title: Repetitive measurements of intrarenal oxygenation in vivo using L band electron paramagnetic resonance.
abstract: Intrarenal oxygenation is heterogeneous with oxygen levels normally being highest in the superficial cortex and lowest in the inner medulla. Reduced intrarenal oxygenation has been implied in the pathology of several kidney diseases. However, there is currently no method available to repetitively monitor regional renal oxygenation using minimally invasive procedures. We therefore evaluated implantable lithium phthalocyanine (LiPc) probes, which display a close correlation between EPR line width and oxygen availability.LiPc probes were implanted in the kidney cortex and medulla in the same mouse and EPR spectra were acquired using a L band scanner during inhalation of air (21 % oxygen) or a mixture of air and nitrogen (10 % oxygen). In order to separate the signals from the two probes, a 1 G/cm gradient was applied and the signals were derived from 40 consecutive sweeps. Peak-to-peak comparison of the EPR line was used to convert the signal to an approximate oxygen tension in MATLAB. Kidney cortex as well as medullary oxygenation was stable over the 45 day period (cortex 56 ± 7 mmHg and medulla 43 ± 6 mmHg). However, 10 % oxygen inhalation significantly reduced oxygenation in both cortex (56 ± 6 to 34 ± 2 mmHg n = 15 p < 0.05) and medulla (42 ± 5 to 29 ± 3 mmHg n = 7 p < 0.05).In conclusion, L band EPR using LiPc probes implanted in discrete intrarenal structures can be used to repetitively monitor regional renal oxygenation. This minimally invasive method is especially well suited for conditions of reduced intrarenal oxygenation since this increases the signal intensity which facilitates the quantification of the EPR signal to absolute oxygenation values.
authors.affiliation: Division of Drug Research, Experimental Renal Medicine, Department of Medical and Health Sciences, Linköping University, Linköping, 58183, Sweden. stephanie.franzen@liu.se.|Center of Medical Image Science and Visualization, Linköping University, Linköping, Sweden. stephanie.franzen@liu.se.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Franzén
authors.affiliation: Division of Drug Research, Experimental Renal Medicine, Department of Medical and Health Sciences, Linköping University, Linköping, 58183, Sweden.
authors.forename: Liselotte
authors.initials: L
authors.lastname: Pihl
authors.affiliation: EPR Center for Viable Systems, Department of Radiology, Geisel School of Medicine, Hanover, NH, USA.
authors.forename: Nadeem
authors.initials: N
authors.lastname: Khan
authors.affiliation: Division of Drug Research, Experimental Renal Medicine, Department of Medical and Health Sciences, Linköping University, Linköping, 58183, Sweden.|Center of Medical Image Science and Visualization, Linköping University, Linköping, Sweden.|Division of Integrative Physiology, Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden.
authors.forename: Fredrik
authors.initials: F
authors.lastname: Palm
authors.affiliation: Center of Medical Image Science and Visualization, Linköping University, Linköping, Sweden.|Department of Biomedical Engineering (MTÖ), County Council of Östergötland, Radiation Physics, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
authors.forename: Håkan
authors.initials: H
authors.lastname: Gustafsson
mesh_terms: D000818:Animals; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods*; D007672:Kidney Cortex / Q000378:metabolism*; D008297:Male; D051379:Mice; D010100:Oxygen / Q000378:metabolism*
chemical_list: D010100:Oxygen