title: NO synthesis and its regulation in the arachidonic-acid-stimulated rat polymorphonuclear leukocytes.
abstract: Nitric oxide (NO) synthesis and free radical generation from polymorphonuclear leukocytes (PMNs) play an important role in several pathological conditions. In the present study, regulation of NO synthesis has been investigated in the unstimulated and arachidonic-acid (AA)-stimulated rat PMNs. L-Citrulline formation or nitrite content was used as a marker of NO synthesis, while AA-induced free radical generation was assessed by flow cytometry using a dye, 2('),7(')-dichlorofluoreseindiacetate. L-Citrulline formation in the unstimulated PMNs increased in a time-dependent manner for up to 120 min. The increase was significantly less (25-55%) in AA-stimulated PMNs at all the time points. AA-induced free radical generation was maximum during the first 15 min followed by a time-dependent decrease. Interestingly, similar experiments under hyperoxic conditions did not exhibit any decrease in L-citrulline and nitrite formation after AA stimulation even though the free radical generation further increased. Scavenging or inhibition of free radicals by several types of interventions increased NO generation from AA-stimulated PMNs. The results of the present study suggest that the availability of oxygen, a common substrate for both NADPH oxidase and NOS, can inversely affect the synthesis of NO and PMNs seem to prefer oxygen utilization over NO synthesis for free radical generation.
authors.affiliation: Division of Pharmacology, Central Drug Research Institute, Lucknow 226001, India.
authors.forename: Prashant
authors.initials: P
authors.lastname: Sharma
authors.forename: Manoj Kumar
authors.initials: MK
authors.lastname: Barthwal
authors.forename: Madhu
authors.initials: M
authors.lastname: Dikshit
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism; D002956:Citrulline / Q000378:metabolism; D016166:Free Radical Scavengers / Q000494:pharmacology; D005609:Free Radicals / Q000378:metabolism; D018496:Hyperoxia / Q000378:metabolism; D009504:Neutrophils / Q000187:drug effects* / Q000378:metabolism*; D009569:Nitric Oxide / Q000096:biosynthesis* / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D002147:Calmodulin; D016166:Free Radical Scavengers; D005609:Free Radicals; D009573:Nitrites; D017382:Reactive Oxygen Species; D016718:Arachidonic Acid; D002956:Citrulline; D009569:Nitric Oxide; D002118:Calcium