this group differs from the previously-developed alpha-adrenoceptor blockers , phentolamine and phenoxybenzamine , in that they do not block the pre-synaptic alpha 2-adrenoceptors which modulate the release of neurotransmitter , and therefore do not cause as much reflex activation of the sympathetic nervous system .
C0034784
alpha-adrenoceptor
C0001639
alpha 2-adrenoceptors