Effects of NO/cGMP inhibitors in a rat model of anaphylactoid shock

Anaphylactic shock can be defined as an acute syndrome, and it is the most severe clinical manifestation of allergic diseases. Anaphylactoid reactions are similar to anaphylactic events but differ in the pathophysiological mechanism. Nitric oxide (NO) inhibitors during anaphylaxis suggest that NO might decrease the signs and symptoms of anaphylaxis but exacerbate associated vasodilation. Therefore, blocking the effects of NO on vascular smooth muscle by inhibiting the guanylate cyclase (GC) would be a reasonable strategy. This study aimed to investigate the effects of NO/cGMP pathway inhibitors methylene blue (MB), N^ω-nitro-L-arginine methyl ester hydrochloride (L-NAME), and indigo carmine (IC) in shock induced by compound 48/80 (C48/80) in rats. The effect was assessed by invasive blood pressure measurement. Shock was initiated by C48/80 intravenous bolus injection 5 min before (prophylactic) or after (treatment) the administration of the inhibitors MB (3 mg/kg), L-NAME (1 mg/kg), and IC (3 mg/kg). Of the groups that received drugs as prophylaxis for shock, only the IC group did not present the final systolic blood pressure (SBP) better than the C48/80 group. Regarding shock treatment with the drugs tested, all groups had the final SBP similar to the C48/80group. Altogether, our results suggested that inhibition of GC and NO synthase in NO production pathway was not sufficient to revert hypotension or significantly improve survival.

Acute but not chronic metabolic acidosis potentiates the acetylcholine-induced reduction in blood pressure: an endothelium-dependent effect

Metabolic acidosis has profound effects on vascular tone. This study investigated the in vivo effects of acute metabolic acidosis (AMA) and chronic metabolic acidosis (CMA) on hemodynamic parameters and endothelial function. CMA was induced by ad libitum intake of 1% NH4Cl for 7 days, and AMA was induced by a 3-h infusion of 6 M NH4Cl (1 mL/kg, diluted 1:10). Phenylephrine (Phe) and acetylcholine (Ach) dose-response curves were performed by venous infusion with simultaneous venous and arterial blood pressure monitoring. Plasma nitrite/nitrate (NOx) was measured by chemiluminescence. The CMA group had a blood pH of 7.15±0.03, which was associated with reduced bicarbonate (13.8±0.98 mmol/L) and no change in the partial pressure of arterial carbon dioxide (PaCO2). The AMA group had a pH of 7.20±0.01, which was associated with decreases in bicarbonate (10.8±0.54 mmol/L) and PaCO2 (47.8±2.54 to 23.2±0.74 mmHg) and accompanied by hyperventilation. Phe or ACh infusion did not affect arterial or venous blood pressure in the CMA group. However, the ACh infusion decreased the arterial blood pressure (ΔBP: -28.0±2.35 mm Hg [AMA] to -4.5±2.89 mmHg [control]) in the AMA group. Plasma NOx was normal after CMA but increased after AMA (25.3±0.88 to 31.3±0.54 μM). These results indicate that AMA, but not CMA, potentiated the Ach-induced decrease in blood pressure and led to an increase in plasma NOx, reinforcing the effect of pH imbalance on vascular tone and blood pressure control.

Morphological, immunohistochemical and biochemical effects of non-pulsatile ex vivo perfusion with crescent pressures in human saphenous veins

AIM

On the average, 15% to 25% of peripheral grafts and 10% to 30% of coronary grafts fail within 5 years. Changes in mechanical forces to which the vein is subjected could be an explanation for this phenomenon. We submitted human saphenous vein segments to non-pulsatile ex vivo perfusion with crescent pressures and evaluated morphology, nitric oxide synthase immunohistochemical expression; tissue levels of nitrite/nitrate and oxidative stress products.

METHODS

Intact segments of human saphenous veins were obtained from 30 patients submitted to elective coronary artery bypass graft surgery. Ex vivo perfusion was performed during 3 hours, using oxygenated Krebs solution, flow of 100 mL/min and pressures of 0, 50, 100, 200 and 300 mmHg, defining five groups.

RESULTS

Optical microscopy showed that veins of groups perfused with 200 and 300 mmHg presented increased luminal area and endothelial denuding. Electron microscopy transmission showed alterations in veins perfused with 200 and 300 mmHg. Immunohistochemical expression of the three nitric oxide synthase isoforms was observed in all vein layers, without significant difference among groups. Tissue levels of nitrite/nitrate were not significantly different among distinctive perfusion. Nitrotyrosine was not immunohistochemically expressed in all veins and malondialdehyde tissue levels were not different among groups.

CONCLUSION

Non-pulsatile ex vivo perfusion during 3h caused morphological alterations in human saphenous veins (HSVs), which were not accompanied by immunohistochemical and biochemical alterations. Even with mechanical lesions, HSVs maintained the ability of express nitric oxide synthase (NOS) and release nitric oxide.

The effect of extracellular pH changes on intracellular pH and nitric oxide concentration in endothelial and smooth muscle cells from rat aorta

Aims

It has been known for more than a century that pH changes can alter vascular tone. However, there is no consensus about the effects of pH changes on vascular response. In this study, we investigated the effects of extracellular pH (pH_o) changes on intracellular pH (pH_i) and intracellular nitric oxide concentration ([NO]_i) in freshly isolated endothelial cells and cross sections from rat aorta.

Main Methods

The HCl was used to reduce the pH_o from 7.4 to 7.0 and from 7.4 to 6.5; the NaOH was used to increase the pH_o from 7.4 to 8.0 and from 7.4 to 8.5. The fluorescent dyes 5-(and-6)-carboxy SNARF-1, acetoxymethyl ester, acetate (SNARF-1) and diaminofluorescein-FM diacetate (DAF-FM DA) were employed to measure the pH_i and [NO]_i, respectively. The fluorescence intensity was measured in freshly isolated endothelial cells by flow cytometry and in freshly obtained aorta cross sections by confocal microscopy.

Key Findings

The endothelial and vascular smooth muscle pH_i was increased at pH_o 8.5. The extracellular acidification did not change the endothelial pH_i, but the smooth muscle pH_i was reduced at pH_o 7.0. At pH_o 8.5 and pH_o 6.5, the endothelial [NO]_i was increased. Both extracellular alkalinization and acidification increased the vascular smooth muscle [NO]_i.

Significance

Not all changes in pH_o did result in pH_i changes, but disruption of acid-base balance in both directions induced NO synthesis in the endothelium and/or vascular smooth muscle.

Nitric oxide synthase in heart and thoracic aorta after liver ischemia and reperfusion injury: an experimental study in rats

OBJECTIVES

We tested the effects of liver reperfusion in the immunohistochemical expression of nitric oxide synthase on the thoracic aorta and the heart.

MATERIALS AND METHODS

We randomized 24 male Wistar rats into 3 groups: (1) control; (2) R2 group, with 60 minutes of partial (70%) liver ischemia and 2 hours of global liver reperfusion; (3) and R6 group, with 60 minutes of partial liver ischemia and 6 hours of global liver reperfusion.

RESULTS

In the heart, there was little, diffuse immunohistochemical endothelial staining; immunohistochemical inducible nitric oxide synthase staining was expressed in the adventitia layer of intramyocardial vessels in both cases, with a time-dependent but not statistically significant increase. In the thoracic aorta, a time-dependent decrease in endothelial nitric oxide synthase expression in the muscular layer after reperfusion, which was statistically significant in R6 versus the control. Positive immunostaining for inducible nitric oxide synthase was seen in the muscular and endothelial layers, and this varied from moderate in the control group, to light in the endothelium in groups R2 and R6.

CONCLUSIONS

We observed changes that may be implicated in heart injury and impairment of aortal tone after liver ischemia and reperfusion injury.

The protective effect of cilostazol on isolated rabbit femoral arteries under conditions of ischemia and reperfusion: the role of the nitric oxide pathway

OBJECTIVES

The clinical significance of ischemia/reperfusion of the lower extremities demands further investigation to enable the development of more effective therapeutic alternatives. This study investigated the changes in the vascular reactivity of the rabbit femoral artery and nitric oxide metabolites under partial ischemia/ reperfusion conditions following cilostazol administration.

METHODS

Ischemia was induced using infrarenal aortic clamping. The animals were randomly divided into seven groups: Control 90 minutes, Ischemia/Reperfusion 90/60 minutes, Control 120 minutes, Ischemia/Reperfusion 120/90 minutes, Cilostazol, Cilostazol before Ischemia/Reperfusion 120/90 minutes, and Ischemia 120 minutes/Cilostazol/ Reperfusion 90 minutes. Dose-response curves for sodium nitroprusside, acetylcholine, and the calcium ionophore A23187 were obtained in isolated femoral arteries. The levels of nitrites and nitrates in the plasma and skeletal muscle were determined using chemiluminescence.

RESULTS

Acetylcholine-and A23187-induced relaxation was reduced in the Ischemia/Reperfusion 120/90 group, and treatment with cilostazol partially prevented this ischemia/reperfusion-induced endothelium impairment. Only cilostazol treatment increased plasma levels of nitrites and nitrates. An elevation in the levels of nitrites and nitrates was observed in muscle tissues in the Ischemia/Reperfusion 120/90, Cilostazol/Ischemia/Reperfusion, and Ischemia/ Cilostazol/Reperfusion groups.

CONCLUSION

Hind limb ischemia/reperfusion yielded an impaired endothelium-dependent relaxation of the femoral artery. Furthermore, cilostazol administration prior to ischemia exerted a protective effect on endothelium-dependent vascular reactivity under ischemia/reperfusion conditions.

Pharmacology of the human saphenous vein

Nowadays, the great saphenous vein is the vascular conduit that is most frequently employed in coronary and peripheral revascularization surgery. It is known that saphenous vein bypass grafts have shorter patency than arterial ones, partly because the wall of the normal saphenous vein has different structural and functional characteristics. The features of this vein can be affected by the large distention pressures it is submitted to during its preparation and insertion into the arterial system. Indeed, a vein graft is subjected to considerable changes in hemodynamic forces upon implantation into the arterial circulation, since it is transplanted from a non-pulsatile, low-pressure, low-flow environment with minimal shear stress to a highpressure system with pulsatile flow, where it undergoes cyclic strain and elevated shear. These changes can be responsible for functional and morphological alterations in the vessel wall, culminating in intima hyperproliferation and atherosclerotic degeneration, which contribute to early graft thrombosis. This review has followed a predetermined strategy for updating information on the human saphenous vein (HSV). Besides presenting the aspects relative to the basic pharmacology, this text also includes surgical aspects concerning HSV harvesting, the possible effects of the major groups of cardiovascular drugs on the HSV, and finally the interference of major cardiovascular diseases in the vascular reactivity of the HSV.

Acidosis induces relaxation mediated by nitric oxide and potassium channels in rat thoracic aorta

We investigated the mechanism by which extracellular acidification promotes relaxation in rat thoracic aorta. The relaxation response to HCl-induced extracellular acidification (7.4 to 6.5) was measured in aortic rings pre-contracted with phenylephrine (Phe, 10(-6) M) or KCl (45mM). The vascular reactivity experiments were performed in endothelium-intact and denuded rings, in the presence or absence of indomethacin (10(-5) M), L-NAME (10(-4) M), apamin (10(-6) M), and glibenclamide (10(-5) M). The effect of extracellular acidosis (pH 7.0 and 6.5) on nitric oxide (NO) production was evaluated in isolated endothelial cells loaded with diaminofluorescein-FM diacetate (DAF-FM DA, 5μM). The extracellular acidosis failed to induce any changes in the vascular tone of aortic rings pre-contracted with KCl, however, it caused endothelium-dependent and independent relaxation in rings pre-contracted with Phe. This acidosis induced-relaxation was inhibited by L-NAME, apamin, and glibenclamide, but not by indomethacin. The acidosis (pH 7.0 and 6.5) also promoted a time-dependent increase in the NO production by the isolated endothelial cells. These results suggest that extracellular acidosis promotes vasodilation mediated by NO, K(ATP) and SK(Ca), and maybe other K(+) channels in isolated rat thoracic aorta.

Effects of partial liver ischemia followed by global liver reperfusion on the remote tissue expression of nitric oxide synthase: lungs and kidneys

Hepatic ischemia followed by reperfusion (IR) results in mild to severe remote organ injury. Oxidative stress and nitric oxide (NO) seem to be involved in the IR injury. Our aim was to investigate the effects of liver I/R on hepatic function and lipid peroxidation, leukocyte infiltration and NO synthase (NOS) immunostaining in the lung and the kidney. We randomized 24 male Wistar rats into 3 groups: 1) control; 2) 60 minutes of partial (70%) liver I and 2 hours of global liver R; and 3) 60 minutes of partial (70%) liver I and 6 hours of global liver R. Groups 2 and 3 showed significant increases in plasma alanine and aspartate aminotransferase levels and in tissue malondialdehyde and myeloperoxidase contents. In the kidney, positive endothelial NOS (eNOS) staining was significantly decreased in group 3 compared with group 1. However, staining for inducible NOS (iNOS) and neuronal NOS (nNOS) did not differ among the groups. In the lung, the staining for eNOS and iNOS did not show significant differences among the groups; no positive nNOS staining was observed in any group. These results suggested that partial liver I followed by global liver R induced liver, kidney, and lung injuries characterized by neutrophil sequestration and increased oxidative stress. In addition, we supposed that the reduced NO formation via eNOS may be implicated in the moderate impairment of renal function, observed by others at 24 hours after liver I/R.

Diabetes and vascular disease: basic concepts of nitric oxide physiology, endothelial dysfunction, oxidative stress and therapeutic possibilities

The vascular manifestations associated with diabetes mellitus (DM) result from the dysfunction of several vascular physiology components mainly involving the endothelium, vascular smooth muscle and platelets. It is also known that hyperglycemia-induced oxidative stress plays a role in the development of this dysfunction. This review considers the basic physiology of the endothelium, especially related to the synthesis and function of nitric oxide. We also discuss the pathophysiology of vascular disease associated with DM. This includes the role of hyperglycemia in the induction of oxidative stress and the role of advanced glycation end-products. We also consider therapeutic strategies.

Extracellular alkalinization induces endothelium-derived nitric oxide dependent relaxation in rat thoracic aorta

AIM

To investigate the mechanism through which the extracellular alkalinization promotes relaxation in rat thoracic aorta.

METHODS

The relaxation response to NaOH-induced extracellular alkalinization (7.4-8.5) was measured in aortic rings pre-contracted with phenylephrine (Phe, 10(-6) M). The vascular reactivity experiments were performed in endothelium-intact and -denuded rings, in the presence or and absence of indomethacin (10(-5) M), NG-nitro-l-arginine methyl ester (L-NAME, 10(-4) M), N-(6-Aminohexyl)-5-chloro-1-naphthalenesulfonamide/HCl (W-7, 10(-7) M), 2,5-dimethylbenzimidazole (DMB, 2×10(-5) M) and methyl-β-cyclodextrin (10(-2) M). In addition, the effects of NaOH-induced extracellular alkalinization (pH 8.0 and 8.5) on the intracellular nitric oxide (NO) concentration was evaluated in isolated endothelial cells loaded with diaminofluorescein-FM diacetate (DAF-FM DA, 5 μM), in the presence and absence of DMB (2×10(-5) M).

RESULTS

The extracellular alkalinization failed to induce any change in vascular tone in aortic rings pre-contracted with KCl. In rings pre-contracted with Phe, the extracellular alkalinization caused relaxation in the endothelium-intact rings only, and this relaxation was maintained after cyclooxygenase inhibition; completely abolished by the inhibition of nitric oxide synthase (NOS), Ca(2+)/calmodulin and Na(+)/Ca(2+) exchanger (NCX), and partially blunted by the caveolae disassembly.

CONCLUSIONS

These results suggest that, in rat thoracic aorta, that extracellular alkalinization with NaOH activates the NCX reverse mode of endothelial cells in rat thoracic aorta, thereby the intracellular Ca(2+) concentration and activating the Ca(2+)/calmodulin-dependent NOS. In turn, NO is released promoting relaxation.

Vascular relaxation of canine visceral arteries after ischemia by means of supraceliac aortic cross-clamping followed by reperfusion

BACKGROUND

The supraceliac aortic cross-clamping can be an option to save patients with hipovolemic shock due to abdominal trauma. However, this maneuver is associated with ischemia/reperfusion (I/R) injury strongly related to oxidative stress and reduction of nitric oxide bioavailability. Moreover, several studies demonstrated impairment in relaxation after I/R, but the time course of I/R necessary to induce vascular dysfunction is still controversial. We investigated whether 60 minutes of ischemia followed by 30 minutes of reperfusion do not change the relaxation of visceral arteries nor the plasma and renal levels of malondialdehyde (MDA) and nitrite plus nitrate (NOx).

METHODS

Male mongrel dogs (n = 27) were randomly allocated in one of the three groups: sham (no clamping, n = 9), ischemia (supraceliac aortic cross-clamping for 60 minutes, n = 9), and I/R (60 minutes of ischemia followed by reperfusion for 30 minutes, n = 9). Relaxation of visceral arteries (celiac trunk, renal and superior mesenteric arteries) was studied in organ chambers. MDA and NOx concentrations were determined using a commercially available kit and an ozone-based chemiluminescence assay, respectively.

RESULTS

Both acetylcholine and calcium ionophore caused relaxation in endothelium-intact rings and no statistical differences were observed among the three groups. Sodium nitroprusside promoted relaxation in endothelium-denuded rings, and there were no inter-group statistical differences. Both plasma and renal concentrations of MDA and NOx showed no significant difference among the groups.

CONCLUSION

Supraceliac aortic cross-clamping for 60 minutes alone and followed by 30 minutes of reperfusion did not impair relaxation of canine visceral arteries nor evoke biochemical alterations in plasma or renal tissue.

High-frequency ultrasonic waves cause endothelial dysfunction on canine epicardial coronary arteries

OBJECTIVE

Application of ultrasound energy by an endarterectomy probe can facilitate the removal of atheromatous plaque, but the effect of this procedure on surrounding vessel structure and function is still a matter of experimental investigations.

METHODS

To determine whether ultrasound energy impairs the production of nitric oxide or damages vascular smooth muscle function, isolated canine epicardial coronary artery segments were exposed to either high (25 W) or low (0-10 W) ultrasonic energy outputs, for 15 seconds, using an endarterectomy device prototype. After exposure, segments of epicardial coronary artery were studied in organ chambers. The following drugs were used: adenosine diphosphate (ADP), acetylcholine (Ach) and sodium fluoride (NaF) to study endothelium-dependent relaxation and sodium nitroprusside (SNP) and isoproterenol to evaluate endothelium-independent relaxation.

RESULTS

Application of high ultrasonic energy power impaired endothelium-dependent relaxation to ADP (10(-9)-10(-4) M), Ach (10(-9)-10(-4) M) and NaF (0.5-9.5 mM) in epicardial coronary arteries. However, low ultrasound energy output at the tip of the probe did not alter the endothelium-dependent relaxation (either maximal relaxation or EC50) to the same agonists. Vascular smooth muscle relaxation to isoproterenol (10(-9)-10(-5) M) or SNP (10(-9)-10(-6) M) was unaltered following exposure to either low or high ultrasonic energy outputs.

CONCLUSION

These experiments currently prove that ultrasonic energy changes endothelial function of epicardial coronary arteries at high power. However, ultrasound does not alter the ability of vascular smooth muscle of canine epicardial coronary arteries to relax.

Endothelium dysfunction classification: why is it still an open discussion?

In the nineties, the present author developed a didactic endothelium dysfunction classification based on personal experience while waiting for a consensus about the need of such an accomplishment. As time went by and no publications regarding this subject were released, he published a text entitled "An open discussion about endothelial dysfunction: is it timely to propose a classification? Eight years later and the question about endothelium dysfunction classification remains "an open discussion". Nevertheless, we still keep using our proposed classification although always questioning its suitability and wondering reasons for why the scientific communities avoid discussing this very subject. Based on these thoughts we attempted to hypothesize the causes of why this proposed discussion is not an inciting issue: (I) First hypothesis: An endothelium dysfunction classification is not important; (II) Second hypothesis: Such classification is still a "premature reductionism"; (III) Third hypothesis: Endothelium dysfunction is a multifaceted disorder and involves uncountable variations becoming impossible to propose an adequate classification; (IV) Fourth hypothesis: Vasoplegic syndrome and massive nitric oxide release accounts for the functional classification, thus, it seems that cardiovascular journals feel apprehensive about this since their point of view is closely associated with impaired endothelium nitric oxide release as a cause to increased risk of spasm and thrombosis and; (V) Fifth hypothesis: The classification is so fulfilling that it discards the need of discussion or the pioneer attitude to propose such classification has incited some degree of jealousy. Obviously, the fifth hypothesis is pretentiously and overwhelmed, but we again attempt to reopen this discussion because it is time to update the presented classification. In this manner, we are sure that this issue demands special attention of the scientific community. Therefore, the aim of this text is exclusively to "reopen" the discussion about the need of an effective endothelium dysfunction classification.

Is the cyclic GMP system underestimated by intensive care and emergency teams?

At present, the clinical management inflammatory vasoplegia associated to sepsis or anaphylaxis is symptomatic. Volume is expanded by means of administration of fluids, and low blood pressure is managed by means of administration of positive inotropes and vasoconstrictors. This therapeutic approach is mainly associated to the cyclic AMP (cAMP) and, many times the circulatory shock is refractory to high amines concentrations. However, beside of cAMP-dependent vasoreactivity mechanisms there are other two known vasoplegia involved mechanisms: cyclic GMP (cGMP) and hyperpolarization that is less clinically considered. Also, it is possible to speculate about 'probable vasopressin deficiency'. Methylene blue (MB) is the most useful and clinically safe cGMP blocker. We propose a decision tree for diagnosis and institution of this therapeutical approach many times underestimate by intensive care and emergency teams.