Mechanism of postmortem drastic increase of blood myoglobin concentration: its permeability through vascular wall

We provide the first direct experimental evidence that myoglobin (Mb) diffuses through vascular walls and enters the blood after death. Postmortem Mb concentration in the blood increases rapidly; however, up to this date, no one has reported the responsible mechanism. We hypothesized the direct diffusion of Mb from skeletal muscle into the blood through the vessel wall is causing this concentration change, and proved this morphologically and biochemically, through experiments using animal samples. Firstly, IHC Mb staining of the artery which was directly contacted with skeletal muscle on the adventitia, revealed that the Mb diffuses from adventitia to the intima with time. Then, Mb quantification using ELISA showed Mb exudes through vascular walls into the vessel lumen. For this experiment, a diffusion model was established by sandwiching the artery between gelatin discs with or without Mb. The Mb concentration increased in a time-dependent manner, with approximately 16 % of Mb in its source exuding into the lumen within 5 days. This rate increased significantly when vein was used instead of aorta. These findings clarify a fundamental mechanism of postmortem biochemical redistribution and may enhance the reliability of interpreting postmortem blood protein levels in forensic practice.