Timing of administration of dexamethasone or the nitric oxide synthase inhibitor, nitro-L-arginine methyl ester, is critical for effective treatment of ischaemia-reperfusion injury to rat skeletal muscle.
1. The effects of the nitric oxide synthase (NOS) inhibitors, NG-nitro-L-arginine-methyl ester (L-NAME), nitroiminoethyl-L-ornithine and S. methylisothiourea on skeletal muscle survival following 2 h of tourniquet ischaemia and 24 h of reperfusion were compared with those of the anti-inflammatory steroid, dexamethasone. 2. Administration of each of the NOS inhibitors or dexamethasone 30 min before reperfusion reduced the degree of skeletal muscle necrosis 24 h after reperfusion. 3. The influence of timing of drug administration was investigated. L-NAME administered 30 min before reperfusion, at 3 h after reperfusion, but not thereafter, significantly improved muscle survival compared with saline-treated controls. Dexamethasone administered 30 min before, or at 3 or 8 h after reperfusion, but not at 16 h, significantly improved muscle survival, but neither agent had protective effects when administered before ischaemia. 4. After 8 h of reperfusion of ischaemic skeletal muscle, cell-free homogenates contained Ca(2+)-independent (inducible) NOS activity which was reduced in dexamethasone-treated (2.5 mg/kg) rats. Furthermore, inducible NOS mRNA levels, as detected by reverse transcriptase-PCR, were increased after 8 h of reperfusion in saline, but not in dexamethasone-treated rats. 5. These data suggest a significant deleterious effect of endogenous NO which may be restricted to the first 3 h of the reperfusion phase of ischaemia-reperfusion injury, and raise the possibility of effective treatment of incipient reperfusion injury, even after several hours of reperfusion.
Zhang
B
B
Bernard O'Brien Institute of Microsurgery, St Vincent's Hospital Melbourne, Fitzroy, Victoria, Australia.
Knight
K R
KR
Dowsing
B
B
Guida
E
E
Phan
L H
LH
Hickey
M J
MJ
Morrison
W A
WA
Stewart
A G
AG
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000627:therapeutic use*; D015342:DNA Probes; D003907:Dexamethasone / Q000627:therapeutic use*; D004791:Enzyme Inhibitors / Q000627:therapeutic use; D007191:Indazoles / Q000627:therapeutic use; D007550:Isothiuronium / Q000031:analogs & derivatives / Q000627:therapeutic use; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000187:drug effects / Q000201:enzymology; D019331:NG-Nitroarginine Methyl Ester / Q000627:therapeutic use*; D009336:Necrosis; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D009952:Ornithine / Q000031:analogs & derivatives / Q000627:therapeutic use; D016133:Polymerase Chain Reaction / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D015427:Reperfusion Injury / Q000188:drug therapy* / Q000201:enzymology; D013997:Time Factors
D000893:Anti-Inflammatory Agents; D015342:DNA Probes; D004791:Enzyme Inhibitors; D007191:Indazoles; D007550:Isothiuronium; D003907:Dexamethasone; D009952:Ornithine; D019001:Nitric Oxide Synthase; C027744:S-methylisothiopseudouronium; C080122:7-nitroindazole; D019331:NG-Nitroarginine Methyl Ester