrite (NO2) and nitrate (NO3) were also determined. In the salt-sensitive rats the high-salt dietary intake resulted in severe hypertension, proteinuria and decreased glomerular filtration rate. After 1 month of high-salt intake, the average width of the GBM of salt-sensitive rats was higher by 27% than that of salt-resistant rats. The number of GBM anionic sites (lamina rata externa and interna) was much lower in both salt-sensitive and salt-resistant groups after 1 month of salt loading, 8.04+/-0.36 and 7.8+/-0.25 counts/cm, respectively, compared to the respective values of non-salt-loaded animals, 20.58+/-1.08 counts/cm in the SBH/Y (p < 0.001) and 21+/-1.86 counts/cm in the SBN/Y (p < 0.001). A decreased nitric oxide production was found in the salt-sensitive rats before and after salt loading compared with the salt-resistant group. No correlation was found between the nitric oxide changes and the GBM modifications. It is concluded that high-salt intake may be deleterious to the permselectivity of the GBM. It is suggested that salt restriction in hypertension may have a beneficial effect in preventing GBM permselectivity changes and proteinuria.

Nitric oxide in ischaemic acute renal failure of streptozotocin diabetic rats.

Changes in nitric oxide (NO) levels were determined in ischaemic acute renal failure in streptozotocin-induced diabetes mellitus rats. Two weeks after streptozotocin administration and immediately after right nephrectomy, the left renal artery was occluded for 60 min. Similar procedures were carried out in non-diabetic rats. The nitrite (NO2) + nitrate (NO3) levels were measured in plasma and urine. The effects of chronic oral supplementation with L-arginine and an NO synthase inhibitor (N-omega-nitro-L-arginine) were also studied in both diabetic and non-diabetic rats before and after renal artery clamping. The rats with diabetic acute renal failure had a much lower creatinine clearance (90 +/- 22 microliters.min-1. 100g body weight-1, p < 0.005), and higher fractional excretion of sodium (FENa)% (10.90 +/- 4.2, p < 0.001) and protein excretion (2078 +/- 69 micrograms/ml creatinine clearance, p < 0.001) compared with the respective values in the non-diabetic groups (163 +/- 30; 1.46 +/- 86; 453.3 +/- 31). The plasma and urine NO2 + NO3 levels were significantly higher in the untreated diabetic rats compared with the untreated normal rats before ischaemia (p < 0.001). The ischaemic acute renal failure in non-diabetic rats increased the plasma and urinary NO2 + NO3 excretion after ischaemia. The urinary excretion of these metabolites decreased significantly and their plasma levels remained unchanged in the ischaemic diabetic rats. The L-arginine administration resulted in a small but significantly higher creatinine clearance after clamping in the non-diabetic rats. The NO synthase inhibitor caused deterioration in renal function in all ischaemic and non-ischaemic groups. In summary, the greater vulnerability to ischaemia of the diabetic kidney seems to be associated with both impaired response to and impaired production of NO.

Metabolism of agmatine into urea but not into nitric oxide in rat brain.

Agmatine is a guanidino compound abundant in bacteria and plants where it serves as a precursor for polyamine synthesis. It can interfere with several neurotransmission-related functions and can exert neuroprotective effects after brain injury. Agmatine was recently identified in mammalian brain and its synthesis by arginine decarboxylation was characterized. Its metabolism by the brain is, however, unknown. Here we report evidence indicating that agmatine can be selectively metabolized in the rat brain (cerebellum) into urea and thus, may lead to formation of putrescine, the precursor of polyamine synthesis. In addition, while agmatine can inhibit brain nitric oxide synthase, it did not serve as a substrate for nitric oxide formation.

The effect of human recombinant erythropoietin on the growth of a human neuroblastoma cell line.

Erythropoietin is a growth factor. Cancer can be described as disturbance of the fine balance of positive and negative growth control mechanisms. The effect of human recombinant erythropoietin (EPO) was studied on the cell growth and differentiation of a human neuroblastoma cell line (h-NMB). Cell growth curves, trypan blue staining and thymidine uptake were used to assess cell proliferation and death. To assess cell differentiation, neutral endopeptidase (cell membrane enzyme marker), creatine kinase (cytosolic enzyme marker), dopamine uptake (dopamine transporter marker) and cell morphology were determined. Specific EPO receptor mRNA, by RT-PCR technique, was demonstrated. The incubation of erythropoietin with the tumor cell line resulted in inhibition of cell proliferation as evidenced in a diminished cell growth. EPO was shown to have induced a differentiation process as seen from the two different enzymatic markers, membranal and cytosolic, and from the cells dopamine uptake studies. However, the morphological changes did not document a full differentiation effect. EPO specific antibodies blocked the effects of EPO on cell proliferation and creatine kinase activity. In this study, EPO did not produce any sign of proliferation in the nervous tumor cell line used.

Oral administration of L-arginine and captopril in rats prevents chronic renal failure by nitric oxide production.

The effect of oral supplementation of L-arginine, the substrate of nitric oxide, (1.25 g/liter water) and captopril (15 mg/liter water) was studied in 5/6 nephrectomized rats for a period of three months. N-omega-nitro L-arginine, a nitric oxide synthase inhibitor, was given orally (70 mg/liter water) with or without L-arginine or captopril. The urinary excretion of nitrite (NO2) + nitrate (NO3), the known metabolites of nitric oxide, was taken as an index of nitric oxide production. Chronic renal failure rats were characterized by a low creatinine clearance, high FENa%, proteinuria, hypertension and a low urinary excretion of NO2 + NO3; 0.152 +/- 0.06 (P < 0.001) nmol/micrograms creatinine compared with 0.481 +/- 0.004 (P < 0.001) in normal rats and 0.479 +/- 0.11 (P < 0.001) in untreated sham-operated rats. Both L-arginine and captopril were effective in the normalization of all these parameters. The combination of L-arginine and captopril had no additive effects. The nitric oxide synthase inhibitor significantly diminished the captopril beneficial effect. It is concluded that chronic renal failure in rats is a low nitric oxide production state. The supplementation of L-arginine is shown to overcome this condition. It is suggested that the beneficial effect of captopril on chronic renal failure is through a specific L-arginine--nitric oxide synthase--nitric oxide pathway.