Absorption and motility of the bypassed human ileum. The authors assessed absorption and motility of the human ileum after a prolonged period of disuse. In eight patients with ulcerative colitis, a manometric-catheter assembly was placed via the ileostomy into the unused portion of distal ileum two months after ileal pouch-anal anastomosis and temporary diverting loop ileostomy. The distal ileum was perfused at 5 ml/min with an isosmotic solution of either sodium chloride or ileal chyme diluted with sodium chloride for three hours before and three hours after a meal on two consecutive days. Absorption was measured, single and clustered pressure waves were identified and quantitated with the aid of a computer program, and a motility index was calculated. Mean absorption +/- S.E.M. of both perfusates was poor on day 1 (-10 +/- 2 ml/25 cm x 30 min), and the meal induced no ileal motor response. By day 2, however, absorption of both perfusates was much improved (-1 +/- 2 ml/25 cm x 30 min; P less than 0.05), and the number of discrete clustered contractions and the motility index now clearly increased after the meal (2.6 +/- 0.6 vs. 7.2 +/- 1.0 clustered waves/hr; 7.5 +/- 0.5 vs. 9.7 +/- 0.2 motility units/30 min; P less than 0.05). The conclusion was that absorption and motility of the human ileum were impaired after two months of disuse, but that ileal absorption and motility improved one day after the introduction of isosmotic ileal perfusates. 