Enema: A solution or compound that is introduced into the RECTUM with the purpose of cleansing the COLON or for diagnostic procedures.Barium Sulfate: A compound used as an x-ray contrast medium that occurs in nature as the mineral barite. It is also used in various manufacturing applications and mixed into heavy concrete to serve as a radiation shield.Administration, Rectal: The insertion of drugs into the rectum, usually for confused or incompetent patients, like children, infants, and the very old or comatose.Mesalamine: An anti-inflammatory agent, structurally related to the SALICYLATES, which is active in INFLAMMATORY BOWEL DISEASE. It is considered to be the active moiety of SULPHASALAZINE. (From Martindale, The Extra Pharmacopoeia, 30th ed)Diverticulum, Colon: A pouch or sac opening from the COLON.Sigmoidoscopy: Endoscopic examination, therapy or surgery of the sigmoid flexure.Phosphorothioate Oligonucleotides: Modified oligonucleotides in which one of the oxygens of the phosphate group is replaced with a sulfur atom.Colitis, Ulcerative: Inflammation of the COLON that is predominantly confined to the MUCOSA. Its major symptoms include DIARRHEA, rectal BLEEDING, the passage of MUCUS, and ABDOMINAL PAIN.Colonoscopy: Endoscopic examination, therapy or surgery of the luminal surface of the colon.Rectum: The distal segment of the LARGE INTESTINE, between the SIGMOID COLON and the ANAL CANAL.Proctocolitis: Inflammation of the RECTUM and the distal portion of the COLON.Colonic Diseases: Pathological processes in the COLON region of the large intestine (INTESTINE, LARGE).Intussusception: A form of intestinal obstruction caused by the PROLAPSE of a part of the intestine into the adjoining intestinal lumen. There are four types: colic, involving segments of the LARGE INTESTINE; enteric, involving only the SMALL INTESTINE; ileocecal, in which the ILEOCECAL VALVE prolapses into the CECUM, drawing the ILEUM along with it; and ileocolic, in which the ileum prolapses through the ileocecal valve into the COLON.Appendix: A worm-like blind tube extension from the CECUM.Proctitis: INFLAMMATION of the MUCOUS MEMBRANE of the RECTUM, the distal end of the large intestine (INTESTINE, LARGE).Aminosalicylic Acids: A group of 2-hydroxybenzoic acids that can be substituted by amino groups at any of the 3-, 4-, 5-, or 6-positions.Fecal Impaction: Formation of a firm impassable mass of stool in the RECTUM or distal COLON.Ileal Diseases: Pathological development in the ILEUM including the ILEOCECAL VALVE.