Histopathology and laser autofluorescence of ischemic kidneys of rats

The purpose of this research was to evaluate the severity of renal ischemia/reperfusion injury as determined by histology and by laser-induced fluorescence (LIF) with excitation wavelengths of 442 nm and 532 nm. Wistar rats (four groups of six animals) were subjected to left renal warm ischemia for 20, 40, 60 and 80 min followed by 10 min of reperfusion. Autofluorescence was determined before ischemia (control) and then every 5-10 min thereafter. Tissue samples for histology were harvested from the right kidney (control) and from the left kidney after reperfusion. LIF and ischemia time showed a significant correlation (p<0.0001 and r(2)=0.47, and p=0.006 and r(2)=0.25, respectively, for the excitation wavelengths of 442 nm and 532 nm). Histological scores showed a good correlation with ischemia time (p<0.0001). The correlations between optical spectroscopy values and histological damage were: LIF at 442 nm p<0.0001, LIF at 532 nm p=0.001; IFF (peak of back scattered light/LIF) at 442 nm p>0.05, and IFF at 532 nm p>0.05. After reperfusion LIF tended to return to preischemic basal levels which occurred in the presence of histological damage. This suggests that factors other than morphological alterations may have a more relevant effect on changes observed in LIF. In conclusion, renal ischemia/reperfusion changed tissue fluorescence induced by laser. The excitation light of 442 nm showed a better correlation with the ischemia time and with the severity of tissue injury.