Healing of experimental colon anastomosis

Abstract

The healing of colonic anastomoses is slower and accompanied by more complications than healing elsewhere in the gastrointestinal tract. The purpose of this study was to investigate local energy metabolism and the synthesis and accumulation of extracellular matrix components central in wound healing (fibronectin, laminin and collagen types I, III, IV and V) in the healing colon anastomosis. Also, the local synthesis of EGF and EGF-receptors during normal healing were of interest because EGF is a potent enhancer of wound healing and it is found in the gastrointestinal tract. 47 female rats had an anastomosis of the sigmoid colon and eight rats served as unoperated controls. The animals were killed 1-21 days after anastomosis and the anastomotic area was removed for study. The following histologic investigations of the anastomotic area were made: conventional histology, immunohistology (with antibodies for type I, III, IV and V collagen, fibronectin and laminin), enzyme-histochemistry (for SDH, LDH, Glu-6-PhDH, NADH, NADPH, acid phosphatase, leucylaminopeptidase and GLDH) and in-situ hybridizations with cDNA clones (for pro alpha 1 (I) and pro alpha 1 (III) collagens, fibronectin, EGF and the EGF-receptor). Further studies were made by Northern hybridizations to estimate the activity of the genes expressed in the anastomotic area. The normal colon has a strong aerobic and anaerobic glycolytic metabolism. Anastomosis causes a deep and long lasting reduction in the energy metabolism in the anastomotic area. These changes are especially extensive in the mucosa and the muscle layers. On the other hand, the energy metabolism in the submucosal layer remains intact after surgery. Aerobic metabolism is not normalized in the mucosa and muscle layers until three weeks after surgery. The repair tissue in the anastomotic gap shows the first LDH activity on day three which is also the time when revascularization and accumulation of fibrillar collagens begin. A fibronectin reaction was seen from day one with maximum on day five. Some of the fibronectin is locally synthesized, according to our gene expression studies. Preexisting collagens and laminin decrease during the first two postoperative days after which they increase to preoperative values or more within a week. New laminin and type IV collagen are also synthesized as basal laminae are formed during revascularization and reepithelization. Activation of type I and III collagen genes are seen in the submucosal layer and in the serosal surface from day one and in the anastomotic repair tissue from day two. The highest expression of the collagen genes is not seen until one week after surgery.(ABSTRACT TRUNCATED AT 400 WORDS)