The role of nitric oxide in edema formation in L-arginine-induced acute pancreatitis.

INTRODUCTION: Nitric oxide (NO) has been implicated in the regulation of the pancreatic circulation, the promotion of the capillary integrity, and the inhibition of leukocyte adhesion. AIMS: To investigate the rates of changes in the pancreatic constitutive NO synthase (cNOS) and inducible NOS (iNOS) activities and the role of NO in the vascular permeability changes during the development of L-arginine (Arg)-induced acute pancreatitis.
METHODOLOGY: Acute pancreatitis was induced in male Wistar rats by injecting 250 mg/100 g body weight of Arg i.p. twice at an interval of 1 hour, as a 20% solution in 0.15 NaCl (group I). The control rats received the same quantity of glycine (group II). In group III, 30 mg/kg N -nitro-L-arginine methyl ester (L-NAME) was injected i.p. 19 hours after the first Arg injection. The rats were killed at 6, 12, 24, or 48 hours following Arg administration, and the plasma amylase concentration and the pancreatic weight/body weight (pw/bw) ratios were evaluated. NOS activity was determined via the conversion of L- C-Arg monohydrochloride to C-citrulline. The vascular permeability was examined by means of the extravasation of Evans blue dye (20 mg/kg bw) into the pancreatic tissue.
RESULTS: The serum amylase level was already increased at 6 hours in group I animals, peaked at 12 hours after the Arg injection (11.800 +/- 590 versus 6.618 +/- 252 U/L in group II), and returned to the control level at 48 hours. The pw/bw ratio peaked at 24 hours in group I (6.63 +/- 0.52 versus 4.02 +/- 0.22 mg/g in group II) and returned to the control level at 48 hours. The cNOS activity was depleted at 6 hours in group I (0.02 +/- 0.003 versus 0.23 +/- 0.02 pmol/min/mg protein in group II); it then gradually increased to a level significantly higher than that in group II and decreased thereafter (0.45 +/- 0.03 and 0.13 +/- 0.01 pmol/min/mg protein at 24 and 48 hours). The iNOS activity was significantly increased at 24 and 48 hours versus that in group II (0.15 +/- 0.05 and 0.07 +/- 0.01 versus 0.04 +/- 0.01 pmol/min/mg protein). The pancreatic concentration of Evans blue dye was significantly higher in group I than in group II (138.59 +/- 11.04 versus 43.57 +/- 2.67 (g/dry weight). Treatment with L-NAME significantly reduced the amylase activity, pw/bw, Evans blue concentration, and cNOS activity of the pancreas but did not exert any beneficial effect on the histologic score at 24 hours after the onset of pancreatitis, as compared with those values in group I (6.528 +/- 673 U/L, 4.56 +/- 0.65 mg/g, 86.84 +/- 3.9 (g/dry weight, 0.14 +/- 0.04 pmol/min/mg protein).
CONCLUSION: Endogenous NO is involved in the formation of pancreatic edema in Arg-induced acute pancreatitis by increasing the vascular permeability and protein extravasation. L-NAME treatment decreased the cNOS activity and edema formation but did not prevent the histologic damage in Arg-induced acute pancreatitis.