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.
摘要
本研究检测了加载外源性L-β-3,4-二羟基苯丙氨酸（L-DOPA）的大鼠肾皮质和肾髓质切片中多巴胺和3,4-二羟基苯乙酸（DOPAC）的形成。还测试了优降宁以及两种分别针对单胺氧化酶（MAO）A 型和 B 型的选择性抑制剂（分别为Ro 41-1049和Ro 19-6327）对与外源性L-DOPA一起孵育的肾切片中新合成多巴胺脱氨基作用的影响。L-DOPA、多巴胺、去甲肾上腺素和DOPAC的测定通过高效液相色谱法和电化学检测进行。2. 用外源性L-DOPA孵育肾切片导致多巴胺和DOPAC浓度依赖性积累；肾髓质切片中新形成的多巴胺和DOPAC的组织水平是皮质切片中的6-8%。3. 优降宁（0.1 mM）使加载1.0 mM L-DOPA的肾切片中DOPAC的形成显著降低（降低84%）；此效应伴随着多巴胺积累增加17%。在更高浓度的优降宁（0.5和1.0 mM）下获得了类似的效果。在5.0和10.0 mM优降宁时，观察到新形成的多巴胺积累显著降低（分别降低46%和76%）。4. 在组织与5和10 μM L-DOPA孵育5、10、20和30分钟的实验中，发现多巴胺和DOPAC的积累是时间依赖性的。优降宁（0.1 mM）在所有孵育时间段均使多巴胺积累增加，并降低了DOPAC的形成。6. 得出的结论是，加载L-DOPA的肾切片中新形成的多巴胺脱氨基是胺失活的重要机制。所呈现的结果还表明，位于多巴胺合成所在隔室内的大多数MAO是A 型。
