Ovary

Vasoactive Peptides in the Luteolytic Process Activated by PGF2alpha in Pseudopregnant Rabbits at Different Luteal Stages

Abstract
To study the role of endothelial factors in luteal function, the dynamic profiles of genes for endothelin-1 (EDN1), its receptor subtypes, EDNRA and EDNRB, and angiotensin converting enzyme (ACE) were examined in corpora lutea (CL), obtained from rabbits at days 4 and 9 of pseudopregnancy after prostaglandin (PG) F2alpha analogue (alfaprostol) treatment; cell type distribution of EDN1 in the ovary and its mechanisms of actions both in vitro and in vivo were also studied. Positive immunostaining for EDN1 was localized in luteal and endothelial cells, in granulosa cells of follicles, and in ovarian epithelium. Basal mRNA levels for EDN1 receptors and ACE were lower (P0.01) in day-4 than in day-9 CL, whereas those for EDN1 did not differ. At day 4, luteal EDN1, EDNRA, EDNRB, and ACE mRNA levels similarly increased two-fold (P0.01) 1.5 h after alfaprostol injection without further changes in the next 24 h. At day 9, alfaprostol challenge transiently up regulated (P0.01) mRNA luteal transcripts of ACE at 1.5 h, and EDN1 at 1.5 and 3 h, whereas EDNRA, and EDNRB genes remained unchanged during the course of luteal regression. EDN1 decreased (P0.01) progesterone release and increased (P0.01) PGF2alpha secretion and NOS activity in day-9, but not in day-4 CL cultured in vitro, via the PLC/PKC pathway. EDN1-, but not alfaprosto-induced luteolysis, was blocked by co-treatment with the ACE antagonist, captopril, in vivo. These findings support the hypothesis that PGF2alpha may regulate luteolysis through intraluteal activation of the renin-angiotensin/EDN1 systems in CL that have acquired luteolytic competence.

Key words: Ovary • Corpus luteum function