Storage at 0°C did not stop every postmortem MDMA concentration change in a rat experiment. Some concentration peaks occurred later under that condition than at 20°C. Because humidity also differed, the comparison tested two storage environments rather than isolating temperature alone. It cannot supply a correction factor for a human autopsy result.
The animals and exposure model
Liang and colleagues randomly assigned 720 male Sprague–Dawley rats, weighing approximately 200 ± 10 g, to four groups of 180. Two groups received 20% ethanol–water as their only drinking liquid for four weeks; the others received water. One ethanol-exposed group and one water group then received intragastric MDMA at 150 mg/kg. The other groups received saline.
The rats were killed by neck concussion 30 minutes after dosing. Thus, the experiment did not establish that MDMA alone, or an MDMA–ethanol interaction, caused their deaths. Despite the paper’s discussion of acute combined use, its alcohol history included four weeks of exposure; it was not simply a single simultaneous drink-and-MDMA challenge.
Body storage and specimen storage were different steps
Each exposure group was divided between 20°C with 70% humidity and 0°C with 50% humidity, with 90 rats per environment. The paper calls the latter “freeze” storage, but the specified temperature was 0°C. It should not be relabeled as a −20°C laboratory-freezer experiment.
At 15 postmortem times from zero through ten days, six rats per exposure group and storage condition supplied specimens. Collected matrices included heart blood, vitreous, urine, brain, heart, lung, liver, spleen, kidney, testicles and biceps femoris muscle. After collection, samples were kept at −70°C until analysis. That later specimen-storage temperature was not the temperature at which the bodies decomposed.
The time course therefore compared animals sampled at different times. It was not repeated blood collection from the same living or deceased rat.
Later peaks show that change continued
Table 5 places the heart-blood MDMA peak at day three under 20°C storage and day four under 0°C storage, both with and without the ethanol-exposure history. In the combined-exposure group, the vitreous peak shifted from day four to day six, and the urine peak from 24 hours to day two.
The changes were specimen-dependent. For example, the combined group’s lung and femoral-muscle peaks did not show the same delay. The authors described an overall pattern of increasing concentrations followed by decreases, with some late results becoming undetectable. They reported significant variation in concentrations over the ten-day period by MANOVA, p < 0.01; that does not make every separate numerical contrast statistically significant.
Why the result is not a pure temperature effect
The colder bodies also had lower environmental humidity. Without comparing temperature while holding humidity constant, the design cannot allocate every observed difference to cooling alone. Tissue water changes, diffusion, degradation and the short dose-to-death interval further complicate interpretation.
Peak concentrations also do not all describe the same moment. Comparing two groups’ maxima can compare different postmortem days. Nor is an area under a postmortem concentration–time curve a measurement of antemortem impairment or absorbed human dose.
The analytical procedure had a defined scope
MDMA quantification used extraction, derivatization and gas chromatography with electron-capture detection, rather than mass-spectrometric confirmation. For heart blood, the reported calibration range was 0.5–100 µg/mL and detection limit 8 ng/mL. Tissue calibration was generally 0.5–50 µg/g. Blood validation in Table 4 reported intra-day imprecision of 1.9–3.4% and inter-day imprecision of 2.3–5.1% at the tested levels.
The report also contains conflicting summaries of the ethanol measurements: the Results state no significant difference between the two alcohol-exposed groups, while the Conclusion describes a significant difference. That discrepancy should not be turned into a demonstrated alcohol effect.
For forensic use, retain the species, high experimental dose, exposure history, anatomical matrix, both storage variables and sampling time. Cold storage reduced or delayed some changes under this protocol; it did not establish preservation of an individual’s concentration during life. See also why a postmortem tissue ratio is not an exact blood reconstruction.
Primary source
Liang M, Zhang J, Zheng N, Liu L. How Postmortem Redistribution of MDMA in Acute Alcohol-MDMA Combined-Use Rats Change under Effects of Alcohol. Scientific Reports. 2017;7:4038. doi:10.1038/s41598-017-04416-y.
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