High Levels ofβ-Endorphin in Hypophyseal Portal Blood*

Abstract

β-Endorphin was measured by RIA in the hypophyseal portal blood of six pig-tailed monkeys after pituitary stalk section. The mean β-endorphin concentration was 4,770 pg/ml (range, 2,900-10,500 pg/ml). This was more than 100 times greater than the mean simultaneous peripheral venous concentration, which was 45 pg/ml. After gel filtration of the portal plasma extracts, the majority of β-endorphin immunoactivity eluted as a single peak coincident with synthetic β-endorphin standard. The demonstration of high levels of β-endorphin in the hypophyseal portal blood suggests that endogenous opioids of hypothalamic origin are secreted into the portal blood and may directly affect the pituitary. (Endocrinology106: 1323, 1980)