The pharmacokinetics of gamma-glutamyl-L-dopa in normal and anephric rats and rats with glycerol-induced acute renal failure

N-acetyl-L-gamma-glutamyl derivatives of p-nitroaniline, sulphamethoxazole and sulphamethizole for kidney-specific drug delivery in rats

Kidney-specific delivery of p-nitroaniline, sulphamethoxazole and sulphamethizole after either intravenous administration of the L-gamma-glutamyl or N-acetyl-L-gamma-glutamyl derivatives or the parent drugs has been examined in a rat model. All L-gamma-glutamyl derivatives were converted to the corresponding parent drugs within 60 min whereas the N-acetyl-L-gamma-glutamyl derivatives were fairly stable in the systemic circulation after parenteral administration. Concentrations of p-nitroaniline and sulphamethoxazole 20 min after administration of the parent drugs were somewhat higher in the kidney than in the liver and lung. The concentration of sulphamethizole in the kidney was dramatically higher than those in the hepatic and pulmonary tissue. Kidney-specific delivery of the drugs of interest was evaluated by determining the tissue concentrations of the released parent drug and the total drug levels (i.e. drug levels after hydrolysis of all conjugate to the parent drug). For L-gamma-glutamyl-p-nitroaniline released renal levels of p-nitroaniline and total p-nitroaniline concentrations were both higher than those obtained after p-nitroaniline dosing. Use of L-gamma-glutamylsulphamethoxazole resulted in higher total sulphamethoxazole concentrations in the kidney, but did not lead to an increase in released (unconjugated) sulphamethoxazole levels. In contrast, no kidney-selective distribution was observed for L-gamma-glutamylsulphamethizole. Markedly increased kidney distribution was observed for both N-acetyl-L-gamma-glutamyl-p-nitroaniline and N-acetyl-L-gamma-glutamylsulphamethoxazole and the liver and lung concentrations were correspondingly reduced in comparison with parent drug dosing. Use of the N-acetyl-L-gamma-glutamyl-p-nitroaniline conjugate increased the concentration of p-nitroaniline in the kidney to the same extent as did L-gamma-glutamyl-p-nitroaniline. In conclusion, N-acetyl-L-gamma-glutamyl derivatization of certain compounds seems to be useful for kidney-specific drug delivery and preliminary data suggests that lipophilic drugs are better substrates than hydrophilic compounds. Results related to the selectivity of tissue distribution of the derivatives and species differences are discussed.

The renal handling of dopamine originating from L-dopa and gamma-glutamyl-L-dopa

1. The formation and outflow of dopamine and its deaminated metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) was studied in cortical fragments of the rat kidney loaded with L-beta-3,4-dihydroxyphenylalanine (L-dopa) or gamma-glutamyl-L-dopa (GluDOPA). Dopamine and DOPAC in the tissues and in the effluent were assayed by means of h.p.l.c. with electrochemical detection. 2. In rats given 30 mg kg-1 L-dopa, tissue and outflow levels of both dopamine and DOPAC were 3 fold those observed with a lower dose of L-dopa (10 mg kg-1). In rats given GluDOPA (16.7 mg kg-1) levels of dopamine in renal tissues and in perifusate samples were found to be higher than those obtained with an equimolar dose of L-dopa (10 mg kg-1); however, no significant difference was observed for DOPAC. The outflow of both dopamine and DOPAC in kidney slices of rats injected with L-dopa (10 and 30 mg kg-1) or GluDOPA (16.7 mg kg-1) was found to decline monophasically with similar slopes of decline. The rate constants of loss (k, min-1) of DOPAC (10 mg kg-1 L-DOPA, k = 0.0070; 30 mg kg-1 L-DOPA, k = 0.0087; 16.7 mg kg-1 GluDOPA, k = 0.0080) were 2 to 3 fold those of dopamine (10 mg kg-1 L-dopa, k = 0.0027; 30 mg kg-1 L-DOPA, k = 0.0034; 16.7 mg kg-1 GluDOPA, k = 0.0030). With both precursors the DOPAC/dopamine ratio in perifusate samples were 2.0 fold those in the tissues. 3. Tissue and outflow levels of dopamine after incubation of renal tissues with L-DOPA, 50 and 100 MicroM were found to be lower than those observed with GluDOPA (50 and 100 MicroM). DOPAC/dopamine ratios in tissues and perifusate samples of experiments performed with L-DOPA were significantly higher(P<0.01) than those observed with GluDOPA. The outflow of both dopamine and DOPAC in renal slices incubated with L-DOPA (50 and 100 MicroM) were found to decline with time, but presented a biphasic shape. DOPAC/dopamine ratios in perifusate samples were 3 fold that in the tissues with both precursors.4. In conclusion, the present results show that both L-DOPA and GluDOPA give origin to substantial amounts of dopamine and the newly-formed amine undergoes considerable deamination to DOPAC.However, dopamine originating from GluDOPA was less deaminated than that resulting from L-DOPA;it appears that this different behaviour may concern aspects related to the formation of the amine and also those related to its deamination and disposition, namely the processes involved in the access of newly-formed dopamine to MAO.

Regional haemodynamic effects of dopamine and its prodrugs L-dopa and gludopa in the rat and in the glycerol-treated rat as a model for acute renal failure

1. In this study the renal selectivity of dopamine and its prodrugs L-dopa and gludopa, with respect to their effects on regional blood flow, vascular resistance and central haemodynamics was investigated in normal rats and in rats with glycerol-induced acute renal failure (ARF). 2. In normal, anaesthetized rats, dopamine as well as its prodrugs caused a dose-dependent reduction of vascular resistance in the kidney (RR), mesentery (MR) and hindquarters (HQR) (dose range: dopamine: 0.1-5 mumol kg-1 h-1; L-dopa and gludopa: 1-200 mumol kg-1 h-1). Blood pressure and heart rate were affected at the highest dose only. 3. Administration of glycerol induced a preferential renal vasoconstriction; renal blood flow (-60%) and vascular resistance (+190%) were significantly more affected than MR (+40%) and HQR (+60%). This was only ameliorated by a low rate (10 mumol kg-1 h-1) infusion of gludopa: the glycerol-induced reduction of renal flow and increase in RR were significantly attenuated. A high dose of gludopa (100 mumol kg-1 h-1) or any dose of L-dopa or dopamine did not induce this beneficial effect. The glycerol-induced increase in MR and HQR was not attenuated by any of the treatments used. 4. The results indicate that gludopa is not renally selective at a pharmacodynamic level in normal, anaesthetized rats. Contrary to this, a low dose of gludopa does cause a renal selective vasodilatation and reduction of RR in rats with glycerol-induced ARF. This difference could be explained by a difference in renal vascular tone between normal rats and glycerol-induced ARF rats. A high dose ofgludopa does not cause these renal-selective effects: renal resistance and renal flow are at the same level as following glycerol and saline. This is probably due to the systemic effects of the released dopamine.

The dopamine prodrug, gludopa, decreases both renal and extrarenal noradrenaline spillover in conscious rabbits

1. Renal and total noradrenaline (NA) spillover rates were examined under control conditions and during graded infusions of gludopa (gamma-L-glutamyl-L-dopa) in conscious rabbits. 2. Gludopa infusion at 25 and 100 micrograms/kg per min did not alter mean arterial pressure (MAP) and heart rate (HR), but had significant dose-related effects on the renal dopamine (DA) system. At the high dose there were pronounced increases in urinary DA excretion (> 6000-fold) and renal DA content (> 100-fold); renal NA content doubled. 3. Renal venous DA increased after gludopa infusion, but arterial plasma DA concentrations were not significantly changed. Mean arterial plasma gludopa and L-dopa concentrations reached 890, 3190 ng/mL and 3, 10 ng/mL at low and high doses, respectively. 4. Gludopa resulted in a pronounced dose-dependent fall in renal NA spillover, which at 100 micrograms/kg per min accounted for almost half of the reduction in overall NA spillover rate. 5. The significant falls in renal and extrarenal NA spillover rate during gludopa infusion are consistent with suppression of renal and overall sympathetic activity. Gludopa-induced inhibition of renal NA spillover is likely to be due to the actions of DA generated in the kidney on presynaptic DA-2 and alpha-2 receptors. A central sympathoinhibitory mechanism may explain the reduced total NA spillover.