What is the action of alpha 2 receptors?

[scilearner]

Hello everyone,

 

Ok my textbook says inhibition of transmitter release, vasoconstriction and more things. Now my question is what does inhibition of transmitter release mean. Since alpha 1 receptor is present on post synaptic membrane, and alpha 2 is present in pre synaptic membrane, does this mean alpha 2 actually controls the action of alpha 1 receptors by inhibiting neurotransmitter release. If that is the case why are there actions similar, shouldn't alpha 2 have oppposite actions of alpha 1 and actually decrease sympathetic activity. Also if you give a non selective alpha agonist which acts on both alpha 1 and alpha 2 receptors does vasodilation occur, how? Thank you