Effects of collection methods and storage on the in vitro stability of canine plasma catecholamines

Norepinephrine (NE) and epinephrine (EPI) collected from dogs were sequentially and temporally measured in blood and plasma at 24 C. Heparin and EDTA anticoagulants, in combination with reduced glutathione and EDTA as a preservative, were also compared. Norepinephrine and EPI concentrations were measured by high-pressure liquid chromatography with electrochemical detection. In heparinized plasma, NE and EPI concentrations were relatively stable in the absence or presence of preservative after 24 hours at 24 C. In EDTA plasma, NE and EPI values were less stable when compared with those in heparinized samples. Norepinephrine concentrations in EDTA plasma without preservative decreased by 163.2 +/- 8.88 pg over 24 hours, compared with an 86.6 +/- 7.92 pg loss of NE in heparinized plasma. The degradation of EPI in EDTA plasma without preservative was also twofold greater, compared with that in heparinized plasma. Addition of preservative had no stabilizing effect on NE or EPI in heparinized or EDTA plasma. During long-term storage at -70 C, plasma NE and EPI values decreased less than 0.6 and less than 0.1 pg/d, respectively. Norepinephrine and EPI values were stable in heparinized blood for 6 hours but decreased to less than 25% and less than 6% of initial base line values, respectively, when plasma separation was delayed 24 hours.