OBJECTIVE: The purposes of this study were: (1) to test whether intravenous infusion of norepinephrine can affect plasma dopamine levels; and (2) to explore to what extent dopamine-2 or alpha 2-receptors play a role in this response. DESIGN: Norepinephrine infusion in man was performed to test whether the increase in norepinephrine during sympathetic stimulation can affect dopamine release. Specific antagonists of presynaptic dopamine-2 and alpha 2-receptors were administered to test the receptor(s) involved in this possible regulatory phenomenon. METHODS: Plasma catecholamine levels were investigated in seven normal subjects before and after administration of domperidone (dopamine-2 antagonist), yohimbine (alpha 2-antagonist) and norepinephrine. RESULTS: Both oral domperidone and yohimbine induced a significant increase in both plasma norepinephrine and plasma dopamine. Norepinephrine infusion induced a significant decrease in plasma dopamine. Pretreatment with domperidone only partially counteracted this inhibitory effect of norepinephrine infusion, whereas yohimbine fully counteracted it. CONCLUSIONS: Our data show that norepinephrine may act as a hormone at plasma concentrations as low as 450 pg/ml. The norepinephrine-induced plasma dopamine decrease seems to be alpha 2-adrenoceptor-mediated. This norepinephrine effect may be involved in the physiologic decrease in plasma dopamine that we demonstrated in the upright position in normal subjects.
OBJECTIVE: The purposes of this study were: (1) to test whether intravenous infusion of norepinephrine can affect plasma dopamine levels; and (2) to explore to what extent dopamine-2 or alpha 2-receptors play a role in this response. DESIGN:Norepinephrine infusion in man was performed to test whether the increase in norepinephrine during sympathetic stimulation can affect dopamine release. Specific antagonists of presynaptic dopamine-2 and alpha 2-receptors were administered to test the receptor(s) involved in this possible regulatory phenomenon. METHODS: Plasma catecholamine levels were investigated in seven normal subjects before and after administration of domperidone (dopamine-2 antagonist), yohimbine (alpha 2-antagonist) and norepinephrine. RESULTS: Both oral domperidone and yohimbine induced a significant increase in both plasma norepinephrine and plasma dopamine. Norepinephrine infusion induced a significant decrease in plasma dopamine. Pretreatment with domperidone only partially counteracted this inhibitory effect of norepinephrine infusion, whereas yohimbine fully counteracted it. CONCLUSIONS: Our data show that norepinephrine may act as a hormone at plasma concentrations as low as 450 pg/ml. The norepinephrine-induced plasma dopamine decrease seems to be alpha 2-adrenoceptor-mediated. This norepinephrine effect may be involved in the physiologic decrease in plasma dopamine that we demonstrated in the upright position in normal subjects.
Authors: John J Mooney; Jacqueline A Samson; John Hennen; Kathleen Pappalardo; Nancy McHale; Jonathan Alpert; Martha Koutsos; Joseph J Schildkraut Journal: J Psychiatr Res Date: 2007-08-28 Impact factor: 4.791