Pathogenic Role of Endothelial Nitric Oxide Synthase (eNOS/NOS-III) in Cerulein-Induced Rat Acute Pancreatitis

Abstract

Nitric oxide (NO) is a potent pancreatic vasodilator, yet the pathogenic role of NO in acute pancreatitis remains controversial. NO is generated from L-arginine by NO synthase (NOS), classified into three isozymes: neuronal (nNOS), inducible (iNOS), and endothelial NOS (eNOS). The purpose of the present study was to investigate the role of NO/NOS isozymes in the pathogenesis of cerulein-induced acute pancreatitis in rats. Acute pancreatitis was induced in male Wistar rats by two subcutaneous injections of cerulein (20 microg/kg). NG-Nitro-L-arginine methyl ester (L-NAME: a nonselective NOS inhibitor) or aminoguanidine (a relatively selective iNOS inhibitor) was given orally, while tetrahydrobiopterin (BH4), a critical cofactor for NOS, was administered intraperitoneally 30 min before the first cerulein injection. Cerulein given repeatedly twice produced acute pancreatitis, with concomitant increases in the serum amylase level, pancreas weight, myeloperoxidase activity, lipid peroxidation and microvascular permeability. Prior administration of L-NAME, but not aminoguanidine, significantly prevented these changes, in a dose-dependent manner, and this effect was antagonized by the coadministration of L-arginine, a precursor of NO. The expression of dimetric eNOS in the pancreas was markedly suppressed by cerulein injections, together with a decrease in NO production, but the response was partially but significantly reversed by the prior administration of BH4. The increases in the serum amylase level and pancreas weight, as well as the lipid peroxidation induced by cerulein, were significantly attenuated by the administration of BH4. L-NAME had no effect on pancreatic secretion induced by cerulein. These results suggest that the uncoupled eNOS, probably caused by the decrease in endogenous BH4 availability, plays a deleterious role in the pathogenesis of cerulein-induced acute pancreatitis.

Expression of Nitric Oxide Synthase Isoforms and Nitric Oxide Production in Acute Pancreatitis and Associated Lung Injury

“…However, baseline eNOS expression also remained unchanged throughout a 7-hour cerulein-induced AP timecourse experiment [16] . Another study found a markedly lower dimerization of eNOS [32] after 7 h of cerulein administration, which is associated with reduced eNOS activity [33] . A reduction in eNOS activity has been associated with disruption in the pancreatic microvascular blood flow [16] as well as increased expression of adhesion molecules on the endothelial cells of the blood vessels [34,35] .…”

“…The role of eNOS in pancreatitis has been getting more attention recently; studies have shown that pancreatic eNOS activity decreases during pancreatitis [16,32] . However, baseline eNOS expression also remained unchanged throughout a 7-hour cerulein-induced AP timecourse experiment [16] .…”

Protective effect of inducible nitric oxide synthase inhibitor on pancreas transplantation in rats

“…Vasoactive mediators, such as bradykinin, platelet activating factor, endothelin and NO, participate in the development of pancreatic microcirculatory failure. Recently, in druginduced pancreatitis models, some researchers found that there is a correlation among NF-kappaB activation, serum amylase, reactive oxygen species level and tissue damage, suggesting that NF-kappaB and iNOS play a key role in the pathogenesis of acute pancreatitis [14][15][16] . After treatment with antioxidants or NOS inhibitors, the levels of myeloperoxidase, serum amylase and NO, as well as iNOS activities are decreased significantly, and the pancreatic inflammation is improved [14,15] .…”

“…Recently, in druginduced pancreatitis models, some researchers found that there is a correlation among NF-kappaB activation, serum amylase, reactive oxygen species level and tissue damage, suggesting that NF-kappaB and iNOS play a key role in the pathogenesis of acute pancreatitis [14][15][16] . After treatment with antioxidants or NOS inhibitors, the levels of myeloperoxidase, serum amylase and NO, as well as iNOS activities are decreased significantly, and the pancreatic inflammation is improved [14,15] . Ma et al [16] found that the expression of NF-kappaB and iNOS in peritoneal macrophages is significantly higher in rats with severe acute pancreatitis, and anti-inflammatory agents decrease the expression of TNF-alpha, IL-1 and NO in peritoneal macrophages, reducing the severity of pancreatitis.…”

Crucial Role for Neuronal Nitric Oxide Synthase in Early Microcirculatory Derangement and Recipient Survival following Murine Pancreas Transplantation

“…Beneficial effects were attributed to the endothelial isoform by using the rather unspecific NOS inhibitor N -nitro-L-arginine methyl ester (L-NAME) without further dissecting a possible role of the neuronal isoform [16], [17].…”