Effects of Exogenous βh-Endorphin on Pituitary Hormone Secretionand Its Disappearance Rate in Normal Human Subjects*

Abstract

The disappearance rate of the immunoreactive β_h-endorphin and the effects of β_h-endorphin on pituitary hormone secretion were investigated in normal volunteers. Synthetic human β_h-endorphin was administered as a 2.5-mg iv bolusto five normal women resulting in a 1000-fold increase in concentration of circulating immunoreactive β_h-endorphin within 2.5 min. This was followed by a triple exponential disappearance curve yielding an initial fast component with a halftime (t_½ ± SD)of 4.1 (± 0.6) min, a midrange component with a t_½ of 13.1 (± 0.6) min,and a slow component with (t_½ of 46.2 (± 7.0) min. In both male and female subjects this dose of β-endorphin induced a significant increase in the levels of PRL and a significant decline in the concentration of LH, without altering basal levels of GH and TSH.