ENDOTOXIN-INDUCED CHANGES IN INTRARENAL PO2, MEASURED BY IN-VIVO ELECTRON-PARAMAGNETIC-RESONANCE OXIMETRY AND MAGNETIC-RESONANCE-IMAGING

Electron Paramagnetic Resonance (EPR) oximetry was used to measure tis sue oxygen tension (pO(2)-partial pressure of oxygen) simultaneously i n the kidney cortex and outer medulla in vivo in mice. pO(2) in the co rtex region was higher compared to that in the outer medulla. An intra venous injection of endotoxin resulted in a sharp drop in pO(2) in the cortex and an increase in the medulla region, resulting in a transien t period of equal pO? in both regions. In control kidneys, functional Magnetic Resonance (MR) images showed the cortex region to have high s ignal intensity (T-2-weighted images), indicating that this region wa s well supplied with oxygenated hemoglobin, whereas the outer medulla showed low signal intensity. After administration of endotoxin?rin, we observed an immediate increase in signal intensity in the outer medul la region, reflecting an increased level of oxygenated blood in this r egion. Pretreatment of mice with N-G-monomethyl-L-arginine prevented b oth the changes in tissue pO(2) and distribution of oxygenated hemoglo bin, suggesting that localized production of nitric oxide has a critic al role to play in renal medullary hemodynamics. In combining in vivo EPR with MR images of kidneys, we demonstrate the usefulness of these techniques for monitoring renal pO(2) and changes in the distribution of oxygen.