Study on the correlation between pmi and OD changes in rat's plasma

We chose the UV-Vis spectrophotometry as a new way to investigate the postmortem interval (PMI). One hundred fifty Sprague-Dawley female rats (weight 260 g±10g, from Xi'an Jiaotong University Animal Center) were chosen and sacrificed by cervical dislocation. The bodies were kept in a controlled environmental chamber set at (20 ± 2) °C. The plasma was harvested in course of 0 to 24 hours after death. The optical density (OD) at different wavelengths was measured with an UV-Vis spectrophotometer (type-UV250). It was shown that the OD changes of plasma at 577, 416 and 275 nm in 24 hours were dramatically related to PMI, and the R-indexes were 0.969, 0.97 and 0.898. The regression formulae of these indexes were worked out taking OD as independent variable, and PMI as variable. The quadratic equations were: PMI=231.227ODplasma at wavelength of 577 nm-501.16ODplasma at wavelength of 577 nm²-3.0809 (R²=0.945), PMI=31.7426ODplasma at wavelength of 416 nm-9.1847OD²plasma at wavelength of 416 nm-3.1837 (R²=0.94), and PMI=95.2388ODplasma at wavelength of 275 nm-39.343OD²plasma at wavelength of 275 nm-32.408 (R²=0.795). It was concluded that the OD changes of rat's plasma are good and potential markers for the estimation of PMI and should be very useful in forensic practice.