Endorphins in brains of decapitated and microwave-killed mice

The size distribution of opioid peptides (endorphins) in mouse brain was determined by gel filtration, using the inhibition of stereospecific ³H-etorphine binding to guinea pig brain membranes as a measure of endorphin activity. The largest endorphin was about the same size as β-LPH-(61–91), the next largest was about half this size and the smallest was the size of the pentapeptide enkephalins. There was no important difference in the size distribution between brains of mice killed by rapid microwave irradiation and those killed by decapitation. Thus, opioid peptides of all three size classes appear to be present in the brain $\text{in}$$\text{vivo}$.