Pregnancy Recognition Flashcards
pregnancy recognition
the critical series of events by which the conceptus initially signals its presence to the dam and enables pregnancy to continue
importance in pregnancy recognition
in (almost) all species= key event is preventing luteolysis, which must occur in order for pregnancy to continue
progesterone
progesterone from the CL is required to maintain a state of uterine quiescence
luteolysis
occurs in absence of pregnancy in order to initiate another estrous cycle- occurs when not pregnant
prostaglandin F2a is the hormone responsible for destruction of the CL (lysis)
process of luteolysis
during first half of luteal phase, prostaglandin F2a secretion by endometrium is minimal (diestrus= progesterone dominant)
prostaglandin F2a secretion occurs in large pulses at end of luteal phase- sufficient pulses result in luteolysis
mechanism of luteolysis
estrogen induces the synthesis of oxytocin receptors (causes contraction)- makes irritable, causes contraction
progesterone blocked synthesis of oxytocin receptors- quiescent
oxytocin binding stimulates prostaglandin release- in early diestrus progesterone prevents oxytocin receptors synthesis and prostaglandin release
in late diestrus, progesterone loses ability to block oxytocin receptor synthesis- oxytocin binding stimulates prostaglandin release
Oxytocin receptors
common in late luteal phase
prostaglandin cycling
early on in cycle OTr repressed (lower PGF2a and high P4)- progesterone high during diestrus
during luteolysis OTr increases in number and can more readily bind oxytocin and the receptor number increases greater as P4 falls and PGF2a increases
high OTr end up lysing CL, why progesterone falls
Progesterone cycling
high around day 13 of estrus before drops as oxytocin receptors increases and PGF2a increases which ultimately decreases progesterone secretion
Luteolysis category
categorized as luteolysis once progesterone decreases due to oxytocin receptors and PGF2a
Progesterone
required for pregnancy maintenance
species with CL as sole source of progesterone= pig, goat, llama, dog and cat
species with both CL and placental progesterone= horse, sheep and cow
intact uterus experiments- luteolysis
CL lifespan same as in normal cycle 15-17 days
if uterectomy performed and ovaries remain CL has prolonged lifespan similar to gestation
partial uterectomy contralateral to CL then CL normal lifespan
partial uterectomy ipsilateral to CL will extend lifespan
Experiment conclusion from sheep
uterus responsible for luteolysis
uterus must be near the CL
without uterus no PGF for luteolysis and luteolysis is delayed for duration of gestation
counter current exchange
ovarian artery and UOV
travel across gradient
endometrium-utero-ovarian vein-ovarian artery (vein to artery)
why horn opposite the CL results in normal luteolysis
PGF 2a
to ovary, causes luteolysis
Horse does not use counter current mechanism to deliver PGF to ovary for luteolysis
Luteolysis mechanism in horses
horses= different and PGF doesn’t always travel to ovary by counter current exchange
PGF travels systemically- mare more sensitive to PGF and PGF not as rapidly metabolized as in ruminant
general mechanism of luteolysis
precise intracellular mechanism of luteal destruction is not fully understood
reduced blood flow- vasoconstriction (ischemia) or capillary degeneration= cut off blood supply so shrink and disappear
apoptosis of luteal cells
maternal recognition of pregnancy
in almost all species, luteolysis must be prevented for pregnancy to continue
embryonic secretion of substances
contact with uterine epithelium- elongation/expansion and migration around the uterus
Mare contact with epithelium
movement of the conceptus
cow and sow contact with epithelium
expansion
contact endometrium by getting longer
in Cow Interferon-T needed for maternal recognition
maternal recognition in ruminants
luteolysis occurs on day 18 in cow, 14 in ewe
trophoblast cell of conceptus produce INF-t between days 10 and 21
Interferon t
INF-t binds to endometrium and block endometrial synthesis of estrogen receptors and oxytocin receptors (decrease response to estrogen and oxytocin, interferes with luteolysis)
oxytocin cannot bind and therefore does not stimulate endometrial production of PGF2a
maternal recognition in sow
luteolysis days 13-15
conceptus produces estradiol between 11 and 12 days post ovulation (estradiol changes where prostaglandin goes and directs to uterine lumen)
estrogen causes rerouting of endometrial PGF2a away from circulation and into uterus lumen, lumen PGF2a= little access to circulation so no luteolysis
Pregnancy porcine
when pregnant, estrogen acts to sequester PGF2a in the lumen of the uterus
able to maintain CL and pregnancy
embryonic motility in horse
must occur between 11 and 16 days post ovulation
mare maternal recognition
luteolysis day 15-16 post ovulation
not well defined, conceptus derived signal has not been IDed
whatever signal is it suppresses oxytocin receptors in endometrium and prevents PGF2a release from endometrium
oviductal transport initiated by PGE2 which is secreted by conceptus beginning on day 5 of pregnancy- without pregnancy oocytes retained in oviduct
early maternal recognition in mare experiments
between 11 and 16 days conceptus migrates throughout uterus several times per day
migration necessary for survival
without movement, would think not pregnant
Summary
maternal recognition must occur for conceptus to survive
while species variations in mechanism do exist, all signals will ultimately prolong lifespan of CL
Maternal recognition in Bitch
no signal needed for pregnancy recognition
CL maintained for duration of normal gestation regardless of pregnancy status
with parturition decrease progesterone
maternal recognition in Queen- not pregnant
ovulation without conception
luteal phase 30-45 days and luteolysis will occur prior to time of normal gestation (lack CL support)
induced ovulation
maternal recognition in Queen- pregnant
mating, ovulation and conception
luteal phase 62-65 days
fetoplacental relaxin stimulates prolactin
prolactin luteotropic= due to late timing of this luteal support, some would not consider prolactin a signal for maternal recog.
prolactin does result in longer diestrus in pregnant state than in nonpregnant
relaxin and queen
relaxin produced during pregnancy
produce prolactin which supports CL and continues progesterone production
