Submitted July 6, 2007
Returned for revision August 4, 2007
Accepted December 3, 2007
Ovary
Effects of Endothelin Receptor Type-A and Type-B Antagonists on Prostaglandin F2alpha-Induced Luteolysis of the Sheep Corpus Luteum
Matthew D. Doerr ,
Madhusudan P. Goravanahally ,
Justin D. Rhinehart ,
E. Keith Inskeep ,
and
Jorge A. Flores *
* To whom correspondence should be addressed. E-mail: jflores{at}wvu.edu.
Abstract
Three experiments were designed to examine the mechanisms that govern PGF2alpha-induced regression of the sheep corpus luteum (CL). Evidence is presented supporting the involvement of endothelin 1 (EDN1) in PGF2alpha-induced luteolysis. Experiment 1measured effects of PGF2alpha when actions of EDN1 were blocked by sustained administration of a type-A endothelin (EDNRA) or type-B endothelin (EDNRB) antagonist in vivo. Experiment 2 examined anti-steroidogenic actions of PGF2alpha and EDN1 in the presence of an EDNRA or EDNRB antagonist in d-8 luteal minces. In experiment 3, luteal cellular expression of EDNRA and EDNRB was determined immunohistochemically. Relative gene expression of EDNRA and EDNRB receptors was examined by real-time RT-PCR in d-8 sheep CL. EDNRA, but not EDNRB, participated in anti-steroidogenic actions of EDN1. During the first 12 h after PGF2alpha, EDNRA antagonist did not prevent decline in serum progesterone. Early actions of PGF2alpha are either direct or mediated by other than EDN1. However, beyond 12 h after PGF2alpha, serum progesterone increased in EDNRA antagonist-treated animals until not different from saline-treated controls, whereas an EDNRB antagonist had no effect in vivo or in vitro. The EDNRA antagonist negated the antisteroidogenic actions of EDN1 but only partially abolished the actions of PGF2alpha in vitro. In contrast, the EDNRB antagonist was ineffective in abolishing antisteroidogenic actions of EDN1 and PGF2alpha. Whereas real-time RT-PCR demonstrated high expression of EDNRA and low expression of EDNRB, immunohistochemically, only EDNRA was located in small steroidogenic, endothelial, and smooth muscle cells. In summary, studies in ovine CL provided strong evidence that: 1) EDNRA, but not EDNRB, mediate anti-steroidogenic actions of EDN1; 2) actions of PGF2alpha are both independent of and dependent upon, mediation by EDN1; and 3) small steroidogenic cells are targets for anti-steroidogenic effects of EDN1. Furthermore, the results from experiment 1 suggest that the intermediary role of EDN1 may be more important in later stages of luteal regression.
Key words:
Ovary •
Corpus luteum •
Corpus luteum function •
Progesterone •
Steroid hormones
