Departments of 1 Internal Medicine and 2 Medical Physiology, 5 Division of Research and Education, Scott & White Clinic and The Texas A&M University System Health Science Center, College of Medicine, and 3 Central Texas Veterans Health Care System, Temple, Texas 76504; 4 Division of Gastroenterology, Tohoku University School of Med, Aobaku, Sendai 980-8574, Japan; and 6 Division of Gastroenterology, University of Rome, "La Sapienza," Rome 00185, Italy Submitted 25 October 2002 ; accepted in final form 10 March 2003 Tumor necrosis factor (TNF)- plays a critical role in epithelial cell injury. However, the role of TNF- in mediating cholangiocyte injury under physiological or pathophysiological conditions is unknown. Thus we assessed the effects of TNF- alone or following sensitization by actinomycin D on cell apoptosis, proliferation, and basal and secretin-stimulated ductal secretion in cholangiocytes from normal or bile duct-ligated (BDL) rats. Cholangiocytes from normal or BDL rats were highly resistant to TNF- alone. However, presensitization by actinomycin D increased apoptosis in cholangiocytes following BDL and was associated with an inhibition of proliferation and secretin-stimulated ductal secretion. Thus TNF- mediates cholangiocyte injury and altered ductal secretion following bile duct ligation. These observations suggest that cholestasis may enhance susceptibility to cytokine-mediated cholangiocyte injury. bile flow; intrahepatic biliary epithelium; proliferation; secretin Address for reprint requests and other correspondence: T. Patel, Division of Gastroenterology, Scott & White Clinic, Texas A&M Univ. System Health Science Center College of Medicine, 2401 South 31st St., Temple, TX 76502 (E-mail: tpatel{at}medicine.tamu.edu ).