Monitoring Urea Transport in Rat Kidney in vivo Using Hyperpolarized 13C MRI

Cornelius von Morze¹, Robert A. Bok¹, Jeff M. Sands², John Kurhanewicz¹, Daniel B. Vigneron¹

Urea functions as a key osmolyte in the urinary concentrating mechanism of the renal 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 NMR signals in the liquid state, offer a novel means to monitor this process in vivo using MRI. In this study, we detected significant signal differences in the rat kidney between acute diuretic and antidiuretic states, using dynamic ¹³C MRI following a bolus infusion of hyperpolarized [¹³C]urea. More rapid medullary enhancement was observed under antidiuresis, consistent with known upregulation of UT-A1.