Measurement of plasma catecholamines in small samples from mice

Introduction: A method is described by which it is possible to obtain measurements of plasma catecholamines in small samples from resting chronically catheterized mice. Methods: Standard alumina extraction procedures were systematically altered to maximize the recovery of catecholamines from 25-μl samples. The technique used commonly available HPLC with electrochemical detection (EC) equipment which was optimized according to the manufacturers' guidelines. Results: The limit of detection is 40 pg/ml plasma noradrenaline and 20 pg/ml of plasma adrenaline and the resting levels were 300 pg/ml for noradrenaline and 80 pg/ml for adrenaline, both much lower than previously published. Comparison of resting levels from catheterized mice with those obtained by CO2 plus decapitation and rapid decapitation reveal increases comparable to those reported following immobilization stress. The catecholamines adrenaline and noradrenaline were differentially increased by the two euthanasia methods. Discussion: The method was reliable, simple to perform and adequately sensitive. The resting levels of plasma catecholamines in mice are lower than previously published using a different sampling method. Differences in the norepinephine and adrenaline increases produced by the different methods of euthanasia suggest caution in the selection of method in studies of sympathetic function.