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Testosterone, Bound or Free ??
Jun 5, 2001

Hello Doctor Bob,

I some questions about testosterone.

Testosterone exists in the body as two forms. Free and Bound.

Now my question : wich form does the human body uses for feeling well, having interest in sex, erectile function and metabolism ?

Why is free testosterone bound to bounded testosterone ?

Wich form are the testikels forming ? Is it the free, or the bound form ?

And last question : What happends with the bound testosterone ? Why is it bound ?

Thanks very much,

Sincerly Jason

Response from Dr. Frascino

Hell Jason,

Testosterone! One of my favorite hormones! I once heard it said that testosterone sounds like an Italian dessert named after a Greek god! Well, who could resist that?

The actual synthesis and metabolism of testosterone in the body is very complex, but I'll try to briefly reply to your question.

Approximately 1-2% of all testosterone in the circulation is "free;" the remainder is bound to sex hormone-binding proteins called globulins. The bound testosterone cannot interact with the target cells, so it's the "free" stuff that stimulates all our male characteristics. Now there is some equilibrium between the bound and free, so it's really not so cut and dried as 2 different "types" of testosterone. There really is only one type that can link up with these proteins in the blood stream. Most physicians just measure "total" testosterone, which includes both bound and free fractions, to determine if you are low on "love juice."

So why is testosterone bound? Well, maybe because he's so naughty we had to bind him up to make him behave? No, not really. It's all part of a very complicated endocrinological pathway with many regulatory factors, far beyond the scope of this forum. Bottom line is that there is only one type of testosterone, most of which is bound to certain proteins in the blood.

The "unbound" or free testosterone is the stuff that stimulates the receptors that lift our spirits (and other things).

Dr. Bob

sleepless in seattle

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