Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, California, USA.
Am J Physiol Renal Physiol. 2012 Jun 15;302(12):F1658-62. doi: 10.1152/ajprenal.00640.2011. Epub 2012 Apr 4.
Urea functions as a key osmolyte in the urinary concentrating mechanism of the inner medulla. The urea transporter UT-A1 is upregulated by antidiuretic hormone, facilitating faster equilibration of urea between the lumen and interstitium of the inner medullary collecting duct, resulting in the formation of more highly concentrated urine. New methods in dynamic nuclear polarization, providing ∼50,000-fold enhancement of nuclear magnetic resonance signals in the liquid state, offer a novel means to monitor this process in vivo using magnetic resonance imaging. In this study, we detected significant signal differences in the rat kidney between acute diuretic and antidiuretic states, using dynamic (13)C magnetic resonance imaging following a bolus infusion of hyperpolarized [(13)C]urea. More rapid medullary enhancement was observed under antidiuresis, consistent with known upregulation of UT-A1.
尿素在内髓尿液浓缩机制中作为一种关键渗透物发挥作用。抗利尿激素上调尿素转运蛋白 UT-A1，促进尿素在髓袢升支粗段收集管的管腔和间质之间更快地达到平衡，从而形成更高浓度的尿液。动态核极化的新方法提供了约 50,000 倍的液体状态下磁共振信号增强，为使用磁共振成像在体内监测该过程提供了一种新方法。在这项研究中，我们使用超极化 [(13)C]尿素的单次推注后进行动态 (13)C 磁共振成像，在急性利尿和抗利尿状态下检测到大鼠肾脏中的显著信号差异。在抗利尿状态下观察到更快的髓质增强，这与 UT-A1 的已知上调一致。
