Increase of alpha 2-presynaptic adrenoceptor response after neuronal uptake inhibition in vivo

alpha 2-adrenoceptor antagonists, yohimbine or idazoxan (1 mg kg-1 i.p.), administered alone, did not change noradrenaline content in the central and peripheral tissues of the rat (hypothalamus, brain stem, frontal cortex and heart). The inhibition of neuronal uptake by desipramine (DMI) administered alone or prior to alpha 2-adrenoceptor antagonists did not affect the neurotransmitter content either. alpha-methyl-p-tyrosine (alpha-MT) 6 hr before sacrifice, induced a marked disappearance of the noradrenaline content, greater in central nervous tissues than in heart. When the catecholamine synthesis was inhibited by alpha-MT, neither alpha 2-adrenoceptor antagonists nor DMI at the dose used, significantly changed the disappearance rate of noradrenaline in any of the tissues studied. Under these experimental conditions, however, the combination of DMI plus alpha 2-adrenoceptor antagonists significantly decreased the neurotransmitter content in all tissues when the values were compared with the control or DMI-treated groups. The present results might suggest evidence in favour of a functional coupling between presynaptic alpha 2-autoreceptors and noradrenaline uptake mechanism.