Identification of prostaglandin F-producing cells in the liver

Prostaglandin (PG) F synthase forms PGF(2 alpha) and 9 alpha, 11 beta-PGF(2) from PGH(2) and PGD(2), respectively. PGH, is synthesized from arachidonic acid by cyclooxygenase (COX) and then metabolized to various PGs and thromboxane by specific enzymes. PGD(2) is synthesized from PGH(2) by PGD synthase. To identify PGF(2)-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 PGF(2) synthesis in the liver is the sinusoidal endothelial cell.