
Originally Posted by
JohnnyB
ACTION OF STEROIDS
Androgen Receptor Activation
Once a free molecule of steroid reaches the muscle cell, it diffuses into the cell. The diffusion can be with or without transport-protein assistance. Once in the cell, the AAS is makes its way to the cell nucleus where it can bind with an androgen receptor (AR), and activate the receptor. Two of these activated receptor complexes join together to form the androgen response element (ARE). The ARE interacts with DNA in the nucleus, and increases the transcription of certain genes (such as muscle protein genes). As long as the ARE is intact, it accelerates gene transcription. Remember, though, that the AAS and the receptor are in a state of flux (binding and un-binding), just like with the Carrier proteins. So the ARE can be deactivated just by losing one of the two AAS that are bound to the AR's. This equilibrium situation explains why 1 gram per week testosterone is more effective than 1/2 gram per week, even though 1/2 gram appears to be more than enough to saturate all the AR's in the body. The higher concentration makes it more likely that the receptors will be occupied by an AAS, and the ARE will be intact for a longer period of time, on average.
Other Actions
Activation of the androgen receptor is a key mechanism in the action of AAS. However, this mechanism by itself does not explain the differences between steroids (i.e., nandrolone activates the AR better than testosterone, but is not as good of a mass-building product). Other actions involve primarily the central nervous system, and involve actions such as motor activation (muscle coordination) and mood (i.e., aggressiveness). The mechanism by which AAS effect these actions is not well understood at this time. Another effect occurs in the liver, where some steroids cause the release of certain Growth Factors. The different actions of the different AAS explains why a stack of two different types of AAS is often better than one by itself.