performance enhancing drugs?

[doctorFred]

har har. i actually have a steroid question and i'm wondering if goljan has led me astray.

i was under the impression that if you increase thyroxine binding globulin, total t4 will increase but FREE t4 will stay exactly the same. now, on page 265 of first aid, it says that an increase in testosterone binding globulin will actually LOWER free testosterone, leading to gynecomastia in males.

they're very similar hormones with similar binding globulins - so why does an increase in thyroid globulin have no effect on free t4, while an increase in testosterone globulin drops your free testosterone??

---

Members don't see this ad.

 

[osli]

My first thought is that in the case of thyroxine your HPA/thyroid gland compensates. Thus, binding globulin goes up --> more bound T4 --> initial transient drop in free T4 --> more T4 produced by thyroid --> end result of no net change in free T4 but more T4 bound to the globulin. And in the case of testosterone, perhaps there is not as quick and/or adequate of a compensation, such that the initial drop in free hormone persists.

That is, if FA is correct. Anyone have a less presumptuous answer?

 

[GMDMD]

They're both right. FA does just a really crappy job of explaining it. They fail to mention that SHBG binds both testosterone and estrogen, only it has a higher affinity for testosterone. There's no similar interplay with thyroid binding globulin, to my knowledge.

So...
+ SHBG => - testosterone/estrogen ratio => gynecomastia
- SHBG => + testosterone/estrogen ratio => hirsutism

Hope that helps. It was really bugging me too until I found this bit of info in RR Path.

 

[Tiger26]

Man, I really hope they don't piss test us after the test for performance enhancers--I've been popping bovine steroids and HGH like it was going out of style to get a little edge on this thing . . . not to mention the synthetic EPO so that I can allocate some more time towards questions that I would normally spend breathing . . .

 

[osli]

They're both right. FA does just a really crappy job of explaining it. They fail to mention that SHBG binds both testosterone and estrogen, only it has a higher affinity for testosterone. There's no similar interplay with thyroid binding globulin, to my knowledge.

Well, that just makes too much sense.

 

[doctorFred]

They're both right. FA does just a really crappy job of explaining it. They fail to mention that SHBG binds both testosterone and estrogen, only it has a higher affinity for testosterone. There's no similar interplay with thyroid binding globulin, to my knowledge.

So...
+ SHBG => - testosterone/estrogen ratio => gynecomastia
- SHBG => + testosterone/estrogen ratio => hirsutism

Hope that helps. It was really bugging me too until I found this bit of info in RR Path.

that's not so much a "crappy job explaining it" as it is a "complete lack of elucidating the mechanism." and since mechanisms are the name of the game.. etc.