Changes in gastrin levels, food intake, and duodenal mucosal growth during lactation

Changes in morphology and function in small intestinal mucosa after Roux-en-Y surgery in a rat model

BACKGROUND

Currently there is no an appropriate model to study intestinal mucosal atrophy in vivo that preserves the nutritional status of the organism.

MATERIALS AND METHODS

We created a defunctionalized segment of jejunum via a dead-end Roux-en-Y anastomosis in rats. We compared tissue morphometric parameters in the intestinal mucosa of the defunctionalized bowel with that of the mucosa proximal and distal to the anastomosis. We further measured extracellular signal-regulated kinase (ERK) activation within the mucosa as well as sucrase-isomaltase and dipeptidyl peptidase-4 levels as markers of intestinal mucosal differentiation by Western blotting of mucosal scrapings.

RESULTS

Three days after anastomosis, the defunctionalized bowel exhibited decreased diameter and thickness of both the mucosa and the fibromuscular layer compared with adjacent bowel in continuity for luminal nutrient flow or with bowel from control animals. Sucrase-isomaltase and dipeptidyl peptidase-4 levels also were decreased. Furthermore, mucosal ERK activation, assessed as the ratio of phosphorylated to total ERK, also was reduced. Animal weights did not differ between bypassed and control animals.

CONCLUSIONS

Deprivation of nutrient flow in a segment of bowel by defunctionalizing Roux-en-anastomosis produces mucosal atrophy as indicated by altered histology, differentiation marker expression, and ERK signaling, in animals that are otherwise able to maintain enteral nutrition.

Regulation of the intestinal epithelial response to cyclic strain by extracellular matrix proteins

Repetitive mechanical deformation may stimulate intestinal epithelial proliferation. Because the extracellular matrix modulates static intestinal epithelial biology, we examined whether matrix proteins influence intestinal epithelial responses to deformation. Human Caco-2BBE cells and nontransformed human enterocytes (HIPEC) were subjected to 10% average cyclic strain at 10 cycles/min on flexible membranes precoated with matrix proteins without or with plasma fibronectin or functional anti-integrin antibodies in the medium. Strain stimulated proliferation, focal adhesion kinase, extracellular signal-regulated protein kinase (ERK), p38, and Jun N-terminal kinase similarly on collagen I or IV, and more weakly on laminin, but had no effect on fibronectin. MEK blockade (PD98059) prevented strain-stimulated proliferation on collagen but did not affect proliferation on fibronectin. Adding tissue fibronectin to a collagen substrate or plasma fibronectin to the media suppressed strain s mitogenic and signal effects, but not those of epidermal growth factor. Functional antibodies to the alpha5 or alpha(v) integrin subunit blocked strain's effects on Caco-2 proliferation and ERK activation, although ligation of the alpha2 or alpha6 subunit did not. Repetitive strain also stimulated, and fibronectin inhibited, human intestinal primary epithelial cell proliferation. Repetitive deformation stimulates transformed and nontransformed human intestinal epithelial proliferation in a matrix-dependent manner. Tissue or plasma fibronectin may regulate the intestinal epithelial response to strain via integrins containing alpha5 or alpha(v).

In vivo visualization of pyloric mucosal hypertrophy in infants with hypertrophic pyloric stenosis: is there an etiologic role?

OBJECTIVE

Infantile hypertrophic pyloric stenosis (IHPS) is a common condition which presents in infants at 2-12 weeks of postnatal life, and whose cause remains obscure. Multiple associated abnormalities have been recognized within the external hypertrophied pyloric muscle layer, but the internal component of the pyloric mucosa has received scant attention in the literature to date. Our purpose in this study was to show that pyloric mucosal redundancy is a constant finding in infants with IHPS, to discuss its possible cause, and to explore the hypothesis of a relationship between pyloric mucosal redundancy and the development of IHPS.

MATERIALS AND METHODS

We identified 102 consecutive infants with surgically confirmed IHPS and determined the thickness of the pyloric mucosa compared with the thickness of the surrounding hypertrophied muscle. Fifty-one infants who did not have pyloric stenosis served as controls.

RESULTS

Mean mucosal thickness in patients with IHPS approximated mean muscle thickness, with a ratio of 0.89. In infants with IHPS, the pyloric mucosa constitutes approximately one third of the cross-sectional diameter of the pyloric mass and fills and obstructs the pyloric canal.

CONCLUSION

Mucosal redundancy is a constant associated finding in IHPS. Although the origin of the redundancy and a cause-and-effect relationship are difficult to establish, our findings support the hypothesis that hypergastrinemia may be implicated in the pathogenesis of IHPS, and suggest that mucosal thickening could be implicated as one of the initiating factors in its development.

Amplitude-dependent modulation of brush border enzymes and proliferation by cyclic strain in human intestinal Caco-2 monolayers

Little is known about the effects of repetitive deformation during peristaltic distension and contraction or repetitive villus shortening on the proliferation and differentiation of the intestinal epithelium. We sought to characterize the effects of repetitive deformation of a physiologically relevant magnitude and frequency on the proliferation and differentiation of human intestinal epithelial Caco-2 cells, a common cell culture model for intestinal epithelial biology. Human intestinal epithelial Caco-2 cells were cultured on collagen-coated membranes deformed by -20 kPa vacuum at 10 cycles/minute, producing an average 10% strain on the adherent cells. Proliferation was assessed by cell counting and 3H-thymidine incorporation. Alkaline phosphatase and dipeptidyl dipeptidase specific activity were measured in cell lysates. Since cells at the membrane periphery experience higher strain than cells in the center, the topography of brush border enzyme histochemical and immunohistochemical staining was analyzed for strain-dependence. Cyclic strain stimulated proliferation compared to static cells. Proliferation was highest in the membrane periphery where strain was maximal. Strain also modulated differentiation independently of its mitogenic effects, selectively stimulating dipeptidyl dipeptidase while inhibiting alkaline phosphatase. Strain-associated enzyme changes were also maximal in areas of greatest strain. The PKC inhibitors staurosporine and calphostin C ablated strain mitogenic effects while intracellular PKC activity was increased by strain. The strain-associated brush border enzyme changes were attenuated but not blocked by PKC inhibition. Thus, strain of a physiologically relevant frequency and magnitude promotes proliferation and modulates the differentiation of a well-differentiated human intestinal epithelial cell line in an amplitude-dependent fashion. PKC may be involved in coupling strain to increased proliferation.

Amplitude-dependent modulation of brush border enzymes and proliferation by cyclic strain in human intestinal Caco-2 monolayers

Little is known about the effects of repetitive deformation during peristaltic distension and contraction or repetitive villus shortening on the proliferation and differentiation of the intestinal epithelium. We sought to characterize the effects of repetitive deformation of a physiologically relevant magnitude and frequency on the proliferation and differentiation of human intestinal epithelial Caco-2 cells, a common cell culture model for intestinal epithelial biology. Human intestinal epithelial Caco-2 cells were cultured on collagen-coated membranes deformed by -20 kPa vacuum at 10 cycles/minute, producing an average 10% strain on the adherent cells. Proliferation was assessed by cell counting and 3H-thymidine incorporation. Alkaline phosphatase and dipeptidyl dipeptidase specific activity were measured in cell lysates. Since cells at the membrane periphery experience higher strain than cells in the center, the topography of brush border enzyme histochemical and immunohistochemical staining was analyzed for strain-dependence. Cyclic strain stimulated proliferation compared to static cells. Proliferation was highest in the membrane periphery where strain was maximal. Strain also modulated differentiation independently of its mitogenic effects, selectively stimulating dipeptidyl dipeptidase while inhibiting alkaline phosphatase. Strain-associated enzyme changes were also maximal in areas of greatest strain. The PKC inhibitors staurosporine and calphostin C ablated strain mitogenic effects while intracellular PKC activity was increased by strain. The strain-associated brush border enzyme changes were attenuated but not blocked by PKC inhibition. Thus, strain of a physiologically relevant frequency and magnitude promotes proliferation and modulates the differentiation of a well-differentiated human intestinal epithelial cell line in an amplitude-dependent fashion. PKC may be involved in coupling strain to increased proliferation.