title: Possible involvement of neuronal nitric oxide synthase enzyme in early-phase isoflurane-induced hypotension in rats.
abstract: This study was conducted to demonstrate the involvement of nitric oxide synthase (NOS) in the early-phase isoflurane-induced hypotension and to ascertain whether this NOS is neuronal NOS (nNOS) or endothelial NOS (eNOS). Mean arterial pressures (MAPs) were directly measured from the femoral arteries of urethane-anesthetized rats. Isoflurane-induced changes in MAP were monitored in rats following pretreatment with vehicle or one of the following NOS inhibitors: L-NG)monomethyl-L-arginine (L-NMMA), which is non-selective; L-NG)nitro arginine (L-NOARG), which is more selective for nNOS and eNOS; and 7-nitroindazole (7-NI), which is selective for nNOS. Exposure to 2% isoflurane in oxygen produced a triphasic reduction in MAP, including an early phase in which mean arterial pressure (MAP) fell by 25-30% during the initial 2(1/2) min. This early hypotensive response, but not subsequent phases, was abolished by i.v. pretreatment with either L-NMMA or L-NOARG. The early-phase hypotension was also significantly attenuated by i.p. pretreatment with 7-NI; however, the blockade was not as complete as with L-NMMA or L-NOARG. Cerebella and aorta were removed from vehicle- and 7-NI pretreated rats and assayed for NOS activity by determining the conversion of [14C]L-arginine to [14C]L-citrulline. The 7-NI pretreatment significantly reduced NOS activity in the cerebellum but not the aorta. These findings indicate that the early-phase isoflurane-induced hypotension may involve nNOS as well as eNOS. The nNOS may participate in regulation of isoflurane-induced neuronal release of endogenous opioid peptide, which produces a vasodilation that is dependent on NO derived from an action of eNOS.
authors.affiliation: Department of Biomedical Sciences, University of Illinois College of Medicine at Rockford, Rockford, Illinois, USA.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Ellenberger
authors.forename: Heather L
authors.initials: HL
authors.lastname: Lucas
authors.forename: Janet L
authors.initials: JL
authors.lastname: Mueller
authors.forename: Peggy L
authors.initials: PL
authors.lastname: Barrington
authors.forename: Eunhee
authors.initials: E
authors.lastname: Chung
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Ohgami
authors.forename: Raymond M
authors.initials: RM
authors.lastname: Quock
mesh_terms: D000280:Administration, Inhalation; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000201:enzymology; D001794:Blood Pressure / Q000187:drug effects* / Q000502:physiology; D001921:Brain / Q000187:drug effects / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007022:Hypotension / Q000139:chemically induced / Q000201:enzymology* / Q000503:physiopathology; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D052250:Nitric Oxide Synthase Type III; D051381:Rats; D017207:Rats, Sprague-Dawley; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology
chemical_list: D004791:Enzyme Inhibitors; D007530:Isoflurane; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D052250:Nitric Oxide Synthase Type III; C496322:Nos1 protein, rat; C496316:Nos3 protein, rat