I read somewhere that vitamin C is the "missing stress hormone". Since alot of other animals manufacture their own vitamin C (and at much higher doses than is recommended for humnans), I believe this to be true.
The adrenal glands concenctrate vitamin C and release it inside the adrenal gland when a stressor hits. I believe this is to 1. protect the adrenal gland from damage during stress and 2. to regulate the release of cortisol and adrenaline.
When you take optimal amounts of vitamin C the stress response, adrenaline and cortisol are used sparingly instead of having too much released.
It really is the missing stress hormone in the adrenal cortex.