Prostaglandin F 2α Stimulates Endothelial Nitric Oxide Synthase Depending on the Existence of Bovine Granulosa Cells: Analysis by Co‐culture System of Endothelial Cells, Smooth Muscle Cells and Granulosa Cells

Contents Prostaglandin F 2α (PGF 2α ) induces luteolysis in the mid but not in the early luteal phase; despite this, both the early and the mid corpus luteum (CL) have PGF 2α receptor (FPr). We previously indicated that the luteal blood flow surrounding the CL drastically increases prior to a decrease of progesterone (P) in the cows, suggesting that an acute increase of luteal blood flow may be an early sign of luteolysis in response to PGF 2α and that this may be induced by a vasorelaxant nitric oxide (NO). The aim of this study was to investigate the luteal stage‐dependent and the site‐restricted effect of PGF 2α and NO on the mRNA expressions and P secretion. To mimic the local luteal region both of peripheral and central areas of the CL, we utilized co‐cultures using bovine aorta endothelial cells (EC), smooth muscle cells (SMC) and luteinizing granulosa cells (GC) or fully‐luteinized GC. PGF 2α stimulated the expression of endothelial NO synthase (eNOS) mRNA at 0.5 h in mix‐cultures of EC and SMC with fully‐luteinized GC but not with luteinizing GC. The expression of eNOS mRNA in EC was increased by PGF 2α at 1 h only when EC was cultured together with fully‐luteinized GC but not with luteinizing GC. In all co‐cultures, PGF 2α did not affect the mRNA expression of FPr. Treatment of NO donor inhibited P secretion at 0.5 h. In conclusion, the present study suggests that the coexistence of the mature luteal cells (fully‐luteinized GC) with EC/SMC may be crucial for acquiring functional NO synthesis induced by PGF 2α .