title: Modulation of noradrenaline release through activation of presynaptic beta-adrenoreceptors.
abstract: On peripheral noradrenergic nerve endings there exist beta-adrenoreceptors activation of which results in an enhanced release of noradrenaline in response to nerve stimulation. These presynapatic beta-adrenoreceptors do not appear to be activated by neuronally-released noradrenaline. However, adrenaline may be a physiological activator during enhanced adrenomedullary secretion. Adrenaline can also be incorporated into the noradrenergic transmitter stores and be released as a co-transmitter. Under these conditions presynaptic beta-adrenoreceptors may be activated by neuronally-released adrenaline, thus forming a 'positive feedback loop'. The release of adrenaline from the adrenal medullae may also be modulated through facilitatory beta-adrenoreceptors, but the release of noradrenaline from noradrenergic nerves in the central nervous system is not. The facilitatory presynaptic beta-adrenoreceptors appear to be in the main of the beta 2-subtype although precise receptor characterization has not been carried out. Increased activation of presynaptic beta-adrenoreceptors by adrenaline may be implicated in the development of essential hypertension. Part of the antihypertensive action of beta-adrenoreceptor blocking drugs may be due to blockade of these facilitatory presynaptic beta-adrenoreceptors.
mesh_terms: D000313:Adrenal Medulla / Q000378:metabolism; D000818:Animals; D002490:Central Nervous System / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004837:Epinephrine / Q000378:metabolism; D005246:Feedback; D006801:Humans; D006973:Hypertension / Q000503:physiopathology; D009638:Norepinephrine / Q000378:metabolism*; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism
chemical_list: D011941:Receptors, Adrenergic; D011943:Receptors, Adrenergic, beta; D000242:Cyclic AMP; D009638:Norepinephrine; D004837:Epinephrine