Effects of glucose and amino acids on ghrelin secretion in sheep

Effects of Corn and Broken Rice Extrusion on the Feed Intake, Nutrient Digestibility, and Gut Microbiota of Weaned Piglets

Simple Summary

Extruded cereals are largely used in newly weaned piglet diets to increase nutrient digestibility and palatability. Our findings showed that corn and broken rice extrusion diets generated negative effects on average daily feed intake (−63.5 g/day, p = 0.054) and average daily gain (−60.6 g/d, p = 0.015) in weaned piglets. Decreased feed intake was associated with increased plasma levels of the gut-derived hormones, glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), which may have been attributed to increased microbiota pathogen abundance, including Sarcina, Clostridium_sensu_strictio_1, and Terrisporobacter, and decreased short-chain fatty acid-producing microbiota, such as Lactobaillaceae and Bifidobateriaceae. Our results showed that extruded cereals should be used cautiously when formulating diets for newly weaned piglets.

Abstract

In this study, we investigated the effects of corn and rice extrusion diets on feed intake, nutrient digestibility, and gut microbiota in weaned piglets. Animals were divided into four dietary groups and fed a controlled diet containing (1) 62.17% corn (CORN), 15% soybean, 10% extruded full-fat soybean, and 6% fishmeal (2) half the corn replaced by extruded corn (ECORN), (3) broken rice (RICE), and (4) extruded broken rice (ERICE) for 28 days. Rice supplementation increased dry matter total tract digestibility and gross energy. Extruded cereals generated a lower average daily feed intake (ADFI) at 15–28 and 1–28 days, decreased average daily growth (ADG) at 15–28 and 1–28 days, and a lowered body weight (BW) on day 28, regardless of cereal type. Dietary extruded cereals increased the appetite-regulating hormones glucagon-like peptide-1 (GLP-1) and peptide YY (PYY). Piglets fed extruded cereals displayed low short-chain fatty acid (SCFA) levels in plasma and low Lactobaillaceae and Bifidobateriaceae levels in feces, whereas a higher abundance of the potential pathogens Sarcina, Clostridium_sensu_strictio_1 and Terrisporobacter was observed. Piglets fed extruded cereals displayed significantly lower gas and SCFA levels during in vitro fermentation. Combined, 50% corn substituted with extruded corn or broken rice decreased piglet growth performance, possibly by altering their microbiota.

Comprehensive Profiling of GPCR Expression in Ghrelin-Producing Cells

To determine the comprehensive G protein-coupled receptor (GPCR) expression profile in ghrelin-producing cells and to elucidate the role of GPCR-mediated signaling in the regulation of ghrelin secretion, we determined GPCR expression profiles by RNA sequencing in the ghrelin-producing cell line MGN3-1 and analyzed the effects of ligands for highly expressed receptors on intracellular signaling and ghrelin secretion. Expression of selected GPCRs was confirmed in fluorescence-activated cell-sorted fluorescently tagged ghrelin-producing cells from ghrelin-promoter CreERT2/Rosa-CAG-LSL-ZsGreen1 mice. Expression levels of GPCRs previously suggested to regulate ghrelin secretion including adrenergic-β1 receptor, GPR81, oxytocin receptor, GPR120, and somatostatin receptor 2 were high in MGN3-1 cells. Consistent with previous reports, isoproterenol and oxytocin stimulated the Gs and Gq pathways, respectively, whereas lactate, palmitate, and somatostatin stimulated the Gi pathway, confirming the reliability of current assays. Among other highly expressed GPCRs, prostaglandin E receptor 4 agonist prostaglandin E2 significantly stimulated the Gs pathway and ghrelin secretion. Muscarine, the canonical agonist of cholinergic receptor muscarinic 4, stimulated both the Gq and Gi pathways. Although muscarine treatment alone did not affect ghrelin secretion, it did suppress forskolin-induced ghrelin secretion, suggesting that the cholinergic pathway may play a role in counterbalancing the stimulation of ghrelin by Gs (eg, by adrenaline). In addition, GPR142 ligand tryptophan stimulated ghrelin secretion. In conclusion, we determined the comprehensive expression profile of GPCRs in ghrelin-producing cells and identified two novel ghrelin regulators, prostaglandin E2 and tryptophan. These results will lead to a greater understanding of the physiology of ghrelin and facilitate the development of ghrelin-modulating drugs.

Impact of visual, olfactory, and auditory cues on circulating concentrations of ghrelin in wethers

Ghrelin is a hormone that stimulates feed intake and regulates energy homeostasis. A link has been observed in sheep, in which simulated feedings at scheduled meal times resulted in an increase in ghrelin concentrations. The present study sought to characterize the effect of feeding cues outside of scheduled meal times on circulating ghrelin concentrations in sheep. Katahdin wethers (age 201 ± 4.9 d; weight 35 ± 1.2 kg) were not offered feed (CONT; = 5), offered 275 g of feed (FED; = 5), or fitted with a muzzle and offered 275 g of feed (SHAM; = 5) during the sampling period, which began 2.5 h after normally scheduled daily feeding time. Blood samples were collected via jugular catheter every 15 min for 2.5 h. Feed was offered for 15 min 0.5 h after the start of blood sampling. The CONT samples were collected on d 1, and FED and SHAM samples were collected on d 2. The active ghrelin present in the plasma was then analyzed by RIA. After the Shapiro-Wilk W goodness of fit test demonstrated that 1 SHAM wether was an outlier and it was removed, data were tested for effect of treatment (FED, SHAM, or CONT), time, and treatment × time interaction using procedures for repeated measures with JMP Software (SAS Inst. Inc., Cary, NC). There was no treatment or time effect ( > 0.05); however, there was a treatment × time interaction on plasma ghrelin concentrations ( = 0.0028) such that ghrelin concentrations in SHAM wethers were greater than in CONT wethers 15, 60, and 90 min after feeding, whereas ghrelin concentrations in SHAM wethers were greater than those in FED wethers 30, 60, 90, and 120 min after feeding ( < 0.05). Within the SHAM treatment, ghrelin concentrations were greater at 15 min than at -30 min. Moreover, ghrelin concentrations within the FED treatment were greater at -30 min than at 30, 45, 60, 90, 105, and 120 min and at -15 min than at 15 through 120 min. The area under the curve representing circulating concentrations of ghrelin in CONT, FED, and SHAM treatments, determined using the trapezoidal method, yielded a treatment effect with a tendency toward significance ( = 0.0866). These results indicate plasma ghrelin concentrations in scheduled meal-fed wethers are elevated following visual, olfactory, and auditory feeding cues outside of scheduled feeding times.

Cloning and tissue distribution of novel splice variants of the ovine ghrelin gene

Background

The ghrelin axis is involved in the regulation of metabolism, energy balance, and the immune, cardiovascular and reproductive systems. The manipulation of this axis has potential for improving economically valuable traits in production animals, and polymorphisms in the ghrelin (GHRL) and ghrelin receptor (GHSR) genes have been associated with growth and carcass traits. Here we investigate the structure and expression of the ghrelin gene (GHRL) in sheep, Ovis aries.

Results

We identify two ghrelin mRNA isoforms, which we have designated Δex2 preproghrelin and Δex2,3 preproghrelin. Expression of Δex2,3 preproghrelin is likely to be restricted to ruminants, and would encode truncated ghrelin and a novel C-terminal peptide. Both Δex2 preproghrelin and canonical preproghrelin mRNA isoforms were expressed in a range of tissues. Expression of the Δex2,3 preproghrelin isoform, however, was restricted to white blood cells (WBC; where the wild-type preproghrelin isoform is not co-expressed), and gastrointestinal tissues. Expression of Δex2 preproghrelin and Δex2,3 preproghrelin mRNA was elevated in white blood cells in response to parasitic worm (helminth) infection in genetically susceptible sheep, but not in resistant sheep.

Conclusions

The restricted expression of the novel preproghrelin variants and their distinct WBC expression pattern during parasite infection may indicate a novel link between the ghrelin axis and metabolic and immune function in ruminants.

Increased plasma ghrelin suppresses insulin release in wethers fed with a high-protein diet

Ghrelin is a multifunctional peptide that promotes an increase of food intake and stimulates GH secretion. Ghrelin secretion is regulated by nutritional status and nutrients. Although a high-protein (HP) diet increases plasma ghrelin secretion in mammals, the mechanisms and the roles of the elevated ghrelin concentrations due to a HP diet have not been fully established. To clarify the roles of elevated acylated ghrelin upon intake of a HP diet, we investigated the regulation of ghrelin concentrations in plasma and tissues in wethers fed with either the HP diet or the control (CNT) diet for 14 days, and examined the action of the elevated plasma ghrelin by using a ghrelin-receptor antagonist. The HP diet gradually increased the plasma acylated-ghrelin concentrations, but the CNT diet did not. Although the GH concentrations did not vary significantly across the groups, an injection of ghrelin-receptor antagonist enhanced insulin levels in circulation in the HP diet group. In the fundus region of the stomach, the ghrelin levels did not differ between the HP and CNT diet groups, whereas ghrelin O-acyltransferase mRNA levels were higher in the group fed with HP diet than those of the CNT diet group were. These results indicate that the HP diet elevated the plasma ghrelin levels by increasing its synthesis; this elevation strongly suppresses the appearance of insulin in the circulation of wethers, but it is not involved in GH secretion. Overall, our findings indicate a role of endogenous ghrelin action in secretion of insulin, which acts as a regulator after the consumption of a HP diet.

Ingestion of medium chain fatty acids by lactating dairy cows increases concentrations of plasma ghrelin

The purpose of this study was to elucidate the effects of medium-chain fatty acids (MCFAs) on plasma ghrelin concentration in lactating dairy cows. Five early-lactating Holstein cows were randomly assigned to 2 dietary treatments in a crossover design with 2-wk periods. Treatments consisted of diets supplemented or not (control) with calcium salts of MCFAs (MCFA-Ca; 1.5% dry matter). Plasma hormone and metabolite concentrations in blood samples taken from the jugular vein were measured on the morning of feeding on day 14 of each period. Dry matter intake, milk protein, and lactose content of cows fed the MCFA-Ca diet were decreased compared with controls, but with no change in milk yield. Plasma ghrelin concentrations were higher in cows fed the MCFA-Ca diet; however, no significant effect was found on glucagon-like peptide-1 concentrations in plasma. Plasma insulin concentrations decreased, but plasma glucagon concentrations remained unchanged in cows fed the MCFA-Ca diet. The concentrations of nonesterified FAs, total cholesterol, and β-hydroxybutyrate in plasma increased in these cows. In conclusion, dietary MCFAs increase the plasma ghrelin concentrations in lactating dairy cows.

Human ghrelin decreases pituitary response to GnRH in superovulated ewes

In addition to its metabolic role, ghrelin has been found to suppress luteinizing hormone secretion in many species acting mainly at the hypothalamic level. The objectives of the present study were to test the hypothesis that besides its effects on the hypothalamic level, ghrelin exerts a direct action on the pituitary. Twelve cycling ewes were synchronized, using progestagen intravaginal sponges and superovulated using eCG. At the time of sponge withdrawal, animals were allocated into two groups, ghrelin-treated (Gh) and control. Two days after the sponge removal, GnRH was given to synchronize ovulations. Simultaneously with GnRH treatment, animals of the Gh group received the first of four treatments of acylated human ghrelin at a dose of 6 μg/kg body weight iv; three additional treatments of ghrelin iv were given every 15 minutes thereafter. Control animals received saline iv. Blood samples were collected before challenge (-30 and 0 minutes) and at 30, 60, 75, 90, 105, 120, 135, 150, and 180 minutes after GnRH treatment, and were analyzed for LH, FSH, estradiol, progesterone, insulin, and insulin-like growth factor-I concentrations. Ghrelin treatment attenuated GnRH-induced a preovulatory surge of both gonadotrophins, with the effect being greater for LH. No difference was detected for insulin, estradiol, and progesterone concentrations, and insulin-like growth factor-I levels were increased in the Gh group. Our results imply that in sheep, ghrelin conducts specific regulatory effects on the GnRH/LH axis, and provide for the first time strong evidence that besides its central action, ghrelin might regulate gonadotrophin release acting at the pituitary level.

A high-protein diet induces dissociation between plasma concentrations of growth hormone and ghrelin in wethers

High-carbohydrate or high-fat diets have been demonstrated to change ghrelin concentrations in plasma; however, there remains a need to clarify the effects of dietary protein on the interaction between circulating GH and ghrelin concentrations in the ruminant. In this study, we investigated the postprandial changes in plasma concentrations of GH and ghrelin and their interactions when wethers were fed either a high-protein (HP; 40% CP) or a low-protein (LP; 10% CP) diet for 2 wk. The wethers were divided into 2 groups and fed once a day for 2 wk in a randomized crossover design. Each diet contained the same level of ME. Blood was collected from the animals at specific times over 24 h to measure hormones and metabolites. Feeding once a day caused a prompt reduction in the GH and ghrelin concentrations regardless of the type of diet that the wethers consumed. The preprandial concentrations (P = 0.04), area under the curve (AUC; P = 0.04), and incremental AUC (iAUC; P = 0.06) for ghrelin in HP-fed wethers were or tended to be greater than those in LP-fed wethers although concentrations for GH were the same for both diets (P = 0.23). In addition, the time it took for the postprandial ghrelin concentrations to recover to the preprandial concentrations was greater in HP-fed wethers than in LP-fed wethers although this was not true for GH concentrations. Similarly, as for ghrelin, postprandial increase (P < 0.001) and AUC (P = 0.03) for insulin concentration was greater in the HP-fed wethers than in the LP-fed wethers. From these findings, we concluded that dietary proteins (or some other derived metabolites) may dissociate the interaction between plasma concentrations of GH and ghrelin in wethers.

Effect of interaction between testosterone and morphine on serum ghrelin concentration in sheep fed on different dietary energy levels

BACKGROUND

Ghrelin plays an important role in the regulation of food intake and body weight. It also decreases testosterone and opioid secretion.

OBJECTIVES

The goal of the present study was to investigate the effect of testosterone, morphine or simultaneous injection of testosterone and morphine on mean serum ghrelin concentration in sheep.

MATERIALS AND METHODS

Ten sheep were divided into two groups (n = 5 in each group), they were fed with either 50 % or 100 % of their dietary energy needs for 10 days. Body weight was measured on the 1st and 10th day of the experiment. Animals in both groups received testosterone (60 μg/kg), morphine (0.15 mg/kg), or a simultaneous infusion of testosterone (60 μg/kg) and morphine (0.15 mg/kg), on the 8th, 9th, or 10th day of the experiment respectively. Blood samples were collected before and 2 hours after the infusions. Ghrelin concentration was determined by RIA (radio immunoassay).

RESULTS

In the 50 % group, ghrelin concentrations increased significantly on the 8th day of the experiment, compared to the 1st day (P < 0.05). While in the 100 % group, no significant change was observed. In both groups the animals' body weight did not increase significantly on the 10th day compared to the 1st day. Testosterone significantly increased ghrelin levels after injection compared to before infusion, in both groups (P < 0.05). Morphine increased ghrelin concentration in both groups, but this increase was not statistically significant. Simultaneous injection of testosterone and morphine together, significantly increased ghrelin concentration following injection compared to before infusion, in both groups (P < 0.05).

CONCLUSIONS

There is a direct correlation between food restriction, testosterone and ghrelin concentration in ruminants. However, a simultaneous injection of testosterone and morphine did not exert an additive effect on ghrelin secretion.

Plasma ghrelin concentration is decreased by short chain fatty acids in wethers

To examine the effects of short chain fatty acids (SCFAs) on plasma ghrelin concentration, 4 wethers were injected intravenously with SCFA solutions [acetate (ACE), propionate (PRO), and butyrate (BUT) (0.8 mmol/kg BW)] and saline. The experiment was conducted after a 4 × 4 Latin square design. Each solution was injected into the jugular vein catheter with blood samples taken at -10, 0, 5, 10, 15, 20, 25, 30, 40, 50, and 60 min relative to the injection time also from this catheter. Plasma ghrelin concentrations decreased after injection with ACE, PRO, and BUT. Although plasma glucose concentrations increased after injection with PRO and BUT (P < 0.05), the increment areas were greater with BUT than with PRO. Plasma insulin concentrations increased after injection with PRO and BUT (P < 0.05). The decrement areas in plasma ghrelin concentrations were equal in ACE, PRO, and BUT. These data suggest that SCFAs inhibit ghrelin secretion in wethers and not through increased circulating glucose and insulin as previously proposed.

Triennial Growth Symposium: neural regulation of feed intake: modification by hormones, fasting, and disease

Appetite is a complex process that results from the integration of multiple signals at the hypothalamus. The hypothalamus receives neural signals; hormonal signals such as leptin, cholecystokinin, and ghrelin; and nutrient signals such as glucose, FFA, AA, and VFA. This effect is processed by a specific sequence of neurotransmitters beginning with the arcuate nucleus and orexigenic cells containing neuropeptide Y or agouti-related protein and anorexigenic cells containing proopiomelanocortin (yielding the neurotransmitter α-melanocyte-stimulating hormone) or cells expressing cocaine amphetamine-related transcript. These so-called first-order neurons act on second-order orexigenic neurons (containing either melanin-concentrating hormone or orexin) or act on anorexigenic neurons (e.g., expressing corticotropin-releasing hormone) to alter feed intake. In addition, satiety signals from the liver and gastrointestinal tract signal through the vagus nerve to the nucleus tractus solitarius to cause meal termination, and in combination with the hypothalamus, integrate the various signals to determine the feeding response. The activities of these neuronal pathways are also influenced by numerous factors such as nutrients, fasting, and disease to modify appetite and hence affect growth and reproduction. This review will begin with the central nervous system pathways and then discuss the ways in which hormones and metabolites may alter the process to affect feed intake with emphasis on farm animals.