Pregnancy recognition- Lecture 10 Flashcards
Luteolysis mechanism
Estrogen induces the synthesis of oxytocin receptors. Progesterone blocks synthesis of OTr. Oxytocin binding stimulates prostaglandin release. In late diestrus, progesterone loses ability to block OTr synthesis.
Maternal recognition in ruminants
Luteolysis occurs on day 18 (cow) or 14 (ewe). Trophoblast cells produce INFt between day 10-21. INFt binds to the endometrium and blocks the synthesis of estrogen and oxytocin receptors. Oxytocin can’t bind so that PGF2alpha can’t be produced.
Maternal recognition in the bitch
No signal is needed for pregnancy recognition. The CL is maintained for the duration of normal gestation regardless of pregnancy status.
Prevent luteolysis
Progesterone from the CL is required to maintain a state of uterine quiescence.
Parturition stage 1
Preparation- Isolation from herd. Udder: colostrum, edema. Tissue softening.
Maternal recognition of pregnancy
Embryonic secretion of substances. Contact with uterine epithelium: elongation/expansion and migration. Must occur for conceptus to survive. There are species variation in mechanisms but all ultimately prolong the lifespan of the CL.
Maternal recognition in the queen
Non-pregnant: Ovulation without conception, luteal phase 30-45 days, luteolysis occurs prior to time of normal gestation. Pregnant: Luteal phase 62-65 days, fetoplacental relaxin stimulates prolactin, prolactin is luteotropic
Parturition stage 2
Fetal expulsion.
Maternal recognition in the sow
Luteolysis on day 13-15. Conceptus produces estradiol post ovulation. Estrogen causes PGF2alpha to be rerouted away from circulation and into the lumen of the uterus. Lumenal PGF2alpha has no access, so luteolysis cannot occur. In an “open” sow PGF2alpha would be secreted into bloodstream.
Puerperium
Time from fetal delivery until complete uterine involution Varies by species: cow- 1-1.5 months. mare- 2 weeks. bitch- 2 months.
Maternal recognition in the mare
Luteolysis occurs on day 15/16 post ovulation. System not well identified, but it suppresses oxytocin receptors in the endometrium and prevents PGF2alpha release.
Pregnancy recognition
The critical series of events by which the conceptus initially signals its presence to the dam and enables pregnancy to continue.
Equine conceptus movement
Between days 11-16 of pregnancy, the coneptus migrates throughout the uterus several times per day. This migration is necessary for survival. Transport initiated by PGF2alpha, that is secreted by conceptus 5 days into pregnancy.
Enzymatic pathway of progesterone
Fetal cortisol induces placental enzymes which convert progesterone to estradiol. Progesterone falls and estrogen rises.
During estrous cycle
Progesterone decreases over time. OTr increases. PGF2alpha fluctuates a lot but generally increases over cycle. Luteolysis occurs by day 16/17.
Luteolysis
Occurs in the absence of pregnancy in order to initiate another estrous cycle. PGF2alpha is the hormone responsible for destruction of the CL. During first half of luteal phase, PGF2alpha secreted by endometrium a bit. Much more secreted at end of luteal phase. Sufficient pulses result in luteolysis.
Luteolysis mechanism in a horse
Very different. PGF travels systemically. The mare is more sensitive to PGF. PGF is not as rapidly metabolized as in ruminant species.
Uterus role in luteolysis
The uterus is responsible for luteolysis. The uterus must be near the CL. When entire uterus is removed there is no PGF available for luteolysis. Luteolysis delayed for duration of gestation. Opposite horn removed- luteolysis normal.
Progesterone
Falls at term. 1) enzymatic- fetal cortisol induces placental conversion of progesterone to estrogen. 2) luteolysis- PGF2a, important in CL dependent species. Removal of “progesterone block”.
Endometrium-utero-ovarian vein/artery
Countercurrent mechanism. Gets PGF2alpha to the ovary, causing luteolysis.
Progesterone
Species with CL as the sole source- pig, goat, llama, dog and cat. Species with both luteal and placental production- horse, sheep, cow.
Parturition stage 3
Fetal membrane expulsion.
