In Vivo 19F MR Spectroscopy in the Study of Organic Acid Excretion by the Rat Kidney

In traditional clearance studies the urinary excretion of a test substance is measured in relation to its plasma concentration (clearance = UV/P; where V is the urine volume per minute, U the urinary concentration of the test substance, and P the corresponding plasma concentration). If the clearance of inulin, which indicates the glomerular filtration rate, is determined simultaneously, it is possible, while accounting for the binding of the test substance to plasma proteins, to evaluate the filtered amount of the test substance. From the filtered and excreted amounts of a test substance it is possible to calculate how much was secreted or reabsorbed. However, traditional clearance studies give no information on the actual intracellular content of a test substance. Using in vivo 19F magnetic resonance (MR) spectroscopy the intracellular concentration of fluorinated organic acids can be monitored continuously. The 19F nucleus has a nuclear spin of 1/2 and, together with its natural abundance of 100%, offers a high detection sensitivity (83% of that of 1H). As biological systems do not normally contain fluorine, no problems with endogenous 19F signals occur.