Foot-shock induced stress increases β-endorphin levels in blood but not brain

FOOT-SHOCK induced stress promotes a five to sixfold increase in β-endorphin plasma levels. Similar increases were also found for ACTH plasma levels. In the hypothalamus, foot-shock induced stress promotes a decrease of β-endorphin assayed by radioimmunoassays. These data suggest that physiological increases in plasma β-endorphin levels induced by stress do not result in elevated levels of brain β-endorphin.