Autoradiographic distribution of vasoactive intestinal polypeptide receptors in rabbit and rat small intestine

Prebiotics and Bioactive Milk Fractions Affect Gut Development, Microbiota, and Neurotransmitter Expression in Piglets

OBJECTIVE

This study tested the hypothesis that the addition of prebiotics and 2 functional milk ingredients to infant formula would maintain normal growth and gut development, and modify microbiota composition and neurotransmitter gene expression in neonatal piglets.

METHODS

Two-day-old male piglets (n = 24) were fed formula (CONT) or formula with polydextrose (1.2 g/100 g diet), galactooligosaccharides (3.5 g/100 g diet), bovine lactoferrin (0.3 g/100 g diet), and milk fat globule membrane-10 (2.5 g/100 g diet) (TEST) for 30 days. On study day 31, intestinal samples, ileal and colonic contents, and feces were collected. Intestinal histomorphology, disaccharidase activity, serotonin (5'HT), vasoactive intestinal peptide (VIP), and tyrosine hydroxylase (TH) were measured. Gut microbiota composition was assessed by pyrosequencing of the V3-V5 regions of 16S rRNA and quantitative polymerase chain reaction.

RESULTS

Body weight of piglets on TEST was greater (P ≤ 0.05) than CONT on days 17 to 30. Both groups displayed growth patterns within the range observed for sow-reared pigs. TEST piglets had greater jejunal lactase (P = 0.03) and higher (P = 0.003) ileal VIP expression. TEST piglets tended to have greater (P = 0.09) sucrase activity, longer (P = 0.08) ileal villi, and greater (P = 0.06) duodenal TH expression. Microbial communities of TEST piglets differed from CONT in ascending colon (AC, P = 0.001) and feces (P ≤ 0.05). CONT piglets had greater relative abundances of Mogibacterium, Collinsella, Klebsiella, Escherichia/Shigella, Eubacterium, and Roseburia compared with TEST piglets in AC. In feces, CONT piglets harbored lower (P ≤ 0.05) proportions of Parabacteroides, Clostridium IV, Lutispora, and Sutterella than TEST piglets.

CONCLUSIONS

A mixture of bioactive ingredients improved weight gain and gut maturation, modulated colonic and fecal microbial composition, and reduced the proportions of opportunistic pathogens.

Effects of psychological stress on small intestinal motility and expression of cholecystokinin and vasoactive intestinal polypeptide in plasma and small intestine in mice

AIM: To investigate the effects of psychological stress on small intestinal motility and expression of cholecystokinin (CCK) and vasoactive intestinal polypeptide (VIP) in plasma and small intestine, and to explore the relationship between small intestinal motor disorders and gastrointestinal hormones under psychological stress.

METHODS: Thirty-six mice were randomly divided into psychological stress group and control group. A mouse model with psychological stress was established by housing the mice with a hungry cat in separate layers of a two-layer cage. A semi-solid colored marker (carbon-ink) was used for monitoring small intestinal transit. CCK and VIP levels in plasma and small intestine in mice were measured by radioimmunoassay (RIA).

RESULTS: Small intestinal transit was inhibited (52.18±19.15% vs 70.19±17.79%, P<0.01) in mice after psychological stress, compared to the controls. Small intestinal CCK levels in psychological stress mice were significantly lower than those in the control group (0.75±0.53 μg/g vs 1.98±1.17 μg/g, P<0.01), whereas plasma CCK concentrations were not different between the groups. VIP levels in small intestine were significantly higher in psychological stress mice than those in the control group (8.45±1.09 μg/g vs 7.03±2.36 μg/g, P<0.01), while there was no significant difference in plasma VIP levels between the two groups.

CONCLUSION: Psychological stress inhibits the small intestinal transit, probably by down-regulating CCK and up-regulating VIP expression in small intestine.

Effect of zaldaride maleate, an antidiarrheal compound, on intracellular cyclic nucleotide-mediated intestinal ion secretion in rats

The purpose of this study is to clarify the mechanisms of action of zaldaride, a calmodulin inhibitor. 16,16-Dimethyl prostaglandin E(2), forskolin, 8-bromo cAMP, nitroprusside, 8-bromo cGMP and Escherichia coli heat-stable enterotoxin STa increased the short-circuit current in rat colonic mucosa. Zaldaride at >/=10 microM significantly attenuated the 16,16-dimethyl prostaglandin E(2) and Escherichia coli heat-stable enterotoxin STa-induced increase in short-circuit current; whereas it did not affect other secretagogues-induced effects. These results suggest that zaldaride inhibits the activation of Ca(2+)/calmodulin-sensitive adenylate cyclase or guanylate cyclase linked to a receptor.

Motor activity of vascularly perfused rat duodenum. 2. Effects of VIP, PACAP27 and PACAP38

We examined the mechanisms of effects of vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase activating polypeptide (PACAP) 27 and PACAP38 on spontaneously occurring pressure waves in ex vivo perfused rat duodenum. VIP and PACAPs dose-dependently reduced the percentage motor index of pressure waves; this reduction was not prevented by atropine, hexamethonium or tetrodotoxin (TTX). VIP and PACAPs abolished acetylcholine-induced stimulation of pressure waves, even in the presence of TTX. These findings suggest that VIP and PACAPs may exert direct inhibitory effects via VIP/PACAP receptors located on smooth muscle rather than via cholinergic receptors. The inhibitory effects of VIP and PACAPs were partially antagonized by the VIP receptor antagonists VIP(10-28), suggesting that VIP and PACAPs share common receptor sites on intestinal smooth muscle. The effects of VIP and PACAPs were completely antagonized by nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (L-NA), suggesting that NO mediates the inhibitory effects of VIP and PACAPs on duodenal motility. Furthermore, single injection of L-NA stimulated spontaneously occurring pressure waves, while VIP(10-28) did not affect them. These findings suggest that VIP/PACAPs and NO strongly interact as an inhibitory mediator on duodenal motility, but that their modes of action in doing so may differ.

Binding sites for VIP in the reorganizing mucosa of the irradiated bowel

Rats were given radiotherapy (total dose 30 Gy) over the abdomen. Seven days later specimens of the duodenum were prepared for in vitro receptor autoradiography using the radioligand [125I]VIP. The autoradiograms were quantitatively analyzed using a computer system. Histological examination revealed that a very marked reorganization of the mucosa had occurred in response to irradiation. Using receptor autoradiography, we found [125I]VIP-specific binding sites in the reorganizing mucosa, except where denudation had occurred. Such binding sites also occurred in the smooth muscle layer of the duodenal wall. The observations suggest that VIP has profound effects in radiation-induced enteropathy.

Disturbed intestinal movement, bile reflux to the stomach, and deficiency of c-kit-expressing cells in Ws/Ws mutant rats

BACKGROUND & AIMS

Interstitial cells of Cajal (ICCs) are believed to initiate the basic contractile activity of the gastrointestinal tract. Because ICCs in the intestine of mice express c-kit receptor tyrosine kinase and because rats are more commonly used than mice for pathophysiological investigations of the gastrointestinal tract, the number of the c-kit messenger RNA-expressing cells was compared with gastrointestinal movement in rats.

METHODS

The c-kit messenger RNA-expressing cells were detected by in situ hybridization. The autonomous contraction of excised segments of the ileum was recorded. The function of the pyloric sphincter was evaluated by measuring the content of bile acids in the stomach.

RESULTS

The c-kit messenger RNA-expressing cells were not detectable in the stomach of Ws/Ws mutant rats with a small deletion at the tyrosine kinase domain of c-kit, and the number of c-kit messenger RNA-expressing cells decreased to 7% that of normal control rats in the ileum of Ws/Ws rats. The contractile activity of the ileum was apparently impaired, and the content of bile acids in the stomach was significantly increased in Ws/Ws rats.

CONCLUSIONS

The abnormalities in the ileal movement and pyloric sphincter function in Ws/Ws rats were attributable to the deficiency of c-kit messenger RNA-expressing cells.

Insulinlike growth factor I receptors in rabbit gastrointestinal tract. Characterization and autoradiographic localization

Insulinlike growth factor I is a potent mitogen with insulinlike metabolic effects. Insulinlike growth factor I is synthesized in the liver, intestine, and other organs. Insulinlike growth factor I receptors are widely distributed and structurally similar to insulin receptors. Frozen sections of rabbit gastrointestinal tract were incubated in buffer containing 40 pmol/L [125I]insulinlike growth factor I. Binding was saturable, temperature- and time-dependent, and reversible. Saturation binding experiments showed a single class of high-affinity receptors (Kd = 0.9 nmol/L, Bmax = 0.36 pmol/mg protein). The IC50s for insulinlike growth factor I and insulinlike growth factor II were 3 nmol/L and 90 nmol/L, respectively; whereas insulin at 1-3 mumol/L displaced 50% of specific binding. Autoradiography of insulinlike growth factor I binding demonstrated significant differences in receptor density in gastrointestinal smooth muscle, epithelium of the esophagus, stomach, small intestine, and colon. These results indicate that a single class of specific, high-affinity insulinlike growth factor I receptors were distributed in muscular and mucosal layers of the entire rabbit gastrointestinal tract. Insulinlike growth factor I is likely to be an important local mediator of intestinal growth and metabolism.

Simultaneous immunohistochemical demonstration of vasoactive intestinal polypeptide and its receptor in human colon

The present study reports an immunohistochemical approach for localizing the immunoreactivity of vasoactive intestinal polypeptide (VIP) receptor in the human colon, by using a monoclonal antibody which recognizes the VIP-receptor of a human colonic adenocarcinoma cell line. Simultaneous demonstration of immunoreactive VIP-receptor of a human colonic adenocarcinoma cell line. Simultaneous demonstration of immunoreactive VIP-receptor and VIP was achieved by a double-labelling procedure employing immunogold silver staining for VIP-receptor, and a biotinylated secondary antibody followed by streptavidin-Texas Red, to visualize VIP. The immunoreactive VIP receptor was found at two locations receiving dense VIP innervation: myenteric ganglia and mucosal epithelium. Epithelial cells displayed intense labelling at the basolateral membrane, which confirmed earlier binding studies on fractionated membranes. A small number of enteroendocrine cells was also recognized by the VIP-receptor antibody. Smooth muscle and cells of the immune system were not stained by the monoclonal antibody, indicating that it recognized an epitope not common to VIP-receptors of all locations. Thus, the immunohistochemical approach of VIP-receptor localization differs from autoradiography in (a) precise cellular localization, (b) possibility of simultaneous demonstration of receptor and ligand immunoreactivity, and (c) selectivity to a certain receptor population which, however, is presently not fully characterized.

Distribution of vasoactive intestinal peptide and its receptors in the arteries of the rabbit

Vasoactive intestinal peptide (VIP) is a widely distributed neurotransmitter whose dilatory effects on vascular smooth muscle are believed to be mediated via specific receptors. To determine the possible role of VIP in regulating specific vascular beds, we examined the relationship between arterial wall VIP content as determined by radioimmunoassay and VIP receptors mapped by autoradiography. Analysis of arteries from 12 adult New Zealand rabbits showed that VIP receptors were consistently located in the wall of all muscular arteries, and that the 125I-VIP grain density correlated with VIP content. 125I-VIP binding in the mesenteric, renal, and iliac arteries was abundant and their VIP content was 192 +/- 56, 51 +/- 5, and 74 +/- 23 fmole/mg protein, respectively. 125I-VIP binding to the thoracic aorta was indistinguishable from nonspecific binding, its VIP content being 15 +/- 2 fmole/mg protein. The abundance of VIP receptors and the high VIP levels associated with the mesenteric, renal, and iliac arteries suggest that VIP is a potential regulator of flow to the vascular beds supplied by these arteries. In contrast, the much lower density of receptors in the extracranial carotid, which is also a muscular artery, suggests that, in rabbits, control of carotid vasomotion may be less dependent on VIP innervation. Furthermore, these results suggest that VIP receptors and VIP-containing neurons are not uniformly distributed in the arterial vasculature and that VIP may have selective vasodilatory effects.

Distribution of vasoactive intestinal polypeptide and substance P receptors in human colon and small intestine

Vasoactive intestinal polypeptide (VIP) and substance P are found in neurons in the lamina propria and submucosa and muscularis propria of human small intestine and colon. VIP receptors coupled to adenylate cyclase are present on epithelial, smooth muscle, and mononuclear cells. This study analyzes the distribution of [125I]VIP binding and [125I]substance P in human colon and small intestine using autoradiographic techniques. [125I]VIP binding was present in high density in the mucosal layer of colon and small intestine. [125I]VIP binding was not significantly greater than nonspecific binding in smooth muscle layers or the lymphoid follicles. In contrast, [125I]substance P binding was present in high density over the colonic muscle but was not present over the mucosal layer. In human colon cancer, [125I]VIP grain density over the malignant tissue was only slightly higher than background. These autoradiographic studies of [125I]VIP binding indicate that the highest density of VIP receptors was found in the small intestine and superficial colonic mucosa, whereas the density of substance P receptors was highest over the smooth muscle layers. These findings suggest a mismatch between immunochemical content of the peptide and autoradiographic density of the receptor.

VIP receptors and content after bowel transplantation

Advances in immunosuppressive therapy have renewed interest in small bowel transplantation. Little is known, however, about the functional capacity of transplanted intestine. To clarify the potential for normal function, we investigated whether elements of the enteric nervous system are preserved after denervation in our rat model of intestinal transplantation. We investigated whether VIP, a major peptide neurotransmitter of the enteric nervous system, and its receptors are preserved in the bowel after transplantation. In our model of transplantation, avascular fetal jejunum from term Fisher rats is transplanted to the subcutaneous tissues of host syngeneic rats. This "neogut" becomes vascularized and develops characteristics of native small bowel. VIP content was measured by RIA and the in situ distribution of VIP receptors was determined by the technique of receptor autoradiography. Neogut was studied 1 and 3 weeks after transplantation and compared with age-matched rat pup jejunum. Autoradiographs showed high silver grain density, representing VIP binding sites, in the mucosal layers of all tissues studied. VIP content in the transplanted bowel was comparable to that of native gut and showed a rise with developmental age similar to that of native gut. VIP levels (pmole/mg protein, x +/- SEM) were neogut 1 week, 0.26 +/- 0.14; jejunum 1 week, 0.25 +/- 0.07; neogut 3 weeks, 0.60 +/- 0.21; and jejunum 3 weeks, 0.69 +/- 0.16. These results show that VIP receptors and content are preserved in this model of transplantation. This suggests that the enteric nervous system and receptors for peptide neurotransmitters remain intact after transplantation and may retain the potential for regulatory function.

Expression of membrane receptors and (proto)oncogenes during the ontogenic development and neoplastic transformation of the intestinal mucosa

The functional relationship between membrane receptors involved in signal transduction and (proto) oncogene expression has been explored during the ontogenic development and differentiation of the intestinal mucosa in man and rat. The present review develops detailed picture of the current understanding of some mechanisms underlying growth and function of normal, immortalized and cancerous intestinal epithelial cells.

Vasoactive intestinal peptide (VIP) receptors in the canine gastrointestinal tract

Vasoactive intestinal peptide (VIP) is a putative neurotransmitter in both the brain and peripheral tissues. To define possible target tissues of VIP we have used quantitative receptor autoradiography to localize and quantify the distribution of 125I-VIP receptor binding sites in the canine gastrointestinal tract. While the distribution of VIP binding sites was different for each segment examined, specific VIP binding sites were localized to the mucosa, the muscularis mucosa, the smooth muscle of submucosal arterioles, lymph nodules, and the circular and longitudinal smooth muscle of the muscularis externa. These results identify putative target tissues of VIP action in the canine gastrointestinal tract. In correlation with physiological data, VIP sites appear to be involved in the regulation of a variety of gastrointestinal functions including epithelial ion transport, gastric secretion, hemodynamic regulation, immune response, esophageal, gastric and intestinal motility.