Molecular aspects of cytoprotection by modified somatostatins.

Somatostatin and cyclic modifications of this molecule inhibit the development of protrusions on the surface of isolated hepatocytes in presence of phalloidin. This prevention of phalloidin injury is caused by competitive inhibition of the phallotoxin uptake. Transport inhibition is not a hormonal effect of somatostatin. The concentrations needed are in the micromolar range. The most protective somatostatin modifications lack hormonal activity (GH release). Somatostatin and its analogs are substrates of a hepatocellular transporter which also translocates other cyclopeptides, among them phalloidin, antamanide, and several organic anions, such as iodipamide and fusidic acid. Physiological substrates of this multispecific transport system are bile acids. The protection of phallotoxin injury by somatostatin is a specific mechanism only representative for liver cells. No other cell contains the above multispecific transporter.