CONTRAST-ENHANCED DYNAMIC MAGNETIC-RESONANCE-IMAGING OF THE RAT-KIDNEY

This study was designed to assess whether contrast-enhanced dynamic H- 1 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 gadoli nium-DTPA-dimeglumine (Gd-DTPA) (0.025 or 0.1 mmol/kg) was used as a c ontrast agent, The signal intensity in the magnetic resonance images r elative to the precontrast signal intensity (RSI) was assessed as a fu nction of time in the cortex and medulla, In the cortex, no difference s were observed between high and low bolus injection, and between diff erent treatment groups and controls. In the medulla, RSI patterns were different between high and low bolus, with the high bolus showing low er RSI values, because of T-2 shortening at high Gd-DTPA concentration s. No difference was observed between controls and angiotensin It-infu sed animals, This is in line with the finding that angiotensin II did not alter medullary water reabsorption, as evidenced by unchanged urin e flow and osmolality compared with controls. Medullary RSI patterns d uring 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 f urosemide on medullary water reabsorption, It was concluded that, with the method used, small concentration differences of Gd-DTPA in the co rtex resulting from small changes of plus or minus 20% in tubular wate r reabsorption, previously found to be present by direct micropuncture measurements, cannot be detected in rats, However, large changes in r enal concentrating ability do result in different RSI patterns in the medulla.