This apparent synergy is caused by several factors (lets see if I can explain it at 3:00 am).
1) Tren has the capacity to cross-bind with progestin receptors, which winstrol seems to be an antagonist for. By blocking some of those receptors, this leaves more trenbolone free to bind to ar's, as well as reducing some of the side effects.
2) Winstrol has been shown, in doses as low as 10 mg a day, to reduce shbg levels 50% or more. This leaves less shbg to bind to the tren, thus leaving more trenbonlone free to bind to ar's.
3) All steriods have been show to cause an upregulation in androgen receptors (ar's) in order to accomidate the total blood serum levels of androgens. By adding winstrol, one causes further upregulation. The steroids in the bloodstream compete for these receptors, but tren being the far more androgenic of the two, will tend to win the majority of the time. This gives the trenbolone more receptors to bind too, this increasing its potency. It should also be noted that winstrol, unlike other mild adrogens, is 17-aa, which means it has an effective half-life in the bloodstream of several hours, rather than several minutes. This means that despite it losing initially to tren in the competition for receptors (with only a small % of it binding without being displated by the tren), it continues to linger in the bloodstream, thus signalling the need for further upregulation. I believe, although I cannot prove it, that for this reason compounds such as winstrol and dbol may cause more rapid and more ar upregulation than other compounds. This may also account for the gains winstrol seems to cause when stacked with stronger androgens. It should also be noted taht for this reason, the winstrol stays in the bloodstream longer and has more time to bind to estragen and progestin receptors as an agonist, thus yielding its harden effects.
Just my 2 cc's...
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