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M Pestana

Publications and source records attributed to M Pestana.

At least 37 records · Page 2Linked to original sources
PubMed1998

Evidence for the involvement of P-glycoprotein on the extrusion of taken up L-DOPA in cyclosporine A treated LLC-PK1 cells.

1. The present work has examined the effects of short- (30 min) and long-term (14 h) exposure to cyclosporine A (CsA) on the uptake of L-DOPA, its decarboxylation to dopamine and the cellular extrusion of taken up L-DOPA and of newly-formed amine in monolayers of LLC-PK1 cells. 2. In the presence of benserazide (50 microM), L-DOPA was rapidly accumulated in LLC-PK1 cells (cultured in collagen-treated plastic) attaining equilibrium at 30 min of incubation. Non-linear analysis of the saturation curves revealed a Km of 113+/-16 microM and a Vmax of 5581+/-297 pmol mg(-1) protein 6 min(-1). 3. In the absence of benserazide, LLC-PK1 cells incubated with increasing concentrations of L-DOPA (10 to 500 microM) for 6 min accumulate newly-formed dopamine by a saturable process with apparent Km and Vmax values of 31+/-6 microM and 1793+/-91 pmol mg(-1) protein 6 min(-1), respectively. The fractional outflow of newly-formed dopamine was found to be 20%. Up to 200 microM of intracellular newly-formed dopamine, the outward transfer of the amine was found to be a non-saturable process. 4. Short-term exposure to CsA (0.3, 1.0 and 3.0 microg ml(-1)) was found not to change the intracellular concentrations of newly-formed dopamine, but increased the levels of dopamine in the incubation medium (143% to 224% increase) and the total amount of dopamine formed (31% to 59% increase). Long-term exposure to CsA (0.03 to 3.0 microg ml(-1)) reduced the total amount of dopamine (15% to 39% reduction) and the intracellular levels of the amine (11% to 56% reduction), without changing dopamine levels in the incubation medium. Both short- and long-term exposure to CsA resulted in a concentration-dependent increase in the fractional outflow of newly-formed dopamine. 5. Short-term exposure to CsA (3.0 microg ml(-1)) reduced the apical extrusion of intracellular L-DOPA by 15% (P<0.05), whereas long-term exposure to CsA reverted this effect and decreased its intracellular availability (15% reduction; P<0.05). 6. Detection of P-glycoprotein activity was carried out by measuring verapamil- or UIC2-sensitive rhodamine 123 accumulation. Both UIC2 (3 microg ml(-1)) and verapamil (25 microM) significantly increased the accumulation of rhodamine 123 in LLC-PK1 cells. A 30 min exposure to CsA was found not to affect the accumulation of rhodamine 123 in the presence of verapamil (25 microM), whereas a 14 h exposure to CsA was found to reduce the accumulation of rhodamine 123. 7. In conclusion, the increase and the reduction in the formation of dopamine after short- and long-term exposure to CsA, respectively, correlate with the effects of the immunosuppressant on the apical cell extrusion of taken up L-DOPA, suggesting the involvement of P-glycoprotein. The effects of CsA on the fractional outflow of newly-formed dopamine appear to be mediated by a different mechanism.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1998

Renal dopaminergic system in nephrotic syndrome and after remission.

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1998

Reduced urinary excretion of dopamine and metabolites in chronic renal parenchymal disease.

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1998

[An increase in renal dopamine production after the administration of radiographic contrast agents].

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.

Adult↗
PubMed1997

Assessment of renal dopaminergic system activity during the recovery of renal function in human kidney transplant recipients.

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1996

High sodium intake increases the urinary excretion of L-3,4-dihydroxyphenylalanine but fails to alter the urinary excretion of dopamine and amine metabolites in Wistar rats.

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1996

Antagonistic actions of renal dopamine and 5-hydroxytryptamine: endogenous 5-hydroxytryptamine, 5-HT1A receptors and antinatriuresis during high sodium intake.

1. The present study has examined the effect of (+)-WAY 100135, a selective antagonist of 5-HT1A receptors, and ketanserin, an antagonist of 5-HT2 receptors, on the urinary excretion of Na+, K+, dopamine, 5-hydroxytryptamine (5-HT) and their metabolites in rats treated with the selective type A monoamine oxidase (MAO-A) inhibitor, Ro 41-1049 (15 mg kg-1 day-1) in conditions of normal sodium (NS) and high sodium (HS; 1.0% NaCl in drinking water) intake. 2. Male Wistar rats were placed in metabolic cages and were given tap water (NS diet) in the first 4 days of the study and then challenged to a HS diet for another 7 days. Ro 41-1049 was given in drinking water only in the last 3 days of the HS diet, whereas (+)-WAY 100135 (5 and 10 mg kg-1 day-1, s.c.) or ketanserin (2 mg kg-1 day-1, s.c.) were administered in the last 4 days of the HS intake period. 3. Daily urinary excretion (in nmol kg-1 day-1) of dopamine (82 +/- 2), 3,4-dihydroxyphenylacetic acid (DOPAC; 198 +/- 9), homovanillic acid (HVA; 915 +/- 47), 5-HT (586 +/- 37) and 5-hydroxyindoleacetic acid (5-HIAA; 1035 +/- 64) in the HS intake period was similar or higher than that in NS diet (dopamine = 68 +/- 2, DOPAC = 197 +/- 4, HVA = 923 +/- 42, 5-HT = 539 +/- 132, 5-HIAA = 1286 +/- 95). The administration of Ro 41-1049 on 3 consecutive days reduced the urinary excretion of dopamine, DOPAC and HVA, respectively, by 35-51% (P < 0.05), 73-85% (P < 0.05) and 59-66% (P < 0.05); the urinary excretion of 5-HT increased 2 fold (P < 0.01) and the levels of 5-HIAA were reduced by 39-77% (P < 0.05). 4. During HS intake (7 days), daily urinary excretion of Na+ increased 5.5 fold (from 6.7 +/- 0.2 to 36.5 +/- 0.9 mmol kg-1 day-1), without changes in the urinary excretion of K+ (from 11.2 +/- 0.2 to 11.9 +/- 0.5 mmol kg-1 day-1) and urinary osmolality (from 1083.8 +/- 26.7 to 1117.7 +/- 24.1 mOsm kg-1 H2O). MAO-A inhibition during HS intake was found to produce a 47-68% decrease in Na+ excretion (from 39.1 +/- 0.7 to 15.1 +/- 2.5 mmol kg-1 day-1, n = 4; P < 0.02) and urine volume (from 160.4 +/- 3.3 to 43.8 +/- 9.0 ml kg-1 day-1, n = 4; P < 0.02) without changes in K+ (from 11.1 +/- 0.5 to 9.2 +/- 0.6 mmol kg-1 day-1, n = 4) and creatinine (from 29.1 +/- 2.3 to 28.4 +/- 2.1 mg kg-1 day-1) excretion; urine osmolality increased 2 fold (from 936.3 +/- 40.3 to 2210.7 +/- 157.4 mOsm kg-1 H2O, n = 4; P < 0.02). Administration of (+)-WAY 100135 (5 and 10 mg kg-1 day-1), but not of ketanserin (2 mg kg-1 day-1), was found to inhibit the antinatriuretic effect induced by Ro 41-1049 during HS intake. 5. It is suggested that MAO-A inhibition during HS intake leads to an increased availability of 5-HT in renal tissues, the effect of which is a decrease in the urinary excretion of Na+, involving the activation of tubular 5-HT1A receptors.

Animals↗
PubMed1995

Ontogeny of the cell outward dopamine transporter in canine renal tissues.

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)

Aging↗
PubMed1995

Assessment of renal dopaminergic system activity in the nitric oxide-deprived hypertensive rat model.

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.

Amino Acid Oxidoreductases↗
PubMed1995

Assessment of renal dopaminergic system activity during cyclosporine A administration in the rat.

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1995

Studies on the nature of the antagonistic actions of dopamine and 5-hydroxytryptamine in renal tissues.

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)

5-Hydroxytryptophan↗
PubMed1995

24-hour blood pressure profile early after renal transplantation.

Renal transplant patients are often found to have high blood pressure. We studied 12 cyclosporine-treated patients 8-10 days after kidney transplantation by 24-hour ambulatory blood pressure monitoring, and once again at 35-40 days after kidney transplantation. The patients were found to have high mean blood pressure values at 8-10 days after transplantation, with a significant (p < 0.05) decrease at 35-40 days after transplantation (154.2 +/- 4.9/94.4 +/- 2.8 and 142.2 +/- 4.0/88.6 +/- 2.7 mmHg, respectively). A significant (p < 0.05) decrease in blood pressure values was also noted in the second series of measurements, when compared to the first series, in the day-time systolic and in the night-time systolic and diastolic blood pressure values, but not in the day-time diastolic blood pressure values. An abnormal day/night pattern of blood pressure ("non-dipper") was found in these patients in both occasions, with a difference between average blood pressure values during day- and night-time of 1.3/3.0 (systolic/diastolic) and 5.7/7.6 mm Hg at 8-10 and 35-40 days after transplantation, respectively. This tendency towards attenuation of the "non-dipper" pattern occurred in association with the decrease in body weight and of the dose of immunosuppressive drugs. As hemodynamic factors may play a role in both the short and the long-term function and viability of kidney transplant grafts, the high blood pressure and the "non-dipper" pattern of blood pressure found early after kidney transplantation may require a special therapeutic approach.

Adult↗
PubMed1994

Outflow of dopamine and noradrenaline originating from L-dopa and L-threo-DOPS in rat renal tissues.

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)

Animals↗
PubMed1994

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1994

Effect of type A and B monoamine oxidase selective inhibition by Ro 41-1049 and Ro 19-6327 on dopamine outflow in rat kidney slices.

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.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

A comparative study on the synthesis of dopamine in the human, dog and rat kidney.

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)

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

Involvement of tubular sodium in the formation of dopamine in the human renal cortex.

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)

3,4-Dihydroxyphenylacetic Acid↗