Fiber optic surface fluorometry-reflectometry technique in the renal physiology of rats

Most current knowledge on events in the mitochondria leading to acute renal failure originates from studies in which indirect methods were used. The disadvantage of these methods is that they cannot measure the turnover rate of various metabolites, and only one result per animal can be obtained. Chance et al. /9/ developed a method using optical techniques for continuously monitoring the fluorescence of intramitochondrial NADH, which has been applied mainly to the brain. This optical method has not yet been examined quantitatively in the kidney and no attempt has been made to adapt this method for routine measurement in kidney tissue. The purpose of this study was to adapt the surface fluorometry method for monitoring renal NADH redox state in situ, and to determine whether the hemodynamic artifacts involved in fluorometric studies of the renal surface in situ could be eliminated by using a correction factor. Another purpose was to understand the relationship between the changes in reflectance and blood volume in the rat kidney. This was achieved by measuring the reflectance after: a) blood exchange by FC-43 emulsion; b) intrarenal saline flush; c) occlusion of the renal vein, renal artery and reopening of the renal vein; d) calculation of the correlation between changes in kidney weight after renal artery occlusion, and the reflectance. Our results suggest that in the rat kidney, as opposed to the brain, a correction factor of 1:1 is not always applicable. This factor may vary between animals, and it is therefore necessary to adjust it electronically for each rat kidney. This observation contradicts the view suggesting a constant correction factor of 1:1 in the kidney. The results reported herein indicate that changes in the reflectance in the ischemic rat kidney are due to changes in blood volume. In conclusion, it seems that optical techniques for monitoring fluorescence are suitable for localized, continuous and non-invasive recording of tissue mitochondrial NADH redox states under various conditions in the rat kidney.