Regulation of Gastrointestinal Motility by Motilin and Ghrelin in Vertebrates

The energy balance of vertebrates is regulated by the difference in energy input and energy expenditure. Generally, most vertebrates obtain their energy from nutrients of foods through the gastrointestinal (GI) tract. Therefore, food intake and following food digestion, including motility of the GI tract, secretion and absorption, are crucial physiological events for energy homeostasis. GI motility changes depending on feeding, and GI motility is divided into fasting (interdigestive) and postprandial (digestive) contraction patterns. GI motility is controlled by contractility of smooth muscles of the GI tract, extrinsic and intrinsic neurons (motor and sensory) and some hormones. In mammals, ghrelin (GHRL) and motilin (MLN) stimulate appetite and GI motility and contribute to the regulation of energy homeostasis. GHRL and MLN are produced in the mucosal layer of the stomach and upper small intestine, respectively. GHRL is a multifunctional peptide and is involved in glucose metabolism, endocrine/exocrine functions and cardiovascular and reproductive functions, in addition to feeding and GI motility in mammals. On the other hand, the action of MLN is restricted and species such as rodentia, including mice and rats, lack MLN peptide and its receptor. From a phylogenetic point of view, GHRL and its receptor GHS-R1a have been identified in various vertebrates, and their structural features and various physiological functions have been revealed. On the other hand, MLN or MLN-like peptide (MLN-LP) and its receptors have been found only in some fish, birds and mammals. Here, we review the actions of GHRL and MLN with a focus on contractility of the GI tract of species from fish to mammals

Ghrelin Receptor in Two Species of Anuran Amphibian, Bullfrog (Rana catesbeiana), and Japanese Tree Frog (Hyla japonica)

We have identified cDNA encoding a functional growth hormone secretagogue-receptor 1a (GHS-R1a, ghrelin receptor) in two species of anuran amphibian, the bullfrog (Rana catesbeiana), and the Japanese tree frog (Hyla japonica). Deduced receptor protein for bullfrog and Japanese tree frog (tree frog) was comprised of 374- and 371-amino acids, respectively. The two receptors shared 86% identity, and are grouped to the clade of the tetrapod homologs by phylogenetic analysis. In functional analyses, ghrelin and GHS-R1a agonists increased intracellular Ca2+ concentration in GHS-R1a-transfected-HEK293 cell, but ligand selectivity of ghrelin with Ser3 and Thr3 was not observed between the two receptors. Bullfrog GHS-R1a mRNA was mainly expressed in the brain, stomach, and testis. In the brain, the gene expression was detected in the diencephalon and mesencephalon, but not in the pituitary. Tree frog GHS-R1a mRNA was predominantly expressed in the gastrointestinal tract and ovary, but not detected in the pituitary. In bullfrog stomach but not the brain, GHS-R1a mRNA expression increased after 10 days of fasting. For tree frog, GHS-R1a mRNA expression was increased in the brain, stomach and ventral skin by 10 days of fasting, and in the stomach and ventral skin by a dehydration treatment. Intracerebroventricular injection of ghrelin in dehydrated tree frog did not affect water absorption from the ventral skin. These results suggest that ghrelin is involved in energy homeostasis and possibly in osmoregulation in frogs

Ghrelin-like peptide with fatty acid modification and O-glycosylation in the red stingray, Dasyatis akajei

<p>Abstract</p> <p>Background</p> <p>Ghrelin (GRLN) is now known to be an appetite-stimulating and growth hormone (GH)-releasing peptide that is predominantly synthesized and secreted from the stomachs of various vertebrate species from fish to mammals. Here, we report a GRLN-like peptide (GRLN-LP) in a cartilaginous fish, the red stingray, <it>Dasyatis akajei</it>.</p> <p>Results</p> <p>The purified peptide contains 16 amino acids (GVSFHPQPRS¹⁰TSKPSA), and the serine residue at position 3 is modified by <it>n</it>-octanoic acid. The modification is the characteristic of GRLN. The six N-terminal amino acid residues (GVSFHP) were identical to another elasmobranch shark GRLN-LP that was recently identified although it had low identity with other GRLN peptides. Therefore, we designated this peptide stingray GRLN-LP. Uniquely, stingray GRLN-LP was <it>O</it>-glycosylated with mucin-type glycan chains [<it>N</it>-acetyl hexosamine (HexNAc)₃hexose(Hex)₂] at threonine at position 11 (Thr-11) or both serine at position 10 (Ser-10) and Thr-11. Removal of the glycan structure by <it>O</it>-glycanase made the <it>in vitro </it>activity of stingray GRLN-LP decreased when it was evaluated by the increase in intracellular Ca²⁺concentrations using a rat GHS-R1a-expressing cell line, suggesting that the glycan structure plays an important role for maintaining the activity of stingray GRLN-LP.</p> <p>Conclusions</p> <p>This study reveals the structural diversity of GRLN and GRLN-LP in vertebrates.</p

Molecular cloning of growth hormone secretagogue-receptor and effect of quail ghrelin on gastrointestinal motility in Japanese quail

We identified a growth hormone secretagogue-receptor (GHS-R) for ghrelin (GRLN) in the Japanese quail, and examined relationship between its receptor distribution and the effects of ghrelin on the gastrointestinal tract of the quail. GHS-R expression and GRLN-induced response were also investigated in the chicken and compared with quail. Several types of GHS-R, namely GHS-R1a-L, GHS-R1a-S, GHS-R1aV, GHS-R1b, GHS-R1bV and GHS-R1tv-like receptor, were identified in quail cerebellum cDNA. Amino acid sequence of quail GHS-R1a-L was 98% identical to that of chicken GHS-R1a. GHS-R1a mRNA was expressed heterogeneously in the quail gastrointestinal tract with a high expression level in the colon, moderate levels in the esophagus and crop, and low levels in the proventriculus, gizzard and small intestine. The region-specific expression pattern was almost the same as that in the chicken. Chicken and quail GRLN caused contraction in the crop, proventriculus and colon of both the quail and chicken, whereas the small intestine was less sensitive. However, the contractile efficacy was more potent in the chicken than in the quail. Chicken motilin (MTL), another gut peptide, structurally resemble to GRLN, caused marked contraction in the small intestine of both the quail and chicken, and the region-specific effect of MTL was opposite to that of GRLN. In conclusion, GRLN mainly induces the contractile responses of the upper and lower gastrointestinal tract and MTL stimulates motility of the middle intestine in both the quail and chicken. Regions in which GRLN acts were consistent with the distribution of GHS-R1a mRNA, but the contractile efficacy was different in the quail and chicken. These results suggest a species-specific contribution of GRLN in the regulation of avian gastrointestinal contractility

Contractile effects of ghrelin-related peptides on the chicken gastrointestinal tract in vitro

Ghrelin is an endogenous ligand for growth hormone secretagogue receptor (GHS-R), and it stimulates growth hormone (GH) release, food intake and gastrointestinal motility in mammals. Ghrelin has also been identified in the chicken, but this peptide inhibits food intake in the chicken. We examined the effects of ghrelin and related peptides on contractility of the isolated chicken gastrointestinal tract in vitro. Among ghrelin-related peptides examined (1 μM of rat ghrelin, human ghrelin, chicken ghrelin and growth hormone releasing peptide-6 (GHRP-6)), only chicken ghrelin was effective on contraction of the chicken gastrointestinal tract. Des-acyl chicken ghrelin was ineffective, suggesting that octanoylation at Ser3 residue of chicken ghrelin was essential for inducing the contraction. Amplitude of chicken ghrelin-induced contraction was region-specific: highest in the crop and colon, moderate in the esophagus and proventriculus, and weak in the small intestine. The contractile response to chicken ghrelin in the crop was not affected by tetrodotoxin (TTX), but that in the proventriculus was decreased by TTX and atropine to the same extents. d-Lys3-GHRP-6 (a GHS-R antagonist) caused a transient contraction and inhibited the effect of chicken ghrelin without affecting the high-K+-induced contraction. Chicken ghrelin potentiated electrical field stimulation-induced cholinergic contraction without affecting the responsiveness to bath-applied carbachol in the proventriculus. The location of GHS-R differs in the crop (smooth muscle) and proventriculus (smooth muscle and enteric neurons). These results indicate that ghrelin has contractile activity on gastrointestinal tract in the chicken in vitro, and the effect was region-specific. The action would be mediated through the GHS-R, which is highly sensitive to chicken ghrelin

An Analysis of Obstruction in Cooperative Work over a Computer Network

In a cooperative process of designing software spec-i cations, various activities such as deciding, chang-ing or validating a specication are performed. On such activities over a computer network, an ecien-cy of work or a quality of the software products seem to depend heavily on the environment. Those envi-ronments are characterized by the parameters such as face-to-face/distributed work space, verbal/textual me-dia, synchronous/asynchronous communication. In this paper, we report results of the analysis to recog-nize obstruction in cooperative work over a computer network.