Immunohistochemical colocalization of serotonin, substance P and Met-enkephalin-Arg6-Gly7-Leu8 in the endocrine cells of the ruminant duodenum

Biological redundancy of endogenous GPCR ligands in the gut and the potential for endogenous functional selectivity

This review focuses on the existence and function of multiple endogenous agonists of the somatostatin and opioid receptors with an emphasis on their expression in the gastrointestinal tract. These agonists generally arise from the proteolytic cleavage of prepropeptides during peptide maturation or from degradation of peptides by extracellular or intracellular endopeptidases. In other examples, endogenous peptide agonists for the same G protein-coupled receptors can be products of distinct genes but contain high sequence homology. This apparent biological redundancy has recently been challenged by the realization that different ligands may engender distinct receptor conformations linked to different intracellular signaling profiles and, as such the existence of distinct ligands may underlie mechanisms to finely tune physiological responses. We propose that further characterization of signaling pathways activated by these endogenous ligands will provide invaluable insight into the mechanisms governing biased agonism. Moreover, these ligands may prove useful in the design of novel therapeutic tools to target distinct signaling pathways, thereby favoring desirable effects and limiting detrimental on-target effects. Finally we will discuss the limitations of this area of research and we will highlight the difficulties that need to be addressed when examining endogenous bias in tissues and in animals.

Immunolocalisation of serotonin, gastrin, somatostatin and glucagon in entero-endocrine cells of the goose (Anser anser)

The processes of digestion in the avian gastrointestinal tract depend on sophisticated control systems that co-ordinate secretion of digestive juices and movement of the luminal contents. In the current study, the distribution of serotonin-, gastrin-, glucagon- and somatostatin-immunoreactive endocrine cells was investigated by immunocytochemical methods in the intestinal tract of the goose. The number of cells immunoreactive for each antiserum was evaluated in different regions of the intestinal tract. Serotonin-, glucagon- and somatostatin-immunoreactive endocrine cells were seen throughout the intestinal tract, but somatostatin-immunoreactive cells were not detected in the colon of the goose. Gastrin-immunoreactive cells were detected only in the duodenum, jejunum and colon mucosa. It is concluded that the distribution pattern of the entero-endocrine cells in the goose is similar to that of most of the mammalian and other poultry species.

Postnatal development of intestinal endocrine cell populations in the water buffalo

The frequency and distribution of 11 endocrine cell populations were studied in the intestine of differently aged buffalo, grouped on the basis of diet: 2-d-olds (suckling), 5-mo-olds (weaning) and 5-y-olds (ruminant adult diet). The endocrine cell populations were identified immunocytochemically using antisera against 5-hydroxytryptamine (5-HT), somatostatin, gastrin, cholecystokinin (CCK), COOH-terminal octapeptide of gastrin/CCK, neurotensin, motilin, gastric inhibitory polypeptide (GIP), secretin, glucagon/glicentin (GLU/GLI) and polypeptide YY (PYY). In adult buffalos the regional distribution of endocrine cells is similar to that of other adult ruminants. During postnatal development, these cell types showed the following changes in their frequency and distribution: (1) 5-HT, neurotensin and gastrin/CCK immunoreactive cells (i.c.) showed a decrease in frequency with age; (2) somatostatin i.c. frequency remained stable with age; (3) motilin, GIP, secretin and CCK i.c. showed a slight increase in frequency with age; (4) GLU/GLI and PYY i.c. decreased in frequency with age in the small intestine, caecum and proximal colon and an increase in frequency in the rectum. It was hypothesised that the endocrine cell types, whose presence and localisation is substantially stable in all examined ages, probably contain substances that are strictly necessary for intestinal function. In contrast the hormones contained in the cell populations that decreased with age, are probably involved in physiological needs during the milk and weaning diet or play a role in intestinal growth.

Immunohistochemical study of endocrine cells in the gastrointestinal tract of the Philippine carabao (Bubalus bubalis)

The distribution and frequency of occurrence of endocrine cells in the gastrointestinal tract of the Philippine carabao (Bubalus bubalis) were studied by immunohistochemistry. Fourteen types of immunoreactive (IR) endocrine cells were revealed. Among the cell types, only chromogranin, serotonin, and bovine pancreatic polypeptide (BPP) were present in the entire gut, while the others showed restricted distribution: somatostatin, gastrin, and cholecystokinin in the abomasum and small intestine; methionine-enkephalin-Arg6-Gly7-Leu8, motilin, neurotensin, secretin, gastric inhibitory peptide, and substance P in the small intestine; peptide tyrosine tyrosine (PYY) in the large intestine; and glucagon in the whole intestinal tract. Most of the cell types showed peak density in the pyloric, duodenal, or rectal region. The highest cell type heterogeneity was observed in the duodenum. The distribution profile of the gut endocrine cells in the carabao is closely related to that in the Holstein cattle. Important findings include the occurrence of BPP-IR cells in the entire gut and the high frequency of PYY-IR cells in the large intestine.