Prostaglandin F(2α) regulates distinct physiological changes in early and mid-cycle bovine corora lutea

Abstract

Prostaglandin (PG) F(2α) is the primary luteolysin inmost species. A single treatment with PGF(2α) 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 PGF(2α) receptors (FP receptors). This study was designed to determine whether PGF(2α) activated similar intracellular processes in early- and mid-cycle CL. Cows received saline or 25 mg PGF(2α) 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(2α) treatment. Luteal vitamin C concentration and steady-state concentrations of mRNA for 3β-hydroxysteroid dehydrogenase and for PF receptor were decreased by 4 h in both Day 4 and 11 CL treated with PGF(2α) (p < 0.05). These results demonstrate clear actions of PGF(2α) 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(2α) in mid- cycle CL but decreased by PGF(2α) in early-cycle CL (p < 0.05). In addition, treatment of mid-cycle but not early-cycle cows with PGF(2α) decreased luteal and serum progesterone concentrations by 4 h (p < 0.05). In summary, PGF(2α) clearly exerts actions in both early and mid-cycle bovine CL. The lack of PGF(2α)-induced luteolysis in the early CL may be due to specific changes in gene expression, especially PGHS-2, that may prevent intraluteal PGF(2α) production and possibly other key luteolytic processes.