Impacts of peripheral obestatin on colonic motility and secretion in conscious fed rats
Introduction
Obestatin, a novel 23-amino acid peptide recently identified from rat stomach, is derived from the mammalian preproghrelin gene which also encodes ghrelin [38]. It has been proposed that these newly discovered preproghrelin-derived peptides, ghrelin and obestatin, have opposite effects on feeding behaviors, e.g., ghrelin enhances food intake whereas obestatin inhibits it [38]. It was originally suggested that obestatin binds to an orphan G protein-coupled receptor (GRP), termed GPR39 [5], [38]. High levels of GPR39 mRNA have been found in the amygdala, hippocampus, and auditory cortex but not in the hypothalamus [16], [21]. However, recent studies indicate that obestatin is not the endogenous cognate ligand for GRP39 [6], [15], [19], [37].
Obestatin has been shown to inhibit food intake in rodents, however, controversial results exist regarding its anorexigenic actions on feeding behaviors [2], [4], [8], [11], [12], [14], [18], [24], [29], [31], [36], [37], [38], [40]. Obestatin may modulate many brain functions [4], [26], [32], decrease growth hormone secretion in vivo [40], and stimulate the secretion of pancreatic juice enzymes [17] in rats. Human studies indicate that increased obestatin levels, decreased ghrelin levels, and a decreased ghrelin/obestatin ratio characterize obesity in women [35], whereas plasma obestatin level is decreased in patients with type 2 diabetes mellitus and impaired glucose tolerance [25]. Both obestatin and ghrelin levels are increased in anorexic subjects and decreased in human obesity [23], suggesting that obestatin may serve as a marker reflecting changes in the nutritional state in modulating human energy homeostasis. Surprisingly, very recent research identified a new role for obestatin in promoting β-cell and human islet cell survival and stimulating the expression of the main regulatory β-cell genes [13]. Taken together, these observations imply that obestatin may have some unknown but important novel multifaceted roles in the regulation of biological functions that have not been investigated and which deserve further exploration.
With respect to gastrointestinal motility, the majority of obestatin studies have focused on its regulation on the upper gut [1], [8], [10], [11], [38]. For example, peripheral obestatin treatment inhibits gastric emptying and gastroduodenal motility [10], [38], whereas some studies show that obestatin does not impact gastric and small intestinal motility in vivo or in vitro [1], [8], [11]. Ghrelin, the appetite rival of obestatin, accelerates colonic transit time in rats [34]. Very recently, obestatin-immunoreactive cells were found to be present in the pancreas and in the most parts of the gastrointestinal tract in rats, including the colon [39]. Therefore, it would be very intriguing to know the potential effects of obestatin on colon motor functions. Until now, there has been no study performed to address the impacts of obestatin on rat colonic motor functions. In the present study, we attempted to determine the possible effects of intravenously (IV) injected obestatin on colonic motor and secretory functions, including colonic transit time, fecal pellet output, and fecal content in conscious fed rats. Since corticotropin-releasing factor (CRF) is a well-known colonoprokinetic peptide [20], we used it as a stimulatory agent in our newly developed colon transit and secretory model to assess the value of this model for evaluating prokinetics.
Section snippets
Animals
Male Sprague-Dawley rats (National Laboratory Animal Center, Taipei, Taiwan), weighing 250–320 g, were used at the start of the experiment and housed in group cages under controlled illumination (light cycle: 08:00–20:00), humidity, and temperature (22.5 ± 1.5 °C) with free access to water and laboratory chow pellets (LabDiet®, Brentwood, MO, USA). All experiments were performed beginning at 9 AM in freely moving conscious rats, in accordance with guidelines, which have been approved by the
Colonic transit time
IV injection of obestatin at 45, 100, and 300 nmol/kg did not affect the colonic transit time (323.7 ± 31.8, 327.1 ± 40.8, and 354.9 ± 40.0 min vs. 299.3 ± 33.4 min, p > 0.05) compared with IV saline controls (Fig. 1). In contrast, IV injection of h/rCRF at 30 nmol/kg significantly accelerated colonic transit time (68.1 ± 23.9 min vs. 299.3 ± 33.4 min, p < 0.001) in conscious fed rats.
Fecal pellet output
IV obestatin (45, 100, and 300 nmol/kg) did not modify the fecal pellet output (0.83 ± 0.59, 0.50 ± 0.20, and 1.17 ± 0.30 h−1 vs. 1.25 ± 0.61 h−1
Discussion
Our study was carried out to investigate the peripheral effects of obestatin on colonic transit and secretion in rodents. Previous studies only investigated either colonic motility or secretory function. Thus, we designed an animal model for simultaneous measurement of both functions. The mean obtained colonic transit time of IV saline-injected control rats was 299 min in our study which was comparable to a transit time of 320 min in a previous study that used a similar trypan blue dye method [34]
Acknowledgements
This work was supported by grants from Veterans General Hospitals University System of Taiwan Joint Research Program (by Tsou's Foundation, VGHUST96-P1-03 to C.Y.C. and E.J.C.) and in part from National Science Council, Taiwan (NSC 95-2314-B-010-098-MY2 to C.Y.C.). The authors also thank Chung Wen-Pin, MS and Miss Lee Chieh-Ju for their excellent technical assistance, as well as Chi Chin-Wen, Ph.D., Hung Mei-Whey, MS, and the Clinical Research Core Laboratory, Taipei Veterans General Hospital.
References (40)
- et al.
Obestatin improves memory performance and causes anxiolytic effects in rats
Biochem Biophys Res Commun
(2007) - et al.
Des-acyl ghrelin acts by CRF type 2 receptors to disrupt fasted stomach motility in conscious rats
Gastroenterology
(2005) - et al.
Lack of interaction between peripheral injection of CCK and obestatin in the regulation of gastric satiety signaling in rodents
Peptides
(2006) - et al.
Direct and indirect effects of obestatin peptides on food intake and the regulation of glucose homeostasis and insulin secretion in mice
Peptides
(2007) - et al.
Obestatin reduces food intake and suppresses body weight gain in rodents
Biochem Biophys Res Commun
(2007) - et al.
Obestatin does not activate orphan G protein-coupled receptor GPR39
Biochem Biophys Res Commun
(2006) - et al.
Peripheral corticotropin-releasing factor and stress-stimulated colonic motor activity involve type 1 receptor in rats
Gastroenterology
(2000) - et al.
Cloning and characterization of two human G protein-coupled receptor genes (GPR38 and GPR39) related to the growth hormone secretagogue and neurotensin receptors
Genomics
(1997) - et al.
Peripheral corticotropin-releasing factor induces diarrhea in rats: role of CRF1 receptor in fecal watery excretion
Eur J Pharmacol
(2002) - et al.
Obestatin alters sleep in rats
Neurosci Lett
(2006)
Neither intravenous nor intracerebroventricular administration of obestatin affects the secretion of GH, PRL, TSH and ACTH in rats
Regul Pept
Little or no ability of obestatin to interact with ghrelin or modify motility in the rat gastrointestinal tract
Br J Pharmacol
Obestatin inhibits feeding but does not modulate GH and corticosterone secretion in the rat
J Endocrinol Invest
Obestatin-mediated proliferation of human retinal pigment epithelial cells: regulatory mechanisms
J Cell Physiol
Obestatin, acylated and total ghrelin concentrations in the perinatal rat pancreas
Horm Res
Comment on “obestatin, a peptide encoded by the ghrelin gene, opposes ghrelin's effects on food intake”
Science
Effect of peripheral obestatin on gastric emptying and intestinal contractility in rodents
Neurogastroenterol Motil
Distribution and biological activity of obestatin in the rat
J Endocrinol
Obestatin inhibits motor activity in the antrum and duodenum in the fed state of conscious rats
Am J Physiol Gastrointest Liver Physiol
Preproghrelin-derived peptide, obestatin, fails to influence food intake in lean or obese rodents
Obesity
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