Effects of LPA2R, LPA3R, or EP4R agonists on luteal or endometrial function in vivo or in vitro and sirtuin or EP1R, EP2R, EP3R or EP4R agonists on endometrial secretion of PGE and PGF2α in vitro

Abstract In previous work, an EP2 prostanoid receptor (EP2R) agonist in vivo increased mRNA expression of luteal LH receptors (LHR), unoccupied and occupied luteal; LHR, and circulating progesterone, while an EP3R or FPR agonist decreased; mRNA expression of luteal LHR, unoccupied and occupied luteal LHR, and; circulating progesterone. An EP4R and lysophosphatidic acid (LPA) LPA2R and LPA3R agonists were reported to inhibit luteal function and sirtuins have been proposed to increase prostaglandin synthesis. The objectives were to determine; whether an EP4R, LPA2R, or LPA3R agonist affect ovine luteal function in vivo or; in vitro . In addition, whether sirtuin (SIRT)-1, 2, or 3; LPA2R or LPA3R; or EP1R, EP2R, EP3R, or EP4R agonists affect caruncular endometrial PGF 2α or PGE (PGE1+PGE2) secretion in vitro . Day-10 nonpregnant ewes received a single injection of Vehicle (N = 5); an LPA2R (N = 5); LPA3R (N = 6); or EP4R (N = 5) agonist given into the interstitial tissue of the ovarian vascular pedicle adjacent to the luteal-containing ovary to determine effects on circulating progesterone, mRNA expression of luteal LHR, and luteal unoccupied and occupied LHR. In addition, agonists for LPA2R, LPA3R, EP1R, EP2R, EP3R, or EP4R or SIRT-1, SIRT-2, or SIRT-3 activators were incubated with caruncular endometrial slices in vitro to determine their effect on caruncular endometrial PGF 2α , or PGE secretion. LPA2R, LPA3R, or an EP4R agonist in vivo did not affect (P ≥ 0.05) luteal weight, circulating progesterone, or occupied luteal LHR. However, an LPA2R or EP4R agonist, but; not LPA3R agonist, in vivo increased (P ≤ 0.05) mRNA expression of luteal LHR . An; LPA2R, LPA3R, or EP4R agonist increased (P ≤ 0.05) luteal unoccupied LHR, but; not occupied LHR. An LPA2R, LPA3R, or an EP4R agonist did not affect (P ≥ 0.05); luteal progesterone secretion in vitro . An LPA2R or LPA3R agonist did not affect (P ≥ 0.05) luteal PGF 2α , or PGE secretion in vitro . However, an EP4R agonist tended to decrease (P  2α secretion and increased (P ≤ 0.05) luteal PGE; secretion i n vitro . EP1R, EP2R, EP3R, or an EP4R agonist did not affect (P ≥ 0.05); caruncular endometrial PGF 2α secretion in vitro . However, EP1R, EP3R, or an EP4R agonist increased caruncular endometrial PGE secretion in vitro , while two different EP2R agonists did not affect (P ≥ 0.05) caruncular endometrial PGE; secretion. A SIRT-1 activator, but not SIRT-2 or SIRT-3 activators, increased (P ≤ 0.05) caruncular endometrial PGE secretion, while sirtuin 1, 2, or 3 activators did not affect (P ≥ 0.05) caruncular endometrial PGF 2α secretion. In conclusion, receptors for EP4, LPA2, and LPA3 do not appear to be involved; in luteolysis, but EP4R and LPA2R might participate in preventing luteolysis by maintaining luteal mRNA expression for LHR and preventing loss of unoccupied luteal LHR. In addition, SIRT-1, EP1R, EP3R, and EP4R might be involved in; regulating caruncular endometrial PGE secretion, but not PGF 2α secretion.