SYMPATHOINHIBITORY EFFECTS OF R-L-GLUTAMYL-L-DOPA IN CONSCIOUS RABBITS

Renal and total norepinephrine (NE) spillover rates were studied with [H-3] NE kinetic method during graded r-l-glutamyl-l-dopa (gludopa) iv infusion in conscious rabbits. Mean arterial pressure (MAP) and heart rate (HR) remained constant during the experiment, Gludopa iv infusio n at 25 and 100 mug . kg-1 . min-1 produced marked increases in urinar y dopamine (DA) excretion and renal DA content. Although renal venous DA rose after gludopa infusion. the arterial DA was not significantly altered. Arterial plasma gludopa and levodopa levels reached 0.9 +/- 0 .5, 3.2 +/- 0.8 mug . ml-1 and 3.0 +/- 1.8, 10.1 +/- 5.1 ng . ml-1 at the lower and higher gludopa doses, respectively. Gludopa elicited a p ronounced dose-related fall in renal NE spillover, which only accounte d for about one half of the reduction in overall NE spillover rate, Re nal NE content was doubled. These results indicated that gludopa decre ased the renal and extrarenal NE spillover to plasma. This reduction m ay be mediated by intrarenally synthesized DA via presynaptic DA-2 and alpha-2 receptors, but could also be explained by some central sympat ho-inhibitory mechanism.