Phorbol myristate acetate, which was shown previously to elicit eicosanoid synthesis in primary cultures of Kupffer cells, led to a net release of prostaglandins (PG) D2 and E2 from the perfused rat liver. While a substantial amount of PGD2 (the major prostaglandin of Kupffer cells) left the liver, very little PGE2 was found in the effluent. Considerable amounts of immunologically reactive PGD2 and E2 were secreted with the bile. PGE2 rather than PGD2 was able to stimulate glycogenolysis and to increase perfusion pressure. These effects were, however, strongly dependent on the direction of the flow. If the liver was perfused in a retrograde fashion, i.e., from the vena cava to the portal vein, phorbol myristate acetate or PGE2 exerted only minor effects. These observations suggest a topological heterogeneity of producer and responder cells, respectively, in the liver sinusoid.