Prostaglandin E2 Secretion by Oviductal Transport-Stage Equine Embryos1

Abstract

This study was conducted to identify embryonic products whose secretion was temporally associated with the oviductal transport period of the mare. Chemicals secreted by oviductal-transport-stage equine embryos were identified by incubating Day 6 or Day 7 early uterine embryos with 35S-methionine/cysteine, 3H-progesterone, or 3H-arachidonic acid for 24 h, and subsequently identifying radioactively labeled proteins (SDS-PAGE; n = 3 embryos), steroids (HPLC; n = 3 embryos), or prostaglandins (HPLC; n = 3 embryos) in the culture medium. Early uterine embryos secreted 116.1 +/- 45.5 pg of prostaglandin (PG) E2/embryo, 1.0 +/- 0.2 pg of 17 alpha-hydroxy progesterone/embryo, 4.8 +/- 0.6 pg of androstenedione/embryo, and 11.5 +/- 4.5 pg of PGF2 alpha/embryo. They did not secrete detectable quantities of protein, testosterone, or estradiol-17 beta. A second experiment was conducted to measure temporal changes in embryonic PGE2 secretion during the oviductal and early uterine period. Day 3, Day 4, Day 5, and Day 6 embryos (n = 8 embryos/day) were incubated with 3H-arachidonic acid for 24 h, and the concentration of 3H-PGE2 in the culture medium was subsequently measured by HPLC. Embryos did not secrete detectable amounts of PGE2 prior to the expected time of oviductal transport (Day 3 and Day 4). They secreted 5.7 +/- 1.0 pg of PGE2/embryo immediately before and during the expected time of oviductal transport (Day 5), and they secreted significantly of PGE2/embryo immediately before and during the expected time of oviductal transport (Day 5), and they secreted significantly (p less than 0.01) higher amounts (42.0 +/- 11.5 pg) of PGE2/embryo immediately after uterine entry (Day 6).(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandin E(2) and F(2 alpha) production by equine conceptuses and concentrations in conceptus fluids and uterine flushings recovered from early pregnant and dioestrous mares

“…The release of prostaglandins by day 5-16 equine conceptuses incubated in vitro has been documented previously (Watson and Sertich, 1989;Weber et al, 1991aWeber et al, , 1992Vanderwall et al, 1993); in the present study the known period of PGE 2 and PGF 2α secretion was extended to day 32 of gestation. In addition, it was demonstrated that the cyclooxygenase inhibitor flunixin meglumine suppressed the release of PGE 2 by cultured day 14 blastocysts, thereby confirming that PGE 2 is synthesized de novo by the conceptus, at least at this stage of gestation.…”

“…failure of the cyclo-oxygenase inhibitor to reduce PGF 2α secretion markedly during the 1 h incubation indicates that a large proportion of the PGF 2α released during this time was pre-formed. In both cases, prostaglandins secreted by the early equine conceptus appear to derive primarily from the bilaminar omphalopleure, as the bilaminar choriovitellus was the major source of prostaglandins during days 28-32, as it is in day 20-24 sheep conceptuses (Lewis and Waterman, 1985), and because equine conceptuses secrete prostaglandins from as early as day 5 after ovulation (Weber et al, 1991a). In this context, it is not surprising that PGE 2 and PGF 2α were present at higher concentrations in yolk sac than allantoic fluids.…”

“…In large domestic species, further interest has centred on the apparent ability of some prostaglandins, notably PGE 2 , to interfere with the progression of luteolysis, a property that may be of physiological significance during maternal recognition of pregnancy (for a review, see Ottobre et al, 1984). Weber et al (1991aWeber et al ( ,b, 1995 reported that, from as early as day 5 after ovulation, equine embryos secrete PGE 2 , which relaxes the circular smooth muscle of the isthmic region of the oviduct and enables the embryo to pass through the otherwise tightly closed ampullary-isthmic 'sphincter' and into the uterus. However, even after arrival in the uterus, equine embryos continue to secrete PGE 2 (Watson and Sertich, 1989;Weber et al, 1992;Vanderwall et al, 1993) and other prostaglandins, such as PGF 2α and PGI 2 (Watson and Sertich, 1989).…”

Relaxatory Effect of Prostaglandin E2 on Circular Smooth Muscle Isolated from the Equine Oviductal Isthmus1

“…with oviductal transport [Weber et al, 1991a;1992a]; and 3) intraoviductal PGE 2 treatment of bred mares has been found to hasten oviductal transport [Weber et al, 1991b].…”

“…The oviductal transport-stage equine embryo appears to initiate its selective oviductal transport [Freeman et al, 1992]. Prostaglandin E 2 (PGE 2 ) secreted by equine embryos has been proposed to initiate oviductal transport in mares because 1) PGE 2 is a major secretory product of oviductal transport-stage embryos [Weber et al, 1991a]; 2) embryonal secretion and oviductal specific binding of PGE 2 are temporally associated 1 This work was funded by the Idaho Equine Education Bill, and it is part of the Idaho Experiment Station Series No. 94A14.…”