PGE1 or PGE2 not LH Regulates Secretion of Progesterone in Vitro by the 88-90 Day Ovine Corpus Luteum of Pregnancy

Secretion of progesterone $\text{in vitro}$ by mature day 8 ovine corpora lutea (CL) of the estrous cycle was increased linearly by ovine LH (1, 10 and 100 ng/ml) or prostaglandin E₂ (PGE₂) 1, 10 and 100 ng/ml) in a dose dependent manner (P ≤ 0.05). Progesterone secretion $\text{in vitro}$ by 88–90 day ovine CL of pregnancy was not affected P ≥ 0.05 by LH (1, 10 and 100 ng/ml) while prostaglandin E₁ (PGE₁) 1, 10 and 100 ng/ml) increased (P ≤ 0.05) secretion of progesterone in a dose dependent manner and PGE₂ (1, 10 and 100 ng/ml) increased (P ≤ 0.05) secretion of progesterone only at the 100 ng/ml dose. Day 8 ovine CL of the estrous cycle did not secrete (P ≥ 0.05) detectable quantities of prostaglandin F₂α (PGF₂α) or prostaglandin E (PGE) while 88–90 day ovine CL of pregnancy secrete PGE (P ≤ 0.05) but not PGF₂α (P ≥ 0.05).

Regulation of PGE secretion by 88–90 day ovine CL of pregnancy may be via pregnancy specific protein B (PSPB), which increased (P ≤ 0.05) PGE and progesterone but not PGF₂α (P ≥ 0.05) secretion. Secretion of progesterone by CL of 88–90 days of pregnancy was not affected by IGF₁, IGF₂, PAF-16, PAF-18, oxytocin, PGI₂, PGD₂ or leukotriene C₄ (P ≥ 0.05). It is concluded that PGE₁ or PGE₂ but not LH regulates secretion of progesterone $\text{in vitro}$ by 88–90 day ovine CL of pregnancy. In addition, it is concluded that 88–90 day ovine CL of pregnancy secretes it's own luteotropin, which is PGE. Secretion of PGE by ovine CL of pregnancy may be regulated by PSPB.