Summary: We measured, in vivo, the local concentration of nitric oxide (NO) in cerebral tissue, during and after transient middle cerebral artery occlusion in the rat (n = 8). Baseline concentration of NO was <10-8 M; upon initiation of ischemia, NO concentration increased to -10-6 M and then declined. Reperfusion likewise stim ulated an increase in NO concentration to above baseline Nitric oxide (NO) plays a multifaceted and im portant role in the brain. It is a neurotransmitter (Bredt et aI., 1991) and a free radical (Beckman, 1990(Beckman, , 1991, and it has been implicated in the regu lation of cerebral blood flow (Faraci, 1991;Faraci and Heistad, 1992; Kozniewski et aI. , 1992; Iade cola, 1992) and inflammation (Granger et aI., 1990). NO is also an important factor in pathophysiologi cal events in brain. Recent studies have implicated alterations in cerebral NO levels with ischemic cell damage, particularly with glutamate neurotoxicity after cerebral ischemia (Garthwaite, 1991; Dawson et aI., 1991;Snyder and Bredt, 1992; Nowicki et aI. , 1991). Although NO is a subject of great interest in brain research, to our knowledge, direct in vivo measurements of NO in brain after ischemia have not been performed. NO is a reactive molecule, and 355level. Administration of N-nitro-L-arginine methyl ester (n = 4), an inhibitor of nitric oxide synthase, before onset of ischemia, maintained NO at basal levels. Our data in dicate that large increases in NO occur at onset of isch emia, which may affect tissue response to an ischemic insult. Key Words: Nitric oxide-Middle cerebral artery occlusion-Rat.it is therefore difficult to measure in vivo using stan dard chemical techniques. Here we report the first direct measurement of NO in rat brain during and after cerebral ischemia, using a NO sensitive por phyrinic microsensor . MATERIALS AND METHODSEight male Wistar rats (weighing 260--300 g) were anes thetized with 3.5% halothane for induction and 1% halo thane for maintenance, in a 3:1 N20/02 mixture. Four of the animals were administered a nitric oxide synthase in hibitor, L-NAME (N-nitro-L-arginine methyl ester; 30 mg! kg, i. v.), 15 min before induction of middle cerebral ar tery (MCA) occlusion. The femoral artery was cannulated to monitor arterial blood pressure and for sampling of blood gases. The rectal temperature was maintained at 37.0 ± i.O°C. MCA occlusion was induced for 2 h using a method of intraluminal vascular occlusion (Nagasawa and Kogure, 1989; Zea Longa et aI., 1989; Chen et aI., 1992a). Briefly, the right common carotid artery, external carotid artery, and internal carotid artery were isolated via a ven tral midline incision. The distal end of the external carotid artery was ligated with 5-0 silk suture at the branch of the occipital artery, and the origin of the external carotid ar tery was loosely tied with 5-0 silk suture. A microvascular clip was placed across the common carotid artery and internal carotid artery. A 5-cm length of 4-0 nylon mono filament, with its tip rounded by heating near ...

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Nitric oxide is believed to participate in nonspecific cellular immunity. Gram negative bacterial endotoxins increase the production of reactive nitrogen intermediates (RNI) in phagocytic cells by inducing the enzyme nitric oxide synthase II (NOS II). Anti-inflammatory glucocorticoids attenuate endotoxin-induced increases in RNI. This study evaluated the effect of in vivo administration of prednisolone on Escherichia coli lipopolysaccharide endotoxin (LPS)-induced increases in plasma RNI and neutrophil mRNA for NOS II and production of RNI in the rat. We show that LPS rapidly induces mRNA for NOS II and production of RNI (NO2- and NO3- anion) in rat neutrophils within 2 hr after in vivo administration of a sublethal dose of 0.5 mg/kg, i.v. A pharmacologic dose of prednisolone (50 micrograms/kg, im) given 15 min before LPS-attenuated production of NO2- and NO3- by neutrophils and suppressed LPS-stimulated mRNA for NOS II. 3-Amino, 1,2,4-triazine inhibited NO2- and NO3- production without affecting gene expression for NOS II. These data demonstrate that LPS rapidly induces functional gene expression for NOS II and prednisolone prevents induction of NOS II activity by inhibiting transcription of its mRNA.