Abstract
The microtubule poison, colchicine, caused an abnormal output of a variety of proteins into rat bile. After 3 h of exposure to the drug, livers were isolated and perfused with media of defined protein composition. There was no essential change in permeability of the hepatobiliary system to proteins (e.g. bovine serum albumin) entering bile from the perfusion fluid. The rat (serum) albumin and fibrinogen that were secreted into bile from colchicine-treated livers were probably derived from the hepatocytes. Disruption of the microtubular system reduces the secretion of proteins at the sinusoidal face of the hepatocyte and results in an accumulation of secretory vesicles in the cytoplasm. It is suggested that under these conditions some of the vesicles discharge their contents into the bile canaliculus.