Postmortem Stability of Brain 3‐Methoxy‐4‐Hydroxyphenylethyleneglycol and 3,4‐Dihydroxyphenylethyleneglycol in the Rat and Mouse

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Abstract
To assess the postmortem stability of brain 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) and 3,4-dihydroxyphenylethyleneglycol (DHPG) levels, groups of rats and mice were killed by cervical dislocation and left at either 21.degree. or 4.degree. C for intervals of up to 24 h until removal and freezing of whole brain. Whole brain free and total MHPG and DHPG levels were determined simultaneously by gas chromatography-mass fragmentography (GC-MF). By 2 h after death, statistically significant decrements occurred in rat brain free DHPG (20%), total MHPG (21%) and total DHPG (11%) at 4.degree. C, but free MHPG increased significantly (50%) compared with controls. At 21.degree. C, rat brain total MHPG increased compared with controls at 2 h (15%), but decreased at 4 h (15%) and 8 h (15%). Free MHPG levels were increased at these times. Although brain total and conjugated DHPG levels showed little change, free DHPG levels were reduced at all times. In mouse brain, no significant changes occurred in free MHPG and DHPG by 24 h at 4.degree. C. At 21.degree. C, mouse brain DHPG levels decreased whereas DHPG concentrations increased over the 8 h period of study. The findings demonstrate the occurrence of significant postmortem time- and temperature-dependent changes in brain MHPG and DHPG concentrations and indicate caution in the interpretation of changes in these metabolites of norepinephrine in studies employing human postmortem brain tissue.