Prostaglandin F2α regulates distinct physiological changes in early and mid-cycle bovine corpora lutea

Prostaglandin (PG) F-2 alpha is the primary luteolysin in mast species. A single treatment with PGF(2 alpha) will cause regression of the mid-cycle but not the early-cycle (Days 1-5 after estrus) bovine corpus luteum ICL) despite the presence of similar concentrations of high-affinity PGF(2 alpha) receptors (FP receptors), This study was designed to determine whether PGF(2 alpha) activated similar intracellular processes in early-and mid-cycle CL. Cows received saline or 25 mg PGF(2 alpha) injection (i.m,; n = 6/group) on Day 4 or 11 after onset of the LH surge (induced by GnRH injection), and CL were collected at 4 h after treatment, As expected, CL volumes and luteal weights were not different at 4 h after PGF(2 alpha) treatment, Luteal vitamin C concentration and steady-state concentrations of mRNA for 3 beta-hydroxysteroid dehydrogenase and for FP receptor were decreased by 4 h in both Day 4 and 11 CL treated with PGF(2 alpha) (p < 0.05). These results demonstrate clear actions of PGF(2 alpha) in the early CL. In contrast, steady-state concentrations of mRNA encoding PG G/H synthase-2 (PGHS-2) were increased by treatment with PGF(2 alpha) in mid-cycle CL but decreased by PCF2 alpha in early-cycle CL (p < 0.05). in addition, treatment of mid-cycle but not early-cycle cows with PGF(2 alpha) decreased luteal and serum progesterone concentrations by 4 h (p < 0.05). In summary, PGF(2 alpha) clearly exerts actions in both early- and mid-cycle bovine CL. The lack of PGF(2 alpha)-induced luteolysis in the early Ct. may be due to specific changes in gene expression, especially PGHS-2, that may prevent intraluteal PGF(2 alpha) production and possibly other key luteolytic processes.