Bile secretion has been reported to be regulated by circulating hormones and by autonomic liver nerves. In the in situ perfused rat liver, prostaglandins reduce bile flow and bile acid secretion. The aim of this study was to investigate the regulation of bile secretion by prostaglandins in the in vivo situation. The bile duct and portal vein of anaesthetised Wistar rats were cannulated by polyethylene tubes. Bile flow was determined gravimetrically. Bile acids were quantified by the 3-alpha-hydroxy-steroid-dehydrogenase method and by high-pressure-liquid-chromatography (HPLC) separation. Administration of 1 microM prostaglandin F2 alpha into the portal vein over 5 minutes reduced bile flow from 1.57 microliter/min.g liver to 0.95 microliter/min.g liver and bile acids secretion from 148 to 81 nmol/100g/min. The administration of different doses (0.1 microM, 1 microM, 10 microM) of prostaglandin F2 alpha reduced hepatic bile secretion in a dose-dependent manner. Similar effects were observed after infusion of prostaglandin D2. However, the ratio of the bile acids (alpha-tauromuricholic acid), beta-tauromuricholic acid, taurocholic acid, taurochenodeoxycholic acid, and taurodeoxycholic acid) was unchanged by prostaglandin F2 alpha. In conclusion, infusion of prostaglandin F2 alpha into the portal vein results in a reduction of bile flow and bile acid secretion in a dose-dependent manner. These results suggest that the effect is linked to canicular bile secretion.