Short-term oral oleoyl-estrone decreases the expression of ghrelin in the rat stomach

Oleoyl-estrone (OE) mobilizes body fat and decreases food intake. The precise mechanism of its modulation of appetite is unknown. Since the effects of OE on food intake appear early, here we studied the effect of OE on the expression of gut peptides that affect short-term ingestive behavior: ghrelin, leptin, CCK, PYY, and GLP-1. Two hours after a single OE dose, adult male rats were killed and their stomach fundus and intestine sections were dissected and processed for real-time PCR amplification. Semi-quantitative estimation of gene mRNA tissue levels showed that OE markedly decreased ghrelin expression in the stomach; leptin mRNA was unchanged; CCK mRNA decreased in the proximal intestine while PYY and GLP-1 expression in the intestine was not altered. Our results indicate that the short-term decrease in food intake induced by OE may be essentially the consequence of a marked decrease in the expression of ghrelin in the stomach.     

Glucagon receptor expression and glucagon stimulation of ghrelin secretion in rat stomach

The present study was performed to evaluate the role of glucagon in the regulation of ghrelin secretion from the rat stomach. mRNA for ghrelin and glucagon receptor was expressed predominantly in the lower body and pylorus of stomach, but little or not in the upper body and cardia. Ghrelin- and glucagon receptor-immunoreactive cells were detected in lamina propria mucosae of stomach and some cells expressed both. Intravenous administration of glucagon caused transient increases in both acyl- and desacyl-ghrelin levels in the gastric vein within 10 min, which was followed by gradual increases in desacyl-ghrelin levels until 60 min. Steady state levels of ghrelin mRNA in the stomach were increased by 1.9-fold 20 min after glucagon administration, but not at 5 or 120 min. These results suggest that glucagon stimulates acute release of both forms of ghrelin and thereafter upregulates synthesis and release of desacyl-ghrelin in the rat stomach.     

Somatostatin suppresses ghrelin secretion from the rat stomach

Ghrelin is an acylated peptide that stimulates food intake and the secretion of growth hormone. While ghrelin is predominantly synthesized in a subset of endocrine cells in the oxyntic gland of the human and rat stomach, the mechanism regulating ghrelin secretion remains unknown. Somatostatin, a peptide produced in the gastric oxyntic mucosa, is known to suppress secretion of several gastrointestinal peptides in a paracrine fashion. By double immunohistochemistry, we demonstrated that somatostatin-immunoreactive cells contact ghrelin-immunoreactive cells. A single intravenous injection of somatostatin reduced the systemic plasma concentration of ghrelin in rats. Continuous infusion of somatostatin into the gastric artery of the vascularly perfused rat stomach suppressed ghrelin secretion in both dose- and time-dependent manner. These findings indicate that ghrelin secretion from the stomach is regulated by gastric somatostatin.     

Estrogen receptor 1 modulates circadian rhythms in adult female mice

Estradiol influences the level and distribution of daily activity, the duration of the free-running period, and the behavioral phase response to light pulses. However, the mechanisms by which estradiol regulates daily and circadian rhythms are not fully understood. We tested the hypothesis that estrogens modulate daily activity patterns via both classical and “non-classical” actions at the estrogen receptor subtype 1 (ESR1). We used female transgenic mice with mutations in their estrogen response pathways; ESR1 knock-out (ERKO) mice and “non-classical” estrogen receptor knock-in (NERKI) mice. NERKI mice have an ESR1 receptor with a mutation in the estrogen-response-element binding domain, allowing only actions via “non-classical” genomic and second messenger pathways. Ovariectomized female NERKI, ERKO, and wildtype (WT) mice were given a subcutaneous capsule with low- or high-dose estradiol and compared with counterparts with no hormone replacement. We measured wheel-running activity in a light:dark cycle and constant darkness, and the behavioral phase response to light pulses given at different points during the subjective day and night. Estradiol increased average daily wheel-running, consolidated activity to the dark phase, and shortened the endogenous period in WT, but not NERKI and ERKO mice. The timing of activity onset during entrainment was advanced in all estradiol-treated animals regardless of genotype suggesting an ESR1-independent mechanism. We propose that estradiol modifies period, activity level, and distribution of activity via classical actions of ESR1 whereas an ESR1 independent mechanism regulates the phase of rhythms.     

Lysophospholipase I identified as a ghrelin deacylation enzyme in rat stomach

Ghrelin, discovered in rat stomach as an endogenous growth hormone secretagogue, is octanoylated at the Ser3 residue. Since this octanoylation is essential for the functions of ghrelin, the enzymes that catalyze acylation for ghrelin biosynthesis and deacylation (deactivation step) must be considered as important regulators. We found that rat stomach homogenate contained ghrelin deacylation activity, and we isolated the active fractions by column chromatography. After sequencing and expressing candidate proteins, the ghrelin deacylation enzyme in the stomach was identified as lysophospholipase I (LysoPLA I). The enzyme properties were examined using recombinant rat LysoPLA I expressed in Escherichia coli. K(m) and V(max) values were determined as 6.5 microM and 2.3 micromol/min/mg for ghrelin and 2.2 x 10(2) microM and 0.5 micromol/min/mg for lysophosphatidylcholine (LysoPC), respectively. The deacylation of both substrates was inhibited by methyl arachidonyl fluorophosphonate (MAFP), which is known as an irreversible inhibitor of LysoPLA I. These results reveal that LysoPLA I catalyzes the removal of n-octanoic acid from ghrelin to form des-acyl ghrelin. Identification of the ghrelin deacylation enzyme in the stomach and a deacylation inhibitor will be helpful in investigating ghrelin biosynthesis.     

Estrogen modulates the expression of myosin heavy chain in detrusor smooth muscle

The effect of low serum estrogen levels on urinary bladder function remains poorly understood. Using a rabbit model, we analyzed the effects of estrogen on the expression of the isoforms of myosin, the molecular motor for muscle contraction, in detrusor smooth muscle. Expression of myosin heavy chain (MHC) isoforms, which differ in the COOH-terminal (SM1 and SM2) and the NH(2)-terminal (SM-A and SM-B) regions as a result of alternative splicing of the mRNA at either the 3'- or 5'-ends, was analyzed in age-matched female rabbits that were sham operated, ovariectomized (Ovx), and given estrogen after ovariectomy (4 rabbits/group). Ovx rabbits showed a significant decrease in the overall MHC content per gram of wet detrusor smooth muscle compared with controls (P < 0.04), which was reversed by estrogen replacement (P < 0.02). MHC content, as a proportion of total milligram of protein in the bladder tissue extracted, was also increased in estrogen-treated Ovx rabbits. Quantitative competitive RT-PCR revealed 1.72-, 2.63-, and 5.82 x 10(6) copies of MHC mRNA/100 ng total mRNA in Ovx, control, and estrogen-treated rabbits, respectively (P < 0.01). RT-PCR analysis using oligonucleotides specific for the region containing the SM1/SM2 MHC alternative splice sites indicated a lower SM2-to-SM1 ratio in estrogen-treated compared with control and Ovx rabbits (P < 0.05). Similarly, SDS-PAGE analysis of extracted myosin from estrogen-treated rabbits revealed a significantly lower SM2-to-SM1 isoform ratio compared with control and Ovx rabbits (P < 0.05). Expression of the SM-A and SM-B isoforms was not affected. These results indicate that myosin content is increased upon estrogen replacement in Ovx rabbits and that the abundance of SM1 relative to SM2 is greater in estrogen-treated rabbits compared with normal and Ovx rabbits. These data suggest that estrogen affects alternative splicing at the 3'-end of the MHC pre-mRNA to increase the proportion of SM1 vs. SM2.     

Effects of high-fat feeding and fasting on ghrelin expression in the mouse stomach

Ghrelin is a peptide identified as an endogenous ligand for the growth hormone secretagogue receptor. Studies have shown that ghrelin stimulates growth hormone, promotes food intake and decreases energy expenditure. Furthermore, feeding status seems to influence plasma ghrelin levels, as these are increased during fasting, whereas feeding and oral glucose intake reduce plasma ghrelin. This study examined whether standardized obesity and fasting affect cellular expression of ghrelin. Specimens from the gastrointestinal tract of fed or 18-h fasted, low-fat or high-fat fed (10 weeks on diet) C57BL/6J mice were studied by immunocytochemistry (ICC) for ghrelin and in situ hybridization (ISH) for ghrelin mRNA. Ghrelin was expressed in especially the corpus but also the antrum of the stomach of all groups studied. Cells positive for ghrelin and ghrelin mRNA in the stomach were reduced in high-fat fed mice. In contrast, ghrelin expression was not affected by fasting. The reduction in ghrelin expression in the high-fat fed mice was associated with a reduction in plasma levels of ghrelin, whereas after fasting, when expression rate was not altered, there was an increase in plasma ghrelin. In conclusion, ghrelin is highly expressed in the corpus and antrum of the stomach of C57BL/6J mice. This expression is reduced in obesity, whereas fasting has no effect.     

Estrogen directly modulates circadian rhythms of PER2 expression in the uterus

Fluctuations in circulating estrogen and progesterone levels associated with the estrous cycle alter circadian rhythms of physiology and behavior in female rodents. Endogenously applied estrogen shortens the period of the locomotor activity rhythm in rodents. We recently found that estrogen implants affect Period (Per) gene expression in the suprachiasmatic nucleus (SCN; central clock) and uterus of rats in vivo. To explore whether estrogen directly influences the circadian clock in the SCN and/or tissues of the reproductive system, we examined the effects of 17beta-estradiol (E(2)) on PER2::LUCIFERASE (PER2::LUC) expression in tissue explant cultures from ovariectomized PER2::LUC knockin mice. E(2) applied to explanted cultures shortened the period of rhythmic PER2::LUC expression in the uterus but did not change the period of PER2::LUC expression in the SCN. Raloxifene, a selective estrogen receptor modulator and known E(2) antagonist in uterine tissues, attenuated the effect of E(2) on the period of the PER2::LUC rhythm in the uterus. These data indicate that estrogen directly affects the timing of the molecular clock in the uterus via an estrogen receptor-mediated response.     

Regulation of ghrelin gene expression in stomach and feeding response to a ghrelin analogue in two strains of rats

Ghrelin is a peptide produced by the stomach and released into the circulation. As a natural ligand of the growth hormone secretagogue (GHS) receptor, it stimulates growth hormone secretion but it also stimulates feeding in humans and rodents. The orexigenic effect of ghrelin has been related to AgRP/NPY and orexin pathways. We proposed that ghrelin might be involved in the susceptibility to diet induced obesity and in the regulation of macronutrient selection. We have investigated these hypotheses in two strains of rat, the Osborne–Mendel (OM) rat that prefers diets high in fat and is sensitive to dietary obesity and the S5B/P1 (S5B) rat that prefers a low fat diet and is resistant to high fat diet induced obesity.

OM and S5B rats were adapted to a choice of high fat (HF) and low fat (LF) diet for 2 weeks. GHRP-2, an analogue of ghrelin, was injected intraperitoneally into satiated and 24 h fasted rats at doses of 10, 30 and 90 nmol. Food intake was measured over the next 4 h period. In satiated S5B rats, GHRP-2 stimulated intake of the LF diet in a dose dependent manner but did not affect the intake of the HF diet. In satiated OM rats, 90 nmol of GHRP-2 stimulated HF intake. In contrast, neither fasted OM nor S5B rats increased the intake of either HF or LF diet in response to GHRP-2. Fasting for 18 h induced a large rise in ghrelin mRNA in stomach of OM rats but not in S5B rats. There were no significant differences in plasma total ghrelin. An increase in ghrelin mRNA in stomach immediately before the onset of the dark cycle was observed in OM but not in S5B rats. Active ghrelin level was significantly affected by different feeding conditions in both OM and S5B rats adapted on HF diet with a trend to increase after 48 h of fasting and to decline to basal levels following 10 h of refeeding. These data suggest that ghrelin stimulates the intake of the preferred macronutrient. In addition, a differential regulation of ghrelin gene expression between OM and S5B rats may be important in their differential sensitivity to HF diet-induced obesity.     

A-like cells in the rat stomach contain ghrelin and do not operate under gastrin control

Ghrelin is a 28 a.a. gastric peptide, recently identified as a natural ligand of the growth hormone secretagogue receptor (orphan receptor distinct from the receptor for growth hormone releasing hormone). In the present study, radioimmunoassay demonstrated ghrelin-like material in the rat oxyntic mucosa with moderate amounts also in antrum and duodenum. Small amounts were found in the distal intestines and pancreas. Northern blot analysis revealed abundant ghrelin mRNA in the oxyntic mucosa. Immunocytochemistry demonstrated ghrelin-immunoreactivity in endocrine-like cells in the oxyntic mucosa. Such cells occurred in low numbers also in the antrum and duodenum. The rat oxyntic mucosa is rich in endocrine (chromogranin A/pancreastatin-immunoreactive) cells, such as the histamine-rich ECL cells (65-75% of the endocrine cells), the A-like cells (20-25%) and the D cells (somatostatin cells) (10%). The ghrelin-immunoreactive (IR) cells contained pancreastatin but differed from ECL cells and D cells by being devoid of histamine-forming enzyme (ECL cell constituent) and somatostatin (D cell constituent). Hence, ghrelin seems to occur in the A-like cells. The ghrelin-IR cells in the antrum were distinct from the gastrin cells, the serotonin-containing enterochromaffin cells and the D cells. Conceivably, ghrelin cells in the antrum and distally in the intestines also belong to the A-like cell population. The concentration of ghrelin in the circulation was lowered by about 80% following the surgical removal of the acid-producing part of the stomach in line with the view that the oxyntic mucosa is the major source of ghrelin. The serum ghrelin concentration was higher in fasted rats than in fed rats; it was reduced upon re-feeding and seemed unaffected by 1-week treatment with the proton pump inhibitor omeprazole, resulting in elevated serum gastrin concentration. Infusion of gastrin-17 for 2 days failed to raise the serum ghrelin concentration. Omeprazole treatment for 10 weeks raised the level of HDC mRNA but not that of ghrelin mRNA or somatostatin mRNA in the oxyntic mucosa. Hence, unlike the ECL cells, ghrelin-containing A-like cells do not seem to operate under gastrin control.     

Estrogen induces insulin-like growth factor-I expression in the rat uterus

The inability to convincingly demonstrate a mitogenic effect of estrogen on isolated uterine cells in culture suggests that autocrine or paracrine growth factors may be important in the estrogen-induced uterine proliferative response. Here we report that uterine expression of insulin-like growth factor-I (IGF-I), an important mediator of GH action, is increased after 17 beta-estradiol (5 micrograms/100 g bw, ip) administration to ovariectomized prepubertal rats. An increase in uterine IGF-I mRNA abundance, approximately 14-fold above untreated controls, was apparent 6 h after estrogen administration and the level achieved exceeded that seen in the uterus from intact mature rats during diestrus. In contrast to the increase in IGF-I expression in the uterus, no significant change in serum IGF-I concentration or hepatic or renal IGF-I mRNA abundance was demonstrable after 17 beta-estradiol injection of ovariectomized prepubertal rats. The increase in uterine IGF-I expression, was similar in both pituitary-intact and hypophysectomized, ovariectomized rats. We believe this is the first report of induction of IGF-I expression by estrogen in vivo. As such, the finding expands the role and significance of IGF-I as a mediator of growth beyond that related to GH.     

Estrogen and salt sensitivity in the female mRen(2). Lewis rat

The present study determined whether early loss of estrogen influences salt-sensitive changes in blood pressure, renal injury, and cardiac hypertrophy as well as the effects on the circulating renin-angiotensin-aldosterone system (RAAS) in the hypertensive female mRen(2). Lewis strain. Ovariectomy (OVX) of heterozygous mRen(2). Lewis rats on a normal salt (NS) diet (0.5% sodium) increased systolic blood pressure from 137+/-3 to 177+/-5 mmHg (P<0.01) by 15 wk but did not show any changes in cardiac-to-body weight index (CI), proteinuria, or creatinine clearance. Maintenance with a high-sodium (HS) diet (4%) increased blood pressure (203+/-4 mmHg, P<0.01), proteinuria (3.5+/-0.3 vs. 6.4+/-0.7 mg/day, P<0.05), and CI (4.0+/-0.1 vs. 5.2+/-0.1 mg/kg, P<0.01) but decreased creatinine clearance (0.89+/-0.15 vs. 0.54+/-0.06 ml/min, P<0.05). OVX exacerbated the effects of salt on the degree of hypertension (230+/-5 mmHg), CI (5.6+/-0.2 mg/kg), and proteinuria (13+/-3.0 mg/day). OVX increased the urinary excretion of aldosterone approximately twofold in animals on the NS diet (3.8+/-0.5 vs. 6.6+/-0.5 ng.mg creatinine-1.day-1, P<0.05) and HS diet (1.4+/-0.2 vs. 4.5+/-1.0 ng.mg creatinine-1.day-1, P<0.05). Circulating renin, angiotensin-converting enzyme, and angiotensin II were also significantly increased in the OVX group fed a HS diet. These results reveal that the protective effects of estrogen apart from the increase in blood pressure were only manifested in the setting of a chronic HS diet and suggest that the underlying sodium status may have an important influence on the overall effect of reduced estrogen.     

Estrogen potentiates constrictor prostanoid function in female rat aorta by upregulation of cyclooxygenase-2 and thromboxane pathway expression

Estrogen potentiates vascular reactivity to vasopressin (VP) by enhancing constrictor prostanoid function. To determine the cellular and molecular mechanisms, the effects of estrogen on arachidonic acid metabolism and on the expression of constrictor prostanoid pathway enzymes and endoperoxide/thromboxane receptor (TP) were determined in the female rat aorta. The release of thromboxane A2 (TxA2) and prostacyclin (PGI2) was measured in male (M), intact-female (Int-F), ovariectomized-female (OvX-F), and OvX + 17beta-estradiol-replaced female (OvX + ER-F) rats. The expression of mRNA for cyclooxygenase (COX)-1, COX-2, thromboxane synthase (TxS), and TP by aortic endothelium (Endo) and vascular smooth muscle (VSM) of these four experimental groups was measured by RT-PCR. The expression of COX-1, COX-2, and TxS proteins by Endo and VSM was also estimated by immunohistochemistry (IHC). Basal release of TxA2 and PGI2 was similar in M (18.8 +/- 1.9 and 1,723 +/- 153 pg/mg ring wt/45 min, respectively) and Int-F (20.2 +/- 4.2 and 1,488 +/- 123 pg, respectively) rat aortas. VP stimulated the dose-dependent release of TxA2 and PGI2 from both male and female rat aorta. OvX markedly attenuated and ER therapy restored VP-stimulated release of TxA2 and PGI2 in female rats. No differences in COX-1 mRNA levels were detected in either Endo or VSM of the four experimental groups (P > 0.1). The expression of both COX-2 and TxS mRNA were significantly higher (P < 0.05) in both Endo and VSM of Int-F and OvX + ER-F, compared with M or OvX-F. Expression of TP mRNA was significantly higher in VSM of Int-F and OvX + ER-F compared with M or OvX-F. IHC revealed the uniform staining of COX-1 in VSM of the four experimental groups, whereas staining of COX-2 and TxS was greater in Endo and VSM of Int-F and OvX + ER-F than in OvX-F or M rats. These data reveal that estrogen enhances constrictor prostanoid function in female rat aorta by upregulating the expression of COX-2 and TxS in both Endo and VSM and by upregulating the expression of TP in VSM.     

Secretion of ghrelin from rat stomach ghrelin cells in response to local microinfusion of candidate messenger compounds: a microdialysis study

Ghrelin is produced by A-like cells (ghrelin cells) in the mucosa of the acid-producing part of the stomach. The mobilization of ghrelin is stimulated by nutritional deficiency and suppressed by nutritional abundance. In an attempt to identify neurotransmitters and regulatory peptides that may contribute to the physiological, nutrient-related regulation of ghrelin secretion, we challenged the ghrelin cells in situ with a wide variety of candidate messengers, including known neurotransmitters (e.g. acetylcholine, catecholamines), candidate neurotransmitters (e.g. neuropeptides), local tissue hormones (e.g. serotonin, histamine, bradykinin, endothelin), circulating gut hormones (e.g. gastrin, CCK, GIP, neurotensin, PYY, secretin) and other circulating hormones/regulatory peptides (e.g. calcitonin, glucagon, insulin, PTH). Microdialysis probes were placed in the submucosa of the acid-producing part of the rat stomach. Three days later, the putative messenger compounds were administered via the microdialysis probe (reverse microdialysis) at a screening dose of 0.1 mmol l(-1) for regulatory peptides and 0.1 and 1 mmol l(-1) for amines and amino acids. The rats were awake during the experiments. The resulting microdialysate ghrelin concentration was monitored continuously for 3 h (radioimmunoassay), thereby revealing stimulators or inhibitors of ghrelin secretion. Dose-response curves were constructed for each candidate messenger that significantly (p<0.05) affected ghrelin mobilization at the screening dose. Peptides that showed a (non-significant) tendency to affect ghrelin release at the screening dose were also given at a dose of 0.3 or 1 mmol l(-1). Adrenaline, noradrenaline, endothelin and secretin stimulated ghrelin release, while somatostatin and GRP inhibited. Whether these agents act directly or indirectly on the ghrelin cells remains to be investigated. All other candidate messengers were without measurable effects, including acetylcholine, serotonin, histamine, GABA, aspartic acid, glutamic acid, glycine, VIP, PACAP, CGRP, substance P, NPY, PYY, PP, gastrin, CCK, GIP, insulin, glucagon, GLP and glucose.     

Estrogen dynamics in the female rhesus monkey

The metabolic clearance rates (MCR) and interconversions [( rho]BB) values for estrone (E1) and estradiol (E2) in female rhesus (Macaca mulatta) monkeys on Days 9, 14, and 23 of the menstrual cycle were measured using constant infusions of [3H] estradiol and [14C] estrone. The menstrual cycles in these monkeys were reproduced by using Silastic capsules of E2 and progesterone after bilateral ovariectomy. The serum levels of E2 and progesterone were measured by radioimmunoassay and were similar to those for the intact menstrual cycle. The MCR of E2 on Day 14 (52.8 +/- 6.8 l/day/kg) was significantly greater (p less than 0.05) than that measured on Day 9 (31.1 +/- 3.6 l/day/kg) or Day 23 (35.4 +/- 2.1 l/day/kg). The MCR of E1 was also different (p less than 0.05) on Day 14 (77.6 +/- 14.9 l/day/kg) compared to the values on Days 9 and 23 (50.2 +/- 4.9 and 48.2 +/- 3.9 l/day/kg, respectively. There was no change in percentage of free E2, percentage of albumin-bound E2, or sex hormone-binding globulin levels on those 3 days of the cycle. The interconversions between E2 and E1 were not influenced by the day of the cycle. We conclude that the high levels of E2 occurring at the time of the E2 peak result in increases in the MCRs of both E2 and E1 that are not associated with changes in the pattern of protein-binding or in the activity of the 17 beta-hydroxy steroid dehydrogenase.     

Cellular location and hormonal regulation of ghrelin expression in rat testis

Ghrelin, the endogenous ligand for the growth hormone-secretagogue receptor, is a recently cloned 28-amino acid peptide, expressed primarily in the stomach and hypothalamus, with the ability to stimulate growth hormone (GH) release and food intake. However, the possibility of additional, as yet unknown biological actions of ghrelin has been suggested. As a continuation of our recent findings on the expression and functional role of ghrelin in rat testis, we report here the pattern of cellular expression of ghrelin peptide in rat testis during postnatal development and after selective Leydig cell elimination, and we assess hormonal regulation of testicular ghrelin expression, at the mRNA and/or protein levels, in different experimental models. Immunohistochemical analyses along postnatal development demonstrated selective location of ghrelin peptide within rat testis in mature fetal- and adult-type Leydig cells. In good agreement, ghrelin protein appeared undetectable in testicular interstitium after selective Leydig cell withdrawal. In terms of hormonal regulation, testicular ghrelin mRNA and protein expression decreased to negligible levels after long-term hypophysectomy, whereas replacement with human chorionic gonadotropin (CG) (as superagonist of LH) partially restored ghrelin mRNA and peptide expression. Furthermore, acute administration of human CG (25 IU) to intact rats resulted in a transient increase in testicular ghrelin mRNA levels, with peak values 4 h after injection, an effect that was not mimicked by FSH (12.5 IU/rat). In contrast, testicular expression of ghrelin mRNA remained unaltered in GH-deficient rats, under hyper- and hypothyroidism conditions, as well as in adrenalectomized animals. In conclusion, our results demonstrate that mature Leydig cells are the source of ghrelin expression in rat testis, the protein being expressed in both fetal- and adult-type Leydig cells. In addition, our data indicate that testicular expression of ghrelin is hormonally regulated and is at least partially dependent on pituitary LH.     

Developmental gene expression of gastrin receptor in rat stomach

Gastrin, which is present in fetal plasma, may have important roles in the development of gastric mucosa, since it is not only a potent stimulator of gastric acid secretion but also a growth promoting factor. Gastrin regulates various cellular functions via its receptors on cell membrane. Therefore, in order to elucidate a role for gastrin in the development of gastrointestinal system during gestation, Northern blot analysis was performed. The results of the study suggested that gastrin receptor is mainly present on parietal cells. Furthermore, proton pump and gastrin receptor gene expressions in parietal cells were strongly stimulated by the administration of exogenous gastrin. In conclusion, gastrin may be involved in the developmental change of parietal cells through its receptors.     

Effect of GIP, GLP-1, insulin and gastrin on ghrelin release in the isolated rat stomach

Ghrelin release in man depends on the macronutrient composition of the test meal. The mechanisms contributing to the differential regulation are largely unknown. To elucidate their potential role, glucagon-like peptide-1 (GLP-1), gastric inhibitory polypeptide (GIP), insulin, gastrin and somatostatin were examined on isolated rat stomach ghrelin secretion, which offers the advantage of avoiding systemic interactions. Basal ghrelin secretion was in a range that did not permit to consistently evaluate inhibiting effects. Therefore, the effect of gastrointestinal hormones and insulin was analyzed during vagal prestimulation. GLP-1(7-36)amide 10(-8) and 10(-7) M decreased ghrelin secretion significantly. In contrast, GIP 10(-8) and 10(-7) M augmented not only prestimulated, but also basal ghrelin secretion (p<0.05). Insulin reduced ghrelin at 10(-10), 10(-8) and 10(-6) M (p<0.05). Both gastrin 10(-8) M and somatostatin 10(-6) M also significantly inhibited ghrelin secretion. These data demonstrate that GLP-1(7-36)amide, insulin, gastrin and somatostatin are potential candidates to contribute to the postprandially observed inhibition of ghrelin secretion with insulin being the most effective inhibitor in this isolated stomach model. GIP, on the other hand, could attenuate the postprandial decrease. Because protein-rich meals do not effectively stimulate GIP release, other as yet unknown intestinal factors must be responsible for protein-induced stimulation of ghrelin release.