T Nation

Help,who can answer?

I know estrogen in Man is made from aromatization of testosterone.After On-cycle, endogenous T will be suppressed, the Estrogen dominated. But,I am confused, when T was inhibited in off-cycle, Where do estrogen come from? If these estrogen came from anabolic steroid which one used, why do these estrogen have much long active-life?
Is there DHT side effect in off-cycle? As above, DHT have longer active-life also?