Longitudinal mechanical tension induces growth in the small bowel of juvenile rats

Abstract

Introduction: The aim of our study was to apply longitudinal force to the small bowel to increase the length of intestine in juvenile rats.

Methods: Fifty juvenile rats had double barrelled, blind loop ostomies created using an isolated segment of bowel. Our intestinal lengthening device was inserted into one of the loops and the second loop served as a control. Once the device was deployed, the experimental, control, and in situ segments of bowel were evaluated for length, weight, histology, and disaccharidase enzyme activity.

Results: Mechanical tension increased intestinal length by 149%. The lengthened bowel also exhibited a greater total weight (218%), greater mucosal weight (122%), and increased protein mass (164%) compared with the control limb of bowel. Histologically, there was a markedly increased thickness of the muscularis propria in the lengthened bowel (200% increase compared with the control limb). Functionally, we found increased total disaccharidase activity in the lengthened bowel (between 47% and 350%, depending on the particular enzyme tested; p<0.01).

Conclusion: Mechanical tension induces intestinal growth by increasing length, weight of the bowel and mucosa, and protein mass. Histological changes, such as increases in Paneth cells, suggest that increased proliferation and reorganisation of the mucosa and muscularis propria are a response to mechanical tension. Functionally, increased intestinal length corresponds with increased disaccharidase activity, thus implying potential increased absorptive capacity of the lengthened bowel.

Figure 1

Surgical placement of the intestinal lengthening device. (A) A segment of small bowel was isolated, and an enterotomy was placed in the middle of the isolated loop of bowel. For these photos, the long black arrow indicates the unlengthened limb, the short black arrow the lengthened limb, and the white arrow identifies the in situ bowel. (B) A double barrel ostomy was created with one loop for placement of the intestinal lengthening device, and the second as an internal control. (C) Intestinal lengthening device within the loop of bowel. (D) After 30 days, the isolated limb of small bowel is removed.

Figure 2

Schematic diagram of the intestinal lengthening device.

Figure 3

Mechanical tension lengthens the small bowel. These data represent measurements on day 0 and day 30. The “on tension” group represents measurement of the lengthened intestine with the device deployed, and the “off tension” group demonstrates the size of the lengthened limb of bowel with the device removed. At day 0, a 15 mm limb of bowel is opened to create two limbs, the experimental lengthened bowel and the control unlengthened bowel. The in situ bowel was used as a control for normal growth of the animals. The average length of bowel was not different between the lengthened and unlengthened bowel (7.6 (1) mm v 7.7 (1.1) mm; p>0.5, n = 40). After 30 days, the average length of bowel was increased by 228% with the device on tension, and by 148% once the device had been removed (p<0.01).

Figure 4

Measurement of weight of the entire bowel and mucosa of in situ, control limb, and lengthened limb. Mucosa from the lengthened limb of bowel was 121% heavier than that from the unlengthened limb of bowel (60.9 (26.6) mg v 27.4 (23.1) mg; p<0.01, n = 10).

Figure 5

Histology of the lengthened, unlengthened, and in situ small bowel. There were no differences between the lengthened and unlengthened limbs of bowel. The in situ bowel villi were longer than both the lengthened and unlengthened limbs. The lengthened limb of bowel was thicker than both the unlengthened and in situ limbs of bowel. Measurements were taken at 200× magnification.