Metabolism and vascular effects of gamma-L-glutamyl-L-dopa on the isolated rat kidney.

Barthelmebs, Mariette; Caillette, Agnès; Ehrhardt, Jean-Daniel; Velly, Jeanne; Imbs, Jean-Louis

Gamma-L-glutamyl-L-dopa (or gludopa), a dopamine (DA) prodrug, is selectively metabolized in vivo by the kidney through the sequential action of two renal enzymes, gamma-glutamyl transpeptidase (gamma-GT) and aromatic L-amino acid decarboxylase (AADC). This study was designed to analyze, in vitro, the factors regulating gludopa metabolism and its renal vascular effects. Rat kidneys were perfused in closed circuit with a cell-free perfusion buffer containing 6% bovine serum albumin (BSA). Adding gludopa (final concentration 10-5 M in the perfusate) led to the release of DA both into urine and perfusate (0.53 ± 0.21 and 1.38 ± 0.28 nmol/min/g kidney wt, respectively, during the first 5 min after substrate addition, N = 5, mean ± SEM). Total DA release (urine plus perfusate) was 73.7 ± 15.8 nmol/g kidney wt within 30 minutes, of recirculation. In non-filtering kidneys, total DA release m the recirculating medium was lower (12.5 ± 1.4 nmol/g kidney wt, P < 0.01). Glomerular filtration and access to the gamma-GT on the brush border membrane of proximal tubular cells are therefore required for the maximal conversion rate of gludopa. On filtering kidneys, L-dopa was also convened to DA, but at a higher rate than gludopa (total DA formed within 30 min of recirculation = 131.2 ± 31.9 nmol/g kidney wt) and this rate was not reduced in non-filtering kidneys (224.2 ± 41.7 nmol/g kidney wt DA formed within 30 min). Metabolic conversion of L-dopa by AADC is thus preserved in the case of an approach via the basolateral side of the proximal tubular cells. The renal vascular effects of gludopa were studied after vascular tone had been restored by continuous perfusion of PGF2α and after the inhibition of alpha- and beta-adrenoceptors. Gludopa (3.10-6 to 4.10-5 M) elicited concentration-dependent renal vasodilatation. At 4.10-5 M, the renal response was similar to that elicited by DA and L-dopa at concentrations respectively 20 and 2 times lower. These responses were abolished by a DA-1 receptor antagonist, SCH 23390. Inhibition of gamma-GT by AT-125 (10-6 M) reduced gludopa-induced renal vasodilatation. as did carbidopa (10-4 M), on the L-dopa-induced renal response. Gludopa- and L-dopa-induced renal vasodilatations are directly linked to endorenal release of DA which interacts with vascular DA-1 receptors.

DOPAMINE; PRODRUGS; CATECHOLAMINES; RENAL pharmacology; PHARMACODYNAMICS; METABOLISM; LABORATORY rats

Kidney International, 1990, Vol 37, Issue 6, p1414

0085-2538

Academic Journal

10.1038/ki.1990.131