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

Granin-derived peptides

The granin family comprises altogether 7 different proteins originating from the diffuse neuroendocrine system and elements of the central and peripheral nervous systems. The family is dominated by three uniquely acidic members, namely chromogranin A (CgA), chromogranin B (CgB) and secretogranin II (SgII). Since the late 1980s it has become evident that these proteins are proteolytically processed, intragranularly and/or extracellularly into a range of biologically active peptides; a number of them with regulatory properties of physiological and/or pathophysiological significance. The aim of this comprehensive overview is to provide an up-to-date insight into the distribution and properties of the well established granin-derived peptides and their putative roles in homeostatic regulations. Hence, focus is directed to peptides derived from the three main granins, e.g. to the chromogranin A derived vasostatins, betagranins, pancreastatin and catestatins, the chromogranin B-derived secretolytin and the secretogranin II-derived secretoneurin (SN). In addition, the distribution and properties of the chromogranin A-derived peptides prochromacin, chromofungin, WE14, parastatin, GE-25 and serpinins, the CgB-peptide PE-11 and the SgII-peptides EM66 and manserin will also be commented on. Finally, the opposing effects of the CgA-derived vasostatin-I and catestatin and the SgII-derived peptide SN on the integrity of the vasculature, myocardial contractility, angiogenesis in wound healing, inflammatory conditions and tumors will be discussed.

Galanin regulates blood glucose level in the zebrafish: a morphological and functional study

The present study has demonstrated the galaninergic innervation of the endocrine pancreas including sources of the galaninergic nerve fibers, and the influence of galanin receptor agonists on blood glucose level in the zebrafish. For the first time, a very abundant galaninergic innervation of the endocrine pancreas during development is shown, from the second day post-fertilization to adulthood. The fibers originated from ganglia consisting of galanin-IR, non-adrenergic (non-sensory) neurons located rostrally to the pancreatic tissue. The ganglia were found on the dorsal side of the initial part of the anterior intestinal segment, close to the intestinal branch of the vagus nerve. The galanin-IR neurons did not show immunoreactivity for applied antibodies against tyrosine hydroxylase, choline acetyltransferase, and vesicular acetylcholine transporter. Intraperitoneal injections of galanin analog NAX 5055 resulted in a statistically significant increase in the blood glucose level. Injections of another galanin receptor agonist, galnon, also caused a rise in blood glucose level; however, it was not statistically significant. The present findings suggest that, like in mammals, in the zebrafish galanin is involved in the regulation of blood glucose level. However, further studies are needed to elucidate the exact mechanism of the galanin action.

Pancreastatin is an endogenous peptide that regulates glucose homeostasis

Pancreastatin (PST) is a regulatory peptide containing 49 amino acids, first isolated from porcine pancreas. Intracellular and extracellular processing of the prohormone Chromogranin A (Chga) results various bioactive peptides of which PST has dysglycemic activity. PST regulates glucose, lipid, and protein metabolism in liver and adipose tissues. It also regulates the secretion of leptin and expression of leptin and uncoupling protein 2 in adipose tissue. In Chga knockout mice, PST induces gluconeogenesis in the liver. PST reduces glucose uptake in mice hepatocytes and adipocytes. In rat hepatocytes, PST induces glycogenolysis and glycolysis and inhibits glycogen synthesis. In rat adipocytes, PST inhibits lactate production and lipogenesis. These metabolic effects are confirmed in humans. In the dual signaling mechanism of PST receptor, mostly PST activates Gαq/11 protein leads to the activation of phospholipase C β3-isoform, therefore increasing cytoplasmic free calcium and stimulating protein kinase C. PST inhibits the cell growth in rat HTC hepatoma cells, mediated by nitric oxide and cyclic GMP production. Elevated levels of PST correlating with catecholamines have been found in gestational diabetes and essential hypertension. Rise in the blood PST level in Type 2 diabetes suggests that PST is a negative regulator of insulin sensitivity and glucose homeostasis.

Galanin inhibits caerulein-stimulated pancreatic amylase secretion via cholinergic nerves and insulin

Pancreatic exocrine secretion is affected by galanin, but the mechanisms involved are unclear. We aimed to determine the effect and elucidate the mechanism of action of exogenous galanin on basal and stimulated pancreatic amylase secretion in vitro. The effect of galanin on basal-, carbachol-, and caerulein-stimulated amylase secretion from isolated murine pancreatic lobules was measured. Carbachol and caerulein concentration-response relationships were established. Lobules were coincubated with galanin (10(-12) M to 10(-7) M), carbachol (10(-6) M), or caerulein (10(-10) M). Lobules were preincubated with atropine (10(-5) M), tetrodotoxin (10(-5) M), hexamethonium (10(-5) M), or diazoxide (10(-7) M and 10(-4) M) for 30 min followed by incubation with caerulein (10(-10) M) alone or combined with galanin (10(-12) M). Amylase secretion was expressed as percent of total lobular amylase. Immunohistochemical studies used the antigen retrieval technique and antisera for galanin receptor (GALR) 1, 2, and 3. Carbachol and caerulein stimulated amylase secretion in a concentration-dependent manner with maximal responses of two- and 1.7-fold over control evoked at 10(-6) M and 10(-10) M, respectively. Galanin (10(-12) M) completely inhibited caerulein-stimulated amylase secretion but had no effect on carbachol-stimulated or basal secretion. Atropine and tetrodotoxin pretreatment abolished the caerulein-stimulated amylase secretion, whereas hexamethonium had no significant effect. Diazoxide significantly reduced caerulein-stimulated amylase secretion by approximately 80%. Galanin did not affect caerulein-stimulated amylase secretion in the presence of hexamethonium or diazoxide. Glucose-stimulated amylase secretion was also inhibited by galanin. Immunohistochemistry revealed islet cells labeled for GALR2. These data suggest that galanin may modulate caerulein-stimulated amylase secretion by acting on cholinergic nerves and/or islet cells possibly via GALR2 to regulate insulin release.

Natriuretic peptides as regulatory mediators of secretory activity in the digestive system

Atrial natriuretic peptide (ANP) and C-type natriuretic peptide (CNP) are members of the natriuretic peptide family best known for their role in blood pressure regulation. However, in recent years all the natriuretic peptides and their receptors have been described in the gastrointestinal tract, digestive glands and central nervous system, as well as implicated in the regulation of digestive gland functions. The current review highlights the regulatory role of ANP and CNP in pancreatic and other digestive secretions. ANP and CNP stimulate basal as well as induced pancreatic secretion and modify bicarbonate and chloride secretions. Whereas ANP and CNP exert effects directly on pancreatic cells, CNP also acts through a vago-vagal reflex. At high doses both peptides attenuate pancreatic secretion induced by high doses of secretin through the PLC/PKC pathway. With regards to other digestive secretions, ANP and CNP decrease bile secretion in the rat. ANP does not induce salivation by itself but enhances stimulated salivary secretion and modifies salivary composition in rat parotid as well as submandibular glands. In rat pancreatic, hepatic, parotid and submandibular tissues, the NPR-C receptor mediates mostly peripheral responses whereas NPR-A and NPR-B receptors, which are coupled to guanylate cyclase, likely mediate the central response. In addition, ANP modulates gastric acid secretion via a vagal-dependent mechanism. In the intestine, ANP and CNP decrease water and sodium chloride absorption through an increase in cGMP levels. Overall, these findings indicate that ANP and CNP are members of the large group of regulatory peptides affecting digestive secretions.

Neurohumoral control of exocrine pancreatic secretion

PURPOSE OF REVIEW

Advancing knowledge about normal physiology of the exocrine pancreas is essential for investigations into the mechanisms of disorders of the pancreas. To this end, reports published during the past year give further insights into the complexity of the hormonal and neural interactions and processes involved in exocrine pancreatic physiology.

RECENT FINDINGS

Key findings include demonstrations of different biologic effects of cholecystokinin peptides on pancreatic secretion, underlining the importance of measurement techniques to determine specific forms of peptide hormones involved in physiologic processes; investigations of the details of the central neural pathways involved in the vago-vagal reflex in pancreatic secretion; the demonstration of the essential role for intrapancreatic nerves in mediating meal-induced responses; and identification of a modulatory role for leptin in exocrine pancreatic secretion.

SUMMARY

These findings should not only spur further investigations into mechanisms of normal physiology but also provide impetus for application of these findings to studies of pancreatic disorders.

Atrial natriuretic factor stimulates exocrine pancreatic secretion in the rat through NPR-C receptors

Increasing evidence supports the role of atrial natriuretic factor (ANF) in the modulation of gastrointestinal physiology. The effect of ANF on exocrine pancreatic secretion and the possible receptors and pathways involved were studied in vivo. Anesthetized rats were prepared with pancreatic duct cannulation, pyloric ligation, and bile diversion into the duodenum. ANF dose-dependently increased pancreatic secretion of fluid and proteins and enhanced secretin and CCK-evoked response. ANF decreased chloride secretion and increased the pH of the pancreatic juice. Neither cholinergic nor adrenergic blockade affected ANF-stimulated pancreatic secretion. Furthermore, ANF response was not mediated by the release of nitric oxide. ANF-evoked protein secretion was not inhibited by truncal vagotomy, atropine, or Nomega-nitro-l-arginine methyl ester administration. The selective natriuretic peptide receptor-C (NPR-C) receptor agonist cANP-(4-23) mimicked ANF response in a dose-dependent fashion. When the intracellular signaling coupled to NPR-C receptors was investigated in isolated pancreatic acini, results showed that ANF did not modify basal or forskolin-evoked cAMP formation, but it dose-dependently enhanced phosphoinositide hydrolysis, which was blocked by the selective PLC inhibitor U-73122. ANF stimulated exocrine pancreatic secretion in the rat, and its effect was not mediated by nitric oxide or parasympathetic or sympathetic activity. Furthermore, CCK and secretin appear not to be involved in ANF response. Present findings support that ANF exerts a stimulatory effect on pancreatic exocrine secretion mediated by NPR-C receptors coupled to the phosphoinositide pathway.

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.

Large reduction in the number of galanin-immunoreactive cells in pancreatic islets of diabetic rats

Although galanin has been shown to be present in pancreatic islet cells, there is no literature available on the pattern of distribution and the effect of galanin in the pancreas of diabetic animals or human models. The aim of this study was to examine whether galanin immunoreactivity changes after the onset of diabetes mellitus in the rat model. The present study used immunohistochemical techniques to examine the pattern of distribution of galanin-like immunoreactive cells in the pancreas of rats with streptozotocin-induced diabetes. The effect of galanin on insulin secretion from intact rat pancreatic tissue fragments was also investigated using a radioimmunoassay technique. Numerous galanin-like immunoreactive cells were observed in both the peripheral and central regions of the islet of Langerhans of normal rat pancreas. By contrast, the islets of diabetic rat pancreas contained significantly (P < 0.0001) fewer galanin-like immunoreactive cells than nondiabetic rats. Galanin was colocalized with insulin in the islets of normal and diabetic rats. Galanin had an inhibitory effect on insulin secretion from the isolated pancreatic tissue fragments of normal and diabetic rats at all concentrations (10(-12) to 10(-6) M) employed. Galanin at 10(-9) M caused a significant (P < 0.02) decrease in insulin secretion from normal rat pancreatic tissue fragments compared to basal. These observations indicate that galanin may play a significant role in the regulation of insulin secretion.

The role of leucine-enkephalin on insulin and glucagon secretion from pancreatic tissue fragments of normal and diabetic rats

Leucine-enkephalin (Leu-Enk) has been shown to be present in endocrine cells of the rat pancreas and may play a role in the modulation of hormone secretion from the islets of Langerhans. Since little is known about the effect of Leu-Enk on insulin and glucagon secretion, it was the aim of this study to determine the role of Leu-Enk on insulin and glucagon secretion from the isolated pancreatic tissue fragments of normal and diabetic rats. Pancreatic tissue fragments of normal and streptozotocin-induced diabetic rats were incubated for 1 h with different concentrations of Leu-Enk (10(-12)-10(-6)M) alone or in combination with either atropine or yohimbine or naloxone. After the incubation period the supernatant was assayed for insulin and glucagon using radioimmunoassay techniques. Leu-Enk (10(-12 )-10(-6)M) evoked large and significant increases in insulin secretion from the pancreas of normal rats. This Leu-Enk-evoked insulin release was significantly (p < 0.05) blocked by atropine, naloxone and yohimbine (all at 10(-6)M). In the same way, Leu-Enk at concentrations of 10(-12)M and 10(-9)M induced significant (p < 0.05) increases in glucagon release from the pancreas of normal rats. Atropine, yohimbine but not naloxone significantly (p < 0.05) inhibited Leu-Enk-evoked glucagon release from normal rat pancreas. In contrast, Leu-Enk failed to significantly stimulate insulin and glucagon secretion from the pancreas of diabetic rats. In conclusion, Leu-Enk stimulates insulin and glucagon secretion from the pancreas of normal rat through the cholinergic, alpha-2 adrenergic and opioid receptor pathways.

Galanin-like immunoreactive endocrine cells in bovine pancreas

Pancreata of fetal, neonatal and adult cattle were studied immunohistochemically for galanin. The results revealed galanin-like immunoreactivity both in the endocrine cells and in the neural elements. The galanin-like immunoreactive endocrine cells (Gal-LIEC) were confined to the large islets, and were not observed in the islets of Langerhans and exocrine pancreas. They were first detected at the third prenatal month. Their developmental profile showed an increase from fetal to early neonatal stage with a subsequent decrease towards adulthood. The considerable number of Gal-LIEC from late prepartum to early postpartum stage may imply functional significance of galanin during the perinatal development of cattle. Coexistence of galanin and insulin was also observed which may suggest autocrine interaction between the 2 hormones.

Immunohistochemical identification of pancreatic hormones, neuropeptides and cytoskeletal proteins in pancreas of the camel (Camelus dromedarius)

The patterns of distribution of insulin (INS), glucagon (GLU), atrial natriuretic peptide (ANP), neuropeptide-Y (NPY), cholecystokinin-octapeptide (CCK-8), neurofilament-200 protein (NF), S-100 protein (S-100), and vimentin (VIM) in the pancreas of the one-humped camel (Camelus dromedarius) were investigated using immunohistochemical techniques. INS-immunoreactive cells were observed in the central and peripheral parts of the islets of Langerhans, but some solitary INS-positive cells were found outside the islets. INS-positive cells constituted 44.26-90.91% [mean +/- standard deviation (std): 67.34 +/- 14.20] of the total number of islet cells. GLU-immunopositive cells were located mainly in the peripheral region of the islets, and they constituted 11.43-44.44% [mean +/- std: 23.54 +/- 8.27] of the total number of islet cells. ANP and CCK-8 immunoreactivity was observed in neurons and perivascular nerves fibers. NPY was identified in pancreatic neurons and in some peripheral and central cells of the islets of Langerhans. VIM immunoreactivity was observed in the endothelial cells of blood vessels and the nerves located in the perivascular, interlobular and periacinar regions. VIM was also detected immunohistochemically in the periductal nerves of the pancreas. NF occurred only in nerves. S-100 was discerned mainly in the nerves of the interlobular connective tissue and in nerves lying close to blood vessels and acinar tissue. It is concluded that INS, GLU, ANP, NPY, CCK-8, NF, S-100, and VIM are well distributed in the pancreas of the camel.

Pattern of distribution of neuropeptides in the camel lacrimal gland

The pattern of distribution of neuropeptides, including neuropeptide-Y (NPY), vasoactive intestinal polypeptide (VIP), neurotensin (NT), serotonin (5-HT), galanin (GAL), leucine-enkephalin (LEU-ENK) and calcitoningene-related-peptide (CGRP), in the nerves of the camel lacrimal gland was investigated using immunohistochemical techniques. Fresh lacrimal gland segments, obtained from adult camels slaughtered in the local abattoir, were used for the immunohistochemical techniques. NPY and LEU-ENK immunoreactivity was observed in the nerve cell bodies and nerve fibers of the camel lacrimal gland. VIP, GAL and CGRP were demonstrated predominantly in fine varicose nerve fibers lying on the basolateral surfaces of the lacrimal acinar cells. NT and 5-HT were identified mainly in neurons situated in the periacinar regions, close to the basal surfaces of the acinar cells. It is concluded that the camel lacrimal nerves contain several neuropeptides including NPY, VIP, NT, 5-HT, GAL, LEU-ENK and CGRP which may modulate lacrimal fluid and protein secretion.

Innervation of the pancreas of the one-humped camel (Camelus dromedarius) by neuropeptide-Y, galanin, calcitonin-gene-related-peptide, atrial natriuretic peptide and cholecystokinin

The distribution of neuropeptide-Y (NPY), galanin (GAL), cholecystokinin-8 (CCK-8), atrial natriuretic peptide (ANP) and calcitonin gene-related peptide (CGRP) in the pancreas of the camel was investigated using immunohistochemical techniques. NPY-immunoreactive neurons were observed in the pancreatic ganglia and also in the interacinar regions of the exocrine pancreas. NPY was discernible in fine varicose nerve fibres ending on NPY-negative cells and in the walls of blood vessels. ANP immunoreactivity was observed in nerve fibres situated on the basolateral surfaces of the acinar cells. CCK-8, GAL and CGRP immunoreactivity were observed in neurons and varicose nerve fibres in the walls of blood vessels. Of all the neuropeptides investigated, only NPY appeared to be densely distributed in the pancreas of the camel. It is concluded that the pattern of distribution of these neuropeptides in the camel pancreas is similar to those observed in the pancreata of other mammals.