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Sodium‐dependence and ouabain‐sensitivity of the synthesis of dopamine in renal tissues of the rat
Author(s) -
SoaresdaSilva P.,
Fernandes M. Helena
Publication year - 1992
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1992.tb09062.x
Subject(s) - dopamine , ouabain , chemistry , sodium , dihydroxyphenylalanine , endocrinology , medicine , biology , organic chemistry
1 The present study has examined the influence of sodium chloride (0–160 m m ) and ouabain (100 and 500 μ m ), an inhibitor of the enzyme Na + –K + ATPase, on the synthesis of dopamine in slices of rat 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 assay of l ‐DOPA, dopamine and DOPAC in kidney slices was performed by high performance liquid chromatography (h.p.l.c.). with electrochemical detection. 2 The accumulation of newly‐formed dopamine and DOPAC in kidney slices loaded with l ‐DOPA (50 and 100 μ m ) was found to be dependent on the concentration of NaCl in the medium. A similar picture could be observed for DOPAC. The fractional rate of accumulation ( k; m m NaCl −1 ) was at 50 and 100 μ m l ‐DOPA, respectively, 0.00305 ± 0.00036 and 0.00328 ± 0.00029 for dopamine and 0.00672 ± 0.00072 and 0.00641 ±0.00069 for DOPAC. The sodium‐dependent formation of dopamine was completely abolished when the experiments were performed in the absence of oxygen. 3 In experiments performed in the presence of 120 m m NaCl, but not in conditions of low sodium (20 m m NaCl in the medium), ouabain (100 and 500 μ m ) was found to inhibit the accumulation of newly‐formed dopamine and DOPAC (14–57% reduction; P < 0.05); this effect was more marked at 50 and 100 μ m l ‐DOPA. When the experiments were performed in the absence of oxygen the renal production of dopamine and DOPAC became markedly decreased (respectively, 40% and 77% reduction; P < 0.05) and ouabain (100 and 500 μ m ) was no longer able to reduce the accumulation of both newly‐formed dopamine and DOPAC. 4 The formation of dopamine and its deamination to DOPAC in kidney homogenates closely depended on the concentration of l ‐DOPA added to the medium; ouabain (100, 500 and 1000 μ m ) was found to affect neither the formation of dopamine nor its deamination to DOPAC when homogenates were used instead of kidney slices. 5 In conclusion, the results presented here show that the formation of dopamine in kidney slices loaded with l ‐DOPA is sodium‐dependent and ouabain‐sensitive suggesting the involvement of a co‐transport system of sodium and DOPA into the tubular epithelial cell.