Intestinal resection is followed by structural and functional adaptation of the remnant, including motor adaptation. Since changes also occur in intestinal smooth muscle, our aim was to determine whether changes in motor function are related to changes in smooth muscle contractility. Eighteen dogs underwent transection alone (GP I, n = 6), 50% distal resection (GP II, n = 6) and 50% distal resection with jejunocolostomy (GP III, n = 6). Histologic measurements and length-tension studies with response to carbachol were made at 12 weeks. Longitudinal muscle (LM) length tended to increase in the resected animals hut not significantly (174 ± 23 and 180 ± 23 vs 156 ± 16 cm, GP II, GP III, and GP I, respectively). Circular muscle (CM) length was similar in all three groups (8.2 ± 0.9 and 7.9 ± 0.6 vs 7.5 ± 0.6 cm). Both CM and LM tended to be thicker in the resected groups (CM: 660 ± 163 and 733 ± 139 vs 569 ± 199 μm; LM: 213 ± 77 and 246 ± 76 vs 220 ± 104 μm, GP II, GP III, and GP I, respectively, NS). Length-tension relationships for both CM and LM were similar in all three groups. The length (Lo) at which maximal active tension (To) was achieved was 130-140% initially in both LM and CM. Passive tension at Lo and the response to cholinergic stimulation were similar in all three groups. There were no significant differences in absolute active and total tension generated or force/cm2. The carbachol dose responses were similar with the maximal active tension occurring at 10-4 M carbachol. The ED50 was greater in CM than in LM (P < 0.05 for transection animals). The ED50 was lower after resection and bypass (P < 0.05 GP III vs Gp I). There were no significant differences in in vitro smooth muscle length tension relationships or the response to cholinergic stimuli of jejunum 12 weeks after resection with or without bypass of the ICJ. Thus, any changes in motor adaptation during this period are related to earlier transient effects or other factors.
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