Secretagogue-stimulated pancreatic secretion is differentially regulated by constitutive NOS isoforms in mice

Abstract

Nitric oxide (NO) and NO synthase (NOS) play controversial roles in pancreatic secretion. NOS inhibition reduces CCK-stimulated in vivo pancreatic secretion, but it is unclear which NOS isoform is responsible, because NOS inhibitors lack specificity and three NOS isoforms exist: neuronal (nNOS), endothelial (eNOS), and inducible (iNOS). Mice having individual NOS gene deletions were used to clarify the NOS species and cellular interactions influencing pancreatic secretion. In vivo secretion was performed in anesthetized mice by collecting extraduodenal pancreatic duct juice and measuring protein output. Nonselective NOS blockade was induced with N(omega)-nitro-L-arginine (L-NNA; 10 mg/kg). In vivo pancreatic secretion was maximal at 160 pmol.kg(-1).h(-1) CCK octapeptide (CCK-8) and was reduced by NOS blockade (45%) and eNOS deletion (44%). Secretion was unaffected by iNOS deletion but was increased by nNOS deletion (91%). To determine whether the influence of NOS on secretion involved nonacinar events, in vitro CCK-8-stimulated secretion of amylase from isolated acini was studied and found to be unaltered by NOS blockade and eNOS deletion. Influence of NOS on in vivo secretion was further examined with carbachol. Protein secretion, which was maximal at 100 nmol.kg(-1).h(-1) carbachol, was reduced by NOS blockade and eNOS deletion but unaffected by nNOS deletion. NOS blockade by L-NNA had no effect on carbachol-stimulated amylase secretion in vitro. Thus constitutive NOS isoforms can exert opposite effects on in vivo pancreatic secretion. eNOS likely plays a dominant role, because eNOS deletion mimics NOS blockade by inhibiting CCK-8 and carbachol-stimulated secretion, whereas nNOS deletion augments CCK-8 but not carbachol-stimulated secretion.

Cholecystokinin and Gastrin Receptors

“…Binding of 125 I-BoltonHunter-CCK-8 to COS-7 cells expressing this protein was inhibited by CCK-and gastrin-related peptides with potencies in agreement with CCK2R pharmacology. However, the nonpeptide antagonist for the CCK1R (L-364,718) competed with labeled CCK-8 to the recombinant receptor with higher potency (19 nM) than the nonpeptide antagonist of the CCK2R (L-365,260, 130 nM), but this atypical pharmacological feature was further shown to be species specific (38).…”

“…Stimulation of the NO/cGMP signaling cascade in response to CCK has also been observed in rodent pancreatic acini and could be involved in pancreatic secretion in vivo. Indeed, nonselective NOS inhibitors as well as deletion of NOS in transgenic mice decrease pancreatic secretion induced by CCK (2,125). In addition, the gastroprotective role of CCK on gastric mucosal is dependent on this pathway (63, 64, 568).…”

Development of a new mouse model of acute pancreatitis induced by administration of l-arginine

“…Given that our data suggest that it is the metabolite of L-arginine that induces pancreatitis in rodents, we believe that one of the enzymes that metabolizes L-arginine might play a role in the initiation of pancreatitis. One such enzyme is nitric oxide synthase (NOS), which is present in acinar cells (5). Induction of inducible NOS has been reported during the late phase of pancreatitis in rats using L-arginine (25).…”

Inhibition of acinar apoptosis occurs during acute pancreatitis in the human homologue ΔF508 cystic fibrosis mouse

“…Pancreatic acini were dispersed by collagenase digestion of pancreases (14,17), suspended in HEPES-Ringer buffer (pH 7.48) with Eagle's minimal essential amino acids and 1 mg/ml BSA, and equilibrated with 100% O2. Viability of acini was Ͼ95% based on Trypan blue exclusion.…”