Contrast-enhanced dynamic magnetic resonance imaging of the rat kidney

This study was designed to assess whether contrast-enhanced dynamic 1H magnetic resonance imaging (DMRI) can be used to detect the effects of the loop diuretic furosemide and the vasoactive peptide angiotensin II on tubular water reabsorption in the rat kidney. A bolus of gadolinium-DTPA-dimeglumine (Gd-DTPA) (0.025 or 0.1 mmol/kg) was used as a contrast agent. The signal intensity in the magnetic resonance images relative to the precontrast signal intensity (RSI) was assessed as a function of time in the cortex and medulla. In the cortex, no differences were observed between high and low bolus injection, and between different treatment groups and controls. In the medulla, RSI patterns were different between high and low bolus, with the high bolus showing lower RSI values, because of T2 shortening at high Gd-DTPA concentrations. No difference was observed between controls and angiotensin II-infused animals. This is in line with the finding that angiotensin II did not alter medullary water reabsorption, as evidenced by unchanged urine flow and osmolality compared with controls. Medullary RSI patterns during furosemide infusion differed markedly from controls, in a manner suggesting that a lower concentration of Gd-DTPA was present compared with controls. This agrees with the well-known inhibiting effect of furosemide on medullary water reabsorption. It was concluded that, with the method used, small concentration differences of Gd-DTPA in the cortex resulting from small changes of plus or minus 20% in tubular water reabsorption, previously found to be present by direct micropuncture measurements, cannot be detected in rats. However, large changes in renal concentrating ability do result in different RSI patterns in the medulla.