thyroid and menstrual cycles

[arkroyal]

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How does hyperthyroidism cause oligo/amenorrhea? it would seem that hyperthyroidism causes decreased release of TRH and since TRH has a stimulatory effect on prolactin... low TRH would result in low prolactin which causes decreased inhibition of GnRH so why would the menstrual cycles be affected

 

[blz]

Just an educated guess, but GnRH is only effective when it is released in an optimal pulsatile fashion. I'm sure less inhibition of GnRh ruins this pulsatility as much as too little GnRH.

 

[Blesbok]

If I had to guess, I would guess it has something to do with hormone release. It increases metabolism and it lowers cholesterol levels, so I would assume it has an effect on steroid synthesis. However, I have no clue, but would be interested if you find an answer.
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[78222]

Perhaps it's due to the fact that hyperthyroidism increases SHBH synthesis😕😕

 

[Femtochemistry]

i thought nobody really knows the exact mechanism........i remember someone telling me that

 

[ASDIC]

i agree with the person above me.

A lot of the mechanism of actions of thyroid hormone are unknown, mainly due to the fact the hormone directly activates genes, making it harder to study say compared to a hormone that utlizes a cell membrane bound receptor with cytoplasmic signal transduction.

 

[Phloston]

Even though this post is three-years old at this point, I'm just going to clear this up for anyone in the future who comes across this page.

In HYPOthyroidism, the mechanism for amenorrhea is decreased free T3/T4 causing upregulation of TRH, thereby increasing prolactin secretion, which decreases LH/FSH secretion.

In HYPERthyroidism, amenorrhea occurs because free T3/T4 increases sex-hormone binding globulin (SHBG) secretion from the liver, thereby decreasing the ratio of free-/bound-estradiol (and in a male, testosterone and DHT). Since higher free-estradiol concentrations are ultimately responsible for the ovulation-inducing LH-spike, decreased free-estradiol would decrease the probability of the LH-spike occurring.

 

[theTruth_97]

Even though this post is three-years old at this point, I'm just going to clear this up for anyone in the future who comes across this page.

In HYPOthyroidism, the mechanism for amenorrhea is decreased free T3/T4 causing upregulation of TRH, thereby increasing prolactin secretion, which decreases LH/FSH secretion.

In HYPERthyroidism, amenorrhea occurs because free T3/T4 increases sex-hormone binding globulin (SHBG) secretion from the liver, thereby decreasing the ratio of free-/bound-estradiol (and in a male, testosterone and DHT). Since higher free-estradiol concentrations are ultimately responsible for the ovulation-inducing LH-spike, decreased free-estradiol would decrease the probability of the LH-spike occurring.

Pholston you are THE MAN! Thank you so much!

 

[patchouli]

Yes thank you so much!

 

[house@henrygray]

Phloston, you're one of the gods of usmle, thanks for the explanation which was long searched🙂
you rock