A high-energy focused microwave system for killing experimental animals was used to rapidly inactivate enzymes and prevent postmortem breakdown of adenine nucleotides and adenosine, thereby enabling accurate measurements of AMP, ADP, ATP and adenosine in rat brain (the nucleoside adenosine is a product of ATP degradation and is important of cellular metabolism).
Since adenosine levels can change rapidly due to postmortem breakdown of ATP, accurate determinations of purine levels cannot be obtained under conditions where even brief postmortem delays are present (as occurs with decapitation). For comparison, purine levels were measured in brains of rats killed by decapitation, decapitation into liquid nitrogen, or in situ freezing of the brain with liquid nitrogen.
Of the three microwave exposure power levels used, 10, 6.0 or 3.5 kW, rats killed by 10 kW had the highest ATP levels and cellular energy charge value, and the lowest levels of AMP and adenosine. Of the 6 brain regions studied, adenosine levels (pmol/mg protein) ranged from 10 in cerebral cortex to 170 in cerebellum of rats killed using 10 kW microwave irradiation. For comparison it ranged from 840 in cerebral cortex to 2498 in striatum of rats killed by decapitation. Focused microwave killing permits precise measurements of purine in different regions of rat brain.