Furosemide increases water content in renal tissue

The present study was designed to evaluate the short-term effects of intravenous administration of furosemide on key functions in the kidney cortex and the outer and inner medulla of rats by using magnetic resonance imaging (MRI). Renal tissue water content, renal tissue oxygenation (in relation to the magnetic resonance spin-spin relaxation rate), the apparent diffusion coefficient (ADC) of water, and volume of renal blood flow were measured. Furosemide administration resulted in an increased water content in all regions of the kidney. In parallel with this, we found a significant reduction in ADC in the cortex (2.7 ± 0.1 × 10−3 to 2.3 ± 0.1 × 10−3 mm2/s; P < 0.01) and in the outer medulla (2.3 ± 0.1 × 10−3 to 2.0 ± 0.1 × 10−3 mm2/s; P < 0.01), indicating that the intra- to extracellular volume fraction of water increased in response to furosemide administration. Furosemide also decreased the blood oxygenation in the cortex (49.1 ± 2.9 to 40.9 ± 2.0 s−1; P < 0.01), outer medulla (41.9 ± 2.8 to 33.2 ± 1.6 s−1; P < 0.01) and in the inner medulla (37.1 ± 2.9 to 26.7 ± 1.8 s−1; P < 0.01), indicating an increased amount of oxygenated Hb in the renal tissue. Moreover, renal blood flow decreased in response to furosemide (6.9 ± 0.2 to 4.4 ± 0.2 ml/min; P < 0.001). In conclusion, furosemide administration was associated with increased renal water content, an increase in the intra- to extracellular volume fraction of water, an increased oxygen tension, and a decrease in the renal blood flow. Thus MRI provides an integrated evaluation of changes in renal function, leading to decreased renal water and solute reabsorption in response to furosemide, and, in addition, MRI provides an alternative tool to monitor noninvasively changes at the cellular level.