SYMPATHOINHIBITORY EFFECTS OF GAMMA-L-GLUTAMYL-L-DOPA ARE NOT MEDIATED BY ACTIVATION OF DOPAMINE-2 RECEPTORS IN CONSCIOUS RABBITS

AIM: To define the role of dopamine-2 receptors in the sympatho-inhibi tory effects of gamma-l-glutamyl-l-dopa in conscious rabbits. METHOD: gamma-l-glutamyl-l-dopa (gludopa) was infused iv at 25 and 100 mu g . kg(-1) . min(-1) with and without prior dopamine-2 receptor blockade b y YM-09151-2 (50 mu g . kg(-1) iv) in conscious' rabbits. RESULTS: Mea n arterial pressure and heart rate remained unchanged while renal plas ma flow increased. Arterial norepinephrine (NE) concentration, total a nd renal NE spillover rate were markedly decreased in a dose-related m anner, which were not affected by prior dopamine-2 receptor blockade. Gludopa was detected in the whole brain (92 +/- 112 ng/g wet brain tis sue) at the end of experiment although brain tissue levodopa, NE, and dopamine contents were not much different from those in the control gr oup. CONCLUSION: Gludopa decreased dose-dependently plasma NE concentr ation, and total and renal NE overflow to plasma, which were not media ted by activation of dopamine D-2 receptors.