I'm not sure about the cause and effect, but epinephrine and other chemicals that are released by the adrenal gland are elevated when you're angry. Some emotions are caused not by chemicals, but by the lack of them, like depression. Anger may be the same. A lack of serotonin can cause irritability, that could easily lead to anger. Anger is associated with the flight or fight survival response, which is why the adrenal gland is involved.