Prostaglandin F2alpha regulates distinct physiological changes in early and mid-cycle bovine corpora lutea.

Prostaglandin (PG) F2alpha is the primary luteolysin in most species. A single treatment with PGF2alpha will cause regression of the mid-cycle but not the early-cycle (Days 1-5 after estrus) bovine corpus luteum (CL) despite the presence of similar concentrations of high-affinity PGF2alpha receptors (FP receptors). This study was designed to determine whether PGF2alpha activated similar intracellular processes in early- and mid-cycle CL. Cows received saline or 25 mg PGF2alpha 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 PGF2alpha treatment. Luteal vitamin C concentration and steady-state concentrations of mRNA for 3beta-hydroxysteroid dehydrogenase and for FP receptor were decreased by 4 h in both Day 4 and 11 CL treated with PGF2alpha (p < 0.05). These results demonstrate clear actions of PGF2alpha in the early CL. In contrast, steady-state concentrations of mRNA encoding PG G/H synthase-2 (PGHS-2) were increased by treatment with PGF2alpha in mid-cycle CL but decreased by PGF2alpha in early-cycle CL (p < 0.05). In addition, treatment of mid-cycle but not early-cycle cows with PGF2alpha decreased luteal and serum progesterone concentrations by 4 h (p < 0.05). In summary, PGF2alpha clearly exerts actions in both early- and mid-cycle bovine CL. The lack of PGF2alpha-induced luteolysis in the early CL may be due to specific changes in gene expression, especially PGHS-2, that may prevent intraluteal PGF2alpha production and possibly other key luteolytic processes.