Identification of prostaglandin F-producing cells in the liver

Prostaglandin (PG) F synthase forms PGF_2α and 9α, 11β-PGF₂ from PGH₂ and PGD₂, respectively. PGH₂ is synthesized from arachidonic acid by cyclooxygenase (COX) and then metabolized to various PGs and thromboxane by specific enzymes. PGD₂ is synthesized from PGH₂ by PGD synthase. To identify PGF₂-producing cells in the rat liver, the occurrence and localization of PGF synthase and COX were studied with immunochemical and immunohistochemical techniques using anti-liver-type PGF synthase and anti-COX antibodies. In Western blot analyses, positive bands of liver-type PGF synthase and constitutive COX-1 were observed at positions approximately 37 kDa and 70–72 kDa, respectively. However, inducible COX-2 was not detected. In the immunohistochemical study, PGF synthase was present in the cytoplasm of the sinusoidal endothelial cells. COX-1 was present on the membranes of the nucleus and endoplasmic reticulum of the endothelial cells and Kupffer cells. Double immunostaining for PGF synthase and COX-1 showed that both enzymes were present in the same endothelial cells. These results suggest that the main site of PGF₂ synthesis in the liver is the sinusoidal endothelial cell. Accepted: 12 October 1999