What kills (and what saves) a corpus luteum?

[jasonfahy]

Hello,

High school bio teacher here, trying to plug some gaps.

We've got several textbooks which consistently say that after ovulation the corpus luteum survives for 10-14 days, producing estrogen and progesterone to sustain the endometrium; after that the corpus luteum 'degrades' or 'disintegrates' and flow phase begins.

My questions are, what is the corpus luteum's 'clock'; what builds up or runs down which finally causes it
to die...and how is that death prevented if an implanted zygote releases human chorionic gonadotrophin?

(And another one - by month 3 the placenta is producing its own estrogen and progesterone...does the corpus luteum die then? Or does it continue to function? If so, how long?)

[cspacy]

Its clock is based on the uterus' need for it. It it's not fertilized within 10-14 days then the uterus will in turn no longer need progesterone and estrogen to ready for pregnancy. If the oocyte is fertilized and does becomes a zygote then the corpus luteum will continue to secrete progesterone and estrogen for 12 weeks in order soften the endometrial wall of the uterus for pregnancy up until the placenta is formed which will take over the corpus luteum's job. The corpus luteum then becomes(dies) a corpus albicans(scar tissue)(no further function). The major factor in controlling formation and death of the corpus luteum is lutienizing hormone(LH).

[Darby]

You've asked a question that isn't completely answerable yet - here's a bit of info:

http://physrev.physiology.org/cgi/content/full/80/1/1

I would guess that a shutdown of the blood supply is somehow involved as well.

[jasonfahy]

It looks like the time bomb is a positive feedback loop between oxytocin and prostaglandin F2 (PGF2), initiated in the preovulatory follicle.

PGF2...
* causes degeneration of the capillary network supplying the corpus luteum, and
* stimulates endothelial cells to produce endothelin-1, which is a local vasoconstrictor

...so the ever-increasing levels of PGF2 cut off the corpus luteum's blood supply, strangling it.

In pregnant non-primates, it is known that the zygote produces interferon-gamma, which
interferes with the PGF2 loop by blocking the genes which code for the receptors of estradiol
and oxytocin; there is also suspected to be a protein which blocks PGF2 more directly. It doesn't
say if hCG does the same job as interferon-gamma, or if it does direct blocking or what.

I assume from the above that the oxytocin spike which initiates labor would cause a large spike
in PGF2, finally killing the corpus luteum right during/shortly after birth.

Anyway, I now understand more than I did - thank you!