'FREE' VERSES 'BOUND' TESTOSTERONE


Free vs Bound Testosterone
What does this mean? Can we get hold of testosterone for free these days? Many of you would wish, but you can keep dreaming. We're talking here about the state of the testosterone in the blood stream - free or bound. Within your blood stream, only a very small amount of testosterone actually exists in a free and unbound state, where interaction with cellular receptor sites is in fact possible, as described in the last section. What you will find is that much of the testosterone is in fact in a bound state, whereby the testosterone molecule is bound to a type of protein. This protein is known as sex hormone binding globulin or SHBG and albumin. Sometime SHBG is referred to as sex steroid binding globulin or even testosterone-estradiol binding globulin. In this bound state, the testosterone is not free and active and so the hormone is prevented from exerting any activity on the receptor site and the chemical message cannot be passed on. In the body steroid hormones bind to SHBG one thousand times greater than they do to albumin protein, however albumin is present within the body one thousand times greater in concentration than SHBG. What this means is that the activity of both binding proteins in the body is relatively equal. In men, the distribution of bound testosterone is typically that of 45% to SHBG and around 53% bound to albumin. As you can see the actual free and unbound testosterone circulating the blood stream is only about 2% of the total level. It has been measured in women to be even lower at around 1% concentration. A binding protein known as androgen binding protein of ABP is also mediating androgen activity in the reproductive system, although since it is found exclusively in these tissues, it is not really relevant to muscle growth.


Since only a small amount of testosterone is really active at any one given time, the levels of free testosterone in the blood is a very important factor. You should also realise, that as we alter the chemical structure of testosterone, creating new blends of this hormone as new anabolic steroid analogues, we are also altering the hormones ability to bind to these plasma proteins. It makes sense of course, that the higher the percentage of free hormone in a compound, the more active that compound will be on a milligram for milligram basis - the more free testosterone, the more potent, in essence. The variance between different compounds can actually be quite substantial. As an example, Proviron which is 1-methyl dihydrotestosterone, binds with SHBG many more times more than that of testosterone itself. On the other hand you have compounds such as Bolasterone, that's 7, 17 dimethyl testosterone, and Mibolerone, 7, 17 dimethyl-nandrolone, that exhibit absolutely no affinity towards this protein at all. This makes these particular two steroids very, very potent androgens indeed.


Now, the actual level of SHBG within the body does vary, and can be influenced by a number of factors. When we look into how these proteins are affected, it would appear that the largest influencing factors are those of two other hormones - estrogen and thyroid hormone. As these two hormones increase, levels of SHBG also increase. Likewise, in reverse, as the levels of these two hormones decrease, so too do the levels of SHBG decrease. IT has also been dicumented that the administration of higher levels of anabolic androgenic steroids, also has the effect of decreasing the concentrations of this binding protein within the body. There have been studies that cleary show that even a low dosage of oral administered Stanzolol (Winstrol) at a level of around 18mg for a 200lb man (.2mg/kg/day) actually caused levels of SHBG to drop by around 50% after only three days. Similar results have been shown to take place with the administration of injectable testosterone enanthate, only the compound was less potent on a mg for mg basis. It has been shown that results correlate quite accurately on the effects on SHBG levels when the drug is administered orally over other means. Perhaps this is because SHBG is actually produced within the liver, and so we cannot assume that injectable steroids have the same effects as the oral administration route.


So we know that lowering the levels of plasma binding proteins in the blood stream will increase the levels of free testosterone available in the body to perform the task we want of the hormone - delivering the message to the muscle cell to increase anabolism of protein. It is highly possible and logical to assume that steroids that exhibit a high affinity for these binding proteins may also increase free testosterone levels simply by competing with it for binding. Of course, you would also be correct in thinking, that if the testosterone finds it difficult to locate available plasma proteins in the presence of an additional compound, more will be left in an unbound state. There are a number of steroids such as dihydrotestosterone, Proviron, oral Turinabol which display a strong tendancy for this effect. And so from this theoretical stand point, and real world evidence, one can safely assume that by stacking one anabolic steroid alongside another anabolic steroid, the level of free testosterone can be beneficially altered, through these very mechanisms. This process of stacking steroids is discussed in greater depth later. As an example, one could stack Proviron, a poor anabolic, with a very high affinity for the SHBG, with another steroid, making it very useful by allowing the displacement of the other steroid and making it far more active in the target tissues.


Binding proteins, however, are not a bodybuilders enemy of course. It is not your mission to seek out a way to limit or destroy these vital elements from your body. They are in fact there for very good reason. These binding proteins play an absolute vital role in the transportation and functioning of your endogenous androgens. The binding proteins actually protect the steroid from too rapid metabolism, which in turn ensures a far more stable blood concentration level. The binding proteins also facilitate a very even distribution of the hormones to vital organs of the body. There has been more recent research of late that has also discovered the SHBG-R (Sex Hormone Binding Globulin Receptor) - a specific receptor site for this protein, located on the membrane surface of the steroid responsive body cells, suggesting that there is in fact a far more complicated role for this protein than just normal hormone transportation. It remains clear to us at this stage however, that actually manipulating the tendancy of a hormone to exist free in an unbound state is a very effective method to increase the potency of a drug on a mg for mg basis.