Galanin in the porcine pancreas

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.

Galanin receptor 3--a potential target for acute pancreatitis therapy

BACKGROUND

Galanin participates in the pathogenesis of acute pancreatitis (AP). The galanin receptor (GALR) sub-types involved, however, are unclear. We aimed to determine GALRs messenger RNA (mRNA) expression in mouse pancreas, describe their localization, and ascertain if GALR2 and GALR3 are involved in AP.

METHODS

Galanin receptor expression in murine whole pancreas, acinar, and islet cells was quantified by polymerase chain reaction amplification of reverse-transcribed RNA for mRNA, Western blot analysis for protein and in situ hybridization for GALR localization. Isolated acinar cells were used to determine galanin's effect on amylase secretion. Acute pancreatitis was induced in mice by caerulein injections. Mice, with and without AP, were treated with the highly selective GALR2 antagonist M871, or the specific GALR3 antagonist SNAP-37889. Indices of AP were measured at 12 h.

KEY RESULTS

Murine pancreas expresses mRNA for GALRs. In islets the expression of all GALR are comparable, whereas in acinar cells GALR3 is predominantly expressed. Western blot analysis confirmed that the GALR proteins are expressed by acinar cells. In situ hybridization analysis confirmed that GALR3 mRNA is present in islet and acinar cells, while mRNA for GALR1 and 2 is confined to islets. Galanin did not influence basal and caerulein-stimulated amylase release from acinar cells. M871 treatment reduced some, whereas SNAP-37889 treatment reduced all indices of AP (by 40-80%).

CONCLUSIONS & INFERENCES

Galanin receptor mRNA and protein are expressed in mouse pancreas, with GALR3 mRNA predominating. GALR3 antagonism reduced the severity of AP whereas GALR2 antagonism was less effective. GALR3 is a potential target for treatment of AP.

Galanin, galanin receptors, and drug targets

Galanin, a neuropeptide widely expressed in the central and peripheral nervous systems and in the endocrine system, has been shown to regulate numerous physiological and pathological processes through interactions with three G-protein-coupled receptors, GalR1 through GalR3. Over the past decade, some of the receptor subtype-specific effects have been elucidated through pharmacological studies using subtype selective ligands, as well as through molecular approaches involving knockout animals. In this chapter, we summarize the current data which constitute the basis of targeting GalR1, GalR2, and GalR3 for the treatment of various human diseases and pathological conditions, including seizure, Alzheimer's disease, mood disorders, anxiety, alcohol intake in addiction, metabolic diseases, pain and solid tumors.

Galanin-like immunoreactive neural elements in domestic ruminant pancreas

The distribution and ontogeny of the galanin-like immunoreactive (Gal-IR) neural structures in the pancreas of cattle, sheep and goat were investigated immunohistochemically. The present study confirmed the previous findings on the immunolocalization of galanin both in the neural elements and endocrine cells of cattle, and reported for the first time its exclusive localization in the neural elements of sheep and goat. The frequency of Gal-IR nerve fibers and nerve cell bodies was high in cattle and low in sheep and goat. Their first detection was at the first fetal trimester in cattle and third trimester in sheep and goat. In cattle, a marked increase in the frequency of Gal-IR nerve fibers was observed from the third trimester to early neonatal stage followed by a decrease after three months postnatal. In contrast to the non-preferential distribution pattem in sheep, the Gal-IR nerve fibers in cattle and goat pancreas were predominantly associated with the acini, excretory ducts and blood vessels, but rarely detected in the pancreatic islets. The Gal-IR nerve cell bodies were observed as isolated bodies in the intra- and interlobular connective tissues and as a group within the intrapancreatic ganglia. At the vicinity of the nerve cell bodies, Gal-IR nerve fibers were observed. The present findings may suggest that: (1) galanin regulates pancreatic function as neurotransmitter/neuromodulator in ruminants; (2) galanin plays a more important role in large than in small ruminants; and (3) particularly in cattle, it exerts its most dramatic effect during perinatal development.

Functional and immunocytochemical evidence that galanin is a physiological regulator of human jejunal motility

The neuropeptide galanin has species-dependent effects on intestinal motility. It has a contractile effect on rat jejunal muscle while it relaxes guinea-pig ileum by inhibiting cholinergic transmission. Its effect on human gut motility has been unknown. Extensive work led to the discovery of selective galanin analogues such as M15 [galanin(1-12)-Pro-substance-P(5-11)], M35 [galanin(1-12)-Pro-bradykinin(2-9)-amide] that competitively inhibit various actions of galanin in the central nervous system. The present study was designed to examine the effect of galanin, M15 and M35 on longitudinal jejunal smooth muscle strips isolated from humans and rats, and to localize galanin-immunoreactivity in human jejunum. Galanin and ACh were equally effective in stimulating contractions of the isolated jejunal muscle: sigmoid curve fitting showed that maximal contractile response to galanin and ACh were 25.7+/-11.1 mN and 23.7+/-9.7 in humans, while 8.0+/-0.6 and 8.1+/-0.3 mN in rats, respectively. These effects of galanin were not inhibited by either atropine (5 x 10(-6) M) or tetrodotoxin (3 x 10(-6) M). The potency of galanin inducing the contractile actions were similar in humans and rats. Interestingly, neither M15 nor M35 (up to 10(-7) M) were able to inhibit the responses of the smooth muscle to galanin. However, both putative galanin receptor antagonists showed agonist effects in our experimental models. In accordance with the functional studies, both the longitudinal and the circular muscle layers were abundant in nerve fibers and varicosities showing galanin immunoreactivity. Our data suggest that galanin is a potent physiological regulator of jejunal contractions in humans. Its action on the jejunum, however, is mediated by galanin receptors that are different from those located in the central nervous system.

Peptidergic and aminergic neurotransmitters of the exocrine pancreas of the Houbara bustard (Chlamydotis undulata)

The immunochemical distribution of peptidergic and aminergic neurotransmitters in the exocrine pancreas of the Houbara bustard, Chlamydotis undulata, was determined. Immunoreactivity to choline acetyltransferase (ChAT), vasoactive intestinal polypeptide (VIP), and galanin (Gal) occurred mainly as varicose terminals in the walls of capillaries around the acini and arterioles within the connective tissue. Neuronal cell bodies immunoreactive to ChAT were infrequently observed. Neuropeptide Y (NPY), pancreatic polypeptide (PP), and somatostatin (Som) were observed mainly in intra-acinar cell bodies but nerve fibers immunoreactive to these neuropeptides were also seen along the basal surfaces of the acini. Immunoreactivity to NPY and PP was also discernible in cells of the pancreatic ducts. In addition, NPY occurred as varicose terminals in vessels around the ducts. SP occurred rarely in interacinar ganglia. The distribution of tyrosine hydroxylase (TH) was similar to that of ChAT and, in addition, the occasional TH immunoreactive intra-acinar neuronal cell body was observed. Neuronal nitric oxide synthase (nNOS) occurred in neuronal cell bodies among the acinar cells as well as nerve fibers along the bases of the acini. The potential roles of these peptidergic and aminergic neurotransmitters in the neurohormonal control of pancreatic secretion are discussed.

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.

Peptidergic hormones and neuropeptides, and aminergic neurotransmitters of the pancreatic islets of the Houbara bustard (Chlamydotis undulata)

Immunoreactivity to insulin (Ins), somatostatin (Som), glucagon (Glu) and pancreatic polypeptide (PP) was found in 70%, 22%, 15% and 11% respectively of Houbara pancreatic endocrine islet cells. Whilst Ins occurred centrally and SOM was observed both in peripherally and centrally located islets, the other hormones were localised in peripheral islet cells; Som was also observed in neuronal cell bodies and nerve fibres. In addition, the islet cells contained substance P (SP) (65%) in the centre and vasoactive intestinal polypeptide (VIP) (2%) at the periphery. Immunoreactivity to choline acetyltransferase (ChAT), VIP and galanin (Gal) occurred in the walls of blood vessels located mainly at the periphery of islets. Occasionally, VIP and Gal immunoreactive varicose nerve terminals and ChAT immunoreactive cell bodies were also observed in the centre of islets. SP neuronal cell bodies were not observed but prominent SP immunoreactive varicose terminals were discernible in capillary walls within the islets. Neuropeptide Y (NPY) immunoreactive neurons were detected in neuronal cell bodies located mainly peripherally. Neuronal nitric oxide synthase (nNOS) immunoreactivity occurred in neuronal cell bodies and nerve fibres mainly at the periphery and also in centrally located islet endocrine cells. Immunoreactivity to tyrosine hydroxylase (TH) was similar in distribution to that of ChAT. In comparison with other avian species, the islets of the dorsal pancreatic lobe of the bustard contain all the peptidergic hormones normally present in the islets of other avian species, but are not segregated into dark A and light B cells. Many of the insulin containing cells also contained SP. The islets also contained several neuropeptides which are probably involved in their regulation.

Characterization and localization of galanin receptors in human entorhinal cortex

The neuropeptide galanin (GAL) has a widespread distribution throughout the human cortex. The entorhinal cortex (ENT) plays a crucial role in the transfer of cortico-cortical information related to memory and displays severe degeneration in Alzheimer's disease (AD). However, very little is known about the pharmacology of the GAL receptor (GALR) in normal human ENT. Therefore, we pharmacologically visualized their distribution and characterized GALRs using in vitro receptor autoradiography and radioligand binding assays. Autoradiograms revealed intense GALR labeling, mainly in the substantia innominata, hypothalamus, the bed nucleus of the stria terminalis and within layers 2 and 4 of the ENT. Kinetic experiments showed that saturation of GALR sites by [125I]GAL (human) (hGAL) occurred within 2 h and that this binding readily reversed in the presence of a GTP analog, but not in the presence of excess unlabeled hGAL. Analysis of [125I]hGAL binding data from saturation experiments gave KD values of 98.6+/-21.6 pM, Bmax values of 52.9+/-32.4 fmol/mg protein and identified a high and low affinity state of the GALR. The presence of 5'-guanylylimidodiphosphate (GppNHp) or NaCl reduced the agonist labeling of hGALR in ENT membranes.

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.

Immunohistochemical localization of galanin in bovine reproductive organs

The vagina, uterus and oviduct were shown to receive galanin immunoreactive (GAL-IR) nerve fibres, the number of which varied between particular organs. In the ovary, GAL-IR nerves were absent. A small number of these nerves were located in the layers of the oviduct. A moderate number of GAL-IR nerves were situated in the body and uterine horns, whereas the uterine cervix and vagina wall contained a large number of GAL-IR nerve fibres, evenly distributed throughout particular membranes of the organs. GAL-IR nerves were found to contain, simultaneously, either vasoactive intestinal polypeptide (VIP), substance P (SP) or Leu5-enkephalin (ENK). Many of the GAL-IR nerves contained tyrosine hydroxylase (TH). A group of GAL-IR nerves that did not possess immunoreactivity to VIP, SP, ENK or TH was also observed.

Existence and co-existence of vasoactive substances in nerve fibres supplying the abdomino-pelvic arterial tree of the female pig and cow

The occurrence and co-localization of several presumed vasoactive neuropeptides, serotonin, and catecholamine-synthesising enzymes--tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (D beta H) and phenylethanolamine-N-methyltransferase (PNMT)--were investigated in perivascular nerves supplying the systemic and distributing arteries of the abdomino-pelvic arterial tree of the female pig and certain arteries supplying female reproductive organs in the cow. As revealed by single immunofluorescence, perivascular axons immunoreactive for TH, D beta H, neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP) and Leu-enkephalin (LENK) occurred in both species examined, whereas galanin-immunoreactive (GAL-IR) nerve fibres were found exclusively in the pig. PNMT-, serotonin-, dynorphin A-, alpha-neoendorphin-, bombesin- or cholecystokinin-IR nerve terminals were not observed. The following classes of perivascular nerve fibres might be distinguished in the present study: 1) noradrenergic (i.e. TH/D beta H-IR), 2) NPY-, 3) GAL- (pig only), 4) LENK-, 5) VIP-, 6) SP-, 7) VIP/NPY-, 8) SP/CGRP-, 9) SP/GAL- (pig only), 10) SP/VIP- (cow only), 11) TH/D beta H/NPY- and 12) TH/D beta H/NPY/LENK-IR. Distinct differences in the distribution of LENK- and SP-IR axons around particular parts of the studied arterial tree in individual species were also observed. The present data indicate that the abdomino-pelvic arterial tree of the pig and cow receive perivascular nerve fibres that exhibit diverse chemical codes, and that different chemical coding of perivascular nerve fibres in individual species may depend on the target organ of the particular artery.

Canine galanin: sequence, expression and pancreatic effects

To determine if dog galanin is a potent inhibitor of dog insulin secretion we determined its primary structure from its cloned cDNA, evaluated its expression in celiac ganglia and determined its effect on islet hormone secretion. The predicted amino acid sequence differs from the other known species of galanin by three to six amino acids in the C-terminal half of the molecule. In situ hybridization revealed the presence of dog progalanin mRNA in every neuronal cell body in the dog celiac ganglion. The predicted dog galanin peptide was synthesized and infused i.v. at 0.25, 2.5, 25 or 250 pmol/kg/min. It potently inhibited insulin secretion, less potently inhibited pancreatic somatostatin release and stimulated glucagon secretion, similar to the effects of porcine galanin in the dog. In summary, dog galanin is expressed in the neuronal cell bodies that innervate the pancreas and the sequence of the dog galanin preserves the potent insulin inhibitory part of the galanin molecule. These data support the hypothesis that galanin is a sympathetic neurotransmitter in dog pancreas.

Mechanism of galanin's inhibitory action on pancreatic enzyme secretion: modulation of cholinergic transmission--studies in vivo and in vitro

This study examined the inhibitory mechanism of galanin, a 29 amino acid polypeptide on pancreatic enzyme secretion in anaesthetised rats, isolated pancreatic acini, and lobules. Urethane anaesthetised rats with pancreatic fistulas pretreated with 3-0-methyl-glucopyranose (500 mg/kg/h) were stimulated with an intravenous bolus of 2-deoxyglucose (2-DG) (75 mg/kg). Maximal amylase secretion was mean (SEM) 274 (19)% of basal secretion. Atropine (150 micrograms/kg/h) and galanin (10 nmol/kg/h) almost completely inhibited 2-DG stimulated amylase secretion suggesting an inhibition of cholinergic transmission. To further test this possibility this study investigated the effect of galanin on carbachol and cholecystokinin stimulated amylase release from isolated pancreatic acini. Galanin did not suppress carbachol or cholecystokinin stimulated amylase release, indicating that galanin inhibits exocrine secretion by indirect mechanisms. The cholinergic pathway was assessed by using pancreatic lobules containing intrapancreatic neurons. Veratridine, a sodium channel activator, dose dependently stimulated amylase release. Veratridine (100 microM) stimulated amylase release by 411 (10)% of basal secretion. Atropine (1 microM) or tetrodotoxin (1 microM) almost completely blocked veratridine stimulated amylase release. Galanin (1 microM) significantly inhibited veratridine stimulated amylase release with a maximal inhibition of 50% (p < 0.05). In addition, when lobules were incubated with [3H]-choline, galanin significantly (p < 0.05) inhibited veratridine stimulated release of newly synthesised [3H]-acetylcholine. Thus galanin inhibits pancreatic secretion by inhibiting cholinergic transmission. These studies show that galanin inhibits rat pancreatic enzyme secretion by an indirect mechanism by reducing cholinergic transmission.

Tissue-specific reduction of galanin content in the pancreas in alloxan diabetes in the mouse

Galanin inhibits insulin secretion and has been proposed to function as a sympathetic neurotransmitter in the endocrine pancreas in some species, for example in the dog. In this study, pancreatic and adrenal gland galanin content were measured following experimental diabetes induced by alloxan in mice. Three days after administration of alloxan (70 mg kg-1, i.p.) in normal mice, pancreatic content of galanin-like immunoreactivity (GLIR) was reduced to 65 +/- 11% of that in untreated controls (P < 0.01), whereas adrenal gland GLIR was unchanged. Similarly, 8 days after alloxan administration, pancreatic GLIR was reduced (P < 0.002), whereas adrenal gland GLIR was unaffected. Pancreatic GLIR also inversely correlated with plasma glucose levels (r = -0.5055, P < 0.005). To distinguish between the direct effects of alloxan vs. indirect metabolic effects induced by the drug, alloxan-diabetic mice were treated with insulin twice daily, which normalized the plasma glucose levels (7.6 +/- 0.3 mmol l-1). Pancreatic GLIR was then not significantly different from controls. Thus pancreatic but not adrenal gland GLIR content is reduced in alloxan-induced diabetes in mice. The data support a role for galanin as a pancreatic sympathetic neurotransmitter which may participate in the metabolic alterations seen in alloxan diabetes in mice.

Galanin analogues: agonist and antagonist

23 galanin-related peptides were synthesized by solid phase technology or conventional solution method. The purity of the products was carefully assessed by routine analytical criteria. Using these synthetic peptides, we have investigated the effects of galanins and structurally modified galanin peptides on glucose-stimulated insulin release using the isolated perfused rat pancreas, gastrin and somatostatin release using the isolated perfused rat stomach, the neurally-evoked muscle contractions in guinea pig ileum and the C-fiber response in the isolated spinal cord of the new born rat. The results suggest that the galanin amino-terminal 1-15 sequence is crucial for its activity in the above four systems. With the goal of developing a specific antagonist of galanin, synthetic galanin (1-15) analogues [D-Thr6,D-Trp8,9]galanin(1-15)ol, and [D-Trp8,9]galanin(1-15)ol were found to be a potent antagonist for inhibitory effect of galanin on glucose-induced insulin release.

On the effects of human galanin in man

Human galanin was recently isolated and sequenced and was found to differ from porcine galanin, hitherto used for studies in humans, in several important respects. We therefore synthesized and purified human galanin and infused it i.v. at a rate of 74 pmol.kg-1.min-1 into six healthy volunteers for 60 min during a hyperglycaemic clamp. The clamp was achieved by i.v. infusion of glucose at a rate which in a control experiment had been demonstrated to maintain the plasma glucose level at 12-13 mmol/l for 90 min. Galanin concentrations reached a plateau of approximately 1500 pmol/l throughout the infusion as opposed to pre-infusion and control levels of 20-30 pmol/l. The glucose levels obtained in the two experiments were indistinguishable. Plasma levels of C-peptide and insulin increased significantly in both experiments and the dynamic concentration curves were almost identical. Glucagon concentrations in plasma decreased significantly and similarly. Growth hormone levels, however, increased eight-fold during galanin infusions. Galanin was eliminated from plasma with a half-life of 3.7 +/- 0.4 min, similar to that of porcine galanin. It is concluded that human galanin powerfully stimulates growth hormone secretion in man, but has no effect on pancreatic endocrine secretion or glucose metabolism in the concentrations obtained in this study.

Release of immunoreactive somatostatin, vasoactive intestinal polypeptide (VIP), and galanin during propulsive complexes in isolated pig ileum

We studied the release of immunoreactive somatostatin, VIP, and galanin during net aboral propulsive complexes (NAP) in isolated, perfused, 80-cm segments of porcine ileum. Net aboral propulsive complexes were induced by controlled infusion of liquid (perfusion medium, 3.5 ml/min) into the proximal opening of the ileum segment. In response to liquid infusion, the ileum segments generated propulsive complexes rapidly propagating along the entire segment in the aboral direction, resulting in emptying of the luminal contents. The NAPs occurred with an average interval of 7 minutes. The concentrations of galanin, somatostatin, and VIP in the venous effluent, which in control experiments without luminal infusion did not change, increased significantly (by 63.6 +/- 23.7%, 43.8 +/- 31.8%, and 38.8 +/- 14.6%, respectively) during NAPs and emptying. Atropine (10(-6) mol/l) and hexamethonium (10(-5) mol/l) abolished both NAP generation and peptide responses. It is concluded that the enteric neuropeptides, somatostatin, VIP, and galanin, all of which have pronounced intestinal motor effects, may participate in the generation of net aboral propulsive complexes in the ileum of the pig, possibly mainly in descending relaxation.

Galanin message-associated peptide (GMAP)- and galanin-like immunoreactivities: overlapping and differential distributions in the rat

Using the indirect immunofluorescence method the distribution of galanin message associated peptide (GMAP)- and galanin-like immunoreactivities (LI) was compared in brain, intestine and some endocrine tissues of rat. In general, neurons in the peripheral and central nervous system contained both immunoreactivities. However, in retina the cones were GMAP-positive but galanin-negative. A strong GMAP-LI was observed in the prolactin cells in the anterior lobe of the pituitary and in the insulin cells in the islets of Langerhans in the pancreas, whereas incubation with galanin antiserum resulted in staining of fewer cells (anterior pituitary) or a very weak fluorescence (pancreas). The results show that most neurons express both GMAP- and galanin-LI, but raise the possibility that in some systems there is a tissue specific, posttranslational differential processing of preprogalanin.

Effects of noradrenaline and galanin on duodenal motility in the isolated perfused porcine pancreatico-duodenal block

The influence of neurotransmitters on gastrointestinal motility is different in different segments of the gastrointestinal tract. To clarify the regulation of duodenal motility, the aim of the present study was to investigate the effects of alpha-adrenoceptor agonism and blockade and of galanin on duodenal motility. The study was undertaken in the isolated perfused porcine pancreatico-duodenal block. The agents under investigation were administered arterially. Duodenal motility was measured by means of a low-compliance perfusion system using an intraluminal catheter. In addition the concentration of galanin was measured in the portal effluent. We found that spontaneous motility was abolished by noradrenaline by an effect that was counteracted by the alpha 2-adrenoceptor antagonist idazoxan. In contrast, the selective alpha 1-adrenoceptor antagonist prazosin did not influence the effect of noradrenaline. Galanin, like noradrenaline, abolished duodenal motility. Furthermore, the concentration of galanin in the portal effluent was decreased by noradrenaline by an alpha 2-adrenoceptor mediated mechanism. We conclude that alpha 2-adrenoceptor activation and galanin inhibit duodenal motility and that the release of galanin from the pancreatico-duodenal preparation is reduced by alpha 2-adrenoceptors.

Extrinsic control of the release of galanin and VIP from intrinsic nerves of isolated, perfused, porcine ileum

By immunohistochemistry galanin-like immunoreactivity and vasoactive intestinal polypeptide (VIP)-like immunoreactivity were found in nerve cell bodies mostly in the submucous plexus and in nerve fibres in the mucosa, submucosa and muscularis including the myenteric plexus of the porcine ileum and were found to co-exist in most of these structures. Using isolated, perfused porcine ileum we studied the release of galanin and VIP in response to electrical stimulation of the mixed periarterial nerves or to intraarterial infusions of different neuroactive agents. Nerve stimulation (4-10 Hz) inhibited the basal release of galanin and VIP from the ileum (to 69 +/- 6 and 62 +/- 6% of basal release). After infusion of the alpha-adrenergic blocker, phentolamine, (10(-6) M) electrical stimulation increased the release of both galanin and VIP (to 140 +/- 12 and 133 +/- 13% of basal output). This increase was abolished by atropine (10(-6) M) and by hexamethonium (3.10(-5) M). Infusion of norepinephrine (10(-6) M) inhibited, whereas acetylcholine (10(-6) M) stimulated the release of both peptides. The effect of the latter was abolished by atropine. The inhibitory effect of nerve stimulation was not influenced by atropine. Our results suggest that the galanin- and VIP-producing intrinsic neurons receive inhibitory signals by noradrenergic nerve fibers and stimulatory signals mediated by cholinergic nerves, possibly via a cholinergic interneuron.

Structural requirements for galanin inhibition of pentagastrin-stimulated gastric acid secretion in conscious rats

The effects of rat galanin, together with a number of its N- and C-terminal fragments, on pentagastrin-stimulated gastric acid secretion were studied in conscious rats equipped with chronic gastric fistulas. Similarly to its porcine counterpart studied previously, at a dose of 3 nmol/kg per h rat galanin was a potent inhibitor of gastric acid secretion. The N-terminal fragments, rat galanin-(1-10) and -(1-15), retained about 60% of the inhibitory potency of the whole galanin sequence whilst the C-terminal fragments, rat galanin-(2-29), -(3-29) and -(9-29), were unable to produce significant inhibition over comparable dose ranges. Surprisingly, however, simply acetylating the alpha-amino group in position 9 of rat galanin-(9-29) restored almost full gastric acid inhibitory activity in a homologous rat model. We speculate that this could be due to a favorable conformational effect on the C-terminal region produced by alpha-acetylation. These results also suggest that structural features within either the N-terminal or C-terminal regions of rat galanin are able to elicit this particular biological response. One possible explanation for this could be the involvement of more than one rat galanin receptor having different ligand recognition requirements.

Circulating galanin: origin, metabolism, and pharmacokinetics in anesthetized pigs

The concentration of galanin-like immunoreactivity (GAL-LI) was 12.9 +/- 0.9 pmol/l in porcine arterial plasma (n = 9) and ranged from 1 to 14 pmol/g in extracts of porcine gastrointestinal tract (n = 5), the colon being the richest gut segment. A significant (P less than 0.05) arteriovenous concentration difference of circulating endogenous GAL-LI occurred across the kidney (15.1 +/- 2.3 vs. 6.2 +/- 0.5 pmol/l) and a hind leg (15.7 +/- 2.5 vs. 10.2 +/- 1.0 pmol/l), whereas a negative gradient was observed across the intestine (12.5 +/- 2.0 vs. 17.7 +/- 3.3 pmol/l) of anesthetized pigs. Passage through the brain, liver, or lungs did not change the concentration of endogenous GAL-LI significantly. During basal circumstances, the major source of circulating GAL-LI is therefore the gut. During infusion of 20 pmol.kg-1.min-1 of synthetic porcine galanin, a significant extraction occurred across the kidney (64.8 +/- 4.3%), hind leg (20.3 +/- 3.8%), and liver (19.7 +/- 4.3%). The overall metabolic clearance rate was 37.8 +/- 3.7 ml.min-1.kg-1. The half-life of galanin in plasma was 4.6 +/- 0.3 min, and the apparent distribution space was 255.6 +/- 31.4 ml/kg. Incubation studies in vitro showed that the concentration of galanin, added to blood and plasma at 37 degrees C, was halved in 1 h, unless stabilized with EDTA and aprotinin.

Stimulus-specific inhibition of insulin release from rat pancreas by both rat and porcine galanin

The effect of the neuropeptide galanin on insulin and somatostatin secretion in the rat was studied under various conditions. In the perfused rat pancreas, insulin secretion stimulated by arginine, but not cholecystokinin-8 (CCK-8) or acetylcholine (ACh) was inhibited by both rat and porcine galanin, whereas ACh-stimulated somatostatin release was inhibited by rat but not porcine galanin. Neither arginine nor CCK-8 significantly altered somatostatin secretion and galanin was without effect under those conditions. Gastric inhibitory polypeptide-stimulated insulin release from cultured mixtures of purified rat beta- and non-beta-cells was inhibited by rat and porcine galanin in a concentration-dependent and equipotent manner. The results suggest that the inhibitory effect of galanin on insulin and somatostatin secretion may be stimulus-specific and species-specific.

Isolation and primary structure of pituitary human galanin, a 30-residue nonamidated neuropeptide

Galanin (Gal), a 29-amino acid C-terminally amidated neuropeptide, is widely distributed throughout the central and peripheral nervous system. The primary structures of rat and bovine Gals were derived from the cDNA sequences of their precursors. To elucidate the structure of human Gal (hGal), we extracted 280 postmortem pituitaries in trifluoroacetic acid and purified hGal binding activity, by three successive HPLC steps, to homogeneity based on a radioreceptor assay. The primary structure of hGal was determined by automatic Edman degradation to be Gly-Trp-Thr-Leu-Asn-Ser-Ala-Gly-Tyr-Leu-Leu- Gly-Pro-His-Ala-Val-Gly-Asn-His-Arg-Ser-Phe-Ser-Asp-Lys-Asn-Gly-Leu-Thr- Ser-COOH. The structure was confirmed by plasma desorption time-of-flight mass spectrometry, revealing a mass of 3156.1. Compared to the 29-residue porcine, rat, and bovine Gals, hGal uniquely comprises 30 amino acids possessing an additional nonamidated serine residue as C terminus. The nonamidated carboxylic group at the C terminus was proven by synthesis of amidated and nonamidated hGal and by mass spectrometry after selective methylation of all free carboxylic groups. Synthetic hGal possesses full biological activity on isolated rat fundus muscle strips.

Galanin-induced inhibition of insulin secretion from rat islets: effects of rat and pig galanin and galanin fragments and analogues

The 29-amino acid neuropeptide galanin occurs in intrapancreatic nerves and inhibits insulin secretion. To study the structure-activity relations of galanin, we examined the effects of pig and rat galanin, three galanin fragments (galanin-(1-11), galanin-(1-16) and rat galanin-(17-29) and four galanin analogues ([Ala2]pig galanin, [Ala2]rat galanin, [D-Trp2]rat galanin and [D-Trp2]galanin-(1-16] on glucose-stimulated insulin secretion from isolated rat islets. Pig and rat galanin and galanin-(1-11) equipotently inhibited glucose-stimulated (8.3 mM) insulin secretion at and above 10(-7) M (P less than 0.05), whereas galanin-(1-16), inhibited insulin secretion at 10(-6) M (P less than 0.01). In contrast, the C-terminal rat galanin-(17-29) and the galanin analogues did not influence insulin secretion. Thus, rat and pig galanin are equipotent in inhibiting glucose-stimulated insulin secretion from rat islets. The active site resides in the N-terminal part of the molecule. Furthermore, the binding of galanin to its receptor depends on structural characteristics governed by the N-terminal position and in particular by the Trp2 residue.

Neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP), but not galanin, are autonomic cotransmitters in the porcine pancreas

The neuropeptide galanin has been identified as a potential sympathetic cotransmitter in the canine pancreas. Immunoreactive galanin, also present in nerve fibers of the pig pancreas, was therefore measured in the effluent from isolated perfused pig pancreas with preserved sympathetic (splanchnic) or parasympathetic (vagal) innervation with radioimmunoassays directed against both the N-terminus and the C-terminus of galanin. Electrical vagus stimulation increased the pancreatic exocrine secretion, the secretion of insulin and glucagon, and the release of VIP, but did not influence galanin release. Splanchnic nerve stimulation increased perfusion pressure and glucagon secretion, inhibited insulin secretion, and increased the release of NPY, but galanin release was not affected. We conclude that the pancreatic galanin nerve fibers belong neither to the sympathetic nor to the parasympathetic divisions of the efferent nerve supply to the pig pancreas.

Galanin and neuropeptide Y in chromaffin granules from the guinea-pig

We have examined the subcellular distribution of galanin-like immunoreactivity, neuropeptide Y-like immunoreactivity and the catecholamines noradrenaline and adrenaline in the adrenal medulla from guinea-pigs. By differential centrifugation of the adrenal medulla homogenate the neuropeptides as well as the catecholamines sedimented in a 10,000 g pellet. This pellet was resuspended and further examined in discontinuous and continuous density gradients. In the discontinuous gradient the catecholamines peaked in the heavy bottom fraction, assumed to contain chromaffin granules. Galanin-like immunoreactivity and neuropeptide Y-like immunoreactivity were also enriched in this fraction. However, both neuropeptides showed high levels of sedimentable material also in a fraction of intermediate density. In the continuous density gradient, the sum of sedimentable and soluble catecholamines showed peak values in two fractions corresponding to 1.07 and 1.47 M sucrose, respectively. The NA peak in the denser fraction was more pronounced than the corresponding A peak. Galanin-like immunoreactivity showed only one peak, in the fraction corresponding to 1.07 M sucrose. The data suggest that galanin-like immunoreactivity and neuropeptide Y-like immunoreactivity are partly stored with catecholamines in chromaffin granules. However, galanin-like immunoreactivity and neuropeptide Y-like immunoreactivity was also found in fractions lighter than those containing the bulk of the catecholamines.

Release of galanin from isolated perfused porcine adrenal glands: role of splanchnic nerves

We found a high concentration of galanin in extracts of porcine adrenal glands (114 pmol/g). By immunohistochemistry, galanin was localized to groups of medullary cells previously shown to produce norepinephrine. To study mechanisms for the release of galanin, we developed the following in vitro model: isolated perfused porcine adrenals with intact splanchnic nerve supply. When the nerves were electrically stimulated, epinephrine and norepinephrine secretion increased 276- and 291-fold, respectively, and galanin release increased up to 1,300-fold. Acetylcholine at 10(-6) M stimulated galanin release, and hexamethonium almost abolished the response to nerve stimulation. Galanin infusions had no effect on epinephrine and norepinephrine secretion in concentrations of 10(-8) and 10(-7) M, but increased both cortisol and aldosterone secretion (P less than 0.05). Splanchnic nerve stimulation in anesthetized pigs increased the concentration of galanin in the caval vein but not in arterial plasma. It is concluded that galanin, coreleased with catecholamines from the adrenal glands, may have endocrine functions but that galanin may also have local regulatory functions in the adrenals.

Human galanin: primary structure and identification of two molecular forms

From acid/ethanol extracts of surgical specimens of human large intestine we isolated two peptides, in approximately equal amounts, that reacted with an antiserum against porcine galanin. By amino acid analysis, sequence analysis and mass spectrometry, the larger of the two peptides was found to consist of 30 amino acid residues, the sequence of which was identical to that of porcine galanin except for the following substitutions: Val16, Asn17, Asn26, Thr29 and Ser30. Unlike porcine galanin, the carboxy-terminus was not amidated. The smaller peptide corresponded to the first 19 amino acid residues counted from the N-terminus of the 30 residue peptide (again without amidation). The structural analysis was repeated on another batch of tissue with identical results. By HPLC analysis of extracts of specimens from a further 4 patients, the same peptides were identified. Thus, human galanin includes two peptides of 19 and 30 amino acids that share the sequence of the N-terminal 15 residues with other mammalian galanins, but exhibit characteristic differences in the remaining part of the molecules.

Galanin-immunoreactive nerves in the mouse and rat pancreas

Galanin-containing nerve fibers have previously been observed in the human, dog, and pig pancreas. Whether the mouse and rat pancreas also contain galanin nerve fibers has been a matter of debate. Therefore, we examined the distribution of galanin in the mouse and the rat pancreas. Further, the possible localization of galanin to adrenergic nerves was studied using sequential immunostaining for galanin and tyrosine hydroxylase (TH). In the mouse pancreas, numerous galanin-immunoreactive (GIR) nerve fibers occurred around blood vessels. They were less numerous in the exocrine parenchyma and in association with the islets. In contrast, in the rat pancreas, only a few GIR nerves were found. They were located around blood vessels and scattered in the exocrine parenchyma. Occasionally, GIR nerves were also observed in the islets. There was a dense distribution of TH-immunoreactive fibers in both the mouse and the rat pancreas. Sequential immunostaining revealed co-localization of galanin and TH immunoreactivity in nerve fibers in both the mouse and the rat pancreas. Following chemical sympathectomy using 6-hydroxydopamine (6-OHDA), not all GIR nerves disappeared. In the mouse pancreas a remaining population of galanin nerves was found around blood vessels, and occasionally in the islets. In the rat pancreas, a few GIR nerves were seen also after chemical sympathectomy. We conclude that intrapancreatic GIR nerves also occur in the mouse and the rat. These findings suggest that many of the GIR nerves are adrenergic but that non-adrenergic, possibly intrinsic or sensory GIR nerves exist as well in both the mouse and the rat pancreas.

Neural control of islet function by norepinephrine and sympathetic neuropeptides

It is clear that the sympathoadrenal system has a role in the regulation of endocrine pancreatic function and that the sympathetic nerves of the pancreas can change pancreatic hormone secretion to increase the availability of metabolic fuels. It seems likely that the classical sympathetic neurotransmitter, NE, acts in concert with peptide co-transmitters, such as galanin and NPY. Each is released during the stimulation of pancreatic sympathetic nerves and each is capable of influencing either islet function or pancreatic blood flow. There is considerable indirect evidence that the sympathetic innervation of the pancreas is activated during acute stress and influences the endocrine pancreas. However, proving such a physiologic role is difficult because of redundant mechanisms that influence the secretion of the metabolically-crucial hormones, insulin and glucagon. Such definitive proof therefore awaits the development of new techniques to dissect and dissociate these mechanisms.

Galanin inhibits insulin and corticosterone release after injection into the PVN

The neuropeptide galanin (GAL, 1 microgram/0.3 microliters) was injected into the paraventricular nucleus (PVN) at two different times of the 12:12 h light/dark cycle, namely 2 h before the dark ('pre-dark') and before the light ('pre-light') periods. Blood samples were collected 15 min after injection and examined for serum levels of insulin (INS), corticosterone (CORT) and glucose (GLUC). Results indicate that PVN GAL injection in the pre-dark period strongly inhibits both CORT and INS release but has no effect on GLUC levels. These hormone changes, however, were not detected in the blood samples collected in the pre-light period. At this time, baseline levels of CORT were significantly lower than in the pre-dark period, while INS and GLUC levels were generally similar at both time periods. These results indicate that the effects of PVN GAL on CORT and INS secretion are inhibitory in nature and are temporally linked to the diurnal cycle.