Nitric oxide and the renin-angiotensin system. Is there a physiological interplay between the systems?

Experimental and Clinical Evidence of Endothelial Dysfunction in Inflammatory Bowel Disease

The endothelium has a crucial role in proper hemodynamics. Inflammatory bowel disease (IBD) is mainly a chronic inflammatory condition of the gastrointestinal tract. However, considerable evidence points to high cardiovascular risk in patients with IBD. This review positions the basic mechanisms of endothelial dysfunction in the IBD setting (both clinical and experimental). Furthermore, we review the main effects of drugs used to treat IBD in endothelial (dys)function. Moreover, we leave challenging points for enlarging the therapeutic arsenal for IBD with new or repurposed drugs that target endothelial dysfunction besides inflammation.

Reversal of cardiovascular remodelling with candesartan

Cardiovascular remodelling, defined as ventricular and vascular hypertrophy together with fibrosis, characterises hypertension following inhibition of the production of the endogenous vasodilator, nitric oxide (NO). This study has determined whether the cardiovascular remodelling following chronic NO synthase inhibition can be reversed by administration of the selective angiotensin II AT1-receptor antagonist, candesartan. Male Wistar rats were treated with L-nitroarginine methyl ester (L-NAME, 400 mg/l in drinking water) for eight weeks and with candesartan cilexetil (2 mg/kg/day by oral gavage) for the last four weeks. L-NAME-treated rats became hypertensive with systolic blood pressure increasing from 110±4 mmHg (control) to 170±10 mmHg. Rats developed left ventricular hypertrophy (control 1.70±0.06; L-NAME 2.10±0.04 mg/kg body wt) with markedly increased deposition of perivascular and interstitial collagen. Candesartan returned blood pressure, left ventricular weights and collagen deposition to control values. Echocardiographic assessment showed concentric hypertrophy with an increased fractional shortening; this was reversed by candesartan treatment. Heart failure was not evident. In the isolated Langendorff heart, diastolic stiffness increased in L-NAME-treated rats while the rate of increase in pressure (+dP/dt) increased after eight weeks only; candesartan reduced collagen deposition and normalised +dP/dt. In isolated left ventricular papillary muscles, the potency (negative log EC50) of noradrenaline as a positive inotropic compound was unchanged, (control 6.56±0.14); maximal increase in force before ectopic beats was reduced from 5.0±0.4 mN to 2.0±0.2 mN. Noradrenaline potency as a vasoconstrictor in thoracic aortic rings was unchanged, but maximal contraction was markedly reduced from 25.2±2.0 mN to 3.0±0.3 mN; this was partially reversed by candesartan treatment. Thus, chronic inhibition of NO production with L-NAME induces hypertension, hypertrophy and fibrosis with increased toxicity and significant decreases in vascular responses to noradrenaline. These changes were at least partially reversible by treatment with candesartan, implying a significant role of AT1-receptors in L-NAME-induced cardiovascular changes.

Hypotensive and sympathoinhibitory responses to selective central AT2 receptor stimulation in spontaneously hypertensive rats

The type 2 angiotensin receptor (AT2R) has been suggested to counterbalance the type 1 angiotensin receptor (AT1R) in the central regulation of blood pressure and sympathetic tone. In the present study we investigated the blood pressure responses to stimulation of central AT2Rs by the selective agonist Compound 21 in conscious spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto rats (WKY rats). We also assessed the impact on noradrenaline [norepinephrine (NE)] plasma levels, autonomic function, spontaneous baroreflex sensitivity, and the possible involvement of the nitric oxide (NO) pathway and the AT1Rs. Chronic intracerebroventricular Compound 21 infusion lowered blood pressure and NE plasma levels in both rat strains. The night-time hypotensive effect was greater in SHRs compared with WKY rats. Compound 21 improved spontaneous baroreflex sensitivity more in SHRs than in WKY rats. These effects were abolished by co-administration of the AT2R antagonist PD123319 or the NO synthase inhibitor Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME). Central AT1R blockade did not enhance the hypotensive response to Compound 21. Chronic selective stimulation of central AT2Rs lowers blood pressure through sympathoinhibition, and improves spontaneous baroreflex sensitivity more in SHRs than in WKY rats. These responses appear to require a functioning central NO pathway, but are not modified by central AT1R blockade. Collectively, the data demonstrate specific beneficial effects of stimulation of central AT2Rs in hypertension associated with increased sympathetic tone, and suggest that central AT2Rs may represent a potential new therapeutic target for the treatment of neurogenic hypertension.

AT2 receptor signaling and sympathetic regulation

There is a growing consensus that the balance between Angiotensin Type 1 (AT1R) and Angiotensin Type 2 (AT2R) signaling in many tissues may determine the magnitude and, in some cases the direction, of the biological response. Sympatho-excitation in cardiovascular diseases is mediated by a variety of factors and is, in part, dependent on Angiotensin II signaling in the central nervous system. Recent data have provided evidence that the AT2R can modulate sympatho-excitation in animals with hypertension and heart failure. The evidence for this concept is reviewed and a model is put forward to support the rationale that therapeutic targeting of the central AT2R may be beneficial in the setting of chronic heart failure.

Reduced expression of angiotensin I-converting enzyme in caveolin-1 knockout mouse lungs

Reduced lung capillary expression of angiotensin I-converting enzyme (ACE), a key enzyme in cardiovascular pathophysiology, and of caveolin-1, an important regulator of endothelial cell signalling, has been demonstrated in various models of pulmonary arterial hypertension (PAH). We addressed the relationship between PAH and ACE expression in caveolin-1 knockout mice (Cav1(-/-)), which have moderate PAH. Tissue ACE activity was reduced by 50% in lungs from 3-month-old Cav1(-/-) mice compared to wild type (WT). A similar reduction in lung endothelial ACE expression was observed by measuring the lung uptake of (125)I-labeled monoclonal anti-ACE antibody and by quantitative immunohistochemistry. These alterations in ACE are limited to capillary segments of the pulmonary circulation. Functionally, the increase in pulmonary artery pressure (PAP) in response to ACE conversion of angiotensin I to angiotensin II in isolated, perfused mouse lungs was reduced significantly in Cav1(-/-) mice compared to WT. Thus, these complementary approaches demonstrate the dependence of lung microvascular endothelial cell ACE protein expression on caveolin-1 expression and underscore the vital role of caveolin-1-regulated pulmonary vascular homeostasis on endothelial ACE expression and activity. In summary, we have revealed a novel role of caveolin-1 in the regulation of ACE expression in pulmonary capillary endothelial cells. Further understanding of the mechanism by which reduced caveolin-1 expression leads altered pulmonary vascular development, PAH, and reduced ACE expression may have important clinical implications in patients with these severe lung diseases.

The antioxidant effect of angiotensin II receptor blocker, losartan, in streptozotocin-induced diabetic rats

We determined the effect of a short-term angiotensin II signaling blockade on vascular endothelial growth factor (VEGF), soluble intercellular adhesion molecule-1 (sICAM-1), nitric oxide (NO), and malondialdehyde (MDA) (index of lipid peroxidation) levels in the systemic circulation and on peroxynitrite generation and insulitis development in the streptozotocin (STZ) diabetic rats' pancreas. Diabetes was induced in Wistar rats by intraperitoneal STZ injection. Diabetic rats were treated for 1 week with losartan (20 mg/kg/body weight/day in the drinking water), and pancreas and blood were collected for histochemical, immunohistochemical, and biochemical studies. Diabetic rats showed greater VEGF, sICAM-1, NO, and MDA levels, a high score of insulitis, increased nitrotyrosine staining, and markedly reduced pancreatic insulin content when compared with controls. Losartan treatment suppressed the excessive NO and lipid peroxidation production systemically without restoring them to that of healthy subjects and reduced VEGF levels while leaving sICAM-1 levels unchanged. The insulitis score and nitrotyrosine staining were reduced, whereas the pancreatic islets and the beta-cell area were increased significantly in the treated group, indicating the reduction of inflammation and nitrosative stress and an early regeneration of beta-cell mass in the pancreas. Conclusively, in the STZ diabetic rat model, even a short-term losartan treatment improves oxidative and nitrosative stress systemically and locally, improving the islets' environment and accelerating beta-cell regeneration.

Effects of green tea, black tea and Rooibos tea on angiotensin-converting enzyme and nitric oxide in healthy volunteers

OBJECTIVE

Tea has been reported to reduce cardiovascular mortality, but the underlying mechanisms are largely unknown. The aim of the current project was to investigate the effect of green tea (Japanese Sencha), black tea (Indian Assam B.O.P.) and Rooibos tea (South Africa) on angiotensin-converting enzyme (ACE) and nitric oxide (NO).

DESIGN

Seventeen healthy volunteers received a single oral dose of 400 ml green tea, black tea or Rooibos tea in a randomized, three-phase, crossover study. ACE activity and NO concentration were measured (at 0, 30, 60 and 180 min) in all phases. ACE activity was analysed by means of a commercial radioenzymatic assay. Nitrite was analysed as a marker of NO concentration. In addition, ACE genotype was determined using a PCR method.

RESULTS

Oral intake of a single dose of Rooibos tea significantly inhibited ACE activity after 30 min (P < 0.01) and after 60 min (P < 0.05). A significant inhibition of ACE activity was seen with green tea for the ACE II genotype 30 min after intake of the tea (P < 0.05) and for the ACE ID genotype 60 min after intake (P < 0.05). A significant inhibition of ACE activity was also seen with Rooibos tea for the ACE II genotype 60 min after intake (P < 0.05). No significant effect on NO concentration was seen.

CONCLUSIONS

These results suggest that green tea and Rooibos tea may have cardiovascular effects through inhibition of ACE activity.

Renin-angiotensin system inhibitors protect against age-related changes in rat liver mitochondrial DNA content and gene expression

Chronic renin-angiotensin system inhibition protects against liver fibrosis, ameliorates age-associated mitochondrial dysfunction and increases rodent lifespan. We hypothesized that life-long angiotensin-II-mediated stimulation of oxidant generation might participate in mitochondrial DNA "common deletion" formation, and the resulting impairment of bioenergetic capacity. Enalapril (10 mg/kg/d) or losartan (30 mg/kg/d) administered during 16.5 months were unable to prevent the age-dependent accumulation of rat liver mitochondrial DNA "common deletion", but attenuated the decrease of mitochondrial DNA content. This evidence - together with the enhancement of NRF-1 and PGC-1 mRNA contents - seems to explain why enalapril and losartan improved mitochondrial functioning and lowered oxidant production, since both the absolute number of mtDNA molecules and increased NRF-1 and PGC-1 transcription are positively related to mitochondrial respiratory capacity, and PGC-1 protects against increases in ROS production and damage. Oxidative stress evoked by abnormal respiratory function contributes to the pathophysiology of mitochondrial disease and human aging. If the present mitochondrial actions of renin-angiotensin system inhibitors are confirmed in humans they may modify the therapeutic significance of that strategy.

Angiotensin converting enzyme activity and nitric oxide level in serum patients with dehydration

Angiotensin converting enzyme (ACE) and nitric oxide (NO) have been suggested to be involved in the regulation of fluid homeostasis. In the present investigation, ACE activity and NO levels were determined in serum of 20 patients (10 men and 10 women) with dehydration caused by gastroenterocolitis and 20 healthy individuals (10 men and 10 women). Serum and tissue ACE activity was determined by spectrophotometric method using hippuryl-l-histidyl-l-leucine (Hip-His-Leu) as a substrate. NO synthesis was determined by measuring the products of NO, nitrite and nitrate. The concentration of nitrites was determined by classic colorimetric method using Griess reagent. Nitrate concentration was determined indirectly by their reduction with elementary zinc into nitrite. Results have shown that serum ACE activity in patients with dehydration (36,46+/-2,74 U/L) is statistically higher then in healthy individuals (28,71+/-1,77 U/L, p<0,05). The average level of nitrites/nitrates in serum of patients with dehydration (30,57+/-1,05 microM; mean +/- SEM) is also statistically higher then in healthy individuals (12,44+/-0,60 microM, p<0,0001). There was no correlation between ACE activity and NO production. The results indicate that ACE and NO may participate in the regulation of the alteration in blood flow and in the regulation of the water balance in patients with dehydration.

Mitochondrial function and nitric oxide metabolism are modified by enalapril treatment in rat kidney

The renal and cardiac benefits of renin-angiotensin system (RAS) inhibition in hypertension exceed those attributable to blood pressure reduction, and seem to involve mitochondrial function changes. To investigate whether mitochondrial changes associated with RAS inhibition are related to changes in nitric oxide (NO) metabolism, four groups of male Wistar rats were treated during 2 wk with a RAS inhibitor, enalapril (10 mg x kg(-1) x day(-1); Enal), or a NO synthase (NOS) inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME) (1 mg x kg(-1) x day(-1)), or both (Enal+L-NAME), or were untreated (control). Blood pressure and body weight were lower in Enal than in control. Electron transfer through complexes I to III and cytochrome oxidase activity were significantly lower, and uncoupling protein-2 content was significantly higher in kidney mitochondria isolated from Enal than in those from control. All of these changes were prevented by L-NAME cotreatment and were accompanied by a higher production/bioavailability of kidney NO. L-NAME abolished mitochondrial NOS activity but failed to inhibit extra-mitochondrial kidney NOS, underscoring the relevance of mitochondrial NO in those effects of enalapril that were suppressed by L-NAME cotreatment. In Enal, kidney mitochondria H(2)O(2) production rate and MnSOD activity were significantly lower than in control, and these effects were not prevented by L-NAME cotreatment. These findings may clarify the role of NO in the interactions between RAS and mitochondrial metabolism and can help to unravel the mechanisms involved in renal protection by RAS inhibitors.

Effect of Panax ginseng extract (G115) on angiotensin-converting enzyme (ACE) activity and nitric oxide (NO) production

This study investigates the effects of the Panax ginseng (Araliaceae) extract G115 on angiotensin-converting enzyme (ACE) activity and nitric oxide (NO) in cultured human endothelial cells from umbilical veins (HUVEC) and bovine mesenteric arteries (BMA). In HUVEC, ACE activity was significantly reduced after 10 min incubation with aqueous extract of ginseng 5.0 and 10 mg/ml. This effect was additative with the inhibition of the traditional ACE inhibitor enalaprilat. No effect was seen on NO production from the cells. Angiotensin I-induced contraction of BMA was significantly attenuated by 0.1 and 0.5 mg/ml ginseng, while no endothelium-dependent or -independent relaxation was seen. In conclusion, extract of Panax ginseng (G115) inhibits ACE activity, but does not affect NO production in HUVEC and BMA.

Angiotensin II modulates renal sympathetic neurotransmission through nitric oxide in AT2 receptor knockout mice

OBJECTIVE

Angiotensin (Ang) II enhances renal sympathetic neurotransmission and stimulates nitric oxide (NO) release. The present study investigates whether Ang II-mediated modulation of sympathetic neurotransmission is dependent on NO production in the kidney. AT2 -/y receptor-deficient mice are used to identify the Ang II receptor subtype involved.

METHODS

Mice kidneys were isolated and perfused with Krebs-Henseleit solution. Drugs were added to the perfusion solution in a cumulative manner. Release of endogenous noradrenaline (NA) was measured by high-performance liquid chromatography (HPLC). AT1 receptor expression was analysed by real-time polymerase chain reaction (PCR).

RESULTS

Ang II (0.01-30 nmol/l) dose dependently increased pressor responses in kidneys of AT2 -/y mice and wild-type (AT2 +/y) mice. Maximal pressor responses and EC50 values for Ang II was greater in AT2 -/y than in AT2 +/y mice. L-NAME (N(omega)-nitro-L-arginine methyl ester; 0.3 mmol/l) enhanced Ang II-induced pressor responses in both strains. In AT2 -/y mice, Ang II-induced facilitation of NA release was more pronounced than in AT2 +/y mice. L-NAME reduced Ang II-mediated facilitation of NA release in both strains. This reduction was more potent in AT2 -/y mice. In kidneys of AT2 -/y mice the AT1 receptor expression was significantly upregulated.

CONCLUSION

These results suggest that activation of AT1 receptors by Ang II releases NO in mouse kidney to modulate sympathetic neurotransmission. Since AT1 receptors are upregulated in AT2 -/y mice kidneys, NO-dependent effects were greater in these mice. Thus, NO seems to play an important modulatory role for renal sympathetic neurotransmission.

Diabetes in the elderly and in women: cardiovascular risks

The prevalence of diabetes in the United States is on the rise because of changing characteristics of our population. Ours is an aging population; women who are older than 75 years constitute the fastest growing segment of our population. Our population is increasingly more overweight and sedentary and the numbers of minority persons who have a higher prevalence of obesity and diabetes are on the rise. Currently, at least 17 million persons have known diabetes; another 4 million have the disease but have not been diagnosed. There also is a much larger population-perhaps up to 60 million per-sons-who has the metabolic syndrome. Up to 60% of persons who have essential hypertension have impaired insulin resistance and other characteristics of this syndrome. This article focuses on the metabolic syndrome and diabetes in women and the elderly.

Enalapril increases mitochondrial nitric oxide synthase activity in heart and liver

Heart and liver mitochondria isolated from rats treated with enalapril, 3-30 mg/kg/day in the drinking water for 7-120 days, showed a time- and dose-dependent increased nitric oxide (NO) production in the range of 14-250%. Heart and liver mitochondria from control rats produced 0.69 and 0.50 nmol of NO/min/mg of protein, respectively, as determined by dual wavelength spectrophotometry (577-591 nm) following hemoglobin oxidation to methemoglobin. The response to enalapril treatment, attributed to a gene-mediated up-regulation of mitochondrial nitric oxide synthase (mtNOS) activity, was half-maximal at 5-6 days and was maintained up to 120 days. Enalapril-treated animals showed an increased mtNOS functional activity in heart mitochondria that inhibited state 3 O(2) uptake (from 22% in control rats to 43%) and increased state 4 hydrogen peroxide (H(2)O(2)) production (from 30% in control rats to 52%). Calculated heart intramitochondrial NO and H(2)O(2) steady-state concentrations were increased 66% and 20%, respectively, by enalapril treatment. Signaling pathways dependent on mitochondrial NO and H(2)O(2) may account for the beneficial effects of enalapril in aging mammals.

Tissue-specific response to interstitial angiotensin II in humans

Angiotensin II is synthesized locally in various tissues; however, the role of interstitial angiotensin II in the regulation of regional metabolism and tissue perfusion is not clear. We characterized the effect of interstially applied angiotensin II in skeletal muscle and subcutaneous adipose tissue of young, normal-weight, healthy subjects by using the microdialysis technique. Furthermore, we tested the hypothesis that the effect of interstitial angiotensin II is modulated by nitric oxide. Tissues were perfused with 0.01, 0.1, and 1 micro mol/L angiotensin II in the presence of the L- or D-isomer of N(G)-nitro-arginine-methyl ester (L- or D-NAME), the effective and noneffective isomer, respectively, for blocking nitric oxide synthase. Dialysate ethanol, glycerol, glucose, lactate, and pyruvate concentrations were measured to assess changes in blood flow (ethanol dilution technique), lipolysis, and glycolysis, respectively. Baseline blood flow and dialysate concentrations of the metabolites were similar with L- and D-NAME in both tissues. Blood flow and dialysate glucose and lactate did not change significantly in both tissues during perfusion with angiotensin II. Dialysate glycerol dose-dependently increased in adipose tissue (P<0.0438) but decreased in muscle (P<0.007). In muscle, dialysate pyruvate increased (P<0.0002), whereas lactate/pyruvate ratio decreased (P<0.001), both dose-dependently. All effects were similar with L- and D-NAME and could be reversed by nitroprusside. We conclude that in contrast to the profound hemodynamic effect of intravascular angiotensin II, interstitial angiotensin II has a minimal acute effect on blood flow in both tissues. However, interstitial angiotensin II modulates lipid and carbohydrate metabolism in a tissue specific fashion. Thus, the physiology of interstitial angiotensin II cannot be predicted from intravascular studies.

Renal perfusion and the renal hemodynamic response to blocking the renin system in diabetes: are the forces leading to vasodilation and vasoconstriction linked?

In three groups of subjects, those with type 2 diabetes and nephropathy, those with type 1 diabetes without nephropathy, and healthy volunteers subjected to short-term hyperglycemia, we observed a counterintuitive relationship. In all three groups, baseline renal plasma flow (RPF) was positively correlated with the RPF response to blocking the renin-angiotensin system (RAS). This seems paradoxical in that an opposite result would have been expected if angiotensin-dependent renal vasoconstriction was responsible for the renal vasodilator response to RAS blockade. This suggests a link between the renal vasodilator response, mediated by nitric oxide (NO), and the activation of the intrarenal RAS. The complex interrelationships between hyperglycemia, insulin, NO, and the RAS may result in phenotypes that indicate varying risk of diabetic nephropathy and underlying genetic polymorphisms.

Obesity, atherosclerosis and the vascular endothelium: mechanisms of reduced nitric oxide bioavailability in obese humans

It is now well established that obesity is an independent risk factor for the development of coronary artery atherosclerosis. The maintenance of vascular homeostasis is critically dependent on the continued integrity of vascular endothelial cell function. A key early event in the development of atherosclerosis is thought to be endothelial cell dysfunction. A primary feature of endothelial cell dysfunction is the reduced bioavailability of the signalling molecule nitric oxide (NO), which has important anti atherogenic properties. Recent studies have produced persuasive evidence showing the presence of endothelial dysfunction in obese humans NO bioavailability is dependent on the balance between its production by a family of enzymes, the nitric oxide synthases, and its reaction with reactive oxygen species. The endothelial isoform (eNOS) is responsible for a significant amount of the NO produced in the vascular wall. NO production can be modulated in both physiological and pathophysiological settings, by regulation of the activity of eNOS at a transcriptional and post-transcriptional level, by substrate and co-factor provision and through calcium dependent and independent signalling pathways. The present review discusses general mechanisms of reduced NO bioavailability including factors determining production of both NO and reactive oxygen species. We then focus on the potential factors responsible for endothelial dysfunction in obesity and possible therapeutic interventions targetted at these abnormalities.

The metabolic syndrome and related cardiovascular risk

The metabolic syndrome is a complex association of several risk factors including insulin resistance, dyslipidemia, and essential hypertension. Insulin resistance has been associated with sympathetic activation and endothelial dysfunction, which are the main mechanisms involved in the pathophysiology of hypertension and its related cardiovascular risk. According to the Sixth Report of the Joint National Committee, and guidelines of the World Health Organization/International Society of Hypertension, the presence of multiple risk markers suggests that both hypertension and risk factors should be aggressively managed in order to obtain a better outcome. Primary prevention of obesity at different levels--individual, familial, and social-- starting early in childhood has proven to be cost effective, and will be mandatory to reduce the world epidemic of obesity and its severe consequences.

Angiotensin-converting enzyme inhibitors and AT1-receptor antagonist restore nitric oxide synthase (NOS) activity and neuronal NOS expression in the adrenal glands of spontaneously hypertensive rats

During development of hypertension in spontaneously hypertensive (SHR) rats, the activity of adrenal nitric oxide synthase (NOS) was investigated. SHR and Wistar-Kyoto (WKY) rats were studied at different ages: 3-4, 7-8 and 12-13 weeks after birth. Basal NOS activity was measured by the ability of homogenate to convert [3H]-L-arginine to [3H]-L-citrulline. At all ages, SHR rats exhibited 50-60% reduction in NOS activity when compared to age-matched WKY rats. In a following study, SHR rats (12-13 weeks) were treated chronically with the angiotensin I-converting enzyme inhibitors (ACE-I) captopril or enalapril, or the AT1-receptor antagonist losartan (2 x 25, 10 and 60 mg/kg per day for 10 days, respectively). The total NOS activity and protein expression of NOS isoenzymes from adrenals were determined. The basal NOS activity and protein expression of neuronal NOS (nNOS) was significantly increased in treated SHR rats when compared to control rats. The isoforms endothelial NOS and inducible NOS were undetectable. We conclude that impaired NO synthesis in the adrenal glands of SHR rats may contribute to the onset and maintenance of hypertension. The upregulation of nNOS protein in the adrenal glands may be one of the mechanisms by which ACE inhibitors and AT1-receptor antagonists by restoring the NO synthesis, mediate their antihypertensive effects.

The roles of platelet function, thromboxane, blood lipids and nitric oxide in hypertension of children and adolescents

The roles of platelet function, plasma lipids and nitric oxide (NO) were studied in adolescent patients with essential hypertension (JEHT group), with chronic renal failure (CRF) associated with hypertension (CRFH group), and CRF patients with normal blood pressure (CRF group), as compared with normal controls (cont. group). Platelet aggregation and the thromboxane B(2)(TxB(2)) level were significantly higher in the JEHT and CRFH groups as compared with the cont. group, whereas they were significantly lower in the CRF group. On the other hand, the platelet cAMP level was significantly lower in the JEHT and CRFH groups than in the cont. group. The plasma NO level was significantly higher only in the JEHT as compared with the cont. group (120 +/- 39 and 89 +/- 21 microM, respectively). The plasma total cholesterol, triglyceride and LDL cholesterol concentrations were normal in the JEHT group, but high in the CRF and CRFH group, the HDL cholesterol level was lower in the CRF and CRFH groups as compared with the cont. and JEHT groups. There was a positive correlation between the platelet aggregation and the TxB(2)level and between the BP and the platelet aggregation. In conclusion, hyperlipidaemia is commonly present in uraemia with haemodialysis, but is not specific for hypertension in children, while an increased platelet function is frequently associated with hypertension. The increased NO level might play a compensatory role in JEHT.