Only externally applying adenosine to the scalp increases adenosine levels, but not directly INSIDE follicle cells. However, only a fraction of this new surplus is allowed to enter follicle cells, as there is no upregulation of this channel (which would be performed by minoxidil). Thus, on its own, without upregulating adenosine supply to cells, adenosine by itself will not have such a drastic effect; only parts of it will enter cells. minoxidil, on the other hand, makes the adenosine present in the human body available to cells.
In theory, this would also mean that combining minoxidil and adenosine/Adenogen should initiate MASSIVE HAIR REGROWTH.