Objective: Acute pancreatitis is an inflammatory disease of the pancreas resulting in
significant morbidity and mortality, due to distant organ failure. Melatonin exerts
complex physiological and pharmacological effects on multiple systems and organs.
Aim of the study: The present study was designed to investigate the effects of
melatonin pre- and post-treatment with L-arginine (L-Arg.) on some inflammatory
markers in acute pancreatitis in rats. Materials and methods: The present study was
carried out on 75 white albino rats which were randomly classified into five equal
groups; group I (control group); group II (L-arginine injected group); group III
(melatonin pre-treatment with L-arginine); group IV (melatonin post-treatment with
L-arginine) and group V (melatonin injected group). All groups were subjected to
measurements of serum amylase and lipase activities; total antioxidant capacity (TAC)
levels, serum and tissue TNF α levels; MPO and PON1 enzymes activities, in addition
to histopathological examination of all pancreatic specimens. Results: L-arginine
injected group showed severe necrotizing pancreatitis confirmed by histopathological
changes and significant elevations in serum amylase and lipase activities relative to
the control values. Also, significant increase of serum TAC, serum and tissue TNF-α
levels and MPO enzyme activity and significant decrease of PON-1 enzyme activity
were detected in L-arginine injected group as compared to control group. In
melatonin injected groups, either pre- or post- treatment with L-arginine, serum
amylase and lipase activities and both serum and tissue TNF-α levels, MPO activity
were significantly decreased in both groups with significantly lower levels in rats
given melatonin pre- treatment with L-arginine. Also, significant increase of both
serum and tissue PON-1 were found in both groups. Conclusion: These data might
confirm the protective effect of melatonin as an antioxidant in acute pancreatitis.