Hyperplasia and neoplasia of the intestinal tract.

Measurements of RNA and DNA in the rat have been used to identify mucosal hyperplasia in the remaining gut within 48 h of partial intestinal loss. Structural adaptation of the ileum is still present 3 months after jejunal resection, whereas transection of the bowel produces merely transient hyperplasia. A humoral factor can be transmitted between rats linked in vascular parabiosis that is capable of stimulating intestinal cell proliferation. Humoral agents may also explain reduced adaptation of the distal bowel after jejunal bypass as opposed to equivalent resection. Although bile can initiate prompt ileal hyperplasia, the additional presence of pancreatic juice is needed to prolong this effect. Adaptation is controlled by luminal and systemic factors that are closely interlinked. Experimental intestinal carcinogenesis is promoted by proximal enterectomy.