β-Endorphin concentrations in serum, hypothalamus and central gray of hypophysectomized and mediobasal hypothalamus lesioned rats

The serum and brain concentrations of β-endorphin immunoreactivity have been studied in intact, mediobasal hypothalamus (MBH) lesioned and hypophysectomized male rats. After hypophysectomy there is a major reduction (90%) of β-endorphin concentration in the serum but only a partial reduction (20%) in the mediobasal hypothalamus. However, MBH lesions enhance β-endorphin serum values in previously hypophysectomized rats. Long-term MBH lesions alone lead to an almost complete disappearance of β-endorphin in the central gray matter with a slight decrease in the serum. These data clearly show that: (1) the pituitary is the major source of β-endorphin in the serum; (2) the hypothalamus is the major source of β-endorphin in the central gray matter; and (3) there is clear influence of the pituitary on hypothalamic β-endorphin.