Peripherally Administered β-Endorphin Increases Cerebrospinal Fluid Endorphin Immunoreactivity*

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Abstract
There is a discrepancy between the reported effect of iv β-endorphin on behavioral and pain syndromes and previously reported minimal penetrance of β-endorphin into rat and human brains. We examined the cerebrospinal fluid of three depressed subjects before and after iv infusion of β-endorphin and found markedly increased β-endorphin immunoreactivity, ranging from 223-552% of baseline. This elevation was evident up to 17 h after the infusion.