Estradiol production by preimplantation blastocysts and increased serum progesterone following estradiol treatment in llamas

Abstract

Estradiol is a potential candidate for the blastocyst signal responsible for maternal recognition of pregnancy in the llama ( Lama glama). Two experiments were conducted to determine if the llama blastocyst produces estradiol during the presumed period of maternal recognition of pregnancy and if exogenous estradiol can extend the luteal phase. In Experiment 1, llamas were superovulated with eCG and mated 7 days later (Day 0 = day of mating). Blastocysts were collected nonsurgically on Days 7, 9, or 11 or at necropsy on Days 13 and 15 post-mating and cultured for 48 h. Conditioned medium was recovered, replaced with fresh medium at 24-h intervals, and assayed for estradiol-17β. Estradiol production (pg/blastocyst) over the 48-h culture increased ( P < 0.05) by day of gestation where more estradiol ( P < 0.05) was produced by Day 11 compared to Day 7 blastocysts, Day 13 compared to Days 7–11 blastocysts, and Day 15 compared to Days 7–13 blastocysts. A dramatic increase was observed between Days 11 and 13 when estradiol production by Day 13 blastocysts increased ( P < 0.05) more than 50-fold. In Experiment 2, 30 females were induced to ovulate with hCG (Day 0 = day of hCG injection). Starting on Day 7 and continuing through Day 15, animals received daily injections i.m. of 0 ( n = 11), 5 ( n = 7), or 10 mg ( n = 12) estradiol benzoate (EB) dissolved in isopropylmyristate. Sera were collected immediately prior to each injection and on Days 16, 17, 18, 20, and 22 and analyzed for progesterone. Progesterone concentrations were greater ( P < 0.05) on Days 14, 15, 16, and 17 in llamas treated with 10 mg EB compared to llamas treated with 0 mg EB. These results demonstrate that llama blastocysts produce estradiol and exogenous estradiol can enhance and transiently extend luteal progesterone production. Estradiol produced by the preimplantation llama blastocyst may play a role in maternal recognition of pregnancy and early luteal support.