Recordings of the effects of butaprost (A), sulprostone (B), iloprost (C) and U-46,619 (D) on peristalsis. The drugs were administered to the organ bath at the specified concentrations. As can be seen, sulprostone and U-46,619 increased the peristaltic pressure threshold (indicated by arrow heads) whereas butaprost lowered it. Iloprost tended to lower the amplitude of the peristaltic waves.