2. the establishment of pregnancy Flashcards
what is the luteolytic hormone
prostaglandin F2a
what is the principal hormone secreted from the corpus luteum
progesterone
approximately how long is the luteal phase in the cow
16-17 days
what embryonic stage is formed when the embryo hatches from the zona pellucida
blastocyst
where is PgF2a secreted
epithelial cells of the endometrium
how is luteolysis initiated in ruminants
- requres appearance of oxytocin receptors in endometrium
- OXTR absent for most of luteal phase
- reappear before progesterone falls
- oxytocin (from CL) binds to OXTR which stimulates PGF2A release from endometrium
- counter current system = no pg in circulation, direct action on ovary
- increasing oestradiol further increases OXTR expression
when does the oxytonin receptor appear
- short window
- supprossed by progesterone
- reappear just before luteolysis
what is the benefit of the counter current system for transfer of pgf2a between uterus and ovary
pgf2a cant getin into circulation
- rapidly metabolised in lungs, if cant get to lungs, saves from being lost
what is maternal recognition of pregnancy
adaptations of the maternal endocrine system t o the presence of the conceptus
- embryonic derived signal
- occurs before luteolysis
- not conscious decision
what is the action of continued progesterone in pregnancy
- maintains uterine gland secretory function
- stimulates coiling and branching
- histotrph production (nurtures embryo)
- uterine milk secretion
- supresses mymetrial contractions and luteolytic mechanism
- suppresses GnRH secretion (reduces follicular maturation and ovulation)
what is the conceptus signal (maternal recognition hormone) in ruminants
interferon tau (IFNT)
where does interferon tau come from
- blastocyst’s most abundant protein
- expression intitiated during trophoblast elongation
- expressed by the trophectoderm cells
- stimulated by growth factors secreted from uterus
- tight window of expression - only expressed days 12-24 of pregnancy
- production related to embryo size
- INFT largely remains in uterine lumen and exerts action there
- lack of IFNT linked to embryo mortality
how does interferon tau exert its action
- acts on the endmetrium
- suppresses OXTR expression
- stimulates protein synthesis critical for embryo growth
- antiviral activity
- suppresses PGF2a pulsatile secretion
- maintains progesterone (indirectly)
- exogneous administration of IFNT into uterus delays luteolysis
- has some action on CL
what is the MRP signal in pigs
oestradiol
- secreted before implantation
- just detectable in plasma
- re-direct flow of PGF2a away from uterine vein (preventing luteolysis)
what is the MRP signal in horses
unknown
- oxytocin stimulates leuteolysic pgf2a
- embryo suppresses OXTR
- no blastocyst interferon produced
- blastocyst signal unknown
- eCG not signal
outline the timing and signal of MRP in the different species
