Research On The Applicabilities Of Different Methods To Extrapolate The Postmortem Interval Of Rats In Xining

Objective To explore the relationship between corpse temperature and postmortem interval, postmortem interval and rigor mortis, postmortem interval and DNA by measuring the corpse temperature, length of stretching and angle of raising of hind legs, liver nuclei of rats in different intervals.Methods Rats were randomized into different postmortem groups, and the 0 h group was the control group. Rats were killed by neck dislocation and measured corpse temperature by digital thermometer, length of stretching and angle of raising of hind legs by the ruler and protractor. Brain, heart and liver were obtained, fixed in formalin, stained with Feulgen, and then analyzed by Image analysis technology(IAT).The relationship between PMI and DNA was analyzed by measuring AOD, IOD, A, MD, Perimeter and PI.Results 1. Corpse temperature decreased slow after the first fast in laboratory,where the temperature was(19-21)℃ and humidity was(20-31)%, and corpse temperature was the same as the environmental temperature at PMI 10.5h.The regression equations between rectal temperature and PMI:(0~2.5)h:Y=7.438-0.206X(r=-0.979);(2.5~5)h:Y=19.663-0.687X(r=-0.971);(5~10.5)h:Y=47.799-1.978X(r=-0.993).The related coefficients were-0.979,-0.971,-0.993,respectively. 2.The length of stretching and angle of raising of hind legs obviously decreased close to zero, remained for a while and then rapidly increased, as the time was going. There were significant differences in length of stretching and angle of raising during the formation and remission period(P<0.01). During the formation of rigor mortis: there were high negative correlations between stretching and PMI,angle of raising of hind legs and PMI(-0.989 and-0.972, respectively); the linear regression equations between PMI and length of stretching of hind legs: Y=4.632-0.185X; the linear regression equations between PMI and angle of raising of hind legs: Y=4.53-0.106 X.During the remission of rigor mortis: there were high positive correlations between stretching and PMI, angle of raising of hind legs and PMI(0.968 and 0.958,respectively);the linear regression equations between PMI and length of stretching of hind legs: Y=2.307X+9.237;the linear regression equations between PMI and angle of raising of hind legs: Y=1.304X+9.726. 3.AOD,IOD,A,MD and Perimeter in liver, heart and brain had down trends as the time going, and PI had rising trends. The DNA of brain and liver degraded faster than heart. The relationship between PMI and IOD,PI were better than other parameters. At 72 h PMI DNA in three tissues were not degraded completely.Conclusion 1. It was showed by analysis and comparision that three methods have their unique own scopes of application at indoor environment that temperature was 19-21℃ and humidity was 20~31% in xining. Rigor mortis was fully formed at PMI 5h,maintained for 7 h and then began to be relaxed until PMI 72 h.The greatest drop of corpse temperature was occurred in PMI 2.5h,after PMI 10.5h the temperature was same as the environmrnt temperature. DNA was not completely degraded at PMI 72 h. 2.Length of stretching and angle of raising of hind legs might be used as predictors of early postmortem interval. 3. PI and IOD were more specifically suited to estimate the PMI than other indexes related with DNA.