Porcine corpora lutea (CL) fail to show a luteolytic response to prostaglandin-F-2alpha (PGF-2alpha) (ie, luteolytic sensitivity [LS]) until about day 12-13 of the estrous cycle. Although little is known of the control of LS in any species, endothelin-1 (EDN1) is believed to play a role in LS control in ruminants. Therefore, we measured mRNA and protein expression and examined the cellular localization of EDN1 precursor (pre-pro EDN1, or ppEDN1), EDN-converting enzyme-1 (ECE1), and EDN receptors (A, EDNRA and B, EDNRB) in porcine CLs collected on days 4, 7, 10, 13, and 15 of the estrous cycle to look for differences between CLs displaying (days 13-15) versus those lacking (days 4-10) LS. Abundance of ppEDN1 mRNA was greatest (and significant vs all other days) on day 7 of the cycle, whereas EDN1 protein expression did not vary during the cycle and was localized exclusively to endothelial cells (EC). Abundance of ECE1 mRNA was also greatest on day 7 (vs all other days), but ECE1 protein was significantly elevated on day 10 (vs day 4) and was immunolocalized to ECs and large luteal cells (LLC). Abundance of EDNRA mRNA was also maximal on day 7 (vs all other days) of the cycle, whereas EDNRA protein expression was not significantly changed during the cycle and was observed in LLCs, ECs, and small luteal cells (SLC). On day 13, EDNRB mRNA was significantly decreased (versus day 7). Expression of EDNRB protein was decreased on day 10 (versus all other days), and on days 13-15 (vs day 4), and was primarily localized to ECs. In conclusion, the observed elevation in ECE1 protein concentrations on day 10 and the presence of EDNRA on LLC suggests a possible role for EDN1 (resulting from the actions of ECE1) acting via EDNRA in the control of LS in the pig.