Hormonal and neural regulation of intestinal function in pigs

Physiological and metabolic control of diet selection

The fact that most farm animals have no dietary choice under commercial practices translates the dietary decisions to the carers. Thus, a lack of understanding of the principles of dietary choices is likely to result in a high toll for the feed industry. In healthy animals, diet selection and, ultimately, feed intake is the result of factoring together the preference for the feed available with the motivation to eat. Both are dynamic states and integrate transient stimulus derived from the nutritional status, environmental and social determinants of the animal with hard-wired genetic mechanisms. Peripheral senses are the primary inputs that determine feed preferences. Some of the sensory aspects of feed, such as taste, are innate and genetically driven, keeping the hedonic value of feed strictly associated with a nutritional frame. Sweet, umami and fat tastes are all highly appetitive. They stimulate reward responses from the brain and reinforce dietary choices related to essential nutrients. In contrast, aroma (smell) recognition is a plastic trait and preferences are driven mostly by learned experience. Maternal transfer through perinatal conditioning and the individual’s own innate behaviour to try or to avoid novel feed (often termed as neophobia) are known mechanisms where the learning process strongly affects preferences. In addtition, the motivation to eat responds to episodic events fluctuating in harmony with the eating patterns. These signals are driven mainly by gastrointestinal hormones (such as cholecystokinin [CCK] and glucagon-like peptide 1 [GLP-1]) and load. In addition, long-term events generate mechanisms for a sustainable nutritional homeostasis managed by tonic signals from tissue stores (i.e. leptin and insulin). Insulin and leptin are known to affect appetite by modulating peripheral sensory inputs. The study of chemosensory mechanisms related to the nutritional status of the animal offers novel tools to understand the dynamic states of feed choices so as to meet nutritional and hedonic needs. Finally, a significant body of literature exists regarding appetite driven by energy and amino acids in farm animals. However, it is surprising that there is scarcity of knowledge regarding what and how specific dietary nutrients may affect satiety. Thus, a better understanding on how bitter compounds and excess dietary nutrients (i.e. amino acids) play a role in no-choice animal feeding is an urgent topic to be addressed so that right choices can be made on the animal’s behalf.

Effects of weaning on intestinal crypt epithelial cells in piglets

Intestinal epithelial cells in the crypt proliferate in piglets in response to weaning. However, the underlying mechanism has been unclear. We examined 40 piglets from eight litters (five piglets per litter) that were weaned at the age of 14 d, and one piglet from each litter was randomly selected for closer investigation. Based on the distended intestinal sac method, we isolated crypt epithelial cells from the mid-jejunum on Days 0, 1, 3, 5, and 7 post-weaning. Protein expression was analyzed using either isobaric tags for relative and absolute quantification or western blotting. Proteins related to the cell cycle, organization of the cellular macromolecular complex subunit, localization of cellular macromolecules, Golgi vesicle transport, fatty acid metabolism, oxidative phosphorylation, and translational initiation were mainly down-regulated, while those involved in glycolysis, cell cycle arrest, protein catabolism, and cellular amino acid metabolism were up-regulated. The amount of proteins active in the mTOR signaling pathway was generally decreased over time. These results indicate that weaning influences energy metabolism, cellular macromolecule organization and localization, and protein metabolism, thereby affecting the proliferation of intestinal epithelial cells in weaned piglets. Moreover, those cellular processes are possibly controlled by that signaling pathway.

Di- and tripeptide transport in vertebrates: the contribution of teleost fish models

Solute Carrier 15 (SLC15) family, alias H⁺-coupled oligopeptide cotransporter family, is a group of membrane transporters known for their role in the cellular uptake of di- and tripeptides (di/tripeptides) and peptide-like molecules. Of its members, SLC15A1 (PEPT1) chiefly mediates intestinal absorption of luminal di/tripeptides from dietary protein digestion, while SLC15A2 (PEPT2) mainly allows renal tubular reabsorption of di/tripeptides from ultrafiltration, SLC15A3 (PHT2) and SLC15A4 (PHT1) possibly interact with di/tripeptides and histidine in certain immune cells, and SLC15A5 has unknown function. Our understanding of this family in vertebrates has steadily increased, also due to the surge of genomic-to-functional information from 'non-conventional' animal models, livestock, poultry, and aquaculture fish species. Here, we review the literature on the SLC15 transporters in teleost fish with emphasis on SLC15A1 (PEPT1), one of the solute carriers better studied amongst teleost fish because of its relevance in animal nutrition. We report on the operativity of the transporter, the molecular diversity, and multiplicity of structural-functional solutions of the teleost fish orthologs with respect to higher vertebrates, its relevance at the intersection of the alimentary and osmoregulative functions of the gut, its response under various physiological states and dietary solicitations, and its possible involvement in examples of total body plasticity, such as growth and compensatory growth. By a comparative approach, we also review the few studies in teleost fish on SLC15A2 (PEPT2), SLC15A4 (PHT1), and SLC15A3 (PHT2). By representing the contribution of teleost fish to the knowledge of the physiology of di/tripeptide transport and transporters, we aim to fill the gap between higher and lower vertebrates.

Orexin system expression in the gastrointestinal tract of pigs

The aim of the present study was to characterize the expression of both proteins and gene transcripts for orexins (OXA and OXB) and their cognate receptors (OX1R and OX2R) in the different gastrointestinal sections of pigs. Using immunohistochemistry, OXA and OXB were found to be co-expressed in the same endocrine cells localized in the basal third of the glands of the body portion of the stomach. Using double immunostaining technique, these orexin-immunoreactive (IR) cells co-stored ghrelin and gastrin. Apparently, OX1R was also expressed within the same cells, forming the tubular gastric gland which displayed positive immunostaining for orexins and the other peptides. Neurons of the enteric nervous system of the stomach were not immunolabeled. We did not find any definite OXA- or OXB-IR cells as well as any immunosignal for orexin receptors in sections of the duodenum, ileum, cecum and rectum. PPOX, OX1R, OX2R mRNA were similarly expressed in all the gastrointestinal tracts. Gastrin and ghrelin showed the highest levels of expression in the gastric mucosa, but their abundance decreased along the subsequent tracts. Thus, in pigs, orexins do not play any role in the local control of intestinal motility and secretion but may rather be involved as endocrine modulators for the regulation of feeding and metabolic homeostasis. However, the co-localization of ghrelin and gastrin with both orexins in the same endocrine cells of the gastric glands suggests that these gut peptides may collaborate in the regulation of gastric secretion, energy homeostasis, body weight and food intake.

Immunohistochemical distribution of leptin receptor in the major salivary glands of horses

The presence of the leptin receptor (ObR) has already been highlighted in the human major salivary glands and it has been hypothesized that leptin may act by regulating the gland's growth. No data are reported on domestic animals so, considering the important role that these glands play, not only related to food ingestion and digestion, and the important functional role hypothesized to explain the presence of ObR in humans salivary glands, the aim of the present work was to investigate the presence and the distribution of the leptin receptor in horse parotid and mandibular glands, by immunohistochemical techniques. The presence of ObR was evidenced in parotid and mandibular glands, exclusively localized in duct epithelial cells; their positivity was localized in the cytoplasm and was most evident near its apical portion. Immuno-positivity not only affects the intralobular ducts (intercalated and striated) but also the interlobular ones. Our results indicate that horse major salivary glands, like those of humans, are likely targets of leptin actions, suggesting a functional role of leptin on these glands.

Localization of the orexin system in the gastrointestinal tract of fallow deer

The aim of the present study was to investigate by immunohistochemistry the presence and distribution of the orexin system in the stomach and gut of fallow deer. Abundant orexin A-positive cells were localized in the middle and basal portions of the mucosal glands of the cardial and fundic regions of the stomach. In the same gastric areas, orexin B-positive cells were also found, mainly localized in the basal portion of glands. In the intestinal tract, orexin-containing cells were occasionally found in the duodenal epithelium and in the rectal intestinal glands. Immunoreactivity for orexin receptors, type 1 and 2 (OX1R and OX2R), was not detected in the same stomach regions. OX1R-immunopositivity was observed in the enteric neuron ganglia localized in the submucosal and muscular intestinal layers, while OX2R-immunopositivity was found close in contact with the cytoplasmic membrane of epithelial cells in the small intestine.