Inducible nitric oxide synthase mediates delayed cardioprotection induced by morphine in vivo: evidence from pharmacologic inhibition and gene-knockout mice.
BACKGROUND
It is not known whether morphine induces delayed cardioprotection against ischemia and reperfusion. The authors measured the delayed preconditioning induced by morphine and determined the role of inducible nitric oxide synthase (iNOS) in mediating this effect using a pharmacological inhibitor and iNOS gene-knockout mice.


METHODS
Adult male wild-type and iNOS gene-knockout (B6, 129) mice were treated with morphine (0.3 or 0.1 mg/kg intraperitoneal) or saline. Twenty-four hours later, mice were subjected to 45 min of coronary artery occlusion followed by 120 min of reperfusion. S-methylthiourea sulfate (3 mg/kg, intraperitoneal) was given 30 min before the occlusion to block iNOS. Infarct size as a percentage of the area at risk was determined by triphenyltetrazolium chloride staining. iNOS and endothelial nitric oxide synthase expression were measured by Western blot.


RESULTS
Infarct size was significantly reduced in wild-type mice from 43.1 +/- 5.3% in the saline group to 22.4 +/- 4.4% in the higher-dose morphine group (0.3 mg/kg) (P < 0.05). This cardioprotective effect was abolished by S-methylthiourea sulfate (43.3 +/- 3.9%) and was absent in iNOS gene-knockout mice (42.3 +/- 4.7%). Pretreatment with the lower dose of morphine (0.1 mg/kg) did not reduce infarct size (41.1 +/- 5.4%). A significant increase in myocardial iNOS expression was observed 24 h after morphine administration (0.3 mg/kg but not 0.1 mg/kg; P < 0.05), whereas endothelial nitric oxide synthase remained unchanged.


CONCLUSIONS
: Pretreatment with morphine induces delayed cardioprotection in mice. The authors demonstrated an obligatory role for iNOS in mediating morphine-induced delayed cardioprotection.
Jiang
Xiaojing
X
Department of Anesthesiology, Hamamatsu University School of Medicine, Hamamatsu, Japan. jiangxj@hama-med.ac.jp
Shi
Enyi
E
Nakajima
Yoshiki
Y
Sato
Shigehito
S
D000701:Analgesics, Opioid / Q000627:therapeutic use*; D000818:Animals; D015153:Blotting, Western; D003331:Coronary Vessels / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology; D007550:Isothiuronium / Q000031:analogs & derivatives* / Q000494:pharmacology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009020:Morphine / Q000627:therapeutic use*; D009203:Myocardial Infarction / Q000473:pathology / Q000517:prevention & control; D015428:Myocardial Reperfusion Injury / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III
D000701:Analgesics, Opioid; D004791:Enzyme Inhibitors; D007550:Isothiuronium; D009020:Morphine; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496317:Nos2 protein, mouse; C496315:Nos3 protein, mouse; C027744:S-methylisothiopseudouronium