RENAL DOPAMINE RECEPTOR FUNCTION IN OBESE ZUCKER RATS

描述(来自申请的逐字)：多巴胺和D1样受体在 近端肾小管和肾单位的其他区域在 调节肾脏钠排泄。DIA受体缺陷(D1样 受体)功能在高血压动物的近端小管中被报道 和人类。在我们的初步研究中，我们发现D1-Iike受体是 减少50%，多巴胺不能刺激第二信使 (cAMP和IP3)，从而不能抑制Na，K-ATPase和Na，H-交换器 肥胖Zucker大鼠(12周龄)的近端小管。 因此，假设多巴胺减弱的抑制作用 近端小管钠转运蛋白的功能障碍 膜DIA磷酸化改变所致的DIA受体 D1a受体以及从胞浆重新募集新的D1a受体的功能受损。 这种多巴胺受体功能的缺陷导致了 外源性和内源性给药的利钠反应 产生了多巴胺。这一假设将通过进行一系列 确定生化/分子机制的实验(S) DIA受体的缺陷。这些将包括：测量D1a 受体激动剂亲和力测定GTPyS对配体的影响 激动剂依赖的和非依赖的磷酸化的结合、测定 D1a受体激动剂对血管内皮细胞的抑制作用 D1a受体膜及D1a受体蛋白含量的测定 在瘦大鼠和肥胖大鼠的近端小管中。的功能后果 有缺陷的DIA受体功能将通过研究利钠药进行检查 多巴胺和SKF38393的利尿作用以及通过测定 急性扩容对肾脏产生多巴胺和钠的影响 麻醉瘦身和肥胖Zucker大鼠的水分排泄。为了 高胰岛素血症在D1a受体缺陷中的作用 功能和利钠反应，上述实验也将 在瘦小和肥胖的大鼠(7-8周)中进行实验，治疗四周 达格列酮，一种降低胰岛素水平和改善胰岛素的药物 敏感性以及3-4周龄未经治疗的高胰岛素血症和对照组 老鼠。多巴胺受体产生机制的鉴定(S) 功能障碍和对多巴胺的钠尿反应减弱将使我们 为了更好地了解肾脏D1a受体功能与肾功能的关系 肥胖大鼠高胰岛素血症。

DESCRIPTION (Verbatim from the application): Dopamine and D1-like receptors in the proximal tubules and other regions of the nephron play an important role in regulating renal sodium excretion. A defective DIA receptor (a D1-like receptor) function is reported in the proximal tubules of hepertensive animals and humans. In our preliminary studies we found that D1-Iike receptors are reduced by 50 percent and dopamine was unable to stimulate second messengers (cAMP and IP3) and thereby failed to inhibit Na,K-ATPase and Na,H-exchanger in the proximal tubules of obese Zucker rats (12 week old). Therefore, it is hypothesized that the diminished inhibitory effect of dopamine on sodium transporting proteins in the proximal tubules is due to a dysfunction in DIA receptor which results from altered phosphorylation of membranal DIA receptor as well as impaired recruitment of newer D1A receptors from cytosol. Such a defect in dopamine receptor function contributes to the diminished natriuretic response to exogenously administered as well as endogenously produced dopamine. This hypothesis will be tested by conducting a series of experiments to identify the biochemical/molecular mechanism(s) contributing towards the defect in DIA receptors. These will include: measurement of D1A receptor agonist affinity, determination of the effect of GTPyS on ligand binding, determination of agonist-dependent and -independent phosphorylation of D1A receptor, determination of agonist recmitment of D1A receptors on the membrane and measurement of D1A receptor mRNA and DIA receptor protein content in proximal tubules of lean and obese rats. The functional consequence of the defective DIA receptor function will be examined by studying the natriuretic and diuretic effect of dopamine and SKF38393 as well as by determining the effect of acute volume expansion on renal production of dopamine and sodium and water excretion in anesthetized lean and obese Zucker rats. In order to delineate the role of hyperinsulinemia in causing the defective D1A receptor function and the natriuretic response, experiments described above will also be performed in lean and obese rats (7-8 weeks) treated for four weeks with darglitazone, a drug which decreases insulin levels and improve insulin sensitivity as well as in 3-4 week old non-treated hyperinsulinemic and control rats. Identification of the mechanism(s) leading to dopamine receptor dysfunction and the diminished natriuretic response to dopamine would allow us to better understand the relationship between kidney D1A receptor function and hyperinsulinemia in obese rats.