Effect of local interaction of reactive oxygen species with prostaglandin F 2α on the release of progesterone in ovine corpora lutea in vivo

Abstract

Prostaglandin (PG) F 2α is implicated in the process of luteal regression in many species, and has been shown to increase the generation of reactive oxygen species. In this study, the role of reactive oxygen species in the local regulatory mechanisms of functional luteolysis in the ewe was examined. In Experiment 1, we studied local effects of hydrogen peroxide (H 2O 2) and its interaction with PGF 2α on P secretion in ovine corpus luteum (CL) in vivo. For this purpose, a microdialysis system (MDS) was used, where only the cells surrounding the capillary membrane in the microenvironment of the CL are exposed to these factors, and the P secretory ability of the CL is maintained as if intact. The study used a multiple CL model to implant the MDS, enabling us to examine in parallel several experimental infusions into the MDS implanted in different CLs (one MDS line per CL) developed after superovulation in one ewe. On Day 8 after GnRH treatment, the MDS were implanted into multiple CL in both ovaries of six ewes. A 4-h infusion with PGF 2α (10 −6 M) at 8–12 h slightly increased P release during infusion, while a 4-h infusion with H 2O 2 (10 −3 M) at 20–24 h decreased P release at 27–38 h. A pre-infusion with PGF 2α for 4 h at 8–12 h, followed by infusion of H 2O 2 at 20–24 h rapidly decreased the P release at 20–40 h ( P<0.05); this decrease occurred 7 h earlier than in the CL treated with H 2O 2 alone. In Experiment 2, by utilizing the MDS we also applied free radical scavengers to examine their possible weakening effect on the inhibition of P secretion in the microenvironment within the regressing CL induced by PGF 2α treatment. On Day 8 after estrus, the MDS were implanted into the CL (single CL model, two MDS lines per CL). Infusion of free radical scavengers, superoxide dismutase ( SOD; 50 mg/ ml)+ catalase (CAT; 10 mg/ml), at 0–28 h first increased P release until 12 h ( P<0.05), and consequently delayed the decrease in P release until 30 h after administration of PGF 2α i.m. ( P<0.05). The present results support the concept that the leading pathway from PGF 2α induces an increase of reactive oxygen species in luteolysis in the ewe.