70 - 90% of patients with PSC have concurrent inflammatory bowel disease (IBD), mostly ulcerative colitis. Conversely, 7% of patients with IBD have PSC. The close association between inflammatory bowel disease and PSC suggests that substances originating from the inflamed gut may damage the liver and biliary tree. Bacterial products may act as toxic proinflammatory agents. N-formyl L-methionine L-leucine L-tyrosine is a peptide produced by enteric flora. When this peptide was introduced into the colon of rats with colitis, it was absorbed, underwent enterohepatic circulation, and appeared undegraded in bile. Histologic changes in the livers of the rats resembled those in PSC.