Isolation and cDNA cloning of a novel galanin-like peptide (GALP) from porcine hypothalamus

Galanin is a widely distributed neuropeptide with a variety of physiological functions. Three galanin receptor subtypes, GALR1, GALR2, and GALR3, have been reported. We isolated a novel galanin-like peptide (GALP) from porcine hypothalamus by observing its activity for increasing [(35)S]GTPgammaS binding to a membrane preparation of GALR2-transfected cells. The peptide had 60 amino acid residues and a non-amidated C terminus. The amino acid sequence of GALP-(9-21) was completely identical to that of galanin-(1-13). A cloned porcine GALP cDNA indicated that GALP was processed from a 120-amino acid GALP precursor protein. The structures of rat and human GALP-(1-60) were deduced from cloned cDNA, which indicated that the amino acid sequences 1-24 and 41-53 were highly conserved between humans, rats, and pigs. Receptor binding studies revealed that porcine GALP-(1-60) had a high affinity for the GALR2 receptor (IC(50) = 0.24 nM) and a lower affinity for the GALR1 receptor (IC(50) = 4.3 nM). In contrast, galanin showed high affinity for the GALR1 (IC(50) = 0.097 nM) and GALR2 receptors (IC(50) = 0.48 nM). GALP is therefore an endogenous ligand that preferentially binds the GALR2 receptor, whereas galanin is relatively non-selective.

Purification and characterization of galanin and scyliorhinin I from the hybrid sturgeon, Scaphirhynchus platorynchus x Scaphirhynchus albus (Acipenseriformes)

The sturgeons (order Acipenseriformes) are extant representatives of a group of ancient Actinopterygian (ray-finned) fish. Galanin and scyliorhinin I (a tachykinin with limited structural similarity to mammalian substance P) have been isolated from an extract of the gastrointestinal tract of a sturgeon (an F1 hybrid between the shovelnose sturgeon, Scaphirhynchus platorynchus, and the pallid sturgeon, Scaphirhynchus albus). The primary structure of sturgeon galanin (Gly-Trp-Thr-Leu-Asn-Ser-Ala-Gly-Tyr-Leu10-Leu-Gly-Pro-His-Ala-Val -As p-Gly-His-Arg20-Ser-Leu-Ser-Asp-Lys-His-Gly-Leu-Pro.NH2) contains only two amino acid substitutions (Ser23 --> Asn and Pro29 --> Ala) compared with galanin from the bowfin, Amia calva (Amiiformes), but five amino acid substitutions compared with galanin from the trout (Teleostei). Similarly, the sturgeon tachykinin (Ser-Lys-Tyr-His-Gln-Phe-Tyr-Gly-Leu-Met.NH2) contains only one amino acid substitution (Tyr3 --> Ser) compared with scyliorhinin I previously isolated from bowfin stomach but five amino acid substitutions compared with trout substance P. The data support the hypothesis that the Acipenseriformes and the basal Neopterygians (gars and bowfin) share a close phylogenetic relationship.

Galanin-like immunoreactivity in the sea cucumber Holothuria glaberrima

Galanin, a neuropeptide of 29 amino acids originally purified from porcine small intestine, has been found in most vertebrate groups, where it is present in both the central and peripheral nervous systems. In this study, galanin-like immunoreactivity was detected in an invertebrate, the sea cucumber Holothuria glaberrima. In this organism, fibers and cells expressing galanin-like immunoreactivity were found in the enteric nerve plexuses of the esophagus, and large and small intestine, particularly in the serosal layer. Immunoreactivity was also found in the ectoneural portion of the radial nerve and in nervous elements within the body wall. Preabsorbtion tests indicated that the observed immunoreactivity was not due to cross-reactivity of the antibody with other peptides also found in the intestinal plexuses. The immunoreactivity to galanin was quantified in various tissues using radioimmunoassay and partially characterized with high performance liquid chromatography. These results show that although the holothurian peptide shows common immunological determinants with porcine galanin, it differs with regard to certain biochemical properties.

[Galanin, a new neuropeptide. Review]

Galanin is a 29 amino-acid peptide originally isolated from porcine intestine. It is synthesized as part of a large precursor peptide the preprogalanin. Immunological studies has showed that there is interspecies conservation of the N terminal portion although the C-terminal portions has a little of immunoreactivity. Galanin has a number of pharmacological properties in whole animals and isolated tissues. Galanin contracts isolated preparation from rat fundus, ileum, colon and urinary bladder. Direct administration of galanin (pGal) into the rat third ventricule stimulates food intake, increases plasma growth hormone and prolactin levels and decrease dopamine levels in the median eminence. Intravenous infusion in dog and humans induce a hyperglycemia and glucose intolerance and inhibits the insulin, somatostatin and pancreatic polipeptide secretion from pancreas. Galanin is a estrogen-stimulated peptide. Estrogens increase dramatically the synthesis of their mRNA and the peptide in the rat pituitary. Galanin-like immunoreactivity is widely distributed in several mamalian species including humans. In the central nervous system it was found in medium emminence, hypothalamus, arcuate nucleus etc. Its localization in neurosecretory granules suggest that galanin functions as a neurotransmitter. The detection of a Gal-immunorectivity in the plasma after 17 beta estradiol stimulation suggests that galanin has a distal target and therefore, may be an additional anterior pituitary hormone. Galanin has been localized in reproductive tissues and this suggests that it may play an estrogen mediated role in the hypothalamic and pituitary function. However, the molecular mechanisms involved in their function remain to be studied.

An oviposition-inducing peptide: isolation, localization, and function of avian galanin in the quail oviduct

It is well established that avian oviposition is regulated, at least partly, by a neurohypophysial hormone, arginine vasotocin, and ovarian hormones, prostaglandins, are regulated through mechanisms of the induction of uterine contractions. Although abundant nerves are terminated in the musculature in the uterine and vaginal oviduct regions, limited information is available on the neuronal control mechanism of avian oviposition. To identify the oviduct factor that plays an important role in the induction of oviposition as a neurotransmitter or a neuromodulator, a study was conducted to isolate the bioactive substance involved in the vaginal and uterine contractions from mature oviducts of the Japanese quail. Acetic acid extracts of 200 quail oviducts were forced through disposable C-18 reversed-phase cartridges, and then the retained material was subjected to the reversed-phase and cation-exchange HPLC purifications. A purified bioactive substance showed a single peak on the reversed-phase HPLC and was further subjected to amino acid sequence analysis and molecular weight presumption. The substance was identified as avian galanin, which was previously isolated from chicken intestine. The synthetic peptide enhanced contractions of both the vagina and the uterus in a manner similar to the native peptide, and the threshold concentrations were 10(-9) - 10(-8) M in the vagina and 10(-10) - 10(-9) M in the uterus. An intraperitoneal injection of the synthetic peptide significantly evoked quail oviposition during 5 min after injection. Immunohistochemical analysis with the anti-galanin serum revealed that abundant immunoreactive fibers were distributed in muscle layers of the vagina and the uterus. The immunoreaction examined in these regions was completely inhibited by preincubation of the antibody with synthetic peptide. These results suggest that avian galanin in the oviduct evokes oviposition through mechanisms of the induction of uterine and vaginal contractions. This peptide may contribute as a neurotransmitter or a neuromodulator to avian oviposition.

High-performance separation methods in the analysis of a new peptide family: the galanins

An analytical investigation of a new peptide family, the human galanins and their fragments, was carried out by reversed-phase HPLC, capillary zone electrophoresis (CZE) at different pH values and micellar electrokinetic capillary chromatography (MECC) in phosphate-borate-sodium dodecyl sulphate buffer. None of the methods seems to be superior to the others. The complementary nature of the electrophoretic methods is obvious when the profiles of peptides are compared; impurities not separated by HPLC are separated by CZE or MECC and vice versa. With these three different separation methods, a more complex analytical control of the synthetic work can be achieved.

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.

Galanin modulates sphincter of Oddi function in the Australian brush-tailed possum

The neuropeptide galantin (GAL) is found in neurons in the biliary tract of several species. We mapped the distribution of GAL-like immunoreactive nerve (GAL-LI) fibers in the sphincter of Oddi of the Australian brush-tailed possum by immunohistochemistry. The pharmacological effects of GAL in vitro and in vivo were studied by measuring sphincter of Oddi muscle strip contractility and transsphincteric flow, respectively. Muscle layers, and ganglionated and perivascular plexuses, contained GAL-LI nerve fibers. Exogenous GAL caused a concentration-dependent (10(9)-10(-6)M) increase in the spontaneous longitudinal but not circular muscle contractions. At 10(-6) M GAL, contractile activity was elevated two- to fourfold. This response was tetrodotoxin insensitive but competitively inhibited by galantide (10(-8)-10(-7) M). In vivo, intra-arterial bolus injections of GAL (1001000 ng/kg), decreased transsphincteric flow, with a maximum reduction to 80.2 +/- 6.8% of control. In conclusion, GAL appears to selectively stimulate longitudinally oriented sphincter of Oddi smooth muscle via a direct mechanism, which results in a modest reduction in transsphincteric flow.