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Renalase is a recently identified FAD/NADH-dependent amine oxidase mainly expressed in kidney that is secreted into blood and urine where it was suggested to metabolize catecholamines. The present study evaluated central and peripheral dopaminergic activities in the renalase knockout (KO) mouse model and examined the changes induced by recombinant renalase (RR) administration on plasma and urine catecholamine levels. Compared with wild-type (WT) mice, KO mice presented increased plasma levels of epinephrine (Epi), norepinephrine (NE), and dopamine (DA) that were accompanied by increases in the urinary excretion of Epi, NE, DA. In addition, the KO mice presented an increase in urinary DA-to-l-3,4-dihydroxyphenylalanine (l-DOPA) ratios without changes in renal tubular aromatic-l-amino acid decarboxylase (AADC) activity. By contrast, the in vivo administration of RR (1.5 mg/kg sc) to KO mice was accompanied by significant decreases in plasma levels of Epi, DA, and l-DOPA as well as in urinary excretion of Epi, DA, and DA-to-l-DOPA ratios notwithstanding the accompanied increase in renal AADC activity. In addition, the increase in renal DA output observed in renalase KO mice was accompanied by an increase in the expression of the L-type amino acid transporter like (LAT) 1 that is reversed by the administration of RR in these animals. These results suggest that the overexpression of LAT1 in the renal cortex of the renalase KO mice might contribute to the enhanced l-DOPA availability/uptake and consequently to the activation of the renal dopaminergic system in the presence of renalase deficiency.

Renalase is a kidney-secreted catecholamines-degrading enzyme whose expression and activity are downregulated by increased dietary phosphate. A renalase knockout (KO) mouse model was used to explore the mechanisms mediating renalase's effect on phosphate excretion. Compared with wild-type (WT) mice maintained on a regular diet, KO mice show decreased serum PO4(-) (KO = 5.3 ± 0.2 vs. WT = 6.0 ± 0.1, n = 6; P < 0.04) and increased urinary PO4(-) excretion (urine PO4(-)/creatinine: KO = 7.7 ± 0.3 vs. WT = 6.1 ± 0.3, n = 6; P < 0.02). However, both WT and KO mice respond similarly to PO4(-) restriction by increasing renal COMT-1 activity and markedly decreasing PO4(-) excretion, which excludes an intrinsic renal defect in the KO. Renal sodium-phosphate cotransporter Npt2a, sodium proton exchanger NHE3 expression, and MAO-A and B activity did not differ between WT and KO. Only catechol-O-methyl transferase (COMT) expression and activity were significantly increased in KO mice. Despite that, urinary dopamine increased by twofold, whereas urinary l-DOPA excretion decreased by twofold in the KO mouse, indicating an upregulation of renal dopamine (DA) synthesis. These data indicate that renalase deficiency is associated with increased renal DA synthesis, stimulated PO4(-) excretion, and moderately severe hypophosphatemia. The signal to increase renal DA synthesis is strong since it overcomes a compensatory increase in COMT activity.

Aims: In 3/4 nephrectomized (3/4nx) rats the renal dopaminergic system was suggested to be involved in the adaptive increase of sodium excretion two weeks after renal mass ablation. The aim of the present study was to evaluate the renal adaptations in sodium handling and renal dopaminergic system activity in 3/4nx rats up to twenty-six weeks after surgery., Main Methods: The rats were placed in metabolic cages for the collection of 24 h urine for evaluation of sodium, dopamine, dopamine precursor and metabolites. Blood pressure, aromatic L-amino acid decarboxylase (AADC) activity in proximal tubules and the effect of dopamine D(1) receptor selective antagonist (Sch-23390) on natriuresis was evaluated., Key Findings: A time-dependent increase in both systolic and diastolic blood pressure was observed in 3/4nx rats, and this was accompanied by a decrease in urinary levels of dopamine and in renal AADC activity at twenty-six weeks after renal mass ablation. In contrast to what has been found two weeks after renal mass ablation, the natriuretic response to volume expansion was progressively reduced in 3/4nx rats at ten and twenty-six weeks after surgery and this was accompanied by insensitivity of natriuresis to Sch-23390., Significance: In conclusion the renal dopaminergic system activity is compromised in 3/4nx rats in a time-dependent manner after renal mass ablation. It is suggested that this may contribute to compromise sodium excretion and increase blood pressure, in chronic renal insufficiency.

Background: Dopamine of renal origin exerts natriuretic and diuretic effects by activating D1-like receptors located at various regions in the nephron. Two weeks after uninephrectomy the renal dopaminergic system was suggested to be involved in the adaptative increase of sodium excretion., Aim: The aim of the present study was to evaluate the renal adaptations in sodium handling and renal dopaminergic system activity in uninephrectomized (Unx) rats up to 26 weeks after the surgery., Results: A time-dependent increase in both systolic and diastolic blood pressure was observed in Unx rats up to 26 weeks after uninephrectomy. This was accompanied by a compensatory increase in aromatic L-amino acid decarboxylase at 2 weeks but not 10 and 26 weeks after uninephrectomy. In contrast to what has been found 2 weeks after uninephrectomy, at 10 and 26 weeks after surgery the natriuretic response to volume expansion was reduced in Unx rats and this was accompanied by insensitivity of natriuresis to dopamine D1 receptor selective antagonist (Sch23390)., Conclusion: A time-dependent decrease in dopamine sensitive natriuresis is observed in Unx rats throughout the 26 weeks after uninephectomy. It is suggested that this may contribute to compromise sodium excretion and increase blood pressure., (2007 S. Karger AG, Basel)

The present study evaluated the possible role of the renal dopaminergic system in the sodium retention of HgCl2-induced nephrotic syndrome. The time courses of urinary excretion of sodium, protein, dopamine and the precursor l-3,4-dihydroxyphenylalanine (L-Dopa) were evaluated in HgCl2-treated and control rats up to day 21. The renal aromatic l-amino acid decarboxylase (AADC) activity, the enzyme responsible for the synthesis of renal dopamine, was evaluated during negligible proteinuria accompanied with enhanced sodium retention (day 7), increased proteinuria accompanied with greatest sodium retention (day 14) as well as during increased proteinuria accompanied with negative sodium balance (day 21). Also, the influence of volume expansion (VE, 5% bw) and the effects of the D1-like agonist fenoldopam (10 microg kg bw(-1) min(-1)) on natriuresis and on proximal tubular Na+,K+-ATPase activity were examined on day 14. The daily urinary dopamine output and urinary dopamine/L-Dopa ratios were reduced in HgCl2-treated rats from day 2 and beyond. This was accompanied by a marked decrease in renal AADC throughout the study. During VE, the fenoldopam-induced inhibition of proximal tubular Na+,K+-ATPase activity was similar between HgCl2-treated and control rats. However, the urinary sodium excretion during fenoldopam infusion was markedly increased by 60% to 120% in control rats but was not altered in HgCl2-treated rats. It is concluded that HgCl2 nephrosis is associated with a blunted renal dopaminergic system activity. However, the lack of renal dopamine in HgCl2 nephrosis does not appear to be related with the overall renal sodium retention in a state of proteinuria.

Aim: The uninephrectomised and three-quarter nephrectomised (3/4nx) rats present dopamine-sensitive enhanced natriuresis. This is accompanied in uninephrectomised rats by a reduced jejunal Na(+),K(+)-ATPase activity with recovered sensitivity to inhibition by dopamine. The present study examined the jejunal Na(+),K(+)-ATPase activity and the role of dopamine in 3/4nx animals., Methods: Fourteen days after surgery, the L-amino acid decarboxylase activity (AADC) activity, the enzyme responsible for the synthesis of dopamine, and the Na(+),K(+)-ATPase activity, were determined in jejunal epithelial cells from 3/4nx and Sham rats. In addition, the effect of dopamine (1 micromol/L) on jejunal Na(+),K(+)-ATPase activity was evaluated in both groups., Results: The 3/4nx rats presented a reduced AADC activity in jejunal epithelial cells (V(max) in nmol/mg prot/15 min, 142 +/- 6 vs 190 +/- 10, P < 0.05). In addition, the jejunal Na(+),K(+)-ATPase activity was increased in 3/4nx rats (Pi release in nmol/mg prot/min, 137 +/- 1 vs 122 +/- 2, P < 0.05). However, dopamine was unable to inhibit the Na(+),K(+)-ATPase activity in jejunal epithelial cells from both 3/4nx and Sham animals., Conclusions: In contrast to uninephrectomy, the jejunal Na(+),K(+)-ATPase activity is increased in 3/4nx rats and is not sensitive to inhibition by dopamine.

Background: A primary tubular sodium handling abnormality has been implicated in the edema formation of nephrotic syndrome. Dopamine synthesized by renal proximal tubules behaves as an endogenous natriuretic hormone by activating D(1)-like receptors as a paracrine/autocrine substance., Methods: We examined the time courses of the urinary excretion of sodium, protein and dopamine in puromycin aminonucleoside (PAN)-treated and control rats. The rats were sacrificed during greatest sodium retention (day 7) as well as during negative sodium balance (day 14) for the evaluation of renal aromatic l-amino acid decarboxylase (AADC) activity, the enzyme responsible for the synthesis of renal dopamine. Also, the influence of volume expansion (VE) and the effects of the D(1)-like agonist fenoldopam (10 microg/kg bw/min) on natriuresis and on proximal tubular Na(+),K(+)-ATPase activity were examined on day 7., Results: The daily urinary excretion of dopamine was decreased in PAN-treated rats, from day 5 and beyond. This was accompanied by a marked decrease in the renal AADC activity, on days 7 and 14. During VE, the fenoldopam-induced decrease in proximal tubular Na(+),K(+)-ATPase activity was more pronounced in PAN-treated rats than in controls. However, the urinary sodium excretion during fenoldopam infusion was markedly increased in control rats but was not altered in PAN-treated animals., Conclusion: PAN nephrosis is associated with a blunted renal dopaminergic system activity which may contribute to enhance the proximal tubular Na(+),K(+)-ATPase activity. However, the lack of renal dopamine appears not to be related with the overall renal sodium retention in a state of proteinuria.

Background/aims: The present study examined the effects of chronic selective or combined inhibition of type A monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) on daily urinary excretion of dopamine and metabolites and on natriuresis and phosphaturia in 3/4 nephrectomized (3/4nx) and Sham rats., Methods: The 3/4nx and Sham rats were placed in metabolic cages and received the MAO-A-selective inhibitor Ro-411049 (7.5 mg x kg(-1) bid) and/or the COMT-selective inhibitor BIA 3-202 (30 mg x kg(-1) bid) orally for 3 days during high sodium diet., Results: Selective COMT inhibition increased the urinary excretion of the deaminated metabolite (3,4-dihydroxyphenylacetic acid, DOPAC) and decreased the urinary excretion of the methylated (3-methoxytyramine, 3-MT) and deaminated plus methylated metabolite (homovanillic acid, HVA) in both groups. Selective MAO-A inhibition increased the urinary excretion of 3-MT and reduced the urinary excretion of both DOPAC and HVA in either 3/4nx or Sham rats. Combined inhibition of MAO-A and COMT did not significantly change the urinary excretion of DOPAC and markedly decreased the urinary excretion of 3-MT and HVA in both groups. Selective or combined inhibition of MAO-A and COMT did not alter the daily urinary excretion of dopamine, sodium or phosphate in either 3/4nx or Sham rats., Conclusions: Chronic selective or combined inhibition of MAO-A and COMT is not of major importance in regulating the dopamine-dependent natriuresis and phosphaturia in either 3/4nx or Sham rats., (Copyright 2006 S. Karger AG, Basel.)

Background: The occurrence of complementary functions in sodium transport between the intestine and the kidney was suggested to occur when the renal function is immature or compromised and jejunal dopamine has been implicated in this renal-intestinal cross-talk. The jejunal sodium transport was not previously evaluated in the nephrotic syndrome., Methods: We examined the jejunal Na(+),K(+)-ATPase activity and the role of dopamine in puromycin aminonucleoside (PAN) and HgCl(2)-induced nephrotic syndrome rat models., Results: In both nephrotic syndrome rat models, the jejunal Na(+),K(+)-ATPase activity was reduced during greatest sodium retention and ascites accumulation (PAN nephrosis, day 7; HgCl(2) nephrosis, day 14), whereas during enhanced sodium excretion and ascites mobilization the jejunal Na(+),K(+)-ATPase activity was increased in HgCl(2) nephrosis (day 21) and was similar to controls in PAN nephrosis (day 14). In both PAN- and HgCl(2)-induced nephrosis, the jejunal aromatic L-amino acid decarboxylase (AADC) activity, the enzyme responsible for the synthesis of jejunal dopamine, did not differ from controls. In addition, the jejunal Na(+),K(+)-ATPase activity was not sensitive to inhibition by dopamine (1 microM) in both experimental groups throughout the study., Conclusions: In the nephrotic syndrome the jejunal Na(+),K(+)-ATPase activity may respond in a compensatory way to changes in extracellular volume, through dopamine-independent mechanisms., (Copyright 2005 S. Karger AG, Basel.)

Background: Renal dopamine exerts natriuretic and diuretic effects by activating D1-like receptors. Uninephrectomy results in increased renal dopaminergic activity and dopamine-sensitive enhanced natriuresis., Methods: The present study evaluated renal adaptations in sodium handling and the role of dopamine in rats submitted to (3/4) nephrectomy: right nephrectomy and excision of both poles of the left kidney ((3/4)nx rats)., Results: Two weeks after surgery the absolute urinary levels of dopamine were markedly reduced in (3/4)nx rats whereas the urinary dopamine excretion per % of residual nephrons was significantly increased in the remnant kidney of (3/4)nx rats. The V(max) values for renal aromatic L-amino acid decarboxylase, the enzyme responsible for the synthesis of renal dopamine, were decreased in (3/4)nx rats. Renal catechol-O-methyltransferase activity, the enzyme responsible for the methylation of dopamine, was increased in (3/4)nx rats whereas the renal activities of monoamine oxidases A and B did not differ between (3/4)nx and Sham animals. Volume expansion (5% body weight) resulted in similar natriuretic responses in (3/4)nx and Sham rats. During D1 antagonist administration (Sch-23390, 30 microg x h(-1) x kg(-1)) the natriuretic response to volume expansion was reduced in (3/4)nx rats more pronouncedly than in Sham animals., Conclusion: The decrease in absolute renal dopamine output in (3/4)nx rats is related with reduced renal synthesis and enhanced O-methylation of the amine. However, this is accompanied in (3/4)nx rats by increased renal dopamine excretion per residual nephrons and dopamine-sensitive enhanced natriuresis., (Copyright (c) 2005 S. Karger AG, Basel.)

Background: This work evaluates the effect of a low-sodium diet on clinical and neurohumoral parameters and on renal dopaminergic system activity in heart failure (HF) patients., Methods: We included 24 patients with mild-to-moderate stable HF with left ventricle ejection fraction <40%. Twelve patients were studied before and after a 15-day low-sodium diet; 12 maintained their usual diet. Serum sodium and creatinine, plasma l-DOPA, dopamine, its metabolites, BNP and aldosterone, and 24-h urinary sodium, creatinine, l-DOPA, dopamine and metabolites were measured., Results: The two groups were matched respecting to demographic and clinical parameters. Low-sodium diet caused significant reductions in weight, 24-h urinary volume and sodium and sodium fractional excretion. Renal delivery of l-DOPA and urinary excretion of l-DOPA significantly decreased while dopamine and metabolites were not affected. Urinary dopamine/l-DOPA and urinary dopamine/renal delivery of l-DOPA ratios increased, plasma l-DOPA decreased and plasma dopamine increased. Plasma aldosterone slightly rose, BNP decreased and noradrenaline and adrenaline increased. NYHA functional class was not affected by sodium restriction. Controls showed no differences., Conclusions: These results suggest that sodium restriction leads to activation of antinatriuretic antidiuretic systems in HF patients. However, renal ability to synthesize dopamine is increased in this condition, probably as a counter-regulatory mechanism.

Background: Patients with chronic glomerulonephritis exhibit salt-sensitive (SS) hypertension. In the early stage, however, the exact characteristics are still unclear. A decrease in renal dopamine production under basal conditions or after a sodium load has been reported in a subset of patients with SS primary hypertension., Aims: The present study examined 17 untreated IgA-N patients with near-normal renal function, to determine whether salt sensitivity appears before hypertension and whether this sensitivity is related to renal dopamine production., Methods: Daily urinary excretion of dopamine, the amine precursor--L-DOPA, and metabolites was monitored in conditions of basal sodium ingestion, followed by three consecutive 5-day periods of 100, 20 and 350 mmol/day sodium intake. The sodium sensitivity index (SSI) was evaluated in each patient. In addition, the patients were considered SS when showing an increase > or =5 mm Hg in 24-hour mean BP when they changed from a 20- to a 350-mmol/day sodium diet., Results: Urinary dopamine output was lower in SS than in salt-resistant patients throughout the study (p < 0.001). This was accompanied by lower creatinine clearance values and higher urinary protein excretion in SS IgA-N patients. A strong negative relationship was observed in these 17 IgA-N patients between the SSI and the daily urinary excretion of dopamine in conditions of both 20 mmol/day sodium intake (r2 = 0.592; p = 0.0003) and 350 mmol/day sodium diet (r2 = 0.352; p = 0.01). However, urinary dopamine output varied appropriately throughout the study in SS patients, in agreement with changes in sodium intake., Conclusion: We conclude that in IgA-N patients, a rightward shift in the 'pressure natriuresis' can appear before hypertension and is related with a reduced renal production of dopamine. It is suggested that decreased renal dopamine synthesis in SS IgA-N patients results from acquired tubulointerstitial injury. In contrast to what has been found in SS primary hypertension, renal dopamine may behave appropriately in SS IgA-N patients, as a compensatory hormone., (Copyright 2004 S. Karger AG, Basel)

Aim: Dopamine of renal origin reduces tubular sodium reabsorption and controls blood pressure. The present study evaluated renal dopaminergic activity and its response to uninephrectomy in Wistar Han rats from two suppliers, Harlan (W-H) and Charles River (W-CR)., Results: After uninephrectomy, the fractional excretion of sodium (FENa+) increased in both W-CR and W-H rats (W-CR: from 0.17 +/- 0.01 to 0.27 +/- 0.02%; W-H: from 0.39 +/- 0.04 to 0.54 +/- 0.04%, P < 0.05); however, in W-CR rats the FENa+ was lower than in W-H rats in both Sham and uninephrectomized (Unx) animals (P < 0.05). Systolic blood pressure in Unx W-CR rats was higher than in Unx W-H animals (131 +/- 3 vs. 122 +/- 2 mmHg, P < 0.05). Uninephrectomy was accompanied in W-H rats by increases in urinary levels (nmol g kidney(-1) day(-1)) of dopamine (10.3 +/- 0.5 vs. 8.3 +/- 0.7, P < 0.05) and 3,4-dihydroxyphenylacetic acid (DOPAC) (30.5 +/- 3.7 vs. 21.3 +/- 1.4, P < 0.05) and increases (P < 0.05) in maximal velocity values (Vmax in nmol mg prot(-1) 15 min(-1), 325 +/- 12 vs. 265 +/- 3) for renal aromatic L-amino acid decarboxylase (AADC), the enzyme responsible for the synthesis of renal dopamine. By contrast, in W-CR rats uninephrectomy did not change either the urinary levels of dopamine (7.1 +/- 0.5 vs. 7.6 +/- 0.7) and DOPAC (25.0 +/- 1.9 vs. 24.8 +/- 4.1) or AADC activity (Vmax 199 +/- 3 vs. 193 +/- 9). The Vmax values for renal AADC in W-CR rats were lower than those found in corresponding W-H animals., Conclusion: Wistar rats from different suppliers represent an important source of variability in the renal dopaminergic system activity. This may contribute to differences in sodium balance and blood pressure control in response to uninephrectomy.

Background: Dopamine of renal origin exerts natriuretic and diuretic actions by activating specific receptors located in the renal proximal tubular epithelial cells. Heart failure (HF) is accompanied by activation of several neurohumoral systems. The interaction of these systems with the renal dopaminergic system and its effect on sodium handling in HF are not clarified., Methods and Results: We studied 13 patients with decompensated New York Heart Association class III/IV HF and 17 sex- and age-matched patients with mild to moderate stable class I/II HF. We measured plasma catecholamines, aldosterone, type B natriuretic peptide (BNP), sodium, creatinine (UCr), and 24-hour urinary excretion of sodium, UCr, levo-3,4-dihydroxyphenylalanine (L-DOPA), 3-o -methyldopa, dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid and homovallinic acid, and norepinephrine. All patients had HF of ischemic etiology. No statistically significant differences were found between the groups with respect to urine volume (1.79 +/- 0.23 L x d(-1) vs 2.20 +/- 0.18 L x d(-1), P =.18) and urinary sodium (161.3 +/- 27.5 mmol x d(-1) vs 232.9 +/- 28.8 mmol x d(-1), P =.12). Urinary L-DOPA was significantly lower in patients with decompensated class III/IV HF than in the other group (79.0 +/- 13.8 nmol x g UCr(-1) vs 108.4 +/- 10.3 nmol x g UCr(-1), P =.04). Urinary dopamine showed a nonstatistically significant trend to be slightly higher (1294.3 +/- 188.5 nmol x g UCr(-1) vs 953.2 +/- 107.4 nmol x g UCr(-1), P =.14). Consequently, urinary dopamine/L-DOPA ratios were markedly higher in patients with decompensated class III/IV HF than in the other patients (20.6 +/- 3.4 vs 9.0 +/- 0.9, P <.001). Plasma L-DOPA (38.1 +/- 4.4 pmol x mL(-1) vs 40.0 +/- 3.0 pmol x mL(-1), P =.48), dopamine (37.0 +/- 6.3 pmol x mL(-1) vs 41.1 +/- 2.6 pmol x mL(-1), P =.53), 3,4-dihydroxyphenylacetic acid (51.7 +/- 11.7 pmol x mL(-1) vs 56.5 +/- 5.4 pmol x mL(-1), P =.09), and norepinephrine (9.5 +/- 2.4 pmol x mL(-1) vs 5.6 +/- 1.0 pmol x mL(-1), P =.12) did not differ between groups. Plasma aldosterone (180.2 +/- 28.0 pg x mL(-1) vs 69.9 +/- 13.3 pg x mL(-1), P <.001) and BNP (677.5 +/- 133.9 pg x mL(-1) vs 389.4 +/- 88.4 pg x mL(-1), P <.04) levels were higher in the decompensated class III/IV HF group than in the other group, whereas serum sodium was lower (137.3 +/- 1.2 mmol x L(-1) vs 143.2 +/- 1.0 mmol x L(-1), P =.001)., Conclusions: These results suggest that, in patients with HF, the increased renal utilization of L-DOPA may constitute a compensatory mechanism, activated in response to stimuli leading to sodium reabsorption.

The present study evaluates renal dopaminergic activity in 23 patients with heart failure (HF), 10 age-matched controls, and 10 young subjects during normal-salt (NS) intake and after 8 days of low-salt (LS) intake (patients with HF and age-matched controls only). LS intake produced a marked reduction in urine volume in patients with HF but failed to affect urine volume in age-matched controls. Urinary sodium and fractional excretion of sodium were markedly reduced by LS intake in patients with HF and age-matched controls. Daily urinary excretion of L-3,4-dihydroxyphenylalanine (L-dopa) and dopamine was lower in patients with HF than in age-matched controls. LS intake failed to alter L-dopa and dopamine urinary excretion in control subjects. In patients with HF, LS intake produced a significant decrease in urinary L-dopa excretion, but failed to alter the urinary excretion of dopamine. No significant differences were observed in urinary L-dopa, dopamine, and dopamine metabolite levels between aged controls and young healthy subjects. Urinary dopamine-L-dopa ratios in patients with HF on LS intake (24.5 +/- 7.1) were significantly greater than those with NS intake (11.6 +/- 1.3). Urinary dopamine-L-dopa ratios in old control subjects (LS, 9.7 +/- 1.3; NS, 9.3 +/- 1.1) did not differ from those in young healthy subjects (9.2 +/- 0.8). LS intake produced a marked increase in plasma aldosterone levels in both patients with HF (84.6 +/- 14.4 to 148.2 +/- 20.4 pg/mL; P = 0.0008) and controls (102.1 +/- 13.4 to 151.6 +/- 15.7 pg/mL; P < 0.04). Plasma norepinephrine levels were not significantly affected by LS intake in controls (5.1 +/- 1.62 to 6.3 +/- 1.6 pmol/mL; P = 0.22), but were significantly increased in patients with HF (5.8 +/- 0.8 to 7.1 +/- 0.9 pmol/mL; P = 0.04). In conclusion, patients with HF are endowed with an enhanced ability to take up (or decarboxylate) filtered L-dopa, which might counterbalance the reduced renal delivery of L-dopa, contributing to a relative preservation of dopamine synthesis. This may result as a compensatory mechanism, activated by stimuli leading to sodium reabsorption. Age seems to have no influence on renal dopamine production.

The benefits of tailoring therapy with vasodilators in patients with severe heart failure are well documented, but this may lead to neurohormonal activation and sodium retention. Renal dopamine has local natriuretic actions and interacts with other hormones involved in renal sodium handling. The aim of the present work was to determine the effects of arterial underfilling induced by vasodilator therapy on renal sodium handling, neurohormonal activation and the activity of the renal dopaminergic system in patients with severe heart failure. For this purpose we monitored haemodynamic parameters, plasma levels of type B natriuretic peptide (BNP), catecholamines, aldosterone, renin activity (PRA), sodium and creatinine, and urinary excretion of sodium, creatinine, L-DOPA, dopamine and its metabolites, before initiation of sodium nitroprusside therapy and every 6 h thereafter (for 42 h), and again after 5 days of angiotensin-converting enzyme (ACE) inhibition, in 10 male patients with severe heart failure. The results of nitroprusside therapy were a marked increase in cardiac index and a substantial decrease in systemic vascular resistance index. Plasma levels of BNP decreased significantly, while PRA, noradrenaline and aldosterone showed marked increases, resulting in a substantial reduction in urinary sodium excretion. Creatinine clearance was not affected. Urinary dopamine and dopamine metabolites increased in response to nitroprusside therapy. After 5 days of ACE inhibition, urinary sodium returned to baseline values, while urinary dopamine was markedly reduced. These results suggest that the renal dopaminergic system is activated in patients with severe heart failure by stimuli leading to sodium renal reabsorption.

The present report addresses the status of the renal dopaminergic system activity in patients afflicted with different renal disorders and in the remnant kidney of uninephrectomized (UNX) rats, based on the urinary excretion of L-DOPA, dopamine and amine metabolites. In renal transplant recipients with good recovery of graft function (group 1, n=11), the daily urinary excretion of DOPAC, but not that of HVA, was found to increase progressively throughout the first 12 days post-transplantation from 698+/-57 nmol in the first day to 3498+/-414 nmol on day 9, and then remained constant until day 12. This resulted in a 6-fold increase in the urinary DOPAC/dopamine ratios. In renal transplant recipients with acute tubular necrosis (group 2, n=8), the urinary levels of dopamine, DOPAC and HVA were approximately 30% of those in group 1. In a group of 28 patients with chronic renal parenchymal disorders, the daily urinary excretion of L-DOPA, free dopamine and dopamine metabolites (DOPAC and HVA) correlated positively with the degree of deterioration of renal function (P<0.01). However, the U(Dopamine/(L)-DOPA) and U(DOPAC/Dopamine) ratios in patients with chronic renal insufficiency were found to be similar to those observed in patients with normal renal function. In 14 IgA nephropathy (IgA-N) patients with near normal renal function, the changes in 24 h mean blood pressure when going from 20 to 350 mmol/day sodium intake correlated negatively with the daily urinary excretion of dopamine (r(2)=0.597, P<0.01). The urinary excretion of L-DOPA and dopamine in IgA-N patients with salt-sensitive (SS) blood pressure was lower than in salt-resistant (SR) patients (P<0.05), irrespective of their daily sodium intake. However, the rise in urinary dopamine output during salt loading (from 20 to 350 mmol/day) was greater (P<0.05) in IgA-N SS patients (21.2+/-2.5% increase) than in SR patients (6.3+/-1.4% increase). Fifteen days after the surgery, uninephrectomy (UNX) in the rat was accompanied by an enhanced (P<0.05) urinary excretion of dopamine (36+/-3 vs 26+/-2), DOPAC (124+/-11 vs 69+/-6) and HVA (611+/-42 vs 354+/-7) (nmol/g kidney/kg body weight). This was accompanied by an increase in V(max) values for renal aromatic L-amino acid decarboxylase in the remnant kidney of UNX rats (P<0.05). Sch 23390, a D1 dopamine receptor antagonist, produced a marked reduction in the urinary excretion of sodium in UNX rats, whereas in sham-operated rats the decrease in urinary sodium did not attain a significant difference. It is concluded that the study of the renal dopaminergic system in patients afflicted with renal parenchymal disorders should address parameters other than free urinary dopamine, namely the urinary excretion of L-DOPA and dopamine metabolites (DOPAC and HVA). It is also suggested that in SS hypertension of chronic renal parenchymal diseases, renal dopamine produced in the residual tubular units may be enhanced during a sodium challenge, thus behaving appropriately as a compensatory natriuretic hormone.

The present study evaluated renal and intestinal adaptations in sodium handling in uninephrectomized (Unx) rats and the role of dopamine. Two weeks after uninephrectomy, the remnant kidney in Unx rats weighed 33 +/- 2% more than the corresponding kidney in sham-operated (Sham) animals. This was accompanied by increases in urinary levels of dopamine and major metabolites [3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid] and increases in maximal velocity values (169 vs. 115 nmol. mg protein(-1). 15 min(-1)) for renal aromatic L-amino acid decarboxylase, the enzyme responsible for the synthesis of renal dopamine. High salt (HS) intake increased (P < 0.05) the urinary excretion of dopamine and DOPAC in Unx and Sham rats. However, the urinary levels of L-3,4-dihydroxyphenylalanine, dopamine, and DOPAC in Sham rats during HS intake were lower than in Unx rats. Blockade of dopamine D(1) receptors (Sch-23390, 2 x 30 microg/kg) reduced the urinary excretion of sodium in Unx (31% decrease) more pronouncedly than in Sham (19% decrease) rats. However, inhibition of renal Na(+)-K(+)-ATPase activity by dopamine was of similar magnitude in Unx and Sham rats. In parallel, it was observed that uninephrectomy resulted in a significant reduction in jejunal sodium absorption and Na(+)-K(+)-ATPase activity in jejunal epithelial cells. In jejunal epithelial cells from Sham rats, dopamine (1 microM) failed to inhibit Na(+)-K(+)-ATPase activity, whereas in Unx rats it produced a significant reduction. It is concluded that uninephrectomy results in increased renal dopaminergic activity and dopamine-sensitive enhanced natriuresis. Furthermore, it is suggested that decreased jejunal absorption of sodium may take place in response to partial renal ablation, as an example of renal-intestinal cross talk.

Left ventricular systolic dysfunction (LVSD) following acute myocardial infarction (AMI), by decreasing renal blood flow, may interfere with renal L-DOPA availability and, consequently, dopamine synthesis. Dopamine of renal origin exerts local natriuretic effects. We studied 17 post-AMI patients with asymptomatic LVSD (ejection fraction < 40%) and 14 without (ejection fraction > or = 40%), measuring 24-h urinary excretions of L-DOPA, dopamine and its metabolites, and plasma levels of the amines, amine derivatives and type-B natriuretic peptide (BNP). Baseline characteristics were well balanced between the two groups. No differences were observed in urinary volume and sodium and creatinine excretions. The group with asymptomatic LVSD presented lower urinary excretion of L-DOPA (66.8 +/- 10.1 versus 115.3 +/- 21.9 nmol x day(-1), P = 0.04), whereas plasma levels of L-DOPA were identical in both groups. Urinary dopamine was similar in the two groups (1124.2 +/- 172.4 versus 1049.0 +/- 146.4 nmol x day(-1), P = 0.86), resulting in higher urinary dopamine/L-DOPA ratios in patients with asymptomatic LVSD (20.4 +/- 3.0 versus 9.9 +/- 0.8, P < 0.001). Plasma levels of BNP were higher in the asymptomatic LVSD group (348.5 +/- 47.3 versus 146.8 +/- 21.9 microg x ml(-1), P = 0.003). Ejection fraction was negatively correlated with both plasma levels of BNP and urinary dopamine/L-DOPA ratios. Renal dopamine production is well preserved in patients with asymptomatic LVSD and increased neurohumoral activation, despite reduced urinary excretion of its precursor. This suggests that renal uptake and/or decarboxylation of L-DOPA is enhanced in this condition, as a compensatory mechanism, contributing to preservation of urinary sodium excretion.

The present study evaluated the activity of jejunal Na+-K+-ATPase and its sensitivity to inhibition by dopamine in spontaneous hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats during low (LS), normal (NS) and high (HS) salt intake. Basal jejunal Na+-K+-ATPase activity in SHR on LS intake was higher than in WKY rats. Jejunal Na+-K+-ATPase activity in WKY rats, but not in SHR, on LS intake was significantly reduced (20% decrease) by dopamine (1 microM) and SKF 38393 (10 nM), but not quinerolane (10 nM), this being antagonized the D1 receptor antagonist (SKF 83566). Changing from LS to NS or HS intake in WKY rats increased basal jejunal Na+-K+-ATPase activity and attenuated the inhibitory effect of dopamine. In SHR, changing from LS to NS or HS intake increased basal jejunal Na+-K+-ATPase activity. Basal renal Na+-K+-ATPase activity in SHR on LS intake was similar to that in WKY rats and was insensitive to inhibition by dopamine. Changing from LS to NS or HS intake in WKY rats increased basal renal Na+-K+-ATPase activity without affecting the inhibitory effect of dopamine. In SHR, changing from LS to NS or HS intake failed to alter basal renal Na+-K+-ATPase activity. It is concluded that inhibition of jejunal Na+-K+ ATPase activity by D1 dopamine receptor activation is dependent on salt intake in WKY rats, and SHR animals fail to respond to dopamine, irrespective of their salt intake.

The recovery of renal function in renal transplant recipients is accompanied by an enhanced ability to synthesize dopamine (DA), which may contribute to maintain sodium homeostasis. Patients suffering from chronic renal parenchymal disease, a well-recognized form of salt sensitive (SS) hypertension, have a reduced ability to produce DA that correlates well with deterioration of renal function. In patients afflicted with IgA nephropathy, but normal renal function, urinary excretion of DA correlated positively with BP responses to changes from 200 to 20 mmol/day salt intake. In black salt resistant (SR) normotensives (NT) and SR hypertensives, under low salt intake (40 mmol/day), but not SS-NT and SS-HT, the saline infusion induced increments of DA and DOPAC urinary excretion correlated significantly with increments of sodium urinary excretion and sodium fractional excretion. Patients afflicted with heart failure (HF) have a reduced delivery of L-DOPA to the kidney, accompanied by an increase in DA/L-DOPA urinary ratios. This suggests that HF patients have an increased ability to take up or decarboxylate L-DOPA. Sodium restriction resulted in a significant decrease in urinary L-DOPA, DA and DOPAC in HF patients, suggesting that the system responds to sodium. It is concluded that activity of renal dopaminergic system may be altered in SS subjects, despite the level of their BP, and an enhanced delivery of L-DOPA to the kidney may be beneficial in edema formation states.

The present study examined renal dopaminergic activity and its response to high salt (HS) intake in adult (6-month-old) and old (24-month-old) Fischer 344 rats. Daily urinary excretion of L-3, 4-dihydroxyphenylalanine (L-DOPA), dopamine, and its metabolites 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid was similar in adult and old rats; by contrast, daily urinary excretion of norepinephrine in old rats was almost twice that in adult animals. HS intake (1% NaCl) over a period of 24 hours resulted in a 2-fold increase in the urinary excretion of dopamine, DOPAC, and norepinephrine in adult animals but not in old animals. Norepinephrine and L-DOPA plasma levels did not change during HS intake and were similar in both groups of rats. The natriuretic response to an HS intake in old rats (from 4.7+/-0.4 to 10.7+/-2.0 nmol. kg(-1). d(-1); Delta=6.0+/-0.9 nmol. kg(-1). d(-1)) was less than in adult rats (from 5.2+/-0.4 to 13.5+/-2.5 nmol. kg(-1). d(-1); Delta=8.3+/-0.8 nmol. kg(-1). d(-1)). A diuretic response to HS intake was observed in adult rats (from 20.9+/-2.3 to 37.6+/-2.8 mL. kg(-1). d(-1)) but not in old rats (from 37.7+/-5.7 to 42.3+/-6. 0 mL. kg(-1). d(-1)). Dopamine levels and dopamine/L-DOPA ratios in the renal cortex of old rats were greater than in adult rats. HS intake increased both dopamine levels and dopamine/L-DOPA ratios in the renal cortex of adult rats but not in old rats. Aromatic L-amino acid decarboxylase activity was higher in old rats than in adult rats; HS intake increased L-amino acid decarboxylase activity (nmol. mg protein(-1). l5 min(-1)) in adult rats (from 67+/-1 to 93+/-1) but not in old rats (from 86+/-2 to 87+/-2). Dopamine inhibited Na(+),K(+)-ATPase activity in proximal tubules obtained from adult rats, but it failed to exert such an inhibitory effect in old rats. It is concluded that renal dopaminergic tonus in old rats is higher than in adult rats but fails to respond to HS intake as observed in adult rats. This may be due in part to the inability of dopamine to inhibit Na(+),K(+)-ATPase activity in old rats.

Renal vasoconstriction and anti-natriuresis conditioned by radiographic contrast agents (CA) may be antagonised by the administration of exogenous dopamine. However, the influence of CA on the activity of renal synthesis of dopamine has not been studied. This study assessed the daily urinary excretion of dopamine, its precursor. L-3, 4-dihydroxyphenylaline (L-DOPA), and its metabolites (acid 3, 4-dihydroxyphenylacetic, DOPAC; homovanillic acid, HVA) 24 hours before and 48 hours following administration of a non ionic and hyposmolar (lopromide) CA in patients (n = 10; average age 61.3 +/- 4.3 years) submitted to coronary angiography. Urinary excretion of noradrenalin, a marker of sympathetic activity, was also assessed during the same period. The deputation of creatinine (Ccr) and the urinary excretion of sodium (UNa+) lowered after the administration of the CA (Ccr, 79.2 +/- 10.2 vs 72.2 +/- 9.6 ml/min/1.73 m2, p < 0.05; UNa+, 112.8 +/- 9.6 vs 61.7 +/- 25.1 mmol/24 h, p < 0.05). On the contrary, the urinary excretion of potassium increased in the period of 24 h following the administration of the AC (31.7 +/- 5.2 vs 103.8 +/- 10.8 mmol/24 h, p < 0.05). There was an increase in the urinary excretion of dopamine as well as noradrelalin during the 24 hour period following the administration of the CA (dopamine, 1260.2 +/- 196.8 vs 1571.5 +/- 170.2 mmol/24 h p < 0.5; noradrenalin, 186 +/- 36.6 mmol/24 h, p < 0.05). On the contrary, the urinary excretion of L-DOPA lowered after the administration of the CA (115.4 +/- 25.5 vs 80.5 +/- 13.2 mmol/24 h, p < 0.05). These results conditioned an increase in the dopamine/L-DOPA ratio in the urine, after the administration of the CA (12.2 +/- 1.5 vs 22.2 +/- 4.5 mmol/24 h, p < 0.05). In conclusion, the administration of CA is accompanied by an increase in the renal production of dopamine which, in these conditions, may act as a compensatory natriuretic hormone.

Background: Although intrarenal dopamine is known to behave as an endogenous natriuretic hormone the role of the renal dopaminergic system in the sodium handling of nephrotic oedema remains unknown., Study Design: We monitored the daily urinary excretion of free dopamine, L-DOPA-its precursor, and its metabolites, DOPAC and HVA, during sodium retention accompanying the nephrotic state and natriuresis leading to oedema mobilization in eight patients (mean age 8.0+/-2.4 years) with drug-induced remission of minimal-change nephrotic syndrome (MCNS)., Results: During natriuresis the urinary levels of dopamine did not increase in parallel with sodium excretion in any of the eight patients studied. Moreover, after remission of the nephrotic syndrome the urinary levels of dopamine were significantly lower than during the nephrotic state (1565.3+/-361.7 vs 2416.1+/-558.4, P= 0.02). In contrast, the urinary excretion of L-DOPA increased markedly during natriuresis resulting from remission of proteinuria (from 87.0+/-40.5 up to 296.9+/-86.3 nmol/24 h; P< 0.01)., Conclusion: We conclude that the natriuretic response resulting from drug-induced remission of proteinuria in MCNS is accompanied by a decrease in the renal uptake/decarboxylation of L-DOPA to dopamine.

Background: Chronic renal parenchymal diseases are accompanied by a progressive loss of tubular units endowed with the ability to synthesise dopamine from L-3,4-dihydroxyphenylalanine (L-DOPA), and preliminary evidence has suggested that the urinary excretion of free dopamine may be reduced in these disorders. However, it is well recognized now that under in vitro conditions, dopamine newly synthesised in tubular epithelial cells undergoes extensive deamination to 3,4-dihydroxyphenylacetic acid (DOPAC) by monoamine oxidase (MAO); a small amount of the amine is converted to homovanillic acid by both MAO and catechol-O-methyltransferase (COMT) and a minor amount is methylated to 3-methoxytyramine., Aims: The present study aimed at examining the relationship between renal function and daily urinary levels of L-DOPA, free dopamine and its main metabolites, DOPAC and homovanillic acid (HVA) in patients (n = 28) with chronic renal parenchymal disease, in conditions of controlled sodium, potassium and phosphate intake. The levels of 5-hydroxyindolacetic acid (5-HIAA) were also evaluated in the same cohort of patients., Results: The patients were divided in two groups according to creatinine clearance (group 1, 39 +/- 6 ml/min/1.73 m2, n = 14; group 2, 139 +/- 6 ml/min/1.73 m2, n = 14). In patients of group 1, the urinary levels of L-DOPA, dopamine and DOPAC (in nmol/24 h) were significantly lower (60% reduction) than in patients in group 2 (L-DOPA, 134 +/- 36 vs. 308 +/- 51; dopamine, 759 +/- 175 vs. 1,936 +/- 117; DOPAC 2,595 +/- 340 vs. 7,938 +/- 833). Also, the urinary excretion of HVA in patients group 1 was significantly lower (40% reduction) than in patients of group 2 (17,434 +/- 2,455 vs. 27,179 +/- 2,271 nmol/24 h). By contrast, no significant difference was observed in daily urinary excretion of 5-HIAA between the two groups of patients (group 1,27,280 +/- 3,721 nmol/day; group 2, 28,851 +/- 2,854 nmol/day). A positive linear relationship was found in these 28 patients between the creatinine clearance and the daily urinary excretion of L-DOPA (r = 0.64, p < 0.001), free dopamine (r = 0.83; p < 0.0001), DOPAC (r = 0.86; p < 0.0001) and HVA (r = 0.65; p < 0.002), but not with that of 5-HIAA (r = 0.14; ns). The Udopamine:L-DOPA and UDOPAC/dopamine ratios were found to be similar in both groups of patients whereas the UHVA/DOPAC ratios in patients of group 1 were found greater than in group 2 (p < 0.05)., Conclusion: Patients suffering from chronic parenchymal disease with a compromised renal function present with a reduced activity of their renal dopaminergic system which correlates well with the degree of deterioration of renal function. The reduced urinary dopamine output in renal insufficiency is not attributable to enhanced metabolism of renal dopamine. We suggest that the urinary levels of DOPAC may represent a useful parameter for the assessment of renal dopamine synthesis.

Background: The urinary excretion of free dopamine has been used as an index of the renal synthesis of amine. However, it is now well recognized that in the kidney, newly-formed dopamine is significantly inactivated through deamination to 3,4-dihydroxyphenylacetic acid (DOPAC) by monoamine oxidase (MAO). The aim of the present study was to assess the renal dopaminergic system activity during the recovery of renal function in kidney transplant recipients and to assess which parameters are appropriate for the evaluation of renal amine synthesis under these conditions., Methods: Twenty-four-hour urinary excretion of L-DOPA, dopamine and its metabolites (DOPAC; 3-MT; HVA) were continuously monitored in 19 renal transplant recipients from the first day of surgery until the twelfth day post-transplantation., Results: In 11 patients (Group 1), renal function consistently recovered throughout the study (plasma creatinine levels decreased from 6.2 +/- 0.4 to 2.1 +/- 0.1 mg/dl). Eight patients presented with acute tubular necrosis (Group 2) and minimal renal function was maintained until the twelfth post-operative day. The urinary excretion of L-DOPA did not differ throughout the study between the two groups of patients. In contrast, the 24-h urinary levels of dopamine, DOPAC and HVA were significantly higher throughout the study in patients of Group 1: dopamine (Group 1, 179 +/- 26 to 422 +/- 51 nmol/24 h; Group 2, 25 +/- 3 to 57 +/- 13 nmol/ 24 h), DOPAC (Group 1, 698 +/- 57 to 3487 +/- 414 nmol/ 24 h; Group 2, 158 +/- 22 to 1014 +/- 193 nmol/24 h) and HVA (Group 1, 13,058 +/- 1199 to 20,387 +/- 1559 nmol/ 24 h; Group 2, 4140 +/- 848 to 15,219 +/- 1037 nmol/24 h)., Conclusions: The recovery of renal function in renal transplant recipients is accompanied by an enhanced ability to synthesize dopamine and inactivate it to DOPAC and HVA. It is suggested that the urinary levels of DOPAC may be a useful parameter for the assessment of dopamine formation in renal tissues.

1. The present study has examined the daily urinary excretion of L-DOPA, dopamine and its metabolites (DOPAC, 3-MT and HVA) during normal salt (NS) and high salt(HS) diets. 2. Daily urinary excretion of L-DOPA, DA, DOPAC, 3-MT and HVA during the 4-day period of NS diet averaged, respectively, 7.6 +/- 0.4, 71 +/- 5, 217 +/- 22, 570 +/- 90 and 1217 +/- 110 nmol/kg/day. The slight increase in the urinary excretion of DA, DOPAC and 3-MT (16% to 42% increase), when rats were fed a HS diet, did not achieve statistical significance. 3. In contrast, the urinary levels of L-DOPA during the HS diet period (11 +/- 1 nmol/kg/day) were found to be significantly higher than during the NS diet period; the maximal increase in the urinary excretion of L-DOPA (93% increase) was observed in the first day and then a progressive decline was observed towards the end of the HS intake period. 4. During the first 5 days of the HS intake period, the urine output of noradrenaline (NA) was found to increase (27% to 83%) and then to progressively decline to baseline values (13.5 +/- 0.7 nmol/ kg/day). Urinary excretion of adrenaline (AD) during the HS intake period was found to increase (72% to 146%); the mean daily urinary excretion of AD during the NS diet period averaged 2.5 +/- 0.4 nmol/ kg/day. NS and DA contents in the kidney of rats on a NS diet were not significantly different from that of rats in a HS diet. 6. It is concluded that long-term HS intake in Wistar rats fail to change the urinary excretion of DA and of its metabolites (DOPAC, 3-MT and HVA). Furthermore, the discrepant profile in the urinary excretion of L-DOPA and DA during HS intake might be related to a reduction in the tubular uptake of the amino acid, rather than reflecting a decrease in its decarboxylation.

1. Administration of cyclosporine A (CsA; 50 mg kg-1 day-1, s.c.) for 14 days produced an increase in both systolic (SBP) and diastolic (DBP) blood pressure by 60 and 25 mmHg, respectively. The urinary excretion of dopamine, DOPAC and HVA was reduced from day 5-6 of CsA administration onwards (dopamine from 19 to 46%, DOPAC from 16 to 48%; HVA from 18 to 42%). In vehicle-treated rats, the urinary excretion of dopamine and DOPAC increased (from 7 to 60%) from day 5 onwards; by contrast, the urinary excretion of HVA was reduced (from 27 to 60%) during the second week. 2. No significant difference was observed between the Vmax and Km values of renal aromatic L-amino acid decarboxylase (AAAD) in rats treated with CsA for 7 and 14 days or with vehicle. 3. Km and Vmax of monoamine oxidase types A and B did not differ significantly between rats treated with CsA for 7 and 14 days or with vehicle. 4. Maximal catechol-O-methyltransferase activity (Vmax) in homogenates of renal tissues obtained from rats treated with CsA for 7 or 14 days was significantly higher than that in vehicle-treated rats; Km (22.3 +/- 1.5 microM) values for COMT did not differ between the three groups of rats. 5. The accumulation of newly-formed dopamine and DOPAC in cortical tissues of rats treated with CsA for 14 days was three to four times higher than in controls. The outflow of both dopamine and DOPAC declined progressively with time and reflected the amine and amine metabolite tissue contents. No significant difference was observed between the DOPAC/dopamine ratios in the perifusate of renal tissues obtained from CsA- and vehicle-treated rats. In addition, no significant differences were observed in k values or in the slope of decline of both DA and DOPAC between experiments performed with CsA and vehicle-treated animals. 6. The Vmax for the saturable component of L-3,4-dihydroxyphenylalanine (L-DOPA) uptake in renal tubules from rats treated with CsA was twice that of vehicle-treated animals. Km in CsA- and vehicle-treated rats did not differ. 7. The decrease in the urinary excretion of sodium and an increase in blood pressure during CsA treatment was accompanied by a reduction in daily urinary excretion of dopamine. This appears to result from a reduction in the amount of L-DOPA made available to the kidney and does not involve changes in tubular AAAD, the availability of dopamine to leave the renal cells and dopamine metabolism. The enhanced ability of the renal tissues of CsA-treated animals to synthesize dopamine, when exogenous L-DOPA is provided, results from an enhanced activity of the uptake process of L-DOPA in renal tubular cells.

The present work examines the possibility of whether the reciprocal effects of dopamine (DA) and 5-hydroxytryptamine (5-HT) are only dependent on the antagonistic nature of the signal resulting from the activation of their specific receptors or may also result from a competitive type of inhibition at different levels of the synthetic and metabolic pathways shared by DA and 5-HT. Studies performed in isolated proximal convoluted tubules (PCT) have shown that L-5-HTP and L-DOPA use the same transporter in order to be taken up into the cell and both L-DOPA and L-5-HTP exert a competitive type of inhibition upon their cellular uptake. The decrease in the formation of 5-HT in isolated PCT induced by L-DOPA reflects most probably a reduction in the intracellular availability of L-5-HTP. However, in experiments conducted in homogenates of PCT L-DOPA was found to be a better substrate for AAAD than L-5-HTP. Apart from sharing a common synthetic pathway, DA and 5-HT also share a common metabolic pathway; type A monoamine oxidase (MAO-A), the predominant form of MAO in rat renal tissues, converts DA into 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-HT into 5-hydroxyindolacetic acid (5-HIAA). However, in contrast to 5-HT, DA can be metabolized by MAO-B and catechol-O-methyltransferase. Inhibition of MAO-A was found to produce a 2-fold increase in the urinary excretion of 5-HT; this increase in the urinary excretion of 5-HT was accompanied by an unexpected reduction in the urinary excretion of DA.(ABSTRACT TRUNCATED AT 250 WORDS)

1. The present paper reports changes in the urinary excretion of dopamine, 5-hydroxytryptamine and amine metabolites in nitric oxide deprived hypertensive rats during long-term administration of NG-nitro-L-arginine methyl ester (L-NAME). Aromatic L-amino acid decarboxylase (AAAD) activity in renal tissues and the ability of newly-formed dopamine to leave the cellular compartment where the synthesis of the amine has occurred were also determined. 2. Twenty four hours after exposure to L-NAME, both systolic (SBP) and diastolic (DBP) blood pressure were increased by 20 mmHg; heart rate was slightly decreased. During the next 13 days both SBP and DBP increased progressively reaching 170 +/- 3 and 116 +/- 3 mmHg, respectively. 3. Baseline urinary excretion of L-DOPA, dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT) and homovanillic acid (HVA) during the 4 day period of stabilization averaged 4.4 +/- 0.5, 13.8 +/- 0.3, 37.4 +/- 0.8, 180.0 +/- 2.7 and 206.1 +/- 6.7 nmol day-1, respectively. The urinary excretion of L-DOPA, dopamine and DOPAC, but not that of 3-MT and HVA, were increased from day 6-8 of L-NAME administration onwards (L-DOPA, up to 13.4 +/- 2.1; dopamine, up to 23.0 +/- 1.6; DOPAC, up to 62.8 +/- 3.7 nmol day-1). Baseline daily urinary excretion of 5-hydroxytryptamine and 5-hydroxyindolacetic acid (5-HIAA) averaged 73.5 +/- 1.1 and 241.7 +/- 5.4 nmol day-1, respectively. During the first week of L-NAME administration, the urinary excretion of both 5-hydroxytryptamine and 5-HIAA did not change significantly; however, as was found with dopamine and DOPAC, changes in the urinary excretion of 5-hydroxytryptamine were evident during the second week of L-NAME administration. 4. In experiments performed on homogenates of isolated renal tubules, the decarboxylation of L-DOPA to dopamine was dependent on the concentration of L-DOPA used (10 to 5000 microM) and saturable at 1000 microM. AAAD activity as determined in homogenates (Vmax, in nmol mg-1 protein h-1; Km in microM) was significantly (P < 0.01) higher in rats given L-NAME for 14 days (Vmax = 25 +/- 2; Km = 72 +/- 10) than in control rats (Vmax = 14 +/- 1; Km = 63 +/- 7), rats given L-NAME for 7 days (Vmax = 15 +/- 1; Km = 69 +/- 5) and rats given L-NAME plus L-arginine (Vmax = 13 +/- 1; Km = 60 +/- 3) for 14 days. 5. A considerable amount of the total dopamine formed from added L-DOPA in kidney slices escaped into the incubation medium. The application of the Michaelis-Menten equation to the net transport of newly-formed dopamine allowed the identification of a saturable (carrier-mediated transfer) and a non-saturable component (diffusion). No significant differences in the diffusional rate of transfer(0.14 +/- 0.02 micro mol-1) were observed between the four experimental groups. However, the saturable outward transfer of dopamine (Vmax, in micromol mg-1 protein h-1; Km in microM) was higher in control animals(Vmax= 2.3 +/- 0.2; Km = 568 +/- 67) than that in rats treated with L-NAME for 14 days (Vmax = 0.8 +/- 0.02;Km = 241 +/- 21), but similar to that observed in rats receiving L-NAME plus L-arginine (Vmax= 2.4+/- 0.2; Km= 618 +/- 61); the saturable dopamine outward rate of transfer in rats given L-NAME for 7days (Vmax = 3.9 +/- 0.2; Km = 1006 +/- 32) was higher than in controls.6. In conclusion, the present studies show that the hypertensive response resulting from the long-term administration of L-NAME is accompanied by an increased urinary excretion of dopamine and 5-hydroxytryptamine, which appears to follow an enhanced activity of renal AAAD. The observation that the increased AAAD activity can be reversed by the administration of L-arginine to L-NAME treated rats favours the view that the adaptational response which results in an enhanced AAAD activity probably involves a decrease in the generation of nitric oxide.

The present work has determined the activities of aromatic L-amino acid decarboxylase (AAAD) and evaluated the presence of an active transport system for dopamine in renal tissues of developing dogs (newborn puppies less than 24 hours after birth, animals at the age of 10 days and 2 months) and adult animals. AAAD activity (Vmax, in pmol/mg protein/h) as determined in kidney homogenates was found to be in the adult dog kidney (Vmax = 3216 +/- 268) higher (p < 0.05) than that occurring in the three other groups of animals; no significant difference on AAAD activity was observed between the 10 day-old (Vmax = 1139 +/- 185) and the 2 month-old dogs (Vmax = 783 +/- 23). AAAD activity in newborn puppies (Vmax = 259 +/- 40) was markedly lower than in the three other groups. A considerable amount of the total dopamine formed from added L-DOPA in kidney slices, depending on the age, was found to escape into the incubation medium. The application of the Michaelis-Menten equation to the net transport of newly-formed dopamine has allowed the identification of a saturable (carrier-mediated transfer) and a non-saturable component (diffusion). The Vmax (nmol/g/15 min), Km (microM) values for the saturable component and diffusion constant (mumol-1) were as follows: adult (Vmax = 112 +/- 16; Km = 319 +/- 35; diffusion constant = 0.0009 +/- 0.0001), 2 month-old (Vmax = 19 +/- 5; Km = 48 +/- 14; diffusion constant = 0.0007 +/- 0.0002), 10 day-old (Vmax = 25 +/- 3; Km = 69 +/- 20; diffusion constant = 0.0033 +/- 0.0007) and newborn (Vmax = 6 +/- 1; Km = 16 +/- 6; diffusion constant = 0.0095 +/- 0.0010). In conclusion, renal AAAD develops with age, though some AAAD activity can already be detected at birth.(ABSTRACT TRUNCATED AT 250 WORDS)

1. The influence of pargyline and of selective inhibitors of type A and B monoamine oxidase (MAO), Ro 41-1049 and Ro 19-6327 respectively, on the outflow of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) in slices of rat renal cortex loaded with exogenous L-3,4-dihydroxyphenylalanine (L-DOPA) was examined. Dopamine and DOPAC in the tissues and in the effluent were assayed by means of h.p.l.c. with electrochemical detection. 2. The levels of newly-formed dopamine and DOPAC in the perifusate decreased progressively with time. In control conditions, DOPAC/dopamine ratios in the perifusate were 3 to 5 fold those in the tissue and were found to increase progressively with time. The addition of pargyline (100 microM), produced a marked decrease in the outflow levels of DOPAC (45 to 54% reduction) and significantly increased the levels of dopamine in the effluent (102 to 158% increase); DOPAC/dopamine ratios in the perifusate remained stable throughout the perifusion and were similar to those found in the tissues. The addition of the MAO-A inhibitor Ro 41-1049 to the perifusion fluid also significantly decreased DOPAC outflow (41% to 54% reduction) and increased dopamine outflow (19% to 80% increase). In the presence of Ro 41-1049 DOPAC/dopamine ratios in the perifusate were lower (P < 0.01) than in controls; in contrast with the effect of pargyline, this ratio was found to increase (P < 0.01) throughout the perifusion period. Ro 19-6327 did not reduce the outflow of DOPAC, but significantly increased (by 40-60%) that of dopamine. In the presence of Ro 19-6237, the proportion of DOPAC to dopamine in the perifusate was similar to that of controls and significantly increased throughout the perifusion; however, this increase was less than that observed in the control group.3. When benserazide (50 microM) was added to the perifusion fluid, the levels of both dopamine and DOPAC in the effluent were similar to those observed in the absence of benserazide. However, in the presence of benserazide, DOPAC/dopamine ratios in the perifusate did not increase with time. In conditions of decarboxylase inhibition, the effects of pargyline, Ro 41-1049 and Ro 19-6327 on dopamine and DOPAC outflow were less pronounced than in experiments conducted in the absence of benserazide.4. In conclusion, the results presented here show that the fraction of newly-formed dopamine which leaves the compartment where the synthesis has occurred is a constant source for deamination into DOPAC. The results provide evidence favouring the view that MAO-A is the main form of the enzyme involved in this process; however, the data described here suggest that dopamine would also have access to MAO-B.

1. The present study has examined the formation and outflow of newly-formed dopamine (DA) and noradrenaline (NA) in slices of the renal cortex of rats given L-beta-3,4-dihydroxyphenylalanine (L-DOPA) (10, 30 or 100 mg/kg i.p.) and L-threo-3-(3,4-dihydroxyphenyl)serine (L-DOPS) (10, 30 or 100 mg/kg i.p.), respectively. The outflow of 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylglycol (DOPEG), the deaminated metabolites of DA and NA, respectively, was also measured. 2. The accumulation of both newly-formed DA and DOPAC in renal tissues after the administration of L-DOPA was found to be dose dependent; after 30 or 100 mg/kg L-DOPA, the levels of both DA and DOPAC were, respectively, 3- and 20-fold those observed after the administration of 10 mg/kg L-DOPA. The outflow of DA and DOPAC in kidney slices of rats treated with L-DOPA was found to progressively decline with time and reflected the DA and DOPAC tissue contents. The rate constant (k) for DOPAC efflux (k = 0.0097) was higher (P < 0.01) than that for DA efflux (k = 0.0033) and did not depend on the dose of L-DOPA. DOPAC/DA perifusate ratios were 2-fold those occurring in the tissues. 3. The levels of NA in renal tissues of rats given 30 and 100 mg/kg L-DOPS were, respectively, 3- and 6-fold those observed after the administration of 10 mg/kg L-DOPS. The administration of L-DOPS was also found to be accompanied by the accumulation in renal tissues of DOPEG; this was, however, not dose dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

The present work has examined the ability of human, canine and rat renal tissues to synthesize dopamine from added L-3,4-dihydroxyphenylalanine (L-DOPA); the deamination of newly-formed dopamine into 3,4-dihydroxyphenylacetic acid (DOPAC) was also studied. In some experiments, slices of renal cortex obtained from the human, dog and rat kidneys were used; tissues were incubated with increasing concentrations (5-5000 microM) of L-DOPA. The accumulation of newly-formed dopamine was, in all three species, found to be dependent on the concentration of L-DOPA, being the rat renal tissues endowed with a greater ability to produce dopamine, followed by the human and the dog tissues. In experiments performed in kidney homogenates, the decarboxylation of L-DOPA into dopamine was also found to be dependent, in all three species, on the concentration of L-DOPA used (10-5000 microM). AAAD activity as determined in kidney homogenates was found to be in the rat kidney (Vmax = 7.7 +/- 0.8 nmol mg-1 protein h-1) higher than that occurring in the human (Vmax = 5.8 +/- 0.6 nmol mg-1 protein h-1) and the dog kidney (Vmax = 3.9 +/- 0.5 nmol mg-1 protein h-1). No statistically significant differences were found between the Km values of the three species (human, 62 +/- 8 microM; dog, 54 +/- 6 microM; rat, 82 +/- 12 microM). A considerable amount of newly-formed dopamine in both kidney slices and homogenates was converted into DOPAC; the DOPAC/dopamine ratios in these experimental conditions were greater in the human kidney, followed by the rat and dog.(ABSTRACT TRUNCATED AT 250 WORDS)

This study has examined the influence of sodium (0, 20, 40, 80, 120, and 160 mM) and ouabain (100, 500, and 1,000 microM), an inhibitor of the enzyme Na(+)-K+ ATPase, on the synthesis of dopamine in slices of human renal cortex loaded with exogenous L-dihydroxyphenylalanine (L-DOPA). The deamination of newly formed dopamine into 3,4-dihydroxyphenylacetic acid (DOPAC) was also examined. The formation of dopamine and its deamination to DOPAC in slices and homogenates of human renal cortex closely depended on the concentration of L-DOPA added to the medium; in homogenates of renal cortex, the production of dopamine was found to be 74% of that occurring in the renal medulla. Decarboxylation of L-DOPA was found saturable at 1,000 microM L-DOPA, which had Vmax and Km values for L-amino acid decarboxylase activity of, respectively, 5.8 +/- 0.6 nmol/mg of protein per hour and 62 +/- 8 microM. The accumulation of newly formed dopamine and DOPAC in kidney slices loaded with L-DOPA (50 and 100 microM) was found to be partially dependent on the concentration of sodium in the medium; at 0 mM sodium, the synthesis of dopamine from L-DOPA was found to be half of that occurring at 160 mM sodium. A similar picture could be observed for DOPAC. The fractional rate of accumulation (k; mM sodium-1) at 50 and 100 microM L-DOPA was, respectively, 0.0016 +/- 0.0002 and 0.0016 +/- 0.0005 for dopamine and 0.0018 +/- 0.0002 and 0.0021 +/- 0.0005 for DOPAC.(ABSTRACT TRUNCATED AT 250 WORDS)

The accumulation of Ldopa, dopamine (DA) and 3,4-dihydroxyphenylacetic (DOPAC) in kidney slices loaded with Ldopa (10-100 microM) was found to be dependent on the concentration of sodium in the medium (0-160 mM). The constant rate of accumulation did not depend on the concentration of Ldopa used and was about 0.0025, 0.0035 and 0.0065 for Ldopa, DA and DOPAC, respectively. In experiments performed in the presence of 120 and 160 mM sodium, but not with 20 mM sodium in the medium, ouabain (500 and 1000 microM) and amphotericin B (10 and 50 micrograms/ml) significantly reduced the accumulation of both DA and DOPAC (6-21 and 29-56% reduction, respectively). Amiloride (5-100 microM) produced an increase in the accumulation of DA and drastically reduced the formation of DOPAC. This effect was found to be due to inhibition of monoamine oxidase. During monoamine oxidase inhibition ethylisopropylamiloride (1, 5 and 10 microM), but not amiloride (10 and 50 microM), increased the accumulation of newly formed DA in kidney slices and reduced the outflow of the amine into the incubation medium. In conclusion, the results presented here show that the formation of DA in kidney slices loaded with Ldopa is dependent on the concentration of sodium in the medium and sensitive to the inhibition of the enzyme Na(+)-K+ adenosine triphosphatase and activation of mechanisms which bypass the tubular transport of sodium.

1. The present study has examined the formation of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) in slices of the rat renal cortex and the renal medulla loaded with exogenous L-beta-3,4-dihydroxyphenylalanine (L-DOPA). The effects of pargyline and of two selective inhibitors of monoamine oxidase (MAO) types A and B, respectively Ro 41-1049 and Ro 19-6327, on the deamination of newly-synthesized dopamine in kidney slices incubated with exogenous L-DOPA were also tested. The assay of L-DOPA, dopamine, noradrenaline and DOPAC was performed by means of h.p.l.c. with electrochemical detection. 2. Incubation of renal slices with exogenous L-DOPA resulted in a concentration-dependent accumulation of dopamine and DOPAC; the tissue levels of newly-formed dopamine and DOPAC in slices of the renal medulla were 6-8% of those in cortical slices. 3. Pargyline (0.1 mM) produced a marked decrease (84% reduction) in the formation of DOPAC in kidney slices loaded with 1.0 mM L-DOPA; this effect was accompanied by a 17% increase in the accumulation of dopamine. Similar effects were obtained at higher concentrations of pargyline (0.5 and 1.0 mM). At 5.0 and 10.0 mM pargyline, a marked decrease (46 and 76% reduction) in the accumulation of newly-formed dopamine was observed. 4. The accumulation of dopamine and DOPAC was found to be time-dependent in experiments in which tissues were incubated with 5 and 10 microM L-DOPA for 5, 10, 20 and 30 min. Pargyline (0.1 mM) produced an increase in the accumulation of dopamine at all incubation periods and decreased the formation of DOPAC. 6. It is concluded that deamination of newly-formed dopamine in kidney slices loaded with L-DOPA constitutes an important mechanism of amine inactivation. The results presented also suggest that most of the MAO, located inside the compartment where the synthesis of dopamine occurs, is of the A type.

Background: The occurrence of complementary functions in sodium transport between the intestine and the kidney was suggested to occur when the renal function is immature or compromised and jejunal dopamine has been implicated in this renal-intestinal cross-talk. The jejunal sodium transport was not previously evaluated in the nephrotic syndrome. Methods: We examined the jejunal Na+,K+-ATPase activity and the role of dopamine in puromycin aminonucleoside (PAN) and HgCl2-induced nephrotic syndrome rat models. Results: In both nephrotic syndrome rat models, the jejunal Na+,K+-ATPase activity was reduced during greatest sodium retention and ascites accumulation (PAN nephrosis, day 7; HgCl2 nephrosis, day 14), whereas during enhanced sodium excretion and ascites mobilization the jejunal Na+,K+-ATPase activity was increased in HgCl2 nephrosis (day 21) and was similar to controls in PAN nephrosis (day 14). In both PAN- and HgCl2-induced nephrosis, the jejunal aromatic L-amino acid decarboxylase (AADC) activity, the enzyme responsible for the synthesis of jejunal dopamine, did not differ from controls. In addition, the jejunal Na+,K+-ATPase activity was not sensitive to inhibition by dopamine (1 μM) in both experimental groups throughout the study. Conclusions: In the nephrotic syndrome the jejunal Na+,K+-ATPase activity may respond in a compensatory way to changes in extracellular volume, through dopamine-independent mechanisms. Copyright © 2005 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]