L5: The Luteal Phase Flashcards
what phase of estrus is marked by
* low estrogen
* LH surge has just occured
* ovulation occurred recently
metestrus
what phase of estrus
* progesterone peaks and is sustained at high levels (ovulation suppressed)
* estradiol is low
diestrus
what phase of estrus
* maximum corpus luteum size
* elevated progesterone inhibits final follicular development
diestrus
what phase of estrus
* CL regresses (due to release of PGF2alpha) at the end of this phase is there if no pregnancy
Diestrus
granulosa cells secrete _______ and _______ to increase blood supply to the new corpus luteum
vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF)
what is luteal hormone output dependent on
basal LH levels- maintained by pulses of GnRH
how does LH stimulate steroidogenesis
by activating cholesterol desmolase
what enzyme is needed for progesterone synthesis in the granulosa cell
3B-Hydroxysteroid dehydrogenase (3B-HSD)
Progesterone is released when there is an active…?
corpus luteum
what are the effects of progesterone on the hypothalamus
negative feeback - blocks progesterone and estrogen priming
what are the effects of progesterone on the endometrium of the uterus
promotes conditions needed for a fertilized egg
what produces relaxin in the cow
Corpus luteum
(produced by placenta in other animals)
what is the target and function of relaxin
target: uterus, soft CT
function: synergistic effect w/ progesterone to maintain pregnancy
T/F: the CL has a limited lifespan
T
pig,horse,primate,cow: 10-14 d
ewe: 17 d
dog: up to 90 days
at the end of the luteal phase, CL becomes what
corpus albicans
corpus luteum regresses at the end of _______ if there is no pregnancy due to _____ released by uterus
diestrus
PGF2alpha
the CL produces oxytocin in what animals
Cow
the CL produces estradiol in what animals
primates, pigs, rats
during the luteal phase, ______ maintains the corpus luteum
LH (release caused by GnRH pulses)
at the end of the ____ phase, _____ terminates the CL and progesterone secretion
luteal
PGF2alpha
what animals produce PGF2alpha in the endometrium of their uterus
cow, horse, pig, sheep
what is luteolysis
CL regression
what stimulates luteolysis
estrogen/progesterone and oxytocin
what are the 2 main effects of PGF2alpha
- opens Ca channels in granulosa cells, induces apoptosis through high intraceullar Ca
- Activation of PKC which inhibits mitochondrial transport of cholesterol and progesterone synthesis
where does the initial signal for oxytocin positive feedback come form
posterior pituitary
what signals the release of luteal oxytocin that signals back to the uterus
PGF2alpha
what is the role of oxytocin acting through positive feedback on the corpus luteum
oxytocin leads to destruction of CL
oxytocin signals uterus to produce PGF2alpha which destroys CL
in horses, PGF2alpha is released into the ______ blood from either of the uterine horms
systemic blood
what is the vascular pathway for PGF2alpha in cows and sheep?
PGF2alpha is produced in uterus endometrium, **released into ovarian veins **and is transferred to the ipsilateral ovarian artery through a counter current exchange mechanism
what is the effect of endometritis on the luteal phase in cows
it increases the time of the luteal phase
Prolactin (PRL) is secreted from the ______ or the ______ dyring late stage pregnancy in the bitch and rat
anterior pituitary
endometrium
what is the target of prolactin (PRL) in the rat, bitch and ewe? What is the target in mammals
rat , bitch, ewe: targets the CL
all mammals: targets mammary glands
what is the effect of prolactin
luteotropic functions, required for initiation and maintenance of milk synthesis
what suppresses prolactin
dopamine
use of anti prolactin drugs (dopamine agonists or serotonin antagonists) in the bitch will induce _____ in days 4-48 of cycle or induce _______ and cause _______ if given mid pregnancy
estrus if given during days 4-48
if given mid-pregnancy, will induce luteolysis and cause abortion
what (and when) stimulates the release of prolactin in the bitch
increasing levels of estrogen during late diestrus
what stimulates prolactin release in rodents
copulation
