Study of acute renal ischemia in the rat using magnetic resonance imaging and spectroscopy

Magnetic resonance (MR) imaging and spectroscopy, chemical lactate measurements, and microscopic examinations were performed to investigate acute renal ischemia in rats. MR images ( 1 H) and spectra ( 31 P and 1 H) were acquired on a 2.0‐T superconducting small‐bore magnet by using implanted coils. Occlusion of the renal artery induced a significant decrease in signal intensity of the renal parenchyma on T2‐weighted images, which was most obvious in the outer medulla (‐50 ± 15%, n = 8, P 0.001) and was the result of venous congestion, as verified histologically. 31 P spectroscopy demonstrated a drop in pH from 7.3 ± 0.2 to 6.6 ± 0.2 ( n = 18, P 0.001), characterized by a time constant ( T c ) in the same range as that of the depletion of ATP (2.3 ± 1.3 min versus 1.9 ± 1.2 min, n = 10, P = ns). By means of 1 H spectroscopy, a lactate peak was detected within 1.5 to 4 min of ischemia, still increasing in intensity after 1 h of ischemia. The T c of the lactate buildup (15.9 ± 7.5 min, n = 8) was significantly longer than that of the drop in pH ( P 0.005). The chemically measured intrarenal concentration of lactate was 1.3 ± 0.5 Mmol/g in control kidneys and 8.7 ± 3.2 μmol/g ( P < 0.005) in kidneys made ischemic for 1 h. The present study demonstrated important features of acute renal ischemia: (a) acute ischemia induces venous congestion in the medulla; (b) accumulation of lactate is not the main cause of the intracellular acidification observed during ischemia. © 1989 Academic Press, Inc.