Effect of chronic administration of endothelin receptor type a antagonist (bq-610) on functional lifespan of the corpus luteum in sheep

To test the role of endothelin 1 (END1) in luteolysis, an END receptor type A antagonist (BQ-610) was delivered into the corpus luteum (CL) during spontaneous luteolysis in sheep. On day 9 of the estrous cycle, an osmotic mini-pump containing 2 mg of BQ-610 (n = 12) or vehicle (n = 9) were implanted surgically in the ewes. Corpora lutea were collected 12 h after onset of estrus, or on the afternoon of day 21 in ewes that had not returned to estrus, and from untreated ewes on day 10 to 12 of the estrous cycle (mid-cycle CL). Three of 12 BQ-610-treated ewes did not show estrus before day 21 compared to 0 of 9 vehicle-treated ewes. Estrous cycles in vehicle-treated ewes averaged 15.5 ± 0.2 days. In the three BQ-610-treated ewes, luteal weights on day 21 were greater than in vehicle-treated ewes on the day of estrus (0.62 ± 0.05 versus 0.39 ± 0.03 g, respectively; P < 0.001), as were luteal contents of progesterone (P4) (20958.2 ± 1830.9 μg/g versus 1291.2 ± 1057.1 μg/g respectively; P