Nitric oxide: a mediator in rat tubularhypoxia/reoxygenation injury.

Abstract

Nitric oxide (NO), among several other functions, may play a role in hypoxia and reoxygenation injury due to its free radical nature and high reactivity with the superoxide radical to yield peroxynitrite, an oxidant molecule. The present study was undertaken to evaluate a potential role for NO, either endogenous or exogenous, in a model of hypoxia/reoxygenation (H/R) in freshly isolated rat proximal tubules. NO synthase activity, as assessed by conversion of L-[3H]arginine to L-[3Hlcitrulline, was detected in normoxic tubules. This activity could be inhibited by N-nitro-L-argin ne methyl ester (L-NAME), a NO synthase inhibitor, and was stimulated by 15 min of hypoxia. The injury in proximal tubules caused by 15 min of hypoxia followed by 35 min of reoxygenation was completely prevented by L-NAME as assessed by release of lactate dehydrogenase, whereas D-NAME, which does not inhibit NO synthase, had no effect. In contrast, L-arginune (NO substrate) enhanced the H/R injury. These effects were paralleled by nitrite/nitrate production. In separate experiments, the addition of sodium nitroprusside, a NO donor, to proximal tubules enhanced the H/R injury; this effect could be blocked by hemoglobin, a NO scavenger. Also, addition of nitroprusside reversed L-NAME protection against H/R injury. These results demonstrate that NO is synthesized in rat proximal tubules and participates as one of the mediators in rat tubular H/R injury.Nitric oxide (NO) is a major chemical form of endotheliumderived relaxing factor (1, 2), an important regulator of vascular tone, and is released by endothelial cells (3). However, the role of NO is not restricted to the vascular system; several other functions have been described in recent years. NO has an important role in platelet function, causing inhibition of platelet aggregation; in immunological reactions, as a host defense mechanism against tumor cells and invasive organisms; and in the central and peripheral nervous systems, as a neurotransmitter (4, 5). Moreover, alterations in NO synthesis have been incriminated in several other pathophysiological conditions, including arterial hypertension and progression of renal failure (6), as well as septic shock (7), hypoxia-induced vasodilation (8), the vasospasm that follows subarachnoid hemorrhage due to inhibition of NO by hemoglobin (9), and neuronal destruction in vascular stroke and other neurodegenerative conditions (10).While endothelial cells, neurons, macrophages, neutrophils, and platelets are well-known sources of NO, recent studies have suggested that epithelial cells may constitutively generate NO (11). Furthermore, constitutive NO synthase (NOS) has been identified in the kidney, specifically in macula densa cells (12) and in the inner medullary collecting duct (13). Recently, the inducible form of NOS was identified in the rat proximal tubule and inner medullary collecting duct (14). In the kidney, NO has an important role in renal hemodynamic regulation and sodium and water excretion (15).The use of freshly isolated ...

Nitric oxide in gingival crevicular fluid and nitric oxide synthase expression in the gingiva of patients with sickle cell disease

“…SCD is also strongly associated with oxidative stress, increased expression of endothelial cell adhesion molecules, and blood adhesion. Increased iNOS expression and NO production have been observed in the kidneys and the liver in SCD patients [8], in mice [2,3,8,9], and in pigs [4]. During the clinically asymptomatic state, NO bioavailability is reduced in SCD patients due to scavenging of NO by cell-free hemoglobin released from hemolyzed sickle erythrocytes [50] and increased arginase activity [51].…”

“…Assessment of total NO metabolites (NO x : nitrate [NO 3 -] and nitrite [NO 2 -]) is commonly used as a measure of NO production in biologic fluids. GCF samples were obtained using standard paper strips (Periopaper, Ora Flow Inc., NY, USA ) following isolation of the tooth with cotton rolls and removal of any supragingival deposits on tooth surfaces.…”

“…Interactions between abnormal rigid erythrocytes and the vascular wall result in endothelial activation, which may lead to endothelial damage and tissue ischaemia in SCD. Chronic inflammation during both the steady state and vasoocclusive crisis occurs via the action of cytokines and other inflammatory factors [1][2][3][4]. The clinical manifestations of the disease, such as painful crises, anemia, bone necrosis, and leg ulceration, arise due to chronic hemolysis, vaso-occlusion, ischemia, and tissue damage.…”

“…Increased iNOS expression and a consequent increase in tissue nitrite and nitrate production have been observed in the kidneys and liver of SCD patients [8], mice [2,3,8,9], and pigs [4]. Additionally, it was shown that iNOS inhibition significantly limits tissue ischemia-reperfusion injury in the liver and kidneys [10,11]; however, inhibition of iNOS attenuated ischemia-reperfusion injury in the rat heart [12] and did not affect ischemia-reperfusion injury in the rat lung [13].…”

Effects of sirolimus alone or in combination with cyclosporine A on renal ischemia/reperfusion injury

“…Proximal tubules were isolated using previously described methods (19,20). Briefly, rats were anesthetized with sodium pentobarbital (50 mg/kg body weight, ip) and submitted to laparotomy for kidney removal.…”