Soares-da-Silva P
Department of Pharmacology and Therapeutics, Faculty of Medicine, Porto, Portugal.
Biochem Pharmacol. 1993 May 5;45(9):1791-800. doi: 10.1016/0006-2952(93)90435-y.
The synthesis of dopamine, from L-beta-3,4-dihydroxyphenylalanine (L-DOPA), in renal tissue of rats on either a normal sodium (NS) or high sodium (HS) diet for 1 week or 6 weeks was examined. Aromatic L-amino acid decarboxylase (AAAD) activity determined in kidney homogenates in "1 week HS" (Vmax = 11.5 +/- 1.6 nmol/mg protein/hr) and "6 weeks HS" rats (Vmax = 10.6 +/- 1.5 nmol/mg protein/hr) was greater (P < 0.02) than that in "NS" rats (Vmax = 7.7 +/- 0.8 nmol/mg protein/hr). Km (microM) values in "NS", in "1 week HS" and "6 weeks HS" rats were similar. The formation of dopamine in kidney slices loaded with 100 microM L-DOPA depended exponentially on the concentration of sodium in the medium (0-160 mM). In kidney slices obtained from "1 week HS" rats the decarboxylation of added L-DOPA was significantly greater (P < 0.01) than that observed in kidney slices obtained from "NS" and "6 weeks HS" rats; the rate constant of formation of dopamine as a function of sodium concentration in the incubation medium was, however, similar in "NS" rats to that in "1 week HS" and "6 weeks HS" rats. Ouabain produced a concentration dependent decrease in the synthesis of dopamine in all three experimental groups; the magnitude of the inhibitory effect of 1.0 mM ouabain was greater in "1 week HS" rats (77% reduction; P < 0.01) than in "NS" rats (59% reduction; P < 0.01) and in "6 weeks HS" rats (23% reduction; P = 0.08). Activation of protein kinase C by phorbol 12,13-dibutyrate (PDBu) and the calcium ionophore A23187 produced a concentration-dependent reduction in the formation of dopamine in rat kidney slices, but not in kidney homogenates; the magnitude of the inhibitory effect was greater in "1 week HS" rats than in "NS" and "6 weeks HS" rats. Submaximal concentrations of PDBu (10 nM) were synergistic with the inhibitory effect of A23187 on the formation of dopamine: again, this effect was more marked in "1 week HS" rats than in "NS" and "6 weeks HS" rats. The effects of PDBu and PDBu plus A23187, but not those of A23187 alone, were antagonized in a concentration-dependent manner by d-sphingosine, a protein kinase C inhibitor. It is concluded that the increased activity of AAAD in renal tissues of rats submitted to HS intake is accompanied in "1 week HS" but not in "6 weeks HS" rats by enhanced inhibition of dopamine formation during protein kinase C activation.
研究了给予正常钠（NS）或高钠（HS）饮食1周或6周的大鼠肾组织中，由L-β-3,4-二羟基苯丙氨酸（L-DOPA）合成多巴胺的情况。在“1周HS”（Vmax = 11.5±1.6 nmol/mg蛋白质/小时）和“6周HS”大鼠（Vmax = 10.6±1.5 nmol/mg蛋白质/小时）的肾脏匀浆中测定的芳香族L-氨基酸脱羧酶（AAAD）活性，高于“NS”大鼠（Vmax = 7.7±0.8 nmol/mg蛋白质/小时）（P < 0.02）。“NS”、“1周HS”和“6周HS”大鼠的Km（μM）值相似。加载100μM L-DOPA的肾切片中多巴胺的形成，呈指数依赖于培养基中钠的浓度（0 - 160 mM）。从“1周HS”大鼠获得的肾切片中，添加的L-DOPA的脱羧作用显著大于从“NS”和“6周HS”大鼠获得的肾切片中观察到的脱羧作用（P < 0.01）；然而，在“NS”大鼠中，多巴胺形成速率常数作为孵育培养基中钠浓度的函数，与“1周HS”和“6周HS”大鼠中的相似。哇巴因在所有三个实验组中均使多巴胺合成呈浓度依赖性降低；1.0 mM哇巴因的抑制作用程度在“1周HS”大鼠中（降低77%；P < 0.01）大于“NS”大鼠（降低59%；P < 0.01）和“6周HS”大鼠（降低23%；P = 0.08）。佛波醇12,13 - 二丁酸酯（PDBu）和钙离子载体A23187激活蛋白激酶C，使大鼠肾切片中多巴胺的形成呈浓度依赖性降低，但在肾脏匀浆中未观察到这种现象；抑制作用程度在“1周HS”大鼠中大于“NS”和“6周HS”大鼠。亚最大浓度的PDBu（10 nM）与A23187对多巴胺形成的抑制作用具有协同性：同样，这种作用在“1周HS”大鼠中比在“NS”和“6周HS”大鼠中更明显。PDBu和PDBu加A23187的作用，但不是单独A23187的作用，被蛋白激酶C抑制剂d - 鞘氨醇以浓度依赖性方式拮抗。得出结论：摄入HS的大鼠肾组织中AAAD活性增加，在“1周HS”大鼠中伴随着蛋白激酶C激活期间多巴胺形成的增强抑制，但在“6周HS”大鼠中并非如此。
