Peripheral presynaptic adrenoreceptor regulation of norepinephrine release in humans.

The concept of peripheral presynaptic regulation of neuronal norepinephrine (NE) release via alpha 2 adrenoreceptors has received extensive support from in vitro evidence. Despite this, the importance of such a system under physiological and pathophysiological conditions remains to be defined in humans. This largely reflects the limitations of using plasma NE as an index of neuronal amine release in vivo and the difficulties of interpreting the hemodynamic responses to adrenoreceptor agonists or antagonists administered in vivo. Efficient probes and sensitive indices of neuronal NE release are required to clarify the importance of peripheral presynaptic mechanisms in humans.