Effects of cecectomy on digestion and retention time of digesta in rats

Ileocecal Valve Removal Reverses the Constipating Effects of Loperamide in Rats

BACKGROUND

Previous evidence associating ileocecal valve removal (ICVR) with a reduced risk of fecal impaction of the ileocecum in cystic fibrosis indicated possible benefits from ileocecal valve loss in disorders with inhibited proximal colon transit caused by fecal dehydration and hypoperistalsis. We aimed to investigate the ability of ICVR in reversing fecal impaction in a loperamide-induced model of a similar pattern of inhibited proximal colon transit in rats.

MATERIALS AND METHODS

Thirty pubertal Sprague-Dawley rats were rendered constipated with subcutaneous loperamide treatment (1 mg/kg/d) for 7 d. On day four, rats were allocated to groups: ICVR (n = 12), total colectomy (TC, n = 9), and sham operation (SO, n = 9). Fecal pellet number and consistency were assessed daily. On day seven, all rats were gavaged with barium. Two hours later, intestinal transit ratio (distance of barium head from the pylorus adjusted for small intestine length) and adjusted (for total intestine length) barium-to-anus distance were assessed.

RESULTS

ICVR showed higher transit ratio and shorter barium-to-anus distance, that is, faster transit, than SO (P < 0.0001); differences between ICVR and TC were not significant (P > 0.06). Furthermore, ICVR and TC showed similar reduction in hard feces, compared with SO (P < 0.0001). TC showed higher diarrhea rate than ICVR (P < 0.0001).

CONCLUSIONS

ICVR led to an effective, similar to TC, reversal of the constipating effects of loperamide and, unlike TC, was not associated with diarrhea. Our findings support the idea that ICVR might be beneficial in disorders with inhibited proximal colon transit resulting from fecal dehydration and hypoperistalsis, such as refractory cystic fibrosis-related intestinal obstruction. Potential clinical implications merit further study.

Uremic Toxin-Producing Gut Microbiota in Rats with Chronic Kidney Disease

BACKGROUND

In patients with chronic kidney disease (CKD), many metabolites of gut microbiota retain in the body as uremic toxins (UTs). However, the kinds of bacteria producing UTs are rarely discussed.

METHODS

We analyzed UT production and the composition of gut microbiota in CKD rats and cecectomized rats. AST-120, a spherical carbon adsorbent, was administrated to evaluate how the precursors of UT affect gut microbiota. Serum and urine levels of UTs were quantified by liquid chromatography/electrospray ionization-tandem mass spectrometry. Gut microbiota were analyzed using 454-pyrosequencing of the 16S rRNA gene. Operational taxonomic unit (OTU) clustering and UniFrac analysis were performed to compare gut microbiota among the groups.

RESULTS

Serum and urine levels of indoxyl sulfate and phenyl sulfate were higher in CKD versus control rats (p < 0.05). AST-120 administration decreased UT production (p < 0.01) and changed overall gut microbiota composition in CKD rats. UT urinary excretion and gut microbiota composition changed in cecectomized rats, with the relative abundance of Clostridia- and Bacteroidia-affiliated species being significantly reduced (p < 0.01). We identified candidate indole- and phenol-producing intestinal microbiota, 3 Clostridia, and 2 Bacteroidia. These OTUs have a tryptophanase/tyrosine phenol-lyase gene in the closest sequenced genome out of the OTUs declined following cecectomy.

CONCLUSION

Our data suggest that UT production is correlated with a subset of indigenous gut microbiota. However, UT may be induced by other non-symbiotic microbiota that are influenced by factors other than microbiota populations. The relationship between specific microbiota and UTs in patients requires further clarification.

Enhanced trabecular bone resorption and microstructural bone changes in rats after removal of the cecum

The cecum, the proximal part of the large intestine, has the highest rate of calcium absorption compared with other intestinal segments. Previously, we showed that rats with the cecum surgically removed (cecectomized rats) had severe negative calcium balance, low bone mineral density (BMD), and a compensatory increase in colonic calcium absorption. Herein, we used the computer-assisted bone histomorphometric technique and microcomputed tomography (μCT) to analyze bone microstructural defects in cecectomized rats at 1 and 3 mo postsurgery compared with age-matched sham-operated control rats. Relatively low BMD as determined by dual energy X-ray absorptiometry was observed in the femora, tibiae, and lumbar vertebrae of the 3-mo cecectomized rats. μCT analysis revealed decreases in the tibial cortical thickness, periosteal and endosteal perimeters, and moment of inertia in cecectomized rats. The histomorphometric results further showed that trabecular bone volume and number were markedly decreased, whereas trabecular separation was increased in the proximal tibial metaphysis of cecectomized rats, thus leading to a decrease in trabecular volumetric BMD. Since osteoclast surface and eroded surface were increased after cecectomy, such bone loss in cecectomized rats appeared to result from an enhanced bone resorption. Moreover, decreases in bone formation rate and osteoblast surface indicated a suppression of osteoblast-mediated bone formation. In conclusion, cecectomy induced widespread osteopenia in rats presumably by enhancing the osteoclast-mediated bone resorption and suppressing bone formation. The present results underline the important role of cecum in the body calcium homeostasis.

Impaired body calcium metabolism with low bone density and compensatory colonic calcium absorption in cecectomized rats

An earlier study reported that cecal calcium absorption contributes less than 10% of total calcium absorbed by the intestine, although the cecum has the highest calcium transport rate compared with other intestinal segments. Thus, the physiological significance of the cecum pertaining to body calcium metabolism remains elusive. Herein, a 4-wk calcium balance study in cecectomized rats revealed an increase in fecal calcium loss with marked decreases in fractional calcium absorption and urinary calcium excretion only in the early days post-operation, suggesting the presence of a compensatory mechanism to minimize intestinal calcium wasting. Further investigation in cecectomized rats showed that active calcium transport was enhanced in the proximal colon but not in the small intestine, whereas passive calcium transport along the whole intestine was unaltered. Since apical exposure to calcium-sensing receptor (CaSR) agonists similarly increased proximal colonic calcium transport, activation of apical CaSR in colonic epithelial cells could have been involved in this hyperabsorption. Calcium transporter genes, i.e., TRPV6 and calbindin-D(9k), were also upregulated in proximal colonic epithelial cells. Surprisingly, elevated serum parathyroid hormone levels and hyperphosphatemia were evident in cecectomized rats despite normal plasma calcium levels, suggesting that colonic compensation alone might be insufficient to maintain normocalcemia. Thus, massive bone loss occurred in both cortical and trabecular sites, including lumbar vertebrae, femora, and tibiae. The presence of compensatory colonic calcium hyperabsorption with pervasive osteopenia in cecectomized rats therefore corroborates that the cecum is extremely crucial for body calcium homeostasis.