β-Endorphin Suppresses Adrenocorticotropin and Cortisol Levels in Normal Human Subjects

Abstract

To determine the effect of (β-endorphin on the pituitary-adrenal axis, human synthetic β-endorphin was infused iv in 10 normal human subjects. Either β-endorphin (0.3, 1.0, and 3.0 μg/kg·min, each dose for 30 min) or a control (sham) infusion of 5% dextrose water was administered in a blind fashion in the same subjects on 2 successive days. Plasma ACTH and cortisol and serum human GH and PRL levels were measured 30 min before and then every 30 min for 210 min during and after both the β-endorphin and control infusions. In all subjects, cortisol levels decreased below the basal level in response to the infusion of β-endorphin. The threshold dose was 1.0 μg/kg·min, with the mean control cortisol level (12 ± 2 μg/dl) declining significantly to 7 ± 1 μg/dl (1.0 μg/kg·min) and 6 ± 1 μg/dl (3.0 μg/kg·min; P < 0.01). ACTH levels also were significantly lower than the control value (48 ± 6 pg/ml) at the 1.0 μg/kg·min dose (32 ± 4 pg/ml; P < 0.05). The decline in ACTH and cortisol levels was also significantly different from levels obtained during the control infusions (P = 0.001 and P = 0.01, respectively). The results are consistent with short feedback loop inhibition of pituitary ACTH release or suppression of hypothalamic corticotropin-releasing factor release by β-endorphin.