Potent neuropeptide Y Y1 receptor antagonist, 1229U91: blockade of neuropeptide Y-induced and physiological food intake

Neuropeptide Y (NPY) is thought to increase food intake through the action of Y1 (-like) receptors in the hypothalamus. To confirm the involvement of Y1 receptors in feeding behavior, selective and potent antagonists for Y1 receptors are required. In the present study, we showed that a peptide, 1229U91 [(Ile,Glu,Pro,Dpr,Tyr,Arg,Leu,Arg, Tyr-NH2)2 cyclic (2,4'),(2',4)-diamide], is a potent and selective antagonist for Y1 receptors. 1229U91 displaced [125I]peptide YY (PYY) binding to membranes of human neuroblastoma-derived SK-N-MC cells that predominantly express Y1 receptors with a K1 value 0.10 nM and inhibited the NPY-induced increase in intracellular calcium levels(IC50 = 0.27 nM). In contrast, the K1 values for [125I]PYY binding to Y2 receptors in membranes of human neuroblastoma-derived SK-N-BE2 cells and rat hypothalamus were 700 nM and more than 1 microM, respectively. Although [125I]PYY could not detect Y1 receptors in the rat hypothalamic membranes, [125I]1229U91 revealed binding sites with a high affinity (Kd = 18 pM), indicating the presence of Y1 receptors in the hypothalamus. Intracerebroventricular injection of 1229U91 (30 micrograms) into male Sprague-Dawley rats completely inhibited NPY (5 micrograms)-induced food intake without any other behavioral change. Furthermore, intracerebroventricular injection of 1229U91 significantly suppressed physiological feeding behavior after overnight fasting. These results indicate that Y1 receptors in the rat hypothalamus mediate NPY-induced food intake, and that physiological feeding behavior after overnight fasting may be largely regulated by NPY via Y1 receptors. 1229U91 may be useful for further elucidating the pathophysiological roles of NPY in feeding behavior.

Galanin inhibits long-term potentiation at Schaffer collateral-CA1 synapses in guinea-pig hippocampal slices

The role of galanin on long-term potentiation (LTP) of the field excitatory postsynaptic potentials (fEPSPs) at Schaffer collateral-CA1 synapses was investigated in guinea-pig hippocampal slices. Application of galanin (10(-7) M) inhibited the magnitude of LTP without any changes in the amplitude of fEPSP prior to tetanic stimulation. A putative central nervous system (CNS) type galanin receptor antagonist, galanin(1-13)-Pro-Pro-(Ala-Leu)2-Ala-Amide (M40), did not modify the magnitude of LTP when applied alone. However, M40 significantly reversed the inhibition by galanin when applied with galanin simultaneously. These findings suggest that galanin plays an inhibitory role through the CNS type galanin receptors.

Feeding induced by pharmacological blockade of fatty acid metabolism is selectively attenuated by hindbrain injections of the galanin receptor antagonist, M40

Galanin has been shown to stimulate feeding when injected intracranially in rats. Lesion and Fos studies have shown that the neural pathway for feeding stimulated by mercaptoacetate (MA)-induced blockade of fatty acid oxidation includes several structures rich in galanin cell bodies or terminals. In the present experiment, we examined the role of hindbrain galanin in feeding stimulated by MA. We found that galanin (1 nmol) stimulates feeding when injected in the nucleus of the solitary tract (NTS), a site that is crucial for MA-induced feeding, or into the fourth ventricle (4V, 1 or 5 nmol) and that NTS or 4V injections of the galanin receptor antagonist, M40 (1.5 or 5 nmol), completely blocked feeding induced by MA (68 mg/kg). The effect of the M40 appeared to be specific for MA-induced feeding, since M40 did not significantly attenuate either feeding induced by the antimetabolic glucose analog, 2-deoxy-D-glucose (2DG, 100 or 200 mg/kg), or deprivation-induced water intake. Results suggest that feeding induced by decreased fatty acid oxidation relies upon galaninergic terminals in the hindbrain. Furthermore, results indicate that hindbrain neurons involved in MA-induced feeding differ neurochemically from those important for 2DG-induced feeding.

Minireview. Galanin-acetylcholine interactions: relevance to memory and Alzheimer's disease

The neuropeptide, galanin, and its receptors are localized in the cholinergic basal forebrain and its projection areas in mammalian brain. Centrally administered galanin inhibits acetylcholine release in the rat ventral hippocampus, and produces deficits in learning and memory tasks. In Alzheimer's disease, galanin is overexpressed in terminals innervating the nucleus basalis of Meynert cell bodies. Selective galanin receptor antagonists provide a novel approach for increasing cholinergic function, as a potential adjunct to the clinical treatment of dementias.

Galantide distinguishes putative subtypes of galanin receptors in mudpuppy parasympathetic neurons

The effect of the chimeric ligand galantide on the galanin-induced activation of membrane K+ conductance and inhibition of voltage-dependent Ca2+ conductance has been studied using voltage-clamped dissociated mudpuppy parasympathetic neurons. Galantide did not activate the K+ conductance but produced a concentration-dependent antagonism (IC50 = 4 nM) of the galanin-induced increase in K+ conductance. Galantide acted like galanin and inhibited the voltage-dependent Ba2+ current (IBa). The inhibition of IBa also was concentration dependent (IC50 = 16 nM) and the maximum inhibition produced by galantide was approximately 40%. We also demonstrate that the galanin-(1-16) fragment increased the membrane K+ conductance and decreased IBa, suggesting that the NH2 portion of the galanin molecule is sufficient to mediate both actions. One interpretation of these observations is that different galanin receptors mediate the different effects of galanin on the mudpuppy parasympathetic neurons.

Antagonistic properties of [Phe3,Leu13]porcine motilin

We describe the antagonistic properties due to the replacement of Pro3 by phenylalanine in porcine motilin. The analogue, [Phe3,Leu13] porcine motilin (OHM-11526), displaces iodinated [Nle13]porcine motilin bound to a homogenate of rabbit antral smooth muscle tissue. The dissociation constant (pKd) was 9.26 +/- 0.04, versus 9.11 +/- 0.01 for motilin and 8.24 +/- 0.06 for ANQ-11125, the (1-14) fragment of OHM-11526. The Hill coefficient was close to one and Schild plot analysis confirmed the competitive nature of the interaction. In the tissue bath OHM-11526 was unable to induce contractions of segments of rabbit duodenum. At a concentration of 10(-6) M, OHM-11526 was unable to induce contractions of segments of rabbit duodenum. At a concentration of 10(-6) M, OHM-11526 inhibited the effect of maximally effective doses of porcine motilin and of the erythromycin derivative, EM-523, but was without effect on contractions induced by acetylcholine, substance P and serotonin. Increasing doses of OHM-11526 shifted the dose-response curves of motilin and EM-523 to the right, but caused a depression of the maximal response as well. From the motilin curves, and assuming a dual competitive and non-competitive interaction, the pA2 was 7.79 +/- 0.08, the pD'2 6.91 +/- 0.08. The EM-523 curves yielded comparable data (pA2 = 8.10 +/- 0.12 and pD'2 = 7.06 +/- 0.13). OHM-11526 also blocked the motilin responses observed with smooth muscle strips from the rabbit and human antrum. However, in a preparation of the chicken small intestine, OHM-11526 was a full agonist with a potency (pD2 = 6.84) comparable to that of porcine motilin (pD2 = 6.71). Our data confirm the interaction of motilides with the motilin receptor. Due to its increased affinity for the motilin receptor, OHM-11526 will be a valuable took for studying the physiology of motilin and the pharmacology of motilin and motilides.

Binding and agonist/antagonist actions of M35, galanin(1-13)-bradykinin(2-9)amide chimeric peptide, in Rin m 5F insulinoma cells

The chimeric peptide M35 [galanin(1-13)-bradykinin(2-9) amide] is a high-affinity galanin receptor ligand acting as a galanin receptor antagonist in the rat spinal cord, rat hippocampus and isolated mouse pancreatic islets. We have radiolabelled M35 and performed equilibrium binding studies with [125I]M35 on the rat pancreatic beta-cell line Rin m 5F, whereby we show the existence of high-affinity binding site (KD = 0.9 +/- 0.1 nM) with a Bmax of 72 +/- 3 fmol/mg protein. Galanin displaces [125I]M35 with the same affinity (KD = 1 nM) as it displaces [125I]galanin. Displacement of [125I]galanin by M35 from Rin m 5F cell membranes shows the presence of two binding sites for M35 with KD-values of 0.3 +/- 0.1 nM and 0.52 +/- 0.03 microM, respectively. The GTP- and pertussis toxin-sensitivity of M35 binding to Rin m 5F membranes shows that binding of [125I]M35 is almost completely abolished by the presence of GTP or after pertussis toxin treatment of the cells, indicating an agonist-like binding of M35 to the galanin receptors. M35 has a dual effect on the galanin mediated inhibition of forskolin stimulated cyclic AMP production in Rin m 5F cells: at low concentrations M35 antagonises the effect of galanin, whereas at concentrations above 10 nM M35 acts as a galanin receptor agonist. These agonist-like effects of galanin and M35 are not additive, thus the mixed agonist/antagonist properties arise from the chimeric nature of M35[galanin(1-13)-bradykinin(2-9)amide] acting solely at galanin receptors.

New high affinity peptide antagonists to the spinal galanin receptor

1. The role of endogenous galanin in somatosensory processing has been studied with galanin receptor antagonists. The new galanin receptor ligands C7, M32, M38 and M40 bind with high affinity (Kd in nanomolar range) to spinal cord galanin receptors and possess oxidative stability as compared to earlier generations of peptide ligands. These peptides have been examined in the spinal flexor reflex model where exogenous galanin exhibited biphasic excitatory and inhibitory effects. 2. Intrathecal administration of C7 [galanin(1-13)-spantide] and M32 [galanin (1-13)-neuropeptide Y(25-36) amide] blocked facilitation of the nociceptive flexor reflex induced by 30 pmol intrathecal galanin in decerebrate, spinalized rats in a dose-dependent manner, thus behaving as antagonists of the galanin receptor. In contrast, M38[galanin(1-13)-(Ala-Leu)3-Ala amide] and M40 [galanin(1-13)-Pro-Pro-(Ala-Leu)2-Ala amide], exhibited only weak antagonism at high doses in this model. Moreover, lower doses of M40 potentiated galanin-induced reflex facilitation. C7 was neurotoxic at high doses in the rat spinal cord. 3. M32 and C7 were potent antagonists of galanin receptors in rat spinal cord, in correlation with their in vitro binding characteristics. In contrast, M38 and M40, despite their high in vitro affinity, exhibited only very weak antagonism. Moreover, M40 may also behave as a partial agonist. 4. Previous studies have shown that the galanin receptor may be heterogeneous. The discrepancy between in vitro binding and in vivo antagonistic potency of M38 and M40 may also suggest the presence of different galanin receptor subtypes within the rat spinal cord. However, other explanations for the discrepancy, such as differences in metabolic stability, diffusion rates and penetration to the site of action are also possible.

GM-109: a novel, selective motilin receptor antagonist in the smooth muscle of the rabbit small intestine

The pharmacological properties of the cyclic peptide Phe-cyclo[Lys-Tyr(3-tBu)-beta Ala-].trifluoroacetate (GM-109), a selective motilin antagonist, were investigated in the smooth muscle of the rabbit small intestine. GM-109 (0.1-3 microM) competitively inhibited contractions induced by porcine motilin (pMTL) in rabbit isolated duodenum longitudinal strips, with a pA2 value of 7.37 +/- 0.24. However, the contractile response to acetylcholine, to substance P, to prostaglandin F2 alpha and to KCl was unaffected by 10 microM GM-109 in the same preparation. Both GM-109 and pMTL competitively inhibited 125I-pMTL binding to motilin receptors in a homogenate of the rabbit small intestinal smooth muscle tissue. The pKi value of GM-109 and the pKd value of unlabeled pMTL were 7.99 +/- 0.04 and 9.25 +/- 0.06 (each n = 5), respectively. These results indicate that GM-109 is a selective and competitive motilin receptor antagonist in the smooth muscle of the rabbit small intestine. Thus this compound may be a useful pharmacological tool for examining the functional role(s) of motilin.

Galanin--10 years with a neuroendocrine peptide

Galanin is a 29/30 amino acids long neuropeptide which does not belong to any known peptide family. The N-terminal first 16 amino acids of the molecule are both necessary and sufficient for receptor recognition and receptor activation. The main pharmacophores of galanin in its central and pancreatic actions are Gly1, Trp2, Asn5 and Tyr9, respectively. The neuropeptide galanin has multiple effects in both the central and peripheral nervous systems. Centrally, galanin potently stimulates fat intake and impairs cognitive performance. Anoxic glutamate release in the hippocampus is inhibited by galanin and the noradrenergic tonus in the brain is influenced by a hyperpolarizing action of galanin in the locus coeruleus. In the spinal cord galanin inhibits spinal excitability and potentiates the analgesic effect of morphine. In the neuroendocrine system galanin acts in a stimulatory manner on the release of growth hormone and prolactin, and peripherally galanin inhibits glucose induced insulin release. Galanin also causes contraction of the jejunum. The galanin receptor is a Gi-protein-coupled, membrane-bound glycoprotein with an estimated molecular mass of 53 kDa. Several putative tissue specific galanin receptor subtypes have been proposed on a pharmacological basis. The distribution of galanin receptors and of galanin like immunoreactivity are overlapping in the CNS, both being high in areas such as the locus coeruleus, raphe nucleus and hypothalamus. Galanin receptor activation leads to a reduced intracellular Ca(2+)-concentration, either by direct action on voltage sensitive Ca(2+)-channels or indirectly via opening of K(+)-channels or via inhibition of adenylyl cyclase activity. The lowered intracellular Ca2+ level subsequently leads to a reduced PLC activity. Galanin also inhibits cGMP synthesis induced by depolarization. A number of synthetic high affinity galanin receptor antagonists of the peptide type were developed recently, which have enabled the elucidation of functional roles of endogenous galanin in several systems. Furthermore, putative subtypes of galanin receptors can be distinguished by the use of these new galanin receptor ligands.

Galanin contracts and relaxes guinea pig and canine intestinal smooth muscle cells through distinct receptors

BACKGROUND/AIMS

Galanin induces a contraction or a relaxation of digestive smooth muscle. Receptors mediating these effects have not been pharmacologically characterized. The aim of the study was to evaluate properties of two specific galanin antagonists M15 and M35 on galanin effects on muscle cells.

METHODS

Isolated muscle cells were obtained separately from circular and longitudinal layers of guinea pig and dog ileums. Contraction was expressed as percentage decrease in cell length from control.

RESULTS

Galanin induced a contraction of cells from guinea pig circular layer (50% effective concentration [EC50], 80 pmol/L) and dog longitudinal layer (EC50, 100 pmol/L). The antagonists inhibited galanin-induced contraction. The most potent was M15 (50% inhibitory concentration [IC50], 80 pmol/L in guinea pig; 90 pmol/L in dog) which was > M35 (IC50, 4 nmol/L in guinea pig; 1 nmol/L in dog). In dog circular layer, galanin inhibited cholecystokinin-induced contraction by relaxing the cells (EC50, 3 pmol/L). The antagonists inhibited this relaxation. The most potent was M35 (IC50, 60 pmol/L) which was > M15 (IC50, 900 pmol/L).

CONCLUSIONS

Galanin antagonists M15 and M35 inhibit the contraction and the relaxation induced by galanin with different potency, suggesting the presence of distinct galanin receptors in gastrointestinal tract that each mediates a specific effect.

Motilin receptor: a model for development of prokinetics

Erythromycin and related macrolides act as smooth muscle and neural receptors to contract rabbit duodenum and induce phase III migrating motor complex (MMC) activity in intact dogs. A recently developed motilin antagonist confirms that motility effects of erythromycin are mediated by motilin receptors. Despite species, organ, and tissue heterogeneity of motilin receptors, binding experiments with rodent antral smooth muscle tissue provide a good model for the development of this new class of prokinetics.

Motilin synthetic analogues and motilin receptor antagonists

While studying the structure-activity characteristics of motilin with motilin synthetic analogues, two compounds, motilin 1-12 [CH2 NH]3-4 and motilin 1-12 [CH2 NH]10-11, showed high affinity for the motilin receptor combined to a weak contractile activity. The following data suggest that motilin 1-12 [CH2 NH]10-11 is a potent motilin receptor antagonist. It showed a high affinity for the motilin receptor present on membranes of rabbit antrum (pIC50: 8.24 +/- 0.08 for the analogue vs 8.96 +/- 0.02 for the native peptide). When tested in vitro on strips of rabbit duodenum, the dose-response curve to motilin 1-22 was displaced to the right with motilin 1-12 [CH2 NH]10-11 (pIC50: 8.91 +/- 0.06 in presence of saline versus 7.19 +/- 0.40 with the analogue). However, when injected i.v. in dogs, motilin 1-12 [CH2 NH]10-11 was undetectable in the peripheral blood, suggesting enzymatic degradation precluding its use in vivo.

The human galanin receptor: ligand-binding and functional characteristics in the Bowes melanoma cell line

The human galanin receptor has been characterized pharmacologically from the Bowes melanoma cell line. Using porcine [125I]galanin as the radioligand, a single population of non-interacting high-affinity binding sites (KD = 0.05 +/- 0.01 nM; Bmax = 135 +/- 7 fmol/mg protein) was demonstrated. Human galanin peptide competitively inhibited the specific binding of [125I]galanin (IC50 = 0.35 +/- 0.13 nM) and decreased the forskolin-stimulated cAMP production (EC50 = 0.46 +/- 0.05 nM) with a maximal inhibition of 63 +/- 2% at 10(-7) M. Rat and porcine galanin peptides and the chimeric peptides M15, M35, M32, M40 and C7 also dose-dependently inhibited the forskolin-stimulated cAMP production, while the fragment porcine galanin-(3-29) and [D-Trp2]galanin were found to be inactive. The specific binding of [125I]galanin was decreased in a dose-dependent manner by GTP and the cAMP response was inhibited by the pertussis toxin, suggesting the activation of a G-protein dependent process. The Bowes cell line thus appears to be a relevant tool for the study of human galanin receptor.

Spinal antinociception by morphine in rats is antagonised by galanin receptor antagonists

Galanin, a 29 amino acid peptide, has been reported to possess antinociceptive properties at the spinal site and to potentiate opioid-induced antinociception. Our aim was to investigate whether also endogenous galanin interacts with an exogenously administered opioid, morphine, in the rat spinal cord. This question was investigated by use of the recently developed galanin receptor antagonists galantide [M-15, galanin-(1-13)-substance P-(5-11) amide] and M-35 [galanin-(1-13)-bradykinin-(2-9) amide]. Nociception was assessed in the rat tail-flick test using radiant heat and the rat Randall-Selitto model of inflammatory pain using vocalization as the nociceptive criterion. Intrathecal (i.t.) injections were performed in rats under either anaesthesia. Morphine was administered either i.t. or intraperitoneally (i.p.), and the antagonists were injected i.t. [125I]Galanin binding experiments were performed on crude synaptosomal membranes of the rat spinal cord. In the rat tail-flick test, i.t. injection of 3 micrograms morphine evoked antinociception of about 75% of the maximal possible effect (% MPE). Co-injection of either 2 micrograms galantide or 2 micrograms M-35 with morphine almost completely abolished the antinociceptive effect of morphine. I.p. injection of 2.15 mg/kg morphine elicited about 80% MPE when given 10 min prior to i.t. saline injection. Injection of the antagonists instead of saline antagonised the antinociceptive effect of morphine partially thus showing the spinal proportion of the overall antinociceptive effect. In the rat Randall-Selitto test, 3 micrograms morphine, injected i.t., produced antinociception of almost 100% MPE.(ABSTRACT TRUNCATED AT 250 WORDS)

Galanin receptors in human hypothalamus: biochemical and structural analysis

Galanin receptors have been characterized in normal human hypothalamus using 125I-galanin binding assays. Competition experiments of porcine 125I-galanin binding to human hypothalamic membranes with native human, porcine and rat galanin (10(-11) M to 10(-8) M) gave comparable results with IC50 close to 0.1 nM. Scatchard analysis indicated one type of high affinity binding sites (Kd = 0.11 nM) with a capacity of 460 fmol/mg protein. Galanin-(1-15) and galanin-(2-29) inhibited tracer binding (IC50 = 1.5 nM), galanin-(3-29) and galanin-(10-29) being inactive. The galanin receptor antagonist, galantide, 10(-14) M to 10(-8) M, also strongly displaced binding of 125I-galanin to the human receptor (IC50 close to 0.15 nM). Guanine nucleotides (from 10(-8) M to 10(-4) M) decreased tracer binding to human membranes by increasing the dissociation of the galanin-receptor complexes. Structural analysis by covalent labelling indicated that the human galanin receptor behaves as a monomeric protein with a molecular mass of 54,000 daltons.

N-terminally elongated fragments of galanin(1-16) inhibit insulin secretion from isolated mouse islets

The neuropeptide galanin inhibits insulin secretion and has been suggested to be an adrenergic co-transmitter in the endocrine pancreas. Recently, N-terminally elongated forms of galanin have been identified in both porcine brain and adrenals. Whether these elongated peptides show galanin-like biological effects is not known. We therefore synthesized two N-terminally elongated fragments of galanin(1-16), which contains the active site of galanin. The synthesized peptides were galanin(-9-16) and galanin(-7-16), which correspond to amino acids 24-61 and 26-61 in the galanin precursor molecule. Both these peptides were found to potently inhibit glucose-(11.1 mM)-stimulated insulin secretion from isolated mouse islets of Langerhans in all concentrations studied (1-1000 nM) (P < 0.0001). The potency of the peptides was not different from that of synthetic rat galanin. Thus, at 100 nM, insulin secretion was inhibited by galanin(-7-16) by 83 +/- 7% and by galanin(-9-16) by 71 +/- 17% and by rat galanin by 93 +/- 4% (not statistically different). Furthermore, the galanin receptor antagonist, M35 (10 nM), prevented the inhibitory action of the two N-terminally galanin fragments. This study thus shows that N-terminally elongated galanin-fragments as entire galanin inhibits insulin and thus indicates that the effect of galanin on insulin secretion is not dependent on a free amino-terminus.

Role of galanin in stimulation of pituitary luteinizing hormone secretion as revealed by a specific receptor antagonist, galantide

In this study, a specific galanin (GAL) receptor antagonist, galantide, was employed to evaluate the role of endogenous GAL in episodic basal and phasic LH release in rats. To assess the specificity of galantide, a series of experiments was performed. In the first experiment, we observed that administration of GAL (0.62 nm) intracerebroventricularly (icv) in ovarian steroid-primed ovariectomized (ovx) rats rapidly increased plasma LH levels between 10-30 min, and prior injection of galantide icv (5 nm) blocked the GAL-induced LH release. In the second experiment, galantide inhibited the GAL-evoked in vitro release of LHRH from the median eminence-arcuate nucleus (ME-ARC) of ovarian steroid-primed ovx rats. In addition, galantide on its own significantly decreased the basal efflux of LHRH from the ME-ARC of similarly treated rats, thereby suggesting that even the basal LHRH secretion may be a GAL-dependent event. In the third experiment, the effects of galantide on the phasic LH surge elicited by progesterone (P) in estradiol benzoate-primed ovx rats and that occurring spontaneously on proestrus were examined. Ovx rats bearing icv cannulae were primed with estradiol benzoate (30 micrograms/rat, sc) and 2 days later received a P (2 mg/rat, sc) injection at 1000 h to evoke a LH surge in the afternoon. Galantide (1 or 5 nm) in 3 microliters saline or saline was injected icv at 1300, 1400, and 1500 h. The results showed that the two dosages of galantide suppressed the LH surge in the afternoon. On the other hand, only a very high dose of galantide (15 nm) injected iv at 1300, 1400, and 1500 h blunted the P-induced LH hypersecretion. Central injections of galantide (1 or 5 nm) at 1300, 1400, and 1500 h on proestrus also inhibited the preovulatory LH surge and significantly reduced the numbers of rats ovulating the following day. In the final experiment, the role of GAL receptors in modulation of episodic LH release was analyzed in ovx rats. The results showed that an injection of galantide (5 nm, icv) significantly decreased both the mean LH levels and the amplitude of LH episodes during the 3-h observation period. Cumulatively, these results show that normally GAL stimulates LHRH release by activation of a specific receptor located in the ME-ARC, and that GAL may be a key excitatory signal in the hypothalamic neural circuitry involved in the regulation of basal episodic and phasic LHRH secretion in cycling female rats.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential effects of the putative galanin receptor antagonists M15 and M35 on striatal acetylcholine release

The putative galanin receptor antagonists M15 and M35 were examined for their effects on the basal and the galanin-evoked release of acetylcholine in the striatum. Extracellular concentrations of acetylcholine were measured in male rats using in vivo microdialysis and high pressure liquid chromatography techniques. Galanin (300 microM or 3 nmol/10 microliters), perfused through the microdialysis membrane into the striatum, enhanced (100% increase) basal acetylcholine release. M35 (300 microM or 3 nmol/10 microliters) also stimulated the basal acetylcholine release to some extent (about 50%) while M15 at the same concentration failed to do so. When M15 and M35 were coinfused with galanin, the galanin-evoked acetylcholine release was blocked completely by M15 (300 microM or 3 nmol/10 microliters) but only partially by M35 (300 microM or 3 nmol/10 microliters). The increase in acetylcholine release induced by M35 (300 microM) was blocked by M15 (300 microM). It is concluded that M15 is a full galanin receptor antagonist while M35 behaves as a mixed agonist-antagonist in vivo in the rat striatum. Both M15 and M35 fully displaced 0.2 nM [125I]galanin from its binding sites in the striatal membranes. The Hill coefficient of these [125I]galanin displacement curves with M15 and M35 was 0.4-0.5 compared to unity in the case of galanin. Analysis of the displacement curves suggested that both M15 and M35 recognized two classes of galanin binding sites in striatal membranes of the rat. To explain the difference between M15 and M35 it is suggested that there may exist a putative subtype of galanin receptor in the striatum, which is differentially affected by M15 and M35.

Synthetic linear and cyclic glucagon antagonists

The synthesis and biological activities of seven new glucagon analogues are reported. The design of compounds 2-5 is based on potent antagonists recently reported from this laboratory, where we have focused on modifications in the N-terminal region. In this report we have concentrated specifically on modifications to histidine-1. In addition we have prepared two cyclic compounds 7 and 8, related to a linear in vivo antagonist [Glu9]glucagon, reported by Merrifield (Unson et al. (1987) Proc. Natl. Acad. Sci. USA 84, 4083-4087). The N-terminal modifications involved substitution of His1 by the unnatural conformationally constrained residue (S)-5,6,7,8-tetrahydro-5-oxoimidazo(1,5-c)pyrimidine-7-carboxylic acid (Toc), desaminohistidine (dHis) and 3-(4-nitrobenzyl)histidine. The structures of the new compounds are as follows. [Toc1,D-Phe4,Tyr5,Arg12,Lys17,18,Glu21]glucagon (2); [Toc1,D-Phe4,Tyr5,Arg12,Lys17,18,Glu21]glucagon amide (3); [3-(4-nitrobenzyl)His1,D-Phe4,Tyr5,Arg12,Lys17,18,G lu21]glucagon (4); [dHis1,D-Phe4,Tyr5,Arg12,Lys17,18,Glu21]glucagon (5); [dHis1,Glu9]glucagon (6); (desHis1)[Glu9,Lys12]glucagon amide (7); (desHis1)-[Glu9,Lys12,Asp15]glucagon amide (8). The binding potencies of the linear analogues, as expressed a percentage of glucagon binding, are 2.6 (2), 0.13 (3), 0.8 (4), 0.8 (5), 2.2 (6). Both cyclic analogues 7 and 8 show biphasic binding curves. The IC50 values for 7 at the high and low affinity sites are 1.5 and 167 nM, respectively (IC50 of glucagon = 1.3 nM). The IC50 values for 8 at the high and low affinity sites are 4.7 and 3451 nM, respectively. The cyclic analogues are characterized by fast atom bombardment mass spectrometry of endoproteinase ASP-N digests. The specificity of the enzyme used in these studies enables differentiation of isomers of the cyclic glucagon analogues which differ only in the position of cyclic amide bond. Analogues 2, 3 and 5-8 are glucagon receptor antagonists with respect to the glucagon receptor coupled to the adenylate cyclase (AC) system. Analogue 4 is a partial agonist (5.7% compared to glucagon) of AC. Introduction of unusual amino acids which do not contain a primary alpha-amino group such as Toc at the N-terminus is expected to increase in vivo metabolic stability by protecting against degradation by aminopeptidases.

A vasoactive intestinal peptide antagonist inhibits non-small cell lung cancer growth

The most prevalent lung cancer, non-small cell lung cancer (NSCLC) has receptors for vasoactive intestinal peptide (VIP). Here the effects of a VIP antagonist (VIP-hyb) on NSCLC growth were investigated. In vivo, when VIPhyb (10 micrograms, s.c.) was daily injected into nude mice, xenograft formation was significantly inhibited by approximately 80%. In vitro, VIP (100 nM) stimulated colony formation approximately 2-fold, whereas 1 microM VIPhyb inhibited colony formation by approximately 50% when adenocarcinoma cell line NCI-H838 was used. The attenuation of tumor proliferation is receptor mediated, as VIPhyb inhibited specific 125I-labeled VIP binding to cell lines NCI-H157 and NCI-H838 with an IC50 of 0.7 microM. VIP (10 nM) increased the cAMP levels 5-fold when cell line NCI-H838 was used, and 10 microM VIPhyb inhibited the increase in cAMP caused by VIP. Northern blot analysis and radioimmunoassays have shown VIP mRNA and VIP-like immunoreactivity in NSCLC cells. These data suggest that VIP may be a regulatory peptide in NSCLC and that VIPhyb is a VIP receptor antagonist that inhibits proliferation.

Mechanism of action of des-His1-[Glu9]glucagon amide, a peptide antagonist of the glucagon receptor system

We have investigated the mechanisms through which des-His1-[Glu9]glucagon amide functions as a peptide antagonist of the glucagon receptor/adenylyl cyclase system. Studies with radiolabeled peptides identified that (i) the antagonist bound to intact hepatocytes according to a single first-order process, whereas the rate of association of glucagon with the same preparation could be described only by the sum of two first-order processes; (ii) the interaction of the antagonist with saponin-permeabilized hepatocytes was not affected by the addition of GTP to the incubation medium or by the elimination of Mg2+, whereas the interaction of glucagon with the same cell preparation was modified significantly by the presence of the nucleotide or by the absence of the divalent metal ion; (iii) the dissociation of antagonist from intact hepatocytes incubated in buffer was complete, whereas that of agonist was not; and (iv) the antagonist bound to intact hepatocytes at steady state according to a single binding isotherm (as did both agonist and antagonist in permeabilized hepatocytes), whereas glucagon bound to the intact cell system with two clearly defined apparent dissociation constants. A model is presented for the mechanism of action of the glucagon antagonist in which the analog binds to glucagon receptors in a Mg(2+)- and GTP-independent fashion and in which resulting ligand-receptor complexes fail to undergo sequential adjustments necessary for the stimulation of adenylyl cyclase.

Receptor antagonists for gastrointestinal peptides

Receptors for gastrointestinal peptides are all G protein-coupled receptors. Since the discovery that dibutyryl guanosine 3',5'-cyclic monophosphate was a cholecystokinin-receptor antagonist, a variety of receptor antagonists have been developed for a number of different gastrointestinal peptides. These antagonists have been useful in classifying receptors for gastrointestinal peptides and in elucidating complex regulation of gastrointestinal function. Some antagonists also have therapeutic potential. Based on the receptors with which they interact, gastrointestinal peptides can be grouped into families, and, in general, a given receptor antagonist is specific for a given family. This review covers the different families of gastrointestinal peptides and the major antagonists that exist for each family.