In vitro smooth muscle contractility before and after relief of experimental obstruction in the rat: Application to the surgical management of ileal dilatation

PurposeBowel dilatation occurs proximal to an obstruction and predisposes to intestinal dysmotility. The present study sought to determine whether or not changes in smooth muscle contractility and the thickness of the proximal, dilated bowel wall can be reversed following relief of the obstruction.Materials and methodsThree groups of seven male Wistar rats were studied. In 8-week-old animals in a control group and a sham-operated group, a small segment of bowel (designated as R1 for controls and R2 for shams) was resected 5.0 cm from the cecum. In the third (operated) group, a narrow, isoperistaltic intestinal loop was created proximal to an end-to-end anastomosis of the ileum in 4-week-old animals. When these animals were 6 weeks old, the loop was re-anastomosed to the distal small bowel (after resection of the loop's distal portion, referred to as R3). Two weeks later, a small segment of bowel was resected proximal to the anastomosis (R4). We evaluated the thickness of the smooth muscle layers and the in vitro contractile responses of circular smooth muscle ileal strips (R1–R4) to electrical stimulation and pharmacological stimulation (with KCl, acetylcholine (ACh), substance P, NG-nitro-l-arginine methyl ester (L-NAME) and histamine).ResultsThe amplitudes of contraction in response to electrical and Ach-mediated stimulation were higher for R3 than for R4 (P < 0.001), R1 and R2 (both P < 0.05). Compared with R1 and R2, the smooth muscle layer was three times as thick in R3 (P < 0.001) and 2.5 times as thick in R4 (P < 0.01).ConclusionOur study provides evidence of the possible recovery of intestinal motility (in response to neurotransmitters involved in gut function) after the relief of an obstruction. If ileal motility can conceivably return to normal values, conservative surgical procedures in pediatric patients should be preferred (in order to leave a sufficient length of bowel and avoid short bowel syndrome).