Impaired Nitric Oxide Generation Research Articles

Alterations of intracellular calcium concentration and nitric oxide generation in pulmonary artery endothelium after subarachnoid hemorrhage of the rabbit

The present study was designed to investigate whether endothelial intracellular calcium concentration ([Ca 2+] i), endothelial nitric oxide synthase (eNOS) activity and nitric oxide (NO) generation altered in association with impaired endothelium-dependent relaxation (EDR) in pulmonary artery (PA) specimens from experimental subarachnoid hemorrhage (SAH) rabbits. Injecting non-heparinized autologous arterial blood into cisterna magna induced the SAH. Simultaneous measurements of endothelial [Ca 2+] i and isometric tension of PA specimens were performed using fura 2. The subjects included normal control rabbits (group N), SAH rabbits with normal EDR (group A) and with impaired EDR (group B). When treated with 10 − 7 M acetylcholine (ACh), endothelial [Ca 2+] i was significantly lower in group B (74.1 ± 8.5 nM) than that in groups A (153.0 ± 28.0 nM, p < 0.05) and N (184.8 ± 27.8 nM, p < 0.01). Basal and ACh-stimulated cyclic GMP productions as a marker of NO generation were also significantly ( p < 0.005) decreased in group B as compared to those in the other two groups. Meanwhile, there were no differences in eNOS activity per se among the three groups. These results suggest that the attenuated endothelial [Ca 2+] i elevation leads to the impaired NO generation in PA endothelium, which in turn impairs the EDR and possibly increases the vascular resistance of PA following SAH.

Nitric oxide, stomatal closure and abiotic stress

Various data indicate that nitric oxide (NO) is an endogenous signal in plants that mediates responses to several stimuli. Experimental evidence in support of such signalling roles for NO has been obtained via the application of NO (usually in the form of NO donors), via the measurement of endogenous NO and through the manipulation of endogenous NO content via chemical and genetic means. Stomatal closure initiated by abscisic acid (ABA) is effected through a complex symphony of intracellular signalling in which NO appears to be one component. Exogenous NO induces stomatal closure, ABA triggers NO generation, removal of NO by an NO scavenger inhibits stomatal closure in response to ABA and ABA-induced stomatal closure is reduced in mutants that have impaired NO generation. The data indicate that ABA-induced guard cell NO generation requires both a nitric oxide synthase-like activity and, in Arabidopsis, nitrate reductase (NR), in particular NR1. NO stimulates both MAP kinase activity and cGMP production, both of which are required for ABA-induced stomatal closure.Data from other laboratories suggest that drought and salinity stress can induce NO generation, and that NO could activate cellular processes that afford some protection against these stresses. Cellular responses to NO may differ depending on the NO concentration; at higher concentrations NO can cause stomatal opening and may be toxic. Our data for Arabidopsis indicate that responses to NO differ between wilting and turgid tissue and suggest that guard cell responses in planta reflect complex interactions between hormonal and redox signalling.

A High-Carbohydrate, High-Fiber Meal Improves Endothelial Function in Adults With the Metabolic Syndrome

Brachial artery flow-mediated dilation (FMD) using high-resolution ultrasound is a well-accepted, noninvasive bioassay for in vivo endothelium-generated nitric oxide (NO) in humans (1). Impaired NO generation characterizes the endothelial phenotype prone to the development of atherosclerosis and is linked to acute cardiovascular events. In several studies (2,3), endothelial dysfunction is an independent predictor of future cardiovascular morbidity and mortality. The postprandial state may be critical in the development of atherosclerosis (4). A single high-fat meal can induce endothelial dysfunction, whereas low-fat meals generally neither improve nor worsen FMD (5–8). The lack of a reported effect of low-fat meals on FMD may be attributable in part to insufficient dietary fiber in the meal. In particular, increased cereal fiber consumption is associated with reduced cardiovascular disease incidence and mortality (9–11) and lower prevalence of the metabolic syndrome (12) and may reduce systemic inflammation (13). We examined whether a high-carbohydrate meal, rich in cereal fiber, would improve brachial artery FMD in adults with the metabolic syndrome. For comparison, we also examined the impact of a low-carbohydrate, low-fiber meal. Twelve (9 women and 3 men: 44.7 ± 7.9 years of age, 98.9 ± 16.6 kg, 1.70 ± 0.07 m) nonsmoking, nondiabetic adults who met the International Diabetes Federation criteria for the metabolic syndrome participated in the study (14). Subjects were not taking medications to control blood lipids, blood …

Partial inhibition of nitric oxide synthase primes the stimulated pathway of vWF-secretion in man

Increased release of von Willebrand factor (vWF) has been linked to the pathogenesis of atherosclerosis. For this complex disease, impairment of endothelium-derived, nitric oxide production and impaired vascular relaxation has also been reported. Since endothelially produced nitric oxide (NO) is known to inhibit secretion of the Weibel–Palade bodies in animals, we hypothesized that NO could mitigate vWF secretion. In a randomized, placebo controlled cross-over trial, eight male volunteers received N-monomethyl- l-arginine (LNMMA) to block endothelial NO production or placebo, and vWF release was stimulated by infusing desmopressin in three cumulative doses (0.05, 0.15, 0.4 μg/kg) in both periods. At a threshold dose of 0.l5 μg/kg desmopressin, concomitant partial blockade of NO production resulted in 20% higher levels of vWF ( P<0.04). However, maximal vWF release after 0.4 μg/kg desmopressin was unaffected by L-NMMA (Δ7% between periods, P=0.88). These data show the dampening effect of NO production on vWF release in response to threshold concentrations of secretagogues. This may in part explain the higher vWF levels in cardiovascular diseases associated with impaired endothelial NO generation.

Effects of L-arginine on cyclosporin-induced alterations of vascular NO/cGMP generation.

Cyclosporin (CsA)-induced vascular dysfunction has been attributed to a diminished role of the nitric oxide (NO)/cGMP-mediated vasodilator mechanism. The present study was aimed at investigating whether L-arginine, the substrate of NO synthesis, ameliorates CsA-induced vascular dysfunction. Male Sprague-Dawley rats were used throughout the study. The thoracic aorta was isolated from normal rats and acutely treated with CsA (10(-4) mol/l, 60 min) in vitro, or the aorta was taken from rats treated with CsA (25 mg/kg/day, i.m., 1 week). The vascular relaxation response to acetylcholine, and tissue levels of NO metabolites and cGMP were determined. The vascular expression of NO synthase (NOS) isoforms was also determined by western blot analysis. Acute treatment with CsA in vitro markedly attenuated the vasorelaxation response to acetylcholine, which was completely restored by L-arginine. The vascular accumulation of NO metabolites in response to acetylcholine was decreased significantly by CsA, which was prevented by cotreatment with L-arginine. CsA decreased the cGMP accumulation in response to both acetylcholine and sodium nitroprusside. L-Arginine restored, although not completely, acetylcholine-stimulated cGMP generation, whereas it did not affect sodium nitroprusside-stimulated cGMP generation. Following chronic CsA treatment in the whole animal, the vasorelaxation response to acetylcholine was decreased significantly along with tissue levels of NO metabolites; this was preserved by L-arginine-supplementation. Vascular expression of iNOS protein was decreased by CsA treatment along with decreased tissue accumulation of NO metabolites. L-Arginine supplementation did not modify the altered expression of NOS proteins. These results suggest that CsA causes an L-arginine-sensitive vascular dysfunction which is associated with impaired generation of NO and cGMP.

Relaxin counteracts myocardial damage induced by ischemia-reperfusion in isolated guinea pig hearts: evidence for an involvement of nitric oxide.

Relaxin was previously shown to cause coronary vasodilation and to inhibit mast cell activation through a stimulation of endogenous nitric oxide production. This suggests that relaxin may have beneficial effects on ischemia-reperfusion-induced myocardial injury, which is triggered by endothelial damage and impaired nitric oxide generation. In this study, we tested the effect of relaxin on isolated and perfused guinea pig hearts subjected to ischemia and reperfusion. Ischemia was induced by ligature of the left anterior descending coronary artery; removal of the ligature induced reperfusion. Relaxin, at the concentration of 30 ng/ml of perfusion fluid, causes: a significant increase in coronary flow and in nitric oxide generation; a significant decrease in malonyldialdehyde production and in calcium overload, both markers of myocardial injury; an inhibition of mast cell granule exocytosis and histamine release, which are known to contribute to myocardial damage; a reduction of ultrastructural abnormalities of myocardial cells; an improvement of heart contractility. The beneficial effects of relaxin were blunted by the NO synthase inhibitor L-NMMA. The current study provides first experimental evidence that relaxin has a powerful protective effect on the heart undergoing ischemia and reperfusion acting through a nitric oxide-driven mechanism.

Nitric oxide and prostacyclin influence coronary vasomotor tone in perfused rabbit heart and modulate endothelin-1 activity.

Using isolated perfused rabbit heart electrically paced, we assessed the relevance of both nitric oxide (NO) and prostacyclin (PGI2) in regulation of resting coronary perfusion pressure (CPP). In preparations in which NO-synthase was inhibited by NG-monomethyl-L-arginine (L-NMMA, 10 microM), resting CPP increased significantly; this phenomenon was potentiated by indomethacin infusion (3 microM), prevented by L-arginine (100 microM) and significantly reduced by iloprost (55 nM) and defibrotide (200 micrograms/ml). Furthermore, the increase in resting CPP induced by graded doses of endothelin-1 (ET-1 0.6-160 pmol), was further augmented by blocking of prostaglandin biosynthesis with indomethacin (3 microM) and was substantially reduced when the rate of formation of PGI2 was enhanced by defibrotide (200 micrograms/ml). Moreover, the coronary vasoconstriction induced by ET-1 (2, 4, and 8 pmol) was increased in hearts in which NO-synthase was blocked by L-NMMA (10 microM) and this event was abolished in preparations in which PGI2 synthesis was stimulated by defibrotide (200 micrograms/ml). These results further emphasize that rabbit coronary vessels are continuously dilated by NO released from endothelial cells. They also indicate that PGI2 takes part in NO generation in the endothelial-derived relaxing mechanism. Inactivation of this mechanism, owing to decreased formation of NO and PGI2 in rabbit heart, induces hyperreactivity of coronary smooth muscles to ET-1. Finally, an increase in PGI2 production (such as that caused by defibrotide) may counterbalance impaired NO generation and attenuate hyperreactivity of the coronary vasculature.