Lecture 5: Female Reproductive Physiology: The Luteal Phase Flashcards
what happens in metestrus period of estrous cycle
CL forms and begins to secrete progesterone
What happens in diestrus period
Sustained luteal secretion of progesterone, CL develops during metetrus with optimal function during diestrus
Are estrogen levels low or high during metetrus
Low
What are progesterone levels during metetrus
Start low but quickly appears with corpus hemorrhagicum
What are FSH levels in metetrus
Low but may be sufficient to trigger recruitment for next follicular wave
What are progesterone levels during diestrus
High
What are estradiol levels during diestrus
Low and may fluctuate with follicular cycles
Do progesterone levels need to be high or low to suppress ovulation
High
When does the corpus luteum reach maximum size
Diestrus
Elevated ____ inhibits final follicular development preventing ovulation and estrus
Progesterone
If there is no pregnancy at end of diestrus what regresses and what hormone causes the regression
CL regresses due to PGF2alpha being released by uterus
What is responsible for breakdown of follicle wall, tunica, albuginea and surface epithelium during LH surge/ovulation
Cytokines and hydrolytic enzymes
Basal laminate of mural ___-cells are degrades during LH surge
Granulosa
What do granulosa cells secrete to increase blood supply to the new corpus luteum
Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF)
vascularization of follicle is critical to
Steroid synthesis and secretion
Cholesterol is delivered to ___ cell and taken in by ___ and ___ receptors
Luteal, LDL and HDL receptors
LH stimulates steroidogenesis by activating ____
Cholesterol desmolase
What enzyme is necessary for progesterone synthesis
3B-hydroxysteroid dehydrogenase
What are the targets of progesterone
Hypothalamus, anterior pituitary, mammary glands, uterus
What is the role of progesterone on hypothalamus
Acts as a negative feedback inhibiting estrogen priming
How does progesterone act on anterior pituitary
Negative feedback of LH, FSH
What does progesterone do to mammary glands
Acts in positive feedback loop to promote alveolar development
How was progesterone act in the uterus
- Negative feedback on myometrium
- Positive feedback on endometrium which promotes conditions that are food for fertilized eggs
What is relaxin
Hormone that targets the uterus, soft CT and acts synergistically with progesterone to maintain pregnancy. Prepares soft tissue of the pelvic canal for eventual birth
What species produces relaxin in corpus luteum
Cows
What maintains the corpus Luteum
Basal (moderate) secretion of LH
What species only require LH to maintain CL
Horses, cat and cow
What species require LH and prolactin to maintain CL
Dog, sheep, rodents
What maintains LH levels that are needed to maintain Corpus luteum
Pulses of GnRH maintain LH at moderate levels
___ terminates CL and progesterone secretion at end of luteal phase
PGF2alpha
What does corpus luteum become after exposed to PGF2alpha
Corpus albicans
What produces PGF2alpha in cows, horses and sheep
Endometrium
What produces PGF2alpha in primates
Ovaries
What is the stimulus for PGF2alpha
Estrogen/progesterone then oxytocin
What is the target of PGF2alpha
Corpus luteum
What is the effect of PGF2alpha on corpus luteum
Luteolysis
What are the two mechanisms of actions/effects of PGF2alpha
- PGF2alpha- receptor complex opens Ca2+ channels in granulosa cells. This induces apoptosis through high intracellular calcium
- Activation of Protein kinase C inhibits mitochondrial transport of cholesterol and progesterone synthesis
How does oxytocin induce PGFalpha- describe feedback loop
- Signal from posterior pituitary to uterus
- Uterus releases PGF2alpha
- PGFalpha signals release of oxytocin to act in positive feedback to uterus to release more PGF2alpha
- PGF2alpha destroys CL via a positive feedback loop
When does CL become receptive to PGF2alpha in cows
PGF receptors appear ~ 6 days after ovulation
When does CL become receptive to PGF2alpha in horses
PGF2alpha receptors appear~ 5 days after ovulation
If you inject a cow with PGF2alpha 3 days after ovulation what happens
Not much, don’t have PGF2alpha receptors yet
If you inject a cow with PGF2alpha 10 days after ovulation what happens
Will be able to respond and cause CL to regress due to presence of receptors 6 days after ovulation
What is the vascular pathway for PGF2alpha in cow and sheep
Produced in the uterus endometrium is released into the ovarian veins and is transferred to ipsilateral ovarian artery through counter current exchange mechanism
What is the vascular pathway of PGF2alpha in horses
Released in systemic blood from either uterine horn
Absence of both uterine horns (full uterectomy) leads to ___luteal phase, why?
Prolonged because can’t send PGF2alpha from uterine horns into systemic blood, therefore Cl/luteal phase won’t be induced to regress, no oxytocin positive feedback loop. Diestrus is 148 days long
Absence of the uterine horn contralateral to the CL does what to lifespan of CL
Nothing, present uterine horn is on same side as CL therefore can secrete PGF2alpha to that CL to cause regression. Days 15-17
Absence of uterine horn ipsilateral to CL does what to lifespan of CL
Slightly prolongs it to 35 days because still have other uterine horn that will be active during next cycle
Endometritis in cows leads to ___luteolysis. Why?
Decreased, because endometrium is responsible for releasing PGF2alpha so if damaged will have decreased release of PGF2alpha and prolonged luteal
What does E. Coli exposure in cattle do to luteotrophic prostaglandin E2 (PGE2) and luteolytic PGF2alpha
Increases PGE2 and has no effect on PGF2alpha
During pseudopregnancy there is no ____ mechanism
Uterine luteolytic
Pseudopregnancy is associated with what behaviors
Nesting, spontaneous lactation and maternal protection
When does pseudopregnancy occur
50-90 days after estrus
What happens to progesterone and prolactin levels during pseudopregnancy
Decreasing progesterone levels and increasing prolactin levels after long luteal phase
How do wild canids exhibit an adaptive role for pseudopregnancy
Subordinate females exhibit elevated progesterone during dominant females pregnancy
Where is prolactin secreted from in late stage pregnancy in the bitch and rat
Anterior pituitary or the endometrium
What is the stimulus for prolactin in the bitch
Increasing estrogen late in diestrus
What is the stimulus for prolactin in rodents
Copulation that initiates a 9-15 day pseudopregnancy in absence of fertilization
What is the target of prolactin
CL in the rat, bitch and ewe, mammary glands in all mammals
What is the effect of prolactin
Luteotropic. Required for initiation and maintenance of milk synthesis
What types of drugs can be used to induce estrus in the bitch
Anti-prolactin drugs (dopamine agonists and serotonin antagonists)
If anti-prolactin drugs are given mid pregnancy what will happen
Luteolysis and abortion
What does estradiol increase in canine estrous cycle
Proestrus
When does progesterone increase in canine estrous cycle
End of estrus and peaks at beginning of metetrus
When does LH increase in canine estrous cycle
End of estrus to induce ovulation
How can you induce pseudopregnancy in rodents
Tactile stimulation of vagina
Ovulation is induced by ___
LH surge
Decide all endometrial ___maintains murine pseudopregnancy
Prolactin