How is the mechanism of action of adrenergic agonists?

Direct-Acting (act on a and b receptors directly produce similar effect as normal hormones from adrenal medulla, these include Epinephrine, NE, Isoproterenol, phenylephrine) Indirect-Acting (may block uptake of NE cocaine, cause release of NE from vesicles (amphetamines, tyramines)) Mixed-Action Agonists (stimulate adrenoreceptors directly and release NE from adrenergic neuron [ephedrine, pseudo-ephedrine, and metaraminol])