Protective role of endogenous nitric oxide (NO) in lipopolysaccharide - Induced pancreatic damage. (A new experimental model of acute pancreatitis)

Lipopolysaccharide (LPS) derived from the bacterial cell wall activates the inflammatory response in the tissue but the role of LPS in the pathogenesi s of pancreatic damage and in the activation of NO system in the pancreas h as not been fully explained. The aim of this study was to investigate the e ffect of repeated administration of LPS to the rats on the integrity of the pancreas, on the ability of isolated pancreatic acini to secrete the amyla se and on the plasma level of tumor necrosis factor alpha (TNF alpha). The role of NO in the pancreatic resistance to the damage was assessed in anima ls subjected to repeated administration of LPS. To induce pancreatic damage one group of rats received intraperitoneal (i.p.) injection of LPS (from E . coli) every day during 5 consecutive days (10 mg/kg - day). Another group s of animals were given NG-nitro-L-arginine (L-NNA), an inhibitor of NO syn thase (NOS) (20 mg/kg i.p.) alone or in combination with L-arginine (100 mg /kg i.p.), 30 min prior to each LPS injection. Plasma level of TNFa was det ermined by ELISA kit. Repeated administration of LPS produced mild pancreat ic inflammation that was most pronounced at day 5 of LPS treatment and mani fested as edema, neutrophil infiltration and hemorrhage of the pancreas. Th e survival rate after 5 days treatment with LPS was 87.5%. Pancreatic weigh t, plasma levels of TNF alpha and amylase, pancreatic blood flow (PBF) and NO generation by pancreatic acini were markedly increased in rats subjected to repeated administration of LPS whereas the amylase response of isolated pancreatic acini to pancreatic secretagogues was significantly attenuated. Suppression of NOS by L-NNA resulted in a dramatic increase in the mortali ty of the animals reaching 50% and significantly increased inflammatory cha nges in the pancreatic tissue, decreased PBF, abolished the ability of panc reatic acini to release NO and to secrete amylase. Pancreatic weight and pl asma levels of amylase and TNF alpha significantly increased in the group o f rats treated with combination of LPS+L-NNA as compared to the animals rec eived LPS alone. Addition of L-arginine to L-NNA+LPS administration reverse d all harmful effects produced by L-NNA in the pancreas. We conclude that r epeated administration of high doses of bacterial LPS to the rats could ind uce pancreatic tissue damage by itself, however, it is not able to produce severe pancreatitis. Suppression of NO generation significantly aggravates the pancreatic lesion produced by LPS leading to the dramatic mortality in treated rats. The rise of plasma level of TNF alpha corresponds to the seve rity of pancreatic inflammation.