Formation of nitric oxide from L-arginine in the central nervous system: a transduction mechanism for stimulation of the soluble guanylate cyclase.

Abstract

A soluble enzyme obtained from rat forebrain catalyzes the NADPH-dependent formation of nitric oxide (NO) and citrulline from L-arginine. The NO formed stimulates the soluble guanylate cyclase and this stimulation is abolished by low concentrations of hemoglobin. The synthesis of NO and citrulline is dependent on the presence of physiological concentrations of free Ca2+ and is inhibited by NG-monomethyl-L-arginine, but not by its enantiomer NGmonomethylDarginin e or by Lcanavanine. L-Homoarginine, L-argyl-L-apartate, or L-arginine methyl ester can replace L-ginine as substrates for the enzyme. These results indicate that NO is formed from Larginine in the brain through an enzymic reaction similar to that in vascular endothelial cells, neutrophils, and macrophages, adding support to our hypothesis that the formation of NO from L-arginine is a widespread transduction mechanism for the stimulation of the soluble guanylate cyclase. Activated macrophages also synthesize NOj and NO3 from the terminal guanido nitrogen atom(s) of L-arginine (5). This reaction, which occurs via the formation of NO (6), is involved in the cytotoxic activities of these cells (7). We have demonstrated recently that rat peritoneal neutrophils form NO from L-arginine (8).The endothelial cell and macrophage enzyme that forms NO from L-arginine is soluble, is NADPH-dependent, forms citrulline as a coproduct, and is inhibited by NI-monomethyl-L-arginine refs. 6 and 9). Furthermore, in both cells the enzyme requires a divalent cation, which in the case of the macrophage has been suggested to be Mg2+ (6).Some years ago, L-arginine was identified as an endogenous activator of the soluble guanylate cyclase in brain tissue (10). Since this activation resembled that of the nitrovasodilators (11) and NO is known to stimulate soluble guanylate cyclase in the brain (12), we have investigated the existence in the central nervous system of an enzymic system capable of converting L-arginine into NO and citrulline.While this work was in progress Garthwaite et al. (13) Preparation of Crude Synaptosomal Cytosol. Male rats (200-300 g, four for each preparation) were killed by cervical dislocation and the forebrains were rapidly removed and cooled in ice-cold washing buffer (0.32 M sucrose/10 mM Hepes/0.1 mM EDTA, pH 7.4); subsequent procedures were carried out at 0-40C. The tissue was placed in fresh washing buffer, finely minced, washed once with 50 ml of washing buffer and twice with homogenization buffer (0.32 M sucrose/10 mM Hepes, 1 mM DL-dithiothreitol, pH 7.4) to remove contaminating erythrocytes, and homogenized with 20 strokes of a Dounce homogenizer. The homogenate was diluted to 50 ml with homogenization buffer and centrifuged (1400 x g, 10 min); the supernatant obtained was centrifuged (18,000 x g, 10 min) to obtain a crude synaptosomal pellet. After aspiration of the supernatant, 8 ml of 1 mM DLdithiothreitol (dissolved in distilled water) was added to the pellet to cause hypotonic swelling of the synaptosomes, which were then lysed by ho...

Neuroprotective Effect of Steamed and Fermented Codonopsis lanceolata

“…Influx of Ca 2+ is also contributed to activate NO synthase (Knowles et al ., 1989). Glutamate mediated the enhancement of nNOS activity through NMDA receptors (Garthwaite, 1991).…”

Inhibition of nitric oxide synthase by nasal decongestants

“…Nitric oxide (NO) is a free radical that is known to have an important function as mediator in several biological processes amongst which, vasorelaxation [1,2], cellmediated immune responses [3,4], inhibition of platelet aggregation [5] and neurotransmission [6] are extensively investigated. The formation of NO has been described in many mammalian cell types and can be ascribed to three isoforms of nitric oxide synthase (NOS), all of which oxidize L-arginine to L-citrulline.…”

The nitric oxide-cGKII system relays death and survival signals during embryonic retinal development via AKT-induced CREB1 activation

“…Pharmacological activators of the canonical NO pathway such as 8Br-cGMP and Zaprinast (a cGMP phosphodiesterase inhibitor) or the sGC activator YC-1 promoted massive neuronal cell loss in E6 ( Figure 3a) and increased neuronal survival in E8 cultures ( Figure 3c). In addition, SNAP-induced cell death (Figure 3b) or survival ( Figure 3d) was abrogated by 1H- [1,2,4]oxadiazolo [4,3-a]quinoxalin-1-one (ODQ; a sGC inhibitor) or KT5823 (a cGK blocker). However, the thiol dithiothreitol (DTT), which blocks nitroxyl (NO À )-mediated cysteine modification (S-nitrosylation) but not NO (NO.…”

“…The reaction requires molecular oxygen, which produces NO and L-citrulline concomitantly. 3 NO can mediate its effects basically by two mechanisms: first, the classical activation of soluble guanylyl cyclase (sGC) and cGMP-dependent kinases (cGKs), known as the NO/sGC/cGK pathway 4,5 ; second, NO can covalently attach to cysteine residues within the amino-acid sequence of specific proteins, a mechanism known as S-nitrosylation. 6,7 The involvement of NO and its related downstream signaling pathways have been previously demonstrated to control various CNS functions, including neural proliferation, survival and differentiation.…”