Menstrual Cycle - Proliferative and Secretory Phase Flashcards
What occurs during the proliferative phase?
During the proliferative phase:
• The luminal and glandular epithelium proliferate (stem cells)
• Stromal cells proliferative
• Endothelial cells proliferate (and hence blood supply increases)
• Glands enlarge
All the proliferative phase is estrogen dependent:
• Cervical mucous increases
• Mucous is less viscous and more hydrated – sperm can penetrate
• Increases progesterone receptors
Which layer is shed during menstruation, the strata functionalis or the strata basalis?
Just the functional zone is lost at menstruation – the basilar zone is not shed, it contains the stem cells function in re-proliferating the functional zone.
Describe the experiments performed that determine whether estrogen acts at the stromal or epithelial ER to induce proliferation?
Tissue recombination studies:
- Take uterus from BALB/c mice (these do have the receptor, just the neonates that don’t)
- Take the uterus from an ERKO mouse (no receptor)
- Make combinations of the two
- Culture on agar overnight
- Transplant in adult female nude mice
- Ovariectomised after 1 month (removes endogenous estrogen)
- Treat with estrogen
- Analyse proliferative response (BrdU incorporation)
Results:
1) WTS/WTE → both stromal and epithelial cells undergo proliferation
2) WTS/KOE → both stromal and epithelial cells undergo proliferation
3) KOS/WTE → hardly any response. no differences between estrogen and oil treated rats
4) KOS/KOE → again, no response.
Conclude → Stromal ER is obligatory, epithelial ER is neither necessary nor sufficient.
How does the stroma communicate with the epithelium to induce epithelium proliferation in response to estrogen?
• Best evidence is IGF is a paracrine factor:
− IGF produced predominantly by stroma
− IGF receptor expressed in the epithelium and stroma
− in vitro IGF stimulates epithelial and the stroma proliferation
− IGF1 increases during the proiferative phase of the cycle
− Estrogen stimulates IGF1 and receptor expression
− Over expression of IGFBP impairs estrogen effects on uterine growth
− In iGF1 knockouts:
− Uterus is 10% of the wildtype
− epithelial response to estrogen is abolished
• Inhibition of the IGF1 receptor prevents estrogen induced proliferation
− Estrogen stimulates IGF1 expression in the stroma
− PPP is an IGF1 receptor inhibitor
− PPP in the uterine lumen blocks estrogen mediated activation of the IGF1 receptor
− PPP inhibits estrogen stimulated epithelial proliferation
→ So the idea is that estrogen acts on the stromal estrogen receptor, and the stromal cell produces IGF1 which acts on the IGF1 receptor in the epithelium
Does the membrane bound ER have a role in reproductive function?
The Membrane Only Estrogen Receptor (MOER) mouse:
• When MOER female mated with wildtype male → no pregnancies
• The uteri are atrophic → comparable with total ER-a knockout
• Other abnormalities such as cysts and absence of corpus luteum present.
• Nuclear ER-a is therefore needed for normal reproductive function → membrane ER-a is not sufficient.
Does the GPR30 estrogen receptor have a role in reproductive function?
The GPR30 knockout mouse:
• Fertile
• Reproductive organs normal
• Uterine epithelium proliferates in response to estrogen
• GPR30 is therefore not needed for epithelial cell stimulation
Does the epithelial ER-a have any role?
• Dispensible for proliferation, but needed to protect against apoptosis
• Uteterine epithelial specific knockout:
− Estrogen stimulated proliferation maintained
− Loss of epithelial ER-a correlated with increased apoptosis
− → so needed for the cells to survive!
• Also thought it is needed for secretory protein production
• Estrogen induction of secretory protein production requires both stromal AND epithelial ER
− Experiment stained for lactoferrin
− WTS/WTE → lots of staining for lactoferrin
− WTS/KOE → little lectoferrin
− KOS/KOE → little lectoferrin
Does the epithelium have a role in regulating the response to estrogen?
• There may be a role for the GPR30:
− Mainly located in the epithelium
− Activation of the GPR30 using the specific agonist G1 prevents phosphorylation of ER-a in the stroma → ER-a phosophorylation is important for ER-a function
− Activation of the GPR30 inhibits estrogen induced proliferation → may provide a negative balance to ER-a dependent uterine growth.
Summarise the functions of each ER
Classical ER-a:
- Stromal –> required for epithelial and stromal proliferation, and secretory protein production.
- Epithelial –> required for epithelial survival and secretory protein production.
Membrane bound ER-a
-Insufficient for epithelial proliferation
GPR30
- not required for stimulating proliferation
- phosphorylates ERa, needed for ERa function
- may balance ER-a actions by inhibiting proliferation
What are progesterones actions on the uterine epithelium?
• Inhibits epithelial proliferation
• Stimulates:
− Differentiation (decidualisation) of the stromal cells → necessary to get trophoblast cells invading into the epithelium and getting successful implantation
− Tortuous gland development and secretion
− Stroma oedema
− Maturation of the spiral arteries
− Mucous thickening → works as a contraception in this way, thickens mucous to prevent sperm entry.
Describe the experiments performed that determine whether progesterone acts at the stromal or epithelial PR to inhibit estrogen induced proliferation?
Tissue recombination studies:
- Take uterus from BALB/c mice (these do have the receptor, just the neonates that don’t)
- Take the uterus from an PRKO mouse (no receptor)
- Make combinations of the two
- Culture on agar overnight
- Transplant in adult female nude mice
- Ovariectomised after 1 month (removes endogenous estrogen)
- Treat with estrogen
- Analyse proliferative response (BrdU incorporation)
Results:
1) WTS/WTE → estrogen stimulates proliferation, but when progesterone is administered, progesterone inhibits proliferation.
2) WTS/KOE →progesterone inhibits estrogen induced proliferation
3) KOS/WTE → progesterone cant inhibit estrogen induced proliferation
4) KOS/KOE → progesterone cant inhibit estrogen induced proliferation
- So this is similar to what we see with the estrogen receptor
- → Stromal PR is obligatory, epithelial PR is neither necessary nor sufficient.
Define menstruation
The withdrawal of progesterone from an estrogen primed endometrium
How can menstruation be prevented
Administer progesterone within 36 hours of the loss of the corpus luteum
What is menstruation an example of?
Shedding of the basalis functionalis is an example of recurrent physiological injury and repair.
What vascular changes occur during menstruation, and how are these mediated?
• Vasoconstriction of spiral arteries – causes damage and ischaemia
• Followed by periods of vasodilation – leads to the breakdown and leage of blood
• Mediated by:
− Prostaglandins
− Endothelins
− Nitric oxide
