Pathophysiology 19 (2012) 13–20 Contribution of nitric oxide synthase (NOS) in blood–brain barrier disruption during acute focal cerebral ischemia in normal rat Mohammad T. Mohammadi, S. Mostafa Shid-Moosavi, Gholam A. Dehghani ∗ Department of Physiology, Shiraz University of Medical Sciences, Shiraz, Iran Received 25 September 2010; received in revised form 25 July 2011; accepted 25 July 2011 Abstract Endogenous level of nitric oxide (NO) is increased in the brain following the stroke, and deactivation of NO synthase has been shown to attenuate its destructive actions in animal stroke models using middle cerebral artery occlusion (MCAO) procedures. However, little is known about the effects of NO in cerebral vascular integrity and edema during acute cerebral ischemia. Here we investigated whether NO plays any role in the progression of blood–brain barrier (BBB) disruption and edema formation in ischemia/reperfusion injury. Intraperitoneal administration of NO substrate l-arginine (300 mg/kg), or NOS inhibitor (l-NAME, 1 mg/kg), was done in normal rats at 20 min before a 60-min MCAO. Mean arterial blood pressures (MAP) and regional cerebral blood flow (rCBF) were continuously recorded during experiment. Neurological deficit score (NDS) was evaluated 12h after termination of MCAO followed with evaluations of cerebral infarction volume (CIV), edema formation and cerebral vascular permeability (CVP), as determined by the Evans blue dye extravasations (EBE) technique. No significant changes were observed in the values of MAP and rCBF with l-arginine or l-NAME during ischemia or reperfusion periods. There was a 75–85% reduction in rCBF in during MCAO which returned back to its pre-occlusion level during reperfusion. Acute cerebral ischemia with or without l-arginine augmented NDS (4.00 ± 0.44 and 3.00 ± 0.30), in conjunction with increased CIV (518 ± 57 mm 3 and 461 ± 65 mm 3 ), provoked edema (3.09 ± 0.45% and 3.30 ± 0.49%), and elevated EBE (8.28 ± 2.04 g/g and 5.09 ± 1.41 g/g). Inhibition of NO production by l-NAME significantly improved NDS (1.50 ± 0.22), diminished CIV (248 ± 56 mm 3 ), edema (1.18 ± 0.58%) and EBE (1.37 ± 0.12 g/g). This study reconfirms the cerebroprotective properties of reduced tissue NO during acute ischemic stroke, and it also validates the deleterious actions of increased NOS activity on the disruption of cerebral microvascular integrity and edema formation of ischemia/reperfusion injuries in normal rat, without changing arterial blood pressure or blood flows to ischemic regions. © 2011 Elsevier Ireland Ltd. All rights reserved. Keywords: Cerebral ischemia; Reperfusion; Nitric oxide; Blood flow; BBB; Rat 1. Introduction Blood–brain barrier (BBB) ensures an optimally con- trolled homeostasis of the brain’s internal environment by separating the nervous tissues from general circulation. It is composed of specialized microvascular endothelial cells with complex tight junctions that enable them to selectively trans- port substances needed and prohibit most molecules from reaching the brain [1]. Studies performed in the past decade shows that ischemic stroke increases endothelial permeabil- ity of cerebral vascular beds and disrupts BBB integrity ∗ Corresponding author. Tel.: +98 711 2302026; fax: +98 711 2302026; mobile: +98 917 1171966. E-mail address: dehghani@jhsph.edu (G.A. Dehghani). [2,3]. The failure of BBB integrity provokes extravasations of high-molecular weight compounds during reperfusion and intensifies brain edema [4–6]. The progression of stroke is multifactorial; however, it seems that the increased production of endogenous nitric oxide (NO) plays an important role in the pathogenesis of ischemic cerebrovascular injuries [7–10] and neural dam- age [8,9,11]. Although, disruption of BBB integrity due to ischemic/reperfusion (I/R) injury during stroke is well documented [3,12], data about the involvement of NO are conflicting. Some reports have demonstrated that the inhibition of nitric oxide synthase (NOS) activity by l- NAME diminished acute ischemic brain damage by reducing BBB disruption [12,13]. Whereas, others have revealed that the administrations of l-arginine, NO substrate, reduced 0928-4680/$ – see front matter © 2011 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.pathophys.2011.07.003