What are mechanisms of action of adrenergic agonists?

1. Direct-acting agonists: act directly on α or β receptors, producing effects similar to those that occur following stimulation of sympathetic nerves or release of the hormone epinephrine from the adrenal medulla epinephrine, norepinephrine, isoproterenol, and phenylephrine. 2. Indirect-acting agonists: may block the uptake of norepinephrine (uptake blockers) cocaine, cause the release of norepinephrine from the vesicles of the adrenergic neuron (tyramine) amphetamine and tyramine 3. Mixed-action agonists: stimulate adrenoceptors directlyand stimulate the release norepinephrine from the adrenergic neuron ephedrine, pseudo-ephedrine and metaraminol,