Antônio Cláudio Mendes-Ribeiro

The role of bradykinin, AT2 and angiotensin 1-7 receptors in the EDRF-dependent vasodilator effect of angiotensin II on the isolated mesenteric vascular bed of the rat

The mechanisms involved in the vasodilator actions of angiotensin II (Ang II) have not yet been completely elucidated. We investigated the potential mechanisms that seem to be involved in the Ang II vasodilator effect using rat isolated mesenteric vascular bed (MVB). Under basal conditions, Ang II does not affect the perfusion pressure of MVB. However, in vessels precontracted with norepinephrine, Ang II induces vasodilation followed by vasoconstriction. Vasoconstrictor, but not the vasodilation of Ang II, is inhibited by AT1 antagonist (losartan). The vasodilator effect of Ang II was not inhibited by AT2, angiotensin IV and angiotensin 1–7 receptor antagonists alone (PD 123319, divalinal, A 779, respectively). The vasodilator effect of Ang II is significantly reduced by endothelial removal (deoxycholic acid), but not by indomethacin. Inhibition of NO‐synthase by NG‐nitro‐L‐arginine methyl ester (L‐NAME) and guanylyl cyclase by 1H‐[1,2,3] oxadiazolo [4,4‐a] quinoxalin‐1‐one (ODQ) reduces the vasodilator effect of Ang II. This effect is also reduced by tetraethylammonium (TEA) or L‐NAME, and a combination of L‐NAME plus TEA increases the inhibitory effect of the antagonists alone. However, indomethacin does not change the residual vasodilator effect observed in vessels pretreated with L‐NAME plus TEA. In vessels precontracted with norepinephrine and depolarized with KCl 25 mM or treated with Ca2+‐dependent K+ channel blockers (charybdotoxin plus apamin), the effect of Ang II was significantly reduced. However, this effect is not affected by ATP and voltage‐dependent K+ channel blockers (glybenclamide and 4‐aminopyridine). Inhibition of kininase II with captopril significantly potentiates the vasodilator effect of bradykinin (BK) and Ang II in the rat MVB. The inhibitory effect of the B2 receptor antagonist HOE 140 on the vasodilator effect of Ang II is further enhanced by PD 123319 and/or A 779. The present findings suggest that BK plays an important role in the endothelium‐dependent vasodilator effect of Ang II. Probably, the link between Ang II and BK release is modulated by receptors that bind PD 123319 and A 779.

Modulation of cytokines, resistin, and distribution of adipose tissue in C57BL/6 mice by different high-fat diets

OBJECTIVE To investigate whether changing the lipid source induces metabolic changes and/or modulates the adipose tissue distribution in mice fed with a high-fat (HF) diet. METHODS C57BL/6 mice were subjected to a 10-wk control diet (10% fat) or an HF diet (60% fat) containing lard (HF-L), olive oil (HF-O), sunflower oil, or canola oil. Food intake and body weight were measured. At euthanasia, blood was collected and adipose tissue was dissected. Serum hormones and cytokines were determined. RESULTS The plasma insulin levels were higher in the HF-L and HF-O groups than in the other three groups (P < 0.0001). The levels of resistin were highest in the HF-L and HF-O groups (P < 0.0001). Leptin expression was also highest in these two groups (P < 0.0001). Of the four groups, interleukin-6 was expressed at the highest level in the HF-L group (P < 0.0005), whereas adiponectin was expressed at the lowest level (P < 0.0001). The accumulation of subcutaneous and visceral adipose tissues was higher in the HF-L group compared with the other groups. This group was hypertrophic because of excess subcutaneous fat and epididymal fat in the adipocytes. However, the ratio of subcutaneous to visceral fat was significantly lower in the HF-L and HF-O groups compared with the other groups. CONCLUSION In mice fed fat-rich diets, the level of adipokines, the distribution of adipose tissue, and the metabolism of carbohydrates are more significantly influenced by the lipid content rather than the absolute amount of lipid.

Depression and Cardiovascular Disease: Role of Nitric Oxide

Both depression and cardiovascular disease are major public health problems. Growing evidence shows that depression is a risk factor for the development of coronary artery disease (CAD). However, the exact mechanisms underlying the interplay between depression and CAD remain to be elucidated. Depression adversely affects autonomic and hormonal homeostasis, resulting in metabolic abnormalities, inflammation, increased platelet aggregation and endothelial dysfunction. All of these pathological features lead to atherothrombosis and cardiovascular events. However, there is no clear evidence that anti-depressant drugs or psychotherapy will reduce the risk or improve the outcome of CAD. Recent studies suggest that the L-arginine-nitric oxide (NO) pathway is involved in the genesis of depression. NO has many physiological functions, including vasodilatation, neurotransmission and platelet aggregation inhibition. It is synthesised from the cationic amino acid L-arginine by a family of enzymes: NO synthases (NOS). There are three NOS isoforms: inducible NOS (iNOS), endothelial NOS and neuronal NOS (nNOS). The availability and transport of L-arginine modulate rates of NO biosynthesis in circulating blood cells and vasculature, which provides a protective effect against cardiovascular disease. In depressive patients, the L-arginine-nitric oxide pathway seems to be impaired. The present review seeks a better understanding of the mechanisms that could identify depression as a cardiovascular risk factor and introduce new possible therapeutic interventions.

Inhibition of L-arginine transport in platelets by asymmetric dimethylarginine and NG-monomethyl-L-arginine: Effects of arterial hypertension

1. Nitric oxide (NO) produced by human platelets plays an important role in all stages of platelet activation. l‐Arginine, the precursor for NO synthesis, modulates NO production by platelets. The l‐arginine analogues asymmetric dimethylarginine (ADMA) and NG‐monomethyl‐l‐arginine (l‐NMMA) are endogenous inhibitors of nitric oxide synthase (NOS), involved in the physiopathology of arterial hypertension. The aim of the present study was to investigate the inhibitory effects of endogenous and exogenous l‐arginine analogues on l‐arginine influx in platelets from healthy controls and hypertensive patients.

L -arginine-nitric oxide pathway and oxidative stress in plasma and platelets of patients with pre-eclampsia

Pre-eclampsia (PE), a syndrome of pregnancy-induced hypertension, continues to be a leading cause of maternal and fetal morbidity and mortality. The aim of this study was to investigate whether changes in oxidative status are correlated with alterations in the L-arginine-nitric oxide pathway and platelet aggregation in PE. Plasma and platelets from women with PE (n=24) or normotensive pregnancy (NP, n=27) recruited in the third trimester of gestation were used to measure oxidative damage assessed by protein carbonyl content, antioxidant activities of superoxide dismutase (SOD), catalase (CAT) and nitrite levels. Transport of L-[3H]-arginine, as well as the activities of the nitric oxide (NO) synthase (eNOS and inducible NO synthase (iNOS)) and platelet aggregation, were also evaluated. Plasma nitrite levels and the activities of SOD and CAT were reduced in PE (5.2±2.7, 3.4±0.8, 0.3±0.4, respectively, P<0.05) compared with NP (8.7±2.3, 6.7±3.1, 1.0±0.5, respectively), whereas protein carbonyl content and L-arginine levels were not significantly different between PE and NP groups. In platelets, L-arginine transport was reduced in PE (19.2±10.5, P<0.05) compared with NP (62.0±31.1), whereas the NOS activity, eNOS and iNOS expression, nitrite levels and platelet aggregation were unaffected. Protein carbonyl content was increased, and CAT activity was reduced in platelets from PE (0.03±0.02, 0.55±0.30, respectively, P<0.05), compared with NP (0.005±0.005, 1.01±0.36, respectively). The data suggest that a systemic impairment of antioxidant defense mechanisms is associated with decreased plasma nitrite levels, which may contribute to hypertension in PE. Oxidative stress may contribute to the reduced influx of L-arginine in platelets. Compensatory mechanisms may contribute to the maintenance of NO production and its modulatory role on platelet function.

High fat diets modulate nitric oxide biosynthesis and antioxidant defence in red blood cells from C57BL/6 mice.

The consumption of a high fat (HF) diet is considered a risk factor for the development of obesity. On the other hand, a monounsaturated HF diet has beneficial cardiometabolic effects. Since nitric oxide (NO) modulates vascular homeostasis, we investigate whether HF diets that vary in fatty acid composition have a different effect on theL-arginine-NO pathway and oxidative stress in C57BL/6 mice red blood cells (RBC). The olive oil diet induced an activation of L-arginine transport compared to other diets. NO synthase (NOS) activity was increased in all unsaturated HF diets (olive, sunflower and canola oils). Moreover, the expression of endothelial NOS (eNOS) and inducible NOS (iNOS) was increased in the olive oil group. In contrast, NOS activity from the lard group was decreased associated with diminished l-arginine transport. Olive oil also induced superoxide dismutase activation. Inhibition of the L-arginine-NO pathway in the lard group could contribute to cardiovascular diseases, while unsaturated HF diets may have a protector effect via enhanced NO bioavailability.

Chronic exercise reduces platelet activation in hypertension: upregulation of the L-arginine-nitric oxide pathway

Nitric oxide (NO) inhibits platelet function and plays a key role in the regulation of cardiovascular homeostasis. Essential hypertension is characterized by an increased risk of thrombus formation, and by an inhibition of intraplatelet NO bioactivity. We have previously shown that membrane transport of l‐arginine is a rate‐limiting step for platelet‐derived NO synthesis. This study examined the effects of exercise on the platelet l‐arginine–NO pathway and aggregation and systemic inflammation markers in 13 sedentary hypertensive patients subjected to 60 min of training activity (exercise group), predominantly aerobic, three times a week for a period of 12 weeks. Six sedentary hypertensive patients participated in the control group. After 12 weeks, l‐arginine transport was significantly increased and associated with increased platelet NO synthase activity and cGMP levels and reduced platelet aggregation. Moreover, exercise training reduced plasma concentrations of fibrinogen and C‐reactive protein and blood pressure. The control group did not change their previous intraplatelet l‐arginine–NO results and systemic inflammatory markers levels. Thus, exercise training reduces inflammatory responses, restores NO synthesis in platelets and thereby contributes to the beneficial effects of exercise in hypertension. The present study adds exercise as a new tool to reduce morbidity and mortality associated with platelet activation in hypertension.

Chronic exercise leads to antiaggregant, antioxidant and anti-inflammatory effects in heart failure patients

Background Heart failure (HF) patients are at an increased risk of thrombotic events. Here, we investigated the effects of exercise training on platelet function and factors involved in its modulation in HF. Design and methods Thirty HF patients were randomized to 6 months of supervised exercise training or to a control group that remained sedentary. Exercise training consisted of 30 min of moderate-intensity treadmill exercise, followed by resistance and stretching exercises, performed three times a week. Blood was collected before and after the intervention for platelet and plasma obtainment. Results Peak VO2 increased after exercise training (18.0 ± 2.2 vs. 23.8 ± 0.5 mlO2/kg/min; p < 0.05). Exercise training reduced platelet aggregation induced by both collagen and ADP (approximately –6%; p < 0.05), as well as platelet nitric oxide synthase activity (0.318 ± 0.030 vs. 0.250 ± 0.016 pmol/108 cells; p < 0.05). No difference in the above-mentioned variables were observed in the control group. No significant difference was observed in intraplatelet cyclic guanosine monophosphate levels among groups. There was a significant increase in the activity of the antioxidant enzymes superoxide dismutase and catalase in plasma and platelets, resulting in a decrease in both lipid and protein oxidative damage. Systemic levels of the inflammatory markers C-reactive protein, fibrinogen, and tumour necrosis factor α were also reduced in HF after training. Conclusions Our results suggest that regular exercise training is a valuable adjunct to optimal medical management of HF, reducing platelet aggregation via antioxidant and anti-inflammatory effects, and, therefore, reducing the risk of future thrombotic events.

Oxidative stress, l-arginine-nitric oxide and arginase pathways in platelets from adolescents with anorexia nervosa.

Anorexia nervosa (AN) is associated with high cardiovascular mortality. Nitric oxide (NO) inhibits platelet function and regulates the cardiovascular homeostasis. The aim of this study was to investigate the l-arginine-NO-GMPc and arginase pathways and oxidative stress in platelets from patients with AN. Intraplatelet l-arginine transport, NOS expression and activity, cGMP levels, platelet aggregation, arginase expression and oxidative stress were measured in adolescent patients with AN (n=11) and healthy controls (n=12). Plasma l-arginine levels were significantly reduced in AN. l-arginine transport, NOS activity and cGMP basal levels were reduced in platelets associated with unchanged platelet aggregability. The expression of NOS isoforms was not affected. TBARS production was diminished, while the activity of superoxide dismutase was elevated in AN patients. There was an overexpression of arginase II in AN. Alterations of l-arginine-NO-GMPc and arginase pathways in platelets can be early predictors of the incidence of cardiovascular disease into adult life in AN.

INHIBITORY EFFECTS OF ENDOGENOUS l-ARGININE ANALOGUES ON NITRIC OXIDE SYNTHESIS IN PLATELETS: ROLE IN PLATELET HYPERAGGREGABILITY IN HYPERTENSION

1 An increase in plasma concentrations of endogenous l‐arginine analogues, which are inhibitors of nitric oxide (NO) synthesis, may be involved in platelet activation and the increased risk of thrombosis in essential hypertension. Nitric oxide is synthesised in platelets from the amino acid l‐arginine by inducible and constitutive isoforms of NO synthase (NOS), which leads to increased levels of cGMP. 2 In the present study, we investigated basal intraplatelet cGMP levels, platelet aggregation and pro‐inflammatory biomarkers in hypertensive patients. The effects of endogenous (NG‐monomethyl‐l‐arginine (l‐NMMA) and asymmetric dimethylarginine (ADMA); both at 1 mmol/L) and exogenous (aminoguanidine and NG‐nitro‐l‐arginine; both at 1 mmol/L) l‐arginine analogues and the neutral amino acid l‐leucine (1 mmol/L) in inhibiting NOS activity in platelets were also investigated. 3 Twelve healthy controls and 18 hypertensive patients participated in the study. Platelet aggregation induced by collagen was increased in hypertensive patients (95 ± 5%) compared with controls (72 ± 5%). Basal NOS activity and intraplatelet cGMP levels were reduced in hypertensive platelets. Moreover, ADMA, l‐NMMA and l‐leucine were effective inhibitors of NO synthesis in both hypertensive and control platelets. Essential hypertension led to an inflammatory response, with increased plasma concentrations of fibrinogen, C‐reactive protein and cytokines. 4 These findings provide evidence that, in essential arterial hypertension, the enhanced plasma levels of endogenous l‐arginine analogues ADMA and l‐NMMA, potent inhibitors of l‐arginine transport and NO synthesis in platelets, may play a role in increased platelet aggregation via a cGMP‐dependent mechanism.