Investigation of urinary dopamine as a marker of renal function and clinical application to laboratory medicine

采用大鼠肾切除、去神经和多巴脱羧酶抑制剂卡比多巴治疗，研究了尿中多巴胺的来源。尿中释放的游离多巴胺来源于肾小管多巴胺，它在近端小管合成，调节尿钠和利尿。尿中排出的共轭多巴胺来源于肾滤过多巴胺，而肾滤过多巴胺来源于血浆中的共轭多巴胺。由于血浆偶联多巴胺在肾小球处被过滤，肾功能受损患者血浆偶联多巴胺升高。利用尿游离多巴胺、尿偶联多巴胺和血浆偶联多巴胺这些参数，可以对肾功能进行评价。我们研究了尿中多巴胺水平作为肾功能，尤其是肾小管活动的标志物的有效性。我们确定了慢性肾小球肾炎患者和健康志愿者尿液中游离多巴胺水平与一些已建立的肾功能标志物之间的相关性。尿游离多巴胺水平与血清肌酐水平、尿α 1、β 2微球蛋白水平呈负相关，与尿肌酐、尿素氮、钾、无机磷水平呈正相关。结果表明，尿中多巴胺水平是肾功能的一个指标，尿中游离多巴胺水平的测量对评估肾功能损害是有用的。

The origin of dopamine in urine was investigated using rats nephrectomized, denervated the renal nerve and treated with carbidopa, an inhibitor of DOPA decarboxylase. The free dopamine excreted in urine is derived from renal tubular dopamine, which is synthesized at proximal tubules and regulates both natriuresis and diuresis. The conjugated dopamine excreted in urine is derived from renal filtrated dopamine, which is originated from the conjugated dopamine in plasma. As the plasma conjugated dopamine is filtrated at glomerulus, the plasma conjugated dopamine elevates in the patients with impaired renal function. Using these parameters of urinary free dopamine, urinary conjugated dopamine and plasma conjugated dopamine, it is possible to evaluate the renal function. We investigated the usefulness of the urinary level of dopamine as a marker of renal function, especially of tubular activity. We determined the correlations between the urinary level of free dopamine and a number of established markers of renal function in patients with chronic glomerulonephritis and healthy volunteers. The urinary level of free dopamine was negatively correlated with the serum level of creatinine and the urinary levels of alpha1-and beta2-microglobulins, and was positively correlated with urinary level of creatinine, urea nitrogen, potassium and inorganic phosphorus. Findings suggest that the urinary level of dopamine is an index of renal functions and that measurements of the urinary level of free dopamine are useful for evaluating renal impairment.