Nitric oxide and the pancreas: morphological base and role in the control of the exocrine pancreatic secretion.

The distribution of nitric oxide synthase in both neuronal and non-neuronal pancreatic tissues and the role of nitric oxide in the control of exocrine pancreatic secretion are reviewed in this article. Earlier reports based on in vivo studies suggested that nitric oxide can affect the secretory activity of the exocrine pancreas through changes in pancreatic blood flow. More recently, the employment of either nitric oxide synthase inhibitors or nitric oxide donors in in vitro preparations has provided evidence that nitric oxide can exert a direct action on this gland independently on its vascular effects. Most research in this area seems to indicate that modulation of exocrine pancreatic function by nitric oxide is exerted via activation of guanylate cyclase and generation of cGMP, although other pathways cannot be excluded. Experiments performed over the last year in our laboratory reveal a novel and interesting mechanism based on the ability of nitric oxide to control the release of endogenous neurotransmitter in the pancreas and, subsequently, the nerve-mediated enzyme secretion.

Distribution of nitric oxide synthase and secretory role of exogenous nitric oxide in the isolated rat pancreas.

BACKGROUND: Pancreatic production and in vivo effects of nitric oxide (NO) have been shown by several studies. In order to examine the direct actions of the NO donor sodium nitroprusside (SNP), this study used in vitro specimens of the rat pancreas where the distribution of neuronal nitric oxide synthase (NOS) and the secretory effects of SNP and the cyclic GMP (cGMP) analog 8-bromo cyclic GMP (8-Br cGMP) were investigated. METHODS: NO containing pancreatic nerves were visualized by NOS immunohistochemistry. Basal and stimulated amylase output from rat pancreatic segments was measured by an on-line fluorimetric method. Stimulation was achieved by either acetylcholine (ACh) or electrical field stimulation (EFS). Intracellular free calcium concentration ([Ca2+]i) was measured in dispersed pancreatic acinar cells. RESULTS: NOS containing nerves were demonstrated in the vicinity of pancreatic acini and blood vessels. SNP and 8-Br cGMP inhibited both basal and EFS evoked amylase output but failed to inhibit ACh induced amylase output. Basal [Ca2+]i was decreased by both SNP and 8-Br cGMP but neither SNP nor 8-Br cGMP influenced the ACh evoked increase in [Ca2+]i. CONCLUSION: NO is well distributed in the rat exocrine pancreas. Exogenous nitric oxide may have a dual action in the isolated rat pancreas: Inhibition of basal amylase secretion in acinar cells and inhibition of ACh release from intrinsic nerve terminals. Both effects seem to be calcium dependent and possibly mediated by cGMP.

Enzyme- and immunohistochemical localization of nitric oxide synthase in nerves of the porcine pancreas.

The distribution of nitric oxide synthase (NOS) in neuronal and non-neuronal porcine pancreatic tissues was examined using nicotinamide adenine dinucleotide hydrogen phosphate diaphorase (NADPHd) enzymehistochemistry and neuronal type NOS immunohistochemistry. NOS-containing perikarya were regularly discernible in the pancreatic ganglia, whereas positive thin nerve fibers appeared within nerve bundles of the interlobular spaces and as thin varicose fibers in the vicinity of pancreatic blood vessels. Vascular endothelium showed intense staining for NADPHd and most of the islet cells were NOS immunoreactive. The above morphological findings indicate that nitrergic innervation of the porcine pancreas is very similar to that of the pancreata of other mammalian species and suggest that nitric oxide of both neuronal and extraneuronal origin may regulate blood flow and secretion of the porcine pancreas.

[Immunocytochemical demonstration of nitric acid synthase in rat pancreatic tissue]. / A nitrogén-oxid-szintáz immuncitokémiai kimutatása patkányok hasnyálmirigy szöveteiben.

To investigate the age-related alterations of pancreatic distribution of nitric oxide synthase in rats, we applied light microscopic immunocytochemistry. Tissue samples were obtained from the pancreata of 5-day-old rat newborns and 120-day-old adult rats and processed for immunocytochemistry using anti neuronal nitric oxide synthase primary serum with the avidin-biotin-streptavidin complex method. Nitric oxide synthase immunopositive intrinsic nerve cells and perivascular/periacinar nerve fibers could be seen in both the newborn and the adult rat pancreas. In addition to the labelled neuronal structures we detected some immunoreactive acinar cells in the newborns, while the neonatal ductal epithelium and the islet cells were immunonegative. Strong staining for nitric oxide synthase was observed in the adult ductal epithelial cells and moderate positivity was displayed by the adult islet cells. The localization of nitric oxide shows age-related changes mainly in the non-neuronal structures of the rat pancreas: these findings could form the morphological base of pancreatic dysfunctions in the aged.

Immunohistochemical identification and effects of atrial natriuretic peptide, pancreastatin, leucine-enkephalin, and galanin in the porcine pancreas.

This study demonstrates the presence and distribution of atrial natriuretic peptide (ANP) pancreastatin (PST), leucineenkephalin (Leu-ENK), galanin (GAL), and insulin in the pig pancreas. The effects of PST, ANP, Leu-ENK, and GAL on protein and amylase secretion were also investigated to determine their functional role in the control of pancreatic secretion. PST-immunoreactive cells were observed in the islet of Langerhans and in the wall of the ducts. Leu-ENK-immunopositive cells were observed in both the endo-and exocrine pancreas. It is colocalized with insulin in the islet of Langerhans. ANP immunoreactivity was discernible in nerve fibers and cells of the exocrine pancreas. GAL-immunopositive cells were observed in close association with insulin-positive cells in the islets of Langerhans and in the exocrine pancreas. Stimulation of isolated pancreatic segments with either ANP or Leu-ENK resulted in increased protein secretion and amylase output. The Leu-ENK-evoked amylase secretion was antagonized by naloxone. Pancreastatin was effective at all concentrations, but low concentration had more marked secretory effects whereas GAL failed to evoke any significant increases in either protein or amylase secretion. The results of the study have demonstrated a close association of peptidergic fibers with the secretory cells of the pancreas. The nerve fibers can release peptides that in turn can stimulate protein and amylase secretion.