Comparative effects of galanin on isolated smooth muscle cells from ileum in five mammalian species

Changes Caused by Bisphenols in the Chemical Coding of Neurons of the Enteric Nervous System of Mouse Stomach

Bisphenol A (BPA), an organic chemical compound which is widely used in the production of plastics, can severely damage live organisms. Due to these findings, the plastic industry has started to replace it with other substances, most often with bisphenol S (BPS). Therefore, during the present investigation, with the use of double immunofluorescence labeling, we compared the effect of BPA and BPS on the enteric nervous system (ENS) in the mouse corpus of the stomach. The obtained results show that both studied toxins impact the amount of nerve cells immunoreactive to substance P (SP), galanin (GAL), vesicular acetylcholine transporter (VAChT is used here as a marker of cholinergic neurons) and vasoactive intestinal polypeptide (VIP). Changes observed under the impact of both bisphenols depended on the neuronal factor, the type of the enteric ganglion and the doses of bisphenols studied. Generally, the increase in the percentage of neurons immunoreactive to SP, GAL and/or VIP, and the decrease in the percentage of VAChT-positive neurons, was noted. Severity of changes was more visible after BPA administration. However, the study has shown that long time exposure to BPS also significantly affects the ENS.

Changes in the Enteric Neurons Containing Selected Active Substances in the Porcine Descending Colon after the Administration of Bisphenol A (BPA)

Bisphenol A (BPA) is an endocrine disruptor widely distributed in the environment due to its common use in the plastics industry. It is known that it has a strong negative effect on human and animal organisms, but a lot of aspects of this impact are still unexplored. This includes the impact of BPA on the enteric nervous system (ENS) in the large intestine. Therefore, the aim of the study was to investigate the influence of various doses of BPA on the neurons located in the descending colon of the domestic pig, which due to similarities in the organization of intestinal innervation to the human gastrointestinal tract is a good animal model to study processes occurring in human ENS. During this study, the double immunofluorescence technique was used. The obtained results have shown that BPA clearly affects the neurochemical characterization of the enteric neurons located in the descending colon. The administration of BPA caused an increase in the number of enteric neurons containing substance P (SP) and vasoactive intestinal polypeptide (VIP) with a simultaneously decrease in the number of neurons positive for galanin (GAL) and vesicular acetylcholine transporter (VAChT used as a marker of cholinergic neurons). Changes were noted in all types of the enteric plexuses, i.e., the myenteric plexus, outer submucous plexus and inner submucous plexus. The intensity of changes depended on the dose of BPA and the type of enteric plexus studied. The results have shown that BPA may affect the descending colon through the changes in neurochemical characterization of the enteric neurons located in this segment of the gastrointestinal tract.

Effect of Chemically-Induced Diabetes Mellitus on Phenotypic Variability of the Enteric Neurons in the Descending Colon in the Pig

Gastrointestinal neuropathy in diabetes is one of numerous diseases resulting in abnormal functioning of the gastrointestinal tract (GIT), and it may affect any section of the GIT, including the descending colon. In the gastrointestinal system, the neurons are arranged in an interconnecting network defined as the enteric nervous system (ENS) which includes the myenteric plexus and the submucosal plexuses: inner and outer. Regular functioning of the ENS is determined by normal synthesis of the neurotransmitters and neuromodulators. This paper demonstrates the effect of hyperglycaemia on the number of enteric neurons which are immunoreactive to: neural isoform of nitric oxide synthase (nNOS), vasoactive intestinal peptide (VIP), galanin (GAL), calcitonin generelated peptide (CGRP) and cocaine amphetamine-regulated transcript (CART) in the porcine descending colon. It was demonstrated that there was a statistically significant increase in the number of neurons within the myenteric plexus immunoreactive to all investigated substances. In the outer submucosal plexus, the CART-positive neurons were the only ones not to change, whereas no changes were recorded for nNOS or CART in the inner submucosal plexus. This study is the first study to discuss quantitative changes in the neurons immunoreactive to nNOS, VIP, GAL, CGRP and CART in the descending colon in diabetic pigs.

The Influence of Bisphenol A (BPA) on the Occurrence of Selected Active Substances in Neuregulin 1 (NRG1)-Positive Enteric Neurons in the Porcine Large Intestine

Bisphenol A (BPA) is a substance used in the manufacture of plastics which shows multidirectional adverse effects on living organisms. Since the main path of intoxication with BPA is via the gastrointestinal (GI) tract, the stomach and intestine are especially vulnerable to the impact of this substance. One of the main factors participating in the regulation of intestinal functions is the enteric nervous system (ENS), which is characterized by high neurochemical diversity. Neuregulin 1 (NRG1) is one of the lesser-known active substances in the ENS. During the present study (performed using the double immunofluorescence method), the co-localization of NRG1 with other neuronal substances in the ENS of the caecum and the ascending and descending colon has been investigated under physiological conditions and after the administration of BPA. The obtained results indicate that NRG1-positive neurons also contain substance P, vasoactive intestinal polypeptide, a neuronal isoform of nitric oxide synthase and galanin and the degree of each co-localization depend on the type of enteric plexus and the particular fragment of the intestine. Moreover, it has been shown that BPA generally increases the degree of co-localization of NRG1 with other substances.

Mycotoxins and the Enteric Nervous System

Mycotoxins are secondary metabolites produced by various fungal species. They are commonly found in a wide range of agricultural products. Mycotoxins contained in food enter living organisms and may have harmful effects on many internal organs and systems. The gastrointestinal tract, which first comes into contact with mycotoxins present in food, is particularly vulnerable to the harmful effects of these toxins. One of the lesser-known aspects of the impact of mycotoxins on the gastrointestinal tract is the influence of these substances on gastrointestinal innervation. Therefore, the present study is the first review of current knowledge concerning the influence of mycotoxins on the enteric nervous system, which plays an important role, not only in almost all regulatory processes within the gastrointestinal tract, but also in adaptive and protective reactions in response to pathological and toxic factors in food.

Colorectal Cancer Invasion and Atrophy of the Enteric Nervous System: Potential Feedback and Impact on Cancer Progression

Colorectal cancer (CRC) invasion within the large intestine wall results in the replacement of normal tissue architecture by tumour mass. Cancer cells digest the extracellular matrix (ECM) by the release of proteolytic enzymes. The disintegration of matrix ground substance activates several deposited growth factors which stimulate cell proliferation. Stromal (mainly fibroblasts), immune and cancer cells dominate in this area and become involved in a network of multimodal interactions which significantly induce proliferation of colon cancer cells, inhibit their apoptosis and promote their spreading within the local tumour microenvironment. Cancer invasion destroys nerve fibres and neurons of the local enteric nervous system (ENS) and induces subsequent atrophy of the submucosal and myenteric plexuses in areas adjacent to the cancer boundary. Interestingly, the reduction of plexuses' size is accompanied by the increased number of galanin-immunoreactive neurons and increased galanin content in parts of the colon located close to the tumour. Galanin, a neuroprotective peptide, may inhibit the extrinsic pathway of apoptosis and in this way promote cancer cell survival. The possible role of acetylcholine and some ENS neuropeptides was also discussed. Invasion of cancer cells spreads along nerve fibres with the involvement of locally-released neutrophins which promote, via their specific receptors, cancer cell proliferation and pro-survival signalling pathways. Thus, during CRC development cancer cells and neurons of the ENS release many neurotransmitters/neuropeptides which affect key cellular signalling pathways promoting cancer cell proliferation and pro-survival phenotype. The multiple interactions between ENS neurons, cancer cells and other cell types present in the colon wall increase cancer cell invasiveness and have a negative impact on the course of CRC.

Distribution and Neurochemistry of the Porcine Ileocaecal Valve Projecting Sensory Neurons in the Dorsal Root Ganglia and the Influence of Lipopolysaccharide from Different Serotypes of Salmonella spp. on the Chemical Coding of DRG Neurons in the Cell Cultures

The ileocecal valve (ICV)—a sphincter muscle between small and large intestine—plays important roles in the physiology of the gastrointestinal (GI) tract, but many aspects connected with the innervation of the ICV remain unknown. Thus, the aim of this study was to investigate the localization and neurochemical characterization of neurons located in the dorsal root ganglia and supplying the ICV of the domestic pig. The results have shown that such neurons mainly located in the dorsal root ganglia (DRG) of thoracic and lumbar neuromers show the presence of substance P (SP), calcitonin gene-related peptide (CGRP), and galanin (GAL). The second part of the experiment consisted of a study on the influence of a low dose of lipopolysaccharide (LPS) from Salmonella serotypes Enteritidis Minnesota and Typhimurium on DRG neurons. It has been shown that the LPS of these serotypes in studied doses does not change the number of DRG neurons in the cell cultures, but influences the immunoreactivity to SP and GAL. The observed changes in neurochemical characterization depend on the bacterial serotype. The results show that DRG neurons take part in the innervation of the ICV and may change their neurochemical characterization under the impact of LPS, which is probably connected with direct actions of this substance on the nervous tissue and/or its pro-inflammatory activity.

Neurochemical characterization of intramural nerve fibres in the porcine oesophagus

The gastrointestinal (GI) tract is innervated by nerve processes derived from the intramural enteric neurons and neurons localized outside the digestive tract. This study analysed the neurochemical characterization of nerves in the wall of the porcine oesophagus using single immunofluorescence technique. Immunoreactivity to vesicular acetylcholine transporter (VAChT), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), galanin (GAL), neuronal isoform of nitric oxide synthase (nNOS), substance P (SP), leucine enkephalin (LENK), calcitonin gene-related peptide (CGRP) or dopamine beta-hydroxylase (DBH) was investigated in intramuscular and intramucosal nerves of the cervical, thoracic and abdominal oesophagus. The results indicate that all of the substances studied were present in the oesophageal nerves. The density of particular populations of fibres depended on the segment of the oesophagus. The most numerous were fibres immunoreactive to VIP in the longitudinal and circular muscle layers of the abdominal oesophagus: The number of these fibres amounted to 16.4 ± 0.8 and 18.1 ± 3.1, respectively. In turn, the least numerous were CGRP-positive fibres, which were present only in the circular muscle layer of the cervical oesophagus and mucosal layer of the abdominal oesophagus in the number of 0.3 ± 0. The obtained results show that nerves in the porcine oesophageal wall are very diverse in their neurochemical coding, and differences between particular parts of the oesophagus suggest that organization of the innervation clearly depends on the fragment of this organ.

Cocaine- and amphetamine-regulated transcript (CART) peptide in the enteric nervous system of the porcine esophagus

Cocaine- and amphetamine-regulated transcript peptide (CART) is widely distributed within the central and peripheral nervous system. In the brain, CART is considered as the main anorectic peptide involved in the regulation of food intake. Contrary to the central nervous system, a lot of aspects connected with the distribution and functions of CART within the enteric nervous system (ENS) still remain unknown. The aim of the present study was to investigate, for the first time, the population of CART-like immunoreactive (CART-LI) neurons within the porcine esophagus and the denotation of their neurochemical coding. During this experiment, the distribution of CART-LI neurons and the colocalization of CART with other neuronal active substances were examined using standard double- and triple-immunofluorescence techniques in enteric plexuses of cervical, thoracic, and abdominal esophagus fragments. The obtained results showed that CART is present in a relatively high percentage of esophageal neurons (values fluctuated from 45.2±0.9% in the submucous plexus of the thoracic esophagus to 58.1±5.0% in the myenteric plexus of the same fragment of the esophagus). Moreover, CART colocalized with a wide range of other active neuronal substances, mainly with the vesicular acetylcholine transporter (VAChT, a marker of cholinergic neurons), neuronal isoform of nitric oxide synthase (nNOS, a marker of nitrergic neurons), vasoactive intestinal polypeptide (VIP) and galanin (GAL). The number of CART-positive neuronal cells and their neurochemical coding clearly depended on the fragment of esophagus studied and the type of enteric plexus. The obtained results suggest that CART may play important and multidirectional roles in the neuronal regulation of esophageal functions.

The Influence of Inflammation and Nerve Damage on the Neurochemical Characterization of Calcitonin Gene-Related Peptide-Like Immunoreactive (CGRP-LI) Neurons in the Enteric Nervous System of the Porcine Descending Colon

The enteric nervous system (ENS), localized in the wall of the gastrointestinal tract, regulates the functions of the intestine using a wide range of neuronally-active substances. One of them is the calcitonin gene-related peptide (CGRP), whose participation in pathological states in the large intestine remains unclear. Therefore, the aim of this study was to investigate the influence of inflammation and nerve damage using a double immunofluorescence technique to neurochemically characterize CGRP-positive enteric nervous structures in the porcine descending colon. Both pathological factors caused an increase in the percentage of CGRP-positive enteric neurons, and these changes were the most visible in the myenteric plexus after nerve damage. Moreover, both pathological states change the degree of co-localization of CGRP with other neurochemical factors, including substance P, the neuronal isoform of nitric oxide synthase, galanin, cocaine- and amphetamine-regulated transcript peptide and vesicular acetylcholine transporter. The character and severity of these changes depended on the pathological factor and the type of enteric plexus. The obtained results show that CGRP-positive enteric neurons are varied in terms of neurochemical characterization and take part in adaptive processes in the descending colon during inflammation and after nerve damage.

Modulation of the main porcine enteric neuropeptides by a single low-dose of lipopolysaccharide (LPS) Salmonella Enteritidis

Background

The present research was conducted to investigate the influence of a low, single dose of LPS, which does not result in any clinical symptoms of intoxication on the expression of selected neuropeptides within the intestines of the domestic pig.

Methods

This experiment was conducted on immature female pigs of the Pitrain × Duroc breed (n = five per group). Seven days after the intravenous injection of 10 mL saline solution for control animals and 5 μg/kg b.w. (in 10 mL saline solution) LPS Salmonella Enteritidis for the experimental group, the excised segments of duodenum, jejunum, ileum, ileocecal valve, caecum, descending colon, transverse colon, ascending colon and rectum were prepared to extract the main enteric neuropeptides, including GAL, NPY, SOM, SP, VIP.

Results

The results of this research indicate that single low-dose LPS S. Enteritidis produced changes in the content of the selected neuropeptides of the porcine intestine. The most visible changes were observed in the transverse colon, where LPS induced the increase of GAL expression from 19.41 ± 7.121 to 92.92 ± 11.447 ng/g tissue.

Conclusion

The exact functions of the substances studied and mechanisms of responses to LPS action depend on the sections of the intestines. The mechanisms of observed changes are not fully understood, but fluctuations in neuronal active substance levels may be connected with neurodegenerative and/or pro-inflammatory activity of LPS.

Zinc Transporter 3 (Znt3) as an Active Substance in the Enteric Nervous System of the Porcine Esophagus

Zinc transporter 3 (ZnT3), a member of the SLC 30 zinc transporter family, is involved in the transport of zinc ions from the cytoplasm into synaptic vesicles or intracellular organelles. The aim of the present study was to investigate for the first time the percentage of ZnT3-like immunoreactive (ZnT3-LI) neurons in the enteric nervous system (ENS) of the porcine esophagus and denotation of their neurochemical coding. Routine double- and triple-immunofluorescence labeling of cervical, thoracic, and abdominal fragments of esophagus for ZnT3 with protein gene product (PGP 9.5; used as pan-neuronal marker), nitric oxide synthase (NOS), somatostatin, vasoactive intestinal peptide (VIP), vesicular acetylcholine transporter (VAChT), neuropeptide Y (NPY), and galanin (GAL) was performed. The percentage of ZnT3-LI neurons in myenteric ganglia amounted to 50.2 ± 4.7, 63.4 ± 8.3, and 77.1 ± 1.1 % of all PGP 9.5-like immunoreactive neuronal cells in cervical, thoracic, and abdominal esophagus, respectively. In submucous ganglia, these values in particular parts of esophagus amounted to 46.3 ± 6.3, 81.0 ± 8.1, and 74.4 ± 4.4 %. Znt3 co-localized mainly with VAChT, NPY, GAL, NOS, and VIP, but the degree of co-localization depended on the “kind” of enteric ganglia and part of esophagus studied. The obtained results suggest that both ZnT3 and zinc ions may play important and various roles in the neuronal regulation of esophageal functions.

The Influence of Low Doses of Zearalenone on Distribution of Selected Active Substances in Nerve Fibers Within the Circular Muscle Layer of Porcine Ileum

The aim of this study was to investigate, whether low doses (25 % of no observable adverse effect levels values) of zearalenone (ZEN) can affect the expression of active substances in nerve fibers in the muscular layer of porcine ileum. The study was performed on ten immature pigs divided into two groups: experimental group (n = 5), where zearalenone (10 μg/kg body weight) was given for 42 days, and control animals (n = 5), where placebo was administered. Fragments of ileum of all animals were processed for single-labelling immunofluorescence technique using the antibodies against vasoactive intestinal peptide, neuronal form of nitric oxide synthase, cocaine and amphetamine regulatory peptide, galanin, pituitary adenylate cyclase-activating peptide-27 and substance P. The number of nerve fibers immunoreactive to particular substances was evaluated by the counting of nerves per observation field (0.1 mm²). Low doses of zearalenone caused the clear changes in the expression of substances studied. The number of nerve fibers immunoreactive to the majority of substances increased in experimental animals. The exception was only galanin, the expression of which was less after administration of zearalenone. The obtained results for the first time show that even low doses of zearalenone can affect the nerve fibers in the digestive tract.

Characterization of the chicken galanin type I receptor (GalR1) and a novel GalR1-like receptor (GalR1-L)

Galanin is a multi-functional neuropeptide that is widely distributed in the mammalian central nervous system and peripheral tissues. It exerts multiple physiological functions through interaction with 3 known G protein-coupled receptors (GPCR), namely, galanin type I, II and III (GalR1, 2 and 3) receptors, which have only been identified in mammals. In this study, we reported the cloning and characterization of chicken galanin type I receptor (GalR1) and a novel galanin receptor with considerable homology to chicken GalR1, which herein is designated as galanin type I-like receptor (GalR1-L). Chicken GalR1 and GalR1-L full-length cDNAs were cloned from chicken brain and small intestine tissue, respectively. The former encodes a protein of 357 amino acids that shares 84-86% amino acid sequence identities with its mammalian counterparts, whereas the latter encodes a 363-amino acid protein with comparatively lower identities (55-56%) to the mammalian GalR1. Using reverse transcription (RT)-PCR assays, we examined the expression of both receptors in adult chicken tissues. Both receptors were found to be widely distributed in the tissues examined, including brain, small intestine, kidney, ovary, pancreas, pituitary and spleen. Interestingly, cGalR1 expression was detected in different regions of chicken oviduct, while cGalR1-L expression was restricted to the vagina. Using a pGL3-CRE luciferase reporter system, chicken galanin peptide (1-29) was demonstrated to inhibit both basal and forskolin-stimulated luciferase activities, in dose-dependent manners, through the cAMP-mediated signaling pathway in Chinese hamster ovary (CHO) cells expressing either cGalR1 or cGalR1-L, thus suggesting the functional couplings of both receptors to G(i) proteins. Together, the characterization of chicken GalR1 and GalR1-L provides a better understanding of the physiological roles of galanin in avian species.

Inflammation- and axotomy-induced changes in galanin-like immunoreactive (GAL-LI) nerve structures in the porcine descending colon

This study reports on changes caused by chemically driven inflammation and axotomy in galanin-like immunoreactive (GAL-LI) nerve structures in the porcine descending colon. The distribution pattern of GAL-LI structures was studied using the immunofluorescence technique in the circular muscle layer, the myenteric (MP), outer submucous (OSP) and inner submucous plexuses (ISP), and also in the mucosal layer. Under physiological conditions GAL-LI perikarya were shown to constitute 3.68 +/- 0.32%, 7.02 +/- 0.93% and 10.99 +/- 0.71% in MP, OSP and ISP, respectively. Both colitis and axotomy caused an increase in GAL-like immunoreactivity, which was different in particular parts of the bowel segment studied. The numbers of GAL-LI perikarya increased to 14.16 +/- 0.49%, 16.78 +/- 1.09% and 37.46 +/- 1.18% during colitis and 7.92 +/- 0.72%, 10.44 +/- 0.71% and 16.20 +/- 0.96% after axotomy in MP, OSP and ISP, respectively. Both these processes caused an increase in the number of GAL-LI nerve fibres in the circular muscle and mucosal layers as well as the appearance of a population of GAL-LI cells in the mucosa.

Role of galanin receptor 1 in gastric motility in rat

Galanin actions are mediated by distinct galanin receptors (GAL-R), GAL-R1, -R2 and -R3. We investigated the role of GAL-R1 in gastric motility and the expression of GAL-R1 in the rat stomach. In vivo, in urethane-anaesthetized rats, galanin (equipotent for all GAL-Rs) induced a short inhibition of gastric motility, followed by increase in tonic and phasic gastric motility; the latter was significantly reduced by the GAL-R1 antagonist, RWJ-57408. Galanin 1-16 (high affinity for GAL-R1 and -R2) induced a long-lasting decrease of intragastric pressure, which was not modified by RWJ-57408. In vitro, galanin and galanin 1-16 induced increase of intragastric pressure that was not affected by RWJ-57408. Tetrodotoxin (TTX) did not suppress the galanin excitatory effect, whereas the effect of galanin 1-16 on gastric contraction was increased by TTX- or N-nitro-L-arginine, an inhibitor of nitric oxide synthase. GAL-R1 immunoreactivity was localized to cholinergic and tachykinergic neurons and to neurons immunoreactive for nitric oxide synthase or vasoactive intestinal polypeptide. This study suggests that an extrinsic GAL-R1 pathway mediates the galanin excitatory action, whereas an extrinsic, non GAL-R1 pathway is likely to mediate the galanin inhibitory effect in vivo. GAL-R1 intrinsic neurons do not appear to play a major role in the control of gastric motility.

Coexistence of non-adrenergic non-cholinergic inhibitory and excitatory neurotransmitters in a large neuronal subpopulation in the vaginal segment of the chicken oviduct

The presence, distribution and smooth muscle motor effects of galanin and pituitary adenylate cyclase activating peptide (PACAP) were studied in the nerves of the vaginal part of the oviduct of egg-laying hens. Galanin and PACAP immunoreactivity were found both in neuronal perikarya and nerve fibres within the wall of the vaginal segment. Both populations showed a similar distribution pattern. Particularly the circular muscle and the intramural vascular net were richly innervated. A few galanin- and PACAP-IR nerve fibres extended up to the mucosal folds. Multiple labelling showed galanin to be colocalised with PACAP as well as with vasoactive intestinal polypeptide (VIP) and nitric oxide synthase (NOS) in a large, partly intrinsic neuronal subpopulation innervating the smooth muscle wall. Pharmacological in vitro experiments showed that isolated vaginal muscle strips had a spontaneous basal activity that was not affected by the neuronal conductance blocker tetrodotoxin (TTX). Galanin induced concentration-dependent contractions that were TTX-insensitive. PACAP, VIP, nitric oxide (NO) and the NO donor nitroglycerin caused concentration-dependent relaxations that were TTX-insensitive. Electrical field stimulation of isolated muscle strips induced frequency-dependent relaxations that were blocked by TTX and reduced by the NOS blocker L-nitroarginine. These data provide evidence that the vaginal part of the oviduct contains a largely intrinsic, neuronal subpopulation, capable of releasing multiple non-adrenergic, non-cholinergic (NANC) motor agents for the control of local muscular activities. In addition, we provided pharmacological evidence that VIP, NO and PACAP exert an inhibitory and galanin an excitatory action on isolated muscle strips of the vaginal part of the chicken oviduct. Our results suggest that these NANC neurotransmitters play an important role in the regulation of neuromuscular activity in this region.

Distribution of calcitonin gene-related peptide (CGRP), substance P (SP) and galanin (GAL) immunoreactive nerve fibers in the seminal vesicle and prostate of the male sheep

Double immunohistochemistry was used to determine the occurrence and distribution pattern of nerve fibres immunoreactive to calcitonin gene-related peptide (CGRP), substance P (SP) and galanin (GAL) in seminal vesicles and prostate of the male sheep. Numerous CGRP- and SP-immunoreactive (IR) nerve fibres were found in the mucosal layer and smooth musculature of the seminal vesicles and prostate. In both glands nerve terminals immunoreactive to CGRP were more numerous than SP-IR ones. The majority of CGRP-IR nerve fibers showed colocalization of this peptide and SP. In both layers of the seminal vesicle and prostate, rare nerve terminals immunoreactive to GAL were also found. Immunoreactivity to SP was also found in all GAL-IR nerve fibers. The presence of numerous CGRP- and SP-IR nerve fibers in the seminal vesicle and prostate of the male sheep suggests that these neuropeptides may be involved in the sensory transmission and/or control of smooth muscle contractility. On the other hand, a relatively low number of GAL-IR nerve fibers of the seminal vesicle and prostate suggest that this peptide may act as an anti-nociceptive agent. It cannot be excluded that, in the seminal vesicle, GAL may also be involved in the control of the smooth muscle fiber activity. The possible role of CGRP, SP and GAL in the regulation of functions of the accessory sexual glands needs to be determined in further physiological studies.

Effect of TNBS-induced morphological changes on pharmacological contractility of the rat ileum

Intraluminal instillation of 2,4,6-trinitrobenzene sulfonic acid (TNBS) in ethanol is a classical model of colitis in the rat. Little is known about the time-related effect of TNBS on the contractility and morphology of the rat ileum. After 36 h, TNBS induced acute ileitis. Spontaneous activity of longitudinal muscle strips was decreased, as were receptor- and nonreceptor-mediated contractions and contractions induced by electrical stimulation. After 1 week, mucosal integrity was restored, although the thickness of both mucosal and muscle layers was increased. Spontaneous activity, receptor- and nonreceptor-mediated contractions and electrically induced contractions of longitudinal muscle strips were increased due to hypertrophy and hyperplasia of smooth muscle cells. This was confirmed in the contractility study of individual muscle cells. Functional alterations after 1 week were restricted to a decreased response to substance P. TNBS-ileitis in the rat lacks a chronic phase and is accompanied by functional hypocontractility of longitudinal smooth muscle cells during the acute inflammation, whereas the contractility of the longitudinal muscle layer is increased in the postinflammation phase due to structural alterations. There is a selective inhibition of the response to substance P in the postinflammation phase.

Nitric oxide-containing neurons in the bovine gut, with special reference to their relationship with VIP and galanin

The presence and distribution of nicotinamide dinucleotide phosphate diaphorase (NADPH-d)-containing neurons have been studied by means of NADPH-d histochemistry in different regions of the adult cow gut, from the esophagus to the rectum. NADPH-d and nitric oxide synthase (NOS) were constantly recognized to be colocalized in the same neuron. The colocalization of vasoactive intestinal polypeptide (VIP) and galanin in such nitrergic neurons was also studied by means of combined histochemical and immunofluorescence techniques. NADPH-d-positive neurons were present along the myenteric plexus of the entire gut, and in the submucous plexus from the abomasum to the rectum. Notably, they formed two types of nerve networks in the submucous connective tissue of the jejunum-ileum. NADPH-d-positive innervation of the muscle layers occurred throughout the tract, and sometimes a clear correspondence was noted between the number of reactive fibres and the thickness of the muscle. Nitrergic fibres also occurred in the mucosa and often were in relation to glands and blood vessels. The nitrergic neurons varied in size, shape, and intensity of staining, and often their terminals were seen to surround unstained perikarya. Various types of neurons were recognized on the basis of their chemical content; one of them contained galanin, VIP and NOS simultaneously. The present results suggest that the nitrergic neurons of the bovine gastrointestinal tract play roles presumably for controlling the motility of the gut and the conduction of interneuronal impulses.

Interplay between nitric oxide and vasoactive intestinal polypeptide in the pig gastric fundus smooth muscle

The aim of this study was to investigate the exact mechanism of interaction between nitric oxide (NO) and vasoactive intestinal polypeptide (VIP) as inhibitory non-adrenergic non-cholinergic (NANC) neurotransmitters in isolated smooth muscle cells and smooth muscle strips of the pig gastric fundus. In isolated smooth muscle cells, the maximal relaxant effect of VIP (10(-9) M) was inhibited by 94% by the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine (L-NA, 10(-4) M) and by 85% by the inducible NOS (iNOS)-selective inhibitor N-(3-(aminomethyl)-benzyl)acetamide (1400W; 10(-6) M). The relaxant effect of VIP was reduced by more than 70% by the guanylyl cyclase inhibitor 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ; 10(-6) M), the glucocorticoid dexamethasone (10(-5) M) and three protein kinase A inhibitors: (R)-p-cyclic adenosine-3', 5'-monophosphothioate ((R)-p-cAMPS; 10(-6) M), ¿(8R,9S, 11S)-(-)-9-hydroxy-9-n-hexylester-8-methyl-2,3,9,10-tetrahydro-8, 11-epoxy-1H,8H,11H-2,7b,11a-triazadibenzo[a, g]cycloocta[cde]-trin-den-1-one¿ (KT5720; 10(-6) M) and N-(2-(p-bromo-cinnamylamino)ethyl))-5-isoquinoline sulfonamide dihydrochloride (H-89; 10(-5) M). In contrast, no influence of the NOS inhibitors, ODQ, dexamethasone, nor the protein kinase A inhibitors could be observed on the relaxant effect of VIP in smooth muscle strips. These data demonstrate that the experimental method completely changes the influence of NOS inhibitors on the relaxant effect of VIP in the pig gastric fundus. The isolation procedure of the smooth muscle cells might induce iNOS that can be activated by VIP.

Galaninergic signalling and adenylate cyclase

Galanin is a hyperpolarizing, inhibitory neurotransmitter; its recognition by seven transmembrane spanning G-protein-coupled receptors leads to a change in accumulation of cAMP (3'5'-cyclic AMP). Different subtypes of galanin receptor and G-proteins could be manifested in the mode of inhibitory action of galanin receptor on the production of cAMP by adenylate cyclase. Galanin analogues, acting at the adenylate cyclase level as subtype-specific galanin antagonists, can selectively block the inhibitory effect of endogenous galanin and thereby have potential as therapeutic agents for several endocrine, neuroendocrine and neuronal disorders. In this review, the latest results in the field of interplay between galanin-initiated signal transduction and the cAMP pathway are summarized.

The calcitonin gene-related peptide activates both cAMP and NO pathways to induce relaxation of circular smooth muscle cells of guinea-pig ileum

The direct effects and the intracellular pathways of rCGRP were investigated on smooth muscle cells (SMC) isolated by enzymatic digestion from the circular and longitudinal layers of guinea-pig ileum. In circular SMC, rCGRP inhibited CCK8-induced contraction in a concentration-dependent manner (Cmax = 100 microM and EC50 = 0.7 +/- 0.4 nM). Preincubation of SMC with 1 microM Rp-cAMPs, a cAMP antagonist, abolished the relaxing effect of rCGRP; moreover, preincubation of SMC with 100 microM L-NAME, an inhibitor of NOS, inhibited the relaxing effect of rCGRP, hCGRP(8-37), a selective antagonist of rCGRP receptors, inhibited the rCGRP-induced relaxation in a concentration dependent manner whereas the vasoactive intestinal polypeptide (VIP) antagonist had no significant effect. In longitudinal SMC, rCGRP-induced relaxation was abolished by Rp-cAMPs, whereas L-NAME had no effect. In conclusion, rCGRP triggers different intracellular pathways to induce relaxation of circular or longitudinal intestinal SMC; cAMP is involved in cells from both layers while nitric oxide (NO) is involved only in relaxation of circular SMC.

Investigation of 5-HT3 receptor-mediated contraction in guinea-pig distal colon

We investigated the participation of cholinergic and tachykininergic mechanisms in 5-hydroxytryptamine (5-HT)-induced contraction via 5-HT3 receptors in longitudinal and circular muscle of guinea-pig isolated distal colon. 5-HT produced concentration-dependent contractile responses in longitudinal and circular muscle. The 5-HT3 receptor antagonists ramosetron (YM060) ((R)-5-[(1-methyl-3-indolyl) carbonyl]-4,5,6,7-tetrahydro-1H-benzimidazole hydrochloride), YM114 (KAE-393) ((R)-5-[(2,3-dihydro-1-indolyl)carbonyl]-4,5,6,7-tetrahydro-1 H-benzimidazole hydrochloride), ondansetron and granisetron produced a concentration-dependent shift to the right of the 5-HT concentration-response curves in both muscle. However, methysergide and GR113808 had no effect on 5-HT-induced contraction. In the longitudinal muscle, atropine concentration-dependently inhibited 5-HT-induced contraction, and tetrodotoxin abolished it. (+/-)-CP96,345 attenuated the contractile response to 5-HT, but (+/-)-SR48,968 had no effect on it. In the presence of atropine, (+/-)-CP96,345 completely blocked 5-HT-induced contraction. In the circular muscle, atropine had no effect on the contractile response to 5-HT, whereas tetrodotoxin completely suppressed it. The contractile response elicited by 5-HT in the circular muscle was not inhibited by either (+/-)-CP96,345, (+/-)-SR48,968, devazepide, L-365,260 or indomethacin. It is suggested that 5-HT acts via 5-HT3 receptors to release acetylcholine and substance P, which in turn are responsible for contraction of the longitudinal muscle. In the circular muscle, as in the longitudinal muscle, 5-HT-induced contraction is mediated by the 5-HT3 receptor. Unlike the case in longitudinal muscle, however, this contraction involves neither cholinergic nor tachykininergic transmission. It is also suggested that neither cholecystokinin (CCK) nor prostaglandins participate in 5-HT3 receptor-mediated contraction in circular muscle.

VIP-induced relaxation of guinea-pig intestinal smooth muscle cells: sequential involvement of cyclic AMP and nitric oxide

1. A possible interaction between cyclic AMP and nitric oxide (NO) in mediating the relaxant effect of vasoactive intestinal polypeptide (VIP) on intestinal smooth muscle cells has been investigated. The effects of the inhibitor of NO synthesis, NG-nitro-L-arginine methyl ester (L-NAME), have been studied on VIP-, forskolin-, and 8 bromo-cyclic AMP- induced relaxation of cells, dispersed by enzymatic digestion of muscle strips from the circular layer of guinea-pig ileum. 2. VIP alone did not modify the length of isolated muscle cells. By contrast, when the cells were contracted by cholecystokinin octapeptide, CCK8 (10 nM), VIP inhibited this contraction, inducing a concentration-dependent relaxation of the cells. Maximal relaxation was induced by 1 microM VIP (EC50 = 408.2 +/- 16.7 pM). 3. N-ethylmaleimide, inhibitors of adenylate cyclase or somatostatin, abolished the relaxing effect of VIP. (R)-p-cAMPs, an antagonist of cyclic AMP on protein kinase A also inhibited the VIP-induced relaxation by 92.1 +/- 6.3%. Inhibitors of nitric oxide synthase (NOS), L-NAME and L-NMMA, partially inhibited VIP-induced relaxation. The effect of L-NAME was reversed by L-arginine but not by D-arginine. 4. (R)-p-cAMPS and L-NAME also inhibited the cell relaxation induced either by forskolin which directly stimulates adenylate cyclase activity or 8-bromo-cyclic AMP, an analogue of cyclic AMP. 5. When cells were incubated for 30 min with dexamethasone 10 microM, a glucocorticoid known to decrease the synthesis of iNOS, the relaxing effect of a maximal concentration of VIP was decreased by 52 +/- 4% and L-NMMA had no further effect on this residual VIP-induced relaxation. Milrinone, a phosphodiesterase type III inhibitor, potentiated the relaxant effect of VIP. 6. These data demonstrate that the intracellular pathway mediating the relaxant effect of VIP in intestinal smooth muscle cells includes the sequential activation of adenylate cyclase, protein kinase A, activation of NOS and finally production of NO and cyclic GMP. NO could in turn regulate the cyclic AMP-dependent pathway of cell relaxation.

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.

Desensitization of platelet-activating factor receptors, induced by inflammation in guinea pig ileal smooth muscle cells

BACKGROUND/AIMS

Platelet-activating factor (PAF) is involved in the pathophysiology of motility changes induced by intestinal inflammation. The aim of this study was to evaluate a possible desensitization of PAF receptors in guinea pig intestinal smooth muscle cells after experimental inflammation induced by trinitrobenzenesulfonic acid (TNB).

METHODS

Saline or TNB (80 mg/kg) was injected in the intestinal lumen, and the animals were killed 6 days later. Smooth muscle cells from the circular layer were isolated, and cell contraction induced by PAF was measured.

RESULTS

In cells from saline-treated animals, PAF induced a maximal cell contraction at 10 nmol/L and half-maximal contraction (EC50) was 9 +/- 0.2 pmol/L. After TNB injection, the maximal contraction induced by PAF was observed at 1000 nmol/L and EC50 was 300 +/- 70 pmol/L, indicating a 2 logmol/L right shift of the concentration-response curve of PAF. When animals were treated with the PAF antagonist, 20 mg/kg BN52021, or with 2 mg/kg indomethacin for the 6 days after TNB instillation, the right-sided shift of the concentration-response curve of PAF did not occur.

CONCLUSIONS

Desensitization of PAF receptors occurring in intestinal smooth muscle cells after TNB instillation could be mediated in vivo by PAF itself via a prostaglandin-dependent pathway.

Iloprost: intracellular Ca(2+)-dependent contractile effect on isolated smooth muscle cells from guinea-pig ileum

Prostaglandin E2 (PGE2) and iloprost induced a concentration-dependent contraction of smooth muscle cells isolated from the circular layer of guinea-pig ileum. PGE2- and iloprost-induced contractions were inhibited by the selective EP1-receptor antagonist, SC19220 (1-acetyl-2-(8-chloro-10, 11-dihydrodibenz (b,f) (1,4) oxazepine-10-carbonyl)-hydrazine), indicating the involvement of the EP1 subtype of the PGE2 receptor. When cells were incubated for 10 min in the presence of strontium (4 mM L-1), an inhibitor of the release of Ca2+ from intracellular store, the contractile effect of PGE2 and iloprost was inhibited. In contrast, incubation of cells in Ca/2+)-free medium, Ca(2+)-free medium plus EGTA, or in the presence of nifedipine, an organic Ca(2+)-channel blocker, did not alter the PGE2- and iloprost-induced contraction. These observations suggest that the myogenic effect of PGE2 and iloprost on intestinal smooth muscle is dependent on the release of intracellular calcium.

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.

Characterization of cholecystokinin receptors in canine intestinal circular muscle

We localized and characterized the binding of [3H](+/-)-L364,718 in canine small intestine circular muscle. The highest densities of [3H]L364,718 binding were located in the fraction enriched in deep muscular plexus synaptosomal membranes. In this fraction [3H]L364,718 binding was of high density (Bmax 136.78 +/- 53.66 fmol/mg) and high affinity (Kd 1.67 +/- 0.74 nM). Kinetics studies revealed that binding was reversible and yielded a similar Kd value. L364,718, CCK-8-S, and L365,260 fully displaced [3H]L364,718 binding, but ligands at CCKB receptors, gastrin-17, and YM022 did not. Therefore, CCKA receptors in canine intestine circular muscle are located on nerve endings.

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.

Localization and inhibitory actions of galanin at the feline lower esophageal sphincter

Intrinsic reflexes of the lower esophageal sphincter (LES) are mediated by specific arrangements of excitatory and inhibitory nerves. We have previously described an excitatory reflex at the feline LES mediated by a bombesin-like peptide (BN) which causes release of substance P (SP) to directly contract the LES. Galanin is a neurotransmitter in the enteric nervous system which colocalizes in neurons containing vasoactive intestinal peptide (VIP). The aims of this study were to determine: (1) the distribution of galanin at the feline LES; (2) the effect of galanin on basal LES tone; (3) the effect of galanin on agonist-induced LES contractions by BN, SP and bethanechol; and (4) the effect of galanin on LES relaxation induced by esophageal distension and exogenous VIP. Galanin-like immunoreactivity (galanin-LI) was localized in neurons that were widely distributed throughout the LES and adjacent organs. Galanin-LI was most abundant in the circular muscle, muscularis mucosa and myenteric plexus of the LES. In anesthetized cats, intra-arterial galanin had no effect on basal LES pressure in a dose range of 10(-11) to 10(-6) g/kg. Galanin (5.10(-7) g/kg) reduced the LES contractile response to SP by 65 +/- 8% (P = 0.0001). This galanin-mediated inhibition of SP was not blocked by tetrodotoxin. Galanin similarly decreased the LES contractile response to BN (63 +/- 7%, P = 0.005) and bethanechol (55 +/- 17%, P = 0.012). Galanin had no effect on the LES relaxation induced by esophageal distension or exogenous VIP. We conclude: (1) galanin-LI is present in neurons at the feline LES; (2) galanin has no effect on basal sphincter tone, but inhibits contractions of the LES by both direct and indirect agonists; and (3) galanin does not effect the LES relaxation induced by esophageal distension or VIP.

Galanin-induced relaxation in gastric smooth muscle cells is mediated by cyclic AMP

Galanin has numerous effects on gastrointestinal motility in different species; however, its cellular basis of action in mediating these effects is unclear. Dispersed gastric smooth muscle cells have been shown to possess high-affinity galanin receptors that increase cAMP and cause relaxation. Recent studies show some smooth muscle relaxants such as VIP cause relaxation by both cAMP-dependent and -independent mechanisms. It is unknown if galanin's cellular basis of relaxation is similar or different from that of VIP. To investigate galanin's relaxant effect and compare it to VIP's effect, dispersed smooth muscle cells from guinea pig stomach were prepared by collagenase digestion. The mean length in resting cells was 110 +/- 2 microns and, with carbachol treatment, contracted to 89 +/- 2 microns. VIP and galanin alone had no effect on cell length, but each caused a dose-dependent inhibition of carbachol-induced contraction and both had an EC50 of 3-7 nM. Galanin (1 microM) and VIP (1 microM) increased cellular cAMP from 118 +/- 10 pmol/10(6) cells in control to 212 +/- 14 and 214 +/- 12 pmol/10(6) cells, respectively. The protein kinase A inhibitor, Rp-cAMPS, at 100 microM, completely inhibited the relaxant effect of an EC50 concentration of galanin (3 nM), but only inhibited that by VIP by 80% (p < 0.05). Adding the nitric oxide inhibitor, L-NNA (NG-nitro-L-arginine), at 100 microM did not alter the length of resting cells or inhibit carbachol-induced contraction. However, L-NNA (100 microM) decreased VIP-induced relaxation by 45%, whereas it had no effect on galanin-induced relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of galanin on short circuit current and electrolyte transport in rabbit ileum

Galanin decreased short circuit current (Isc) and increased active Na+ and Cl- absorption in rabbit ileum. In the absence of calcium, the galanin-induced decrease in Isc was inhibited by approximately 60%. Tetrodotoxin significantly reduced the effect of galanin on Isc, and tetrodotoxin and EGTA totally blocked the effect, indicating that the nonneuronal mediator of the effect is Ca2+ dependent. Galanin binding to basolateral membranes prepared from ileal epithelial cells was specific and of high affinity. These results suggest the involvement of this peptide in the regulation of intestinal epithelial cell function.

Galanin induces opposite effects via different intracellular pathways in smooth muscle cells from dog colon

Smooth muscle cells isolated by enzymatic digestion were used to determine the direct effects of galanin on circular and longitudinal muscle layers from dog proximal colon and to investigate the intracellular pathways involved in these effects. Effects of galanin were compared to those observed with other contracting [cholecystokinin octapeptide (CCK8)] and relaxing [vasoactive intestinal peptide (VIP)] agents. In longitudinal cells, galanin and CCK8 induced a contraction that was maximal at 1 nM galanin and 1 nM CCK8 and was 23.9 +/- 4.5% and 23.4 +/- 3.4%, respectively, of the length of resting cells. Incubation of cells in Ca(2+)-free medium or in the presence of nifedipine caused an inhibition of galanin-induced contraction whereas it had no effect on the contraction induced by CCK8. Vasoactive intestinal peptide, forskolin, and 8 bromo cAMP inhibited CCK-induced contraction but failed to inhibit contraction induced by galanin. The contraction induced by galanin was abolished; the CCK-induced contraction was unchanged by pertussis toxin. In circular cells, CCK8 induced a contraction that was maximal at 10 nM and was 24.2 +/- 2.6%. Galanin had no effect by itself. When cells were preincubated (1 min) with galanin (10 fM-1 microM), the CCK8-induced contraction was inhibited, with a maximal effect at 10 nM galanin. Likewise, VIP inhibited the CCK8-induced contraction with a maximal effect at 1 microM. Preincubation of cells with somatostatin, N-ethylmaleimide, and (R)-p-cAMPS inhibited galanin- and VIP-induced relaxation. In conclusion, galanin induces a contraction of longitudinal smooth muscle cells that is dependent on an influx of extracellular calcium and an activation of pertussis toxin G-protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological evidence for the release of galanin from rat stomach

The neuropeptide galanin has been shown to occur in nerve fibres in the circular muscle layer of the rat stomach. The present experiments aimed at demonstrating a functional correlate for this observation by testing the motor effects of galanin on circular strips of the rat gastric corpus in vitro. Exogenous galanin elicited only small contractions of the smooth muscle which were dose-related but did not show a clear sigmoid dose-response relationship. These responses were resistant to atropine plus guanethidine or TTX. When the muscle strips were electrically stimulated, they showed pronounced rebound contractions after the end of the stimulus. These rebound contractions were significantly reduced by either desensitizing the strips to galanin or by addition of spantide. It is concluded that galanin is released from the myenteric plexus in the stomach and acts to modulate gastric contractions either postsynaptically or by modifying the release of tachykinins.

Stimulatory (EP1 and EP3) and inhibitory (EP2) prostaglandin E2 receptors in isolated ileal smooth muscle cells

Isolated smooth muscle cells from the circular layer of pig and guinea-pig ileum were used to study the effect of prostaglandin E2 (PGE2) and three PGE2 receptor (EP) agonists; iloprost (EP1), butaprost (EP2) and enprostil (EP3). In pig cells, PGE2 and enprostil induced cell contraction (22.1 and 21.5% shortening of cell length, obtained at 10 nM for PGE2 and 1 nM for enprostil, respectively). Iloprost and butaprost had no contractile effect. However, the cholecystokinin octapeptide (CCK-8; 10 nM)-induced contraction was inhibited when cells were preincubated with iloprost or butaprost. In guinea-pig cells, PGE2, butaprost and iloprost induced cell contraction, whereas enprostil had no effect (23.1% for 10 nM PGE2, 22.8% for 1 nM butaprost and 22.6% for 10 nM iloprost). Preincubation with SC19220 (EP1 antagonist) inhibited the PGE2-, butaprost- and iloprost-induced contractions. When the contractile effect of PGE2, butaprost and iloprost was inhibited by addition of SC19220, these agents inhibited the cell contraction induced by CCK-8 (1 nM). Smooth muscle cells from guinea-pig and pig ileum express two PGE2 receptor subtypes that induce opposite effect. EP1 and EP3 receptors mediate cell contraction in guinea-pig and pig, respectively, whereas EP2 receptors mediate cell relaxation in both species.