Revisiting ischemia and reperfusion injury as a possible cause of necrotizing enterocolitis: Role of nitric oxide and superoxide dismutase.
OBJECTIVE
The pathogenesis of necrotizing enterocolitis (NEC) is unknown. Ischemia and reperfusion (I/R) injury has been considered a major contributing factor. Nitric oxide (NO) and superoxide dismutases (SODs) have been shown to protect bowel from I/R injury. This study aims to assess (1) the ability of premature intestine to resist I/R injury compared with mature intestine and (2) the possible role of NO and SODs in modulating such response.


METHODS
Intestines from 5 groups of rats (n = 6 for each study group) were studied: (1) premature, gestational age 20 days; (2) premature, gestational age 22 days; (3) full-term, newborn; (4) infant, day 15; (5) infant, day 30.


METHODS
(1) The degrees of I/R injury after 0, 30, 60, 90 and 120 minutes, respectively, of ischemia and 25 minutes of I/R were assessed histologically by a pathologist who was unaware of the operative details. (2) Tissue NO and copper levels were measured by electroparamagnetic resonance (EPR) study; and nitric oxide synthases, copper zinc (CuZn) SODs and manganese (Mn) SODs were examined immunohistochemically. (3) and (4) I/R injury was assessed in rats that had received intraperitoneal injections of L-arginine (NO donor) and L-NAME (NO antagonist), respectively.


RESULTS
For premature (1,2), newborn (3) and mature (4,5) intestines, grades of injury at maximum I/R period studied (120 minutes of ischemia, 25 minutes of reperfusion) were 0, 0, and 3, respectively (P <.05); NO levels were 1 u +/- 1.5, 3 +/- 2.5, and 22 u +/- 3.5, respectively (P <.05); Cu levels were 150 u +/- 15, 200 u +/- 41 and 12 u +/- 2, respectively (P <.05); NOS in intestines were +, +, +++ and CuZnSODs were ++, +++, +, respectively; and MnSODs were +++, ++, -, respectively. No change in NO levels was detected in groups (1), (2), or (3) after L-arginine and L-NAME injections.


CONCLUSIONS
Premature rat intestine is highly resistant to I/R injury, which may indicate that I/R alone, in the absence of other predisposing factors (eg, bacterial colonization) may not be sufficient in causing NEC. Nitric oxide does not have a protective role for immature and newborn intestines in I/R as in mature intestine. The high level of SODs of the immature and newborn intestine may play an important role in its high resistance to I/R injury.
Chan
K L
KL
Departments of Surgery, Medicine, Pathology, and Anatomy, University of Hong Kong Medical Centre, Queen Mary Hospital, Hong Kong SAR, China.
Hui
Connie W C
CW
Chan
K W
KW
Fung
Peter C W
PC
Wo
Jana Y H
JY
Tipoe
G
G
Tam
Paul K H
PK
D000818:Animals; D001120:Arginine / Q000008:administration & dosage; D001706:Biopsy; D020345:Enterocolitis, Necrotizing / Q000209:etiology*; D007150:Immunohistochemistry; D007421:Intestine, Small / Q000098:blood supply* / Q000378:metabolism*; D007511:Ischemia / Q000150:complications / Q000378:metabolism; D019331:NG-Nitroarginine Methyl Ester / Q000008:administration & dosage; D009569:Nitric Oxide / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015427:Reperfusion Injury / Q000150:complications* / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism*
D009569:Nitric Oxide; D001120:Arginine; D013482:Superoxide Dismutase; D019331:NG-Nitroarginine Methyl Ester