Title

The use of the plasma metanephrine/normetanephrine ratio to determine an exogenous epinephrine administration in suspected epinephrine poisoning

Date of Completion

January 2003

Keywords

Health Sciences, Toxicology|Biology, Animal Physiology|Health Sciences, Pathology

Degree

Ph.D.

Abstract

An analytical method that combined extractive acetylation and high performance liquid chromatography (HPLC)/mass spectrometry (MS) was developed for the quantitative analysis of rabbit total plasma metanephrine and normetanephrine. Extraction of acetylated metanephrines yielded higher absolute recoveries compared to various extraction methodologies that extract the un-derivatized compounds. The absolute recovery of acetylated metanephrine and normetanephrine from aqueous solutions ranged from 83–106% and 51–53%, respectively. The accuracy of metanephrine and normetanephrine extracted from plasma by extractive acetylation ranged from 88–107% and 84–95%, respectively. The limit of quantitation was 100 pg/mL and the upper limit of linearity was 10,000 pg/mL. The intra-run precision (%CV) calculated from replicate measurements (n = 7) of the slope was 10% and 6% for metanephrine and normetanephrine, respectively. Epinephrine administration studies were performed in anesthetized New Zealand white rabbits to assess the post-administration changes in the concentrations of total plasma metanephrine, normetanephrine and the metanephrine/normetanephrine ratio. Awake rabbits were subjected to immobilization stress and the post-stress changes in the concentrations of total plasma metanephrine, normetanephrine and the metanephrine/normetanephrine ratio were determined. The post-administration plasma metanephrine/normetanephrine ratios in rabbits administered 0.01 mg/kg epinephrine-HCl were distinguishable from the stress induced threshold ratio whereas the plasma metanephrine concentration threshold could not be confidently distinguished from the metanephrine concentrations in the sub-lethal exogenous administration of epinephrine. Although the plasma metanephrine concentrations were not a predictor of survival times in rabbits administered a lethal dose of epinephrine, the metanephrine concentrations post-administration of a lethal dose of epinephrine were significantly greater than the endogenous metanephrine threshold value. Given that the metanephrine/normetanephrine ratio was significantly different in acute death versus death 8 hours post-administration and that the absolute metanephrine concentrations were not significantly different suggests that plasma metanephrine/normetanephrine ratios could be used to establish the relative time of administration of a high dose of epinephrine or may be a predictor of survival to epinephrine poisoning. ^