The aim of the present study was to investigate the protective effect of the pineal secretary product
melatonin in a model of splanchnic artery occlusion
shock (SAO). SAO
shock was induced in rats by clamping both the superior mesenteric artery and the celiac trunk for 45 min, followed thereafter by release of the clamp (reperfusion). At 60 min after reperfusion, animals were sacrificed for tissue histological examination and biochemical studies. There was a marked increase in the oxidation of
dihydrorhodamine 123 to
rhodamine (a marker of
peroxynitrite-induced oxidative processes) in the plasma of the SAO-shocked rats after reperfusion, but not during
ischemia alone. Immunohistochemical examination demonstrated a marked increase in the immunoreactivity to
nitrotyrosine, an index of
nitrogen species such as
peroxynitrite, in the necrotic ileum in shocked rats. SAO-shocked rats developed a significant increase of tissue
myeloperoxidase and
malondialdehyde activity, and marked histological injury to the distal ileum. SAO
shock was also associated with a significant mortality (0% survival at 2 hr after reperfusion). Reperfused ileum tissue sections from SAO-shocked rats showed positive staining for
P-selectin, which was mainly localized in the vascular endothelial cells. Ileum tissue sections obtained from SAO-shocked rats with anti-
intercellular adhesion molecule (ICAM-1) antibody showed a diffuse staining.
Melatonin (applied at 3 mg/kg, 5 min prior to reperfusion, followed by an infusion of 3 mg/kg per hr), significantly reduced
ischemia reperfusion injury in the bowel as evaluated by histological examination. This prevented the infiltration of neutrophils into the reperfused intestine, is evidenced by reduced
myeloperoxidase activity and reduced lipid peroxidation. This was evaluated by
malondialdehyde activity which reduced the production of
peroxynitrite during reperfusion, markedly reduced the intensity and degree of
P-selectin and
ICAM-1 in tissue section from SAO-shocked rats and improved their survival. Taken together, our results clearly demonstrate that
melatonin treatment exerts a protective effect and part of this effect may be due to inhibition of the expression of adhesion molecule and
peroxynitrite-related pathways and subsequent reduction of neutrophil-mediated cellular injury.