EVIDENCE FOR IN-VIVO HIGH-FREQUENCY PERIODICITY OF PLASMA BETA-ENDORPHIN IN HUMANS

Objective: To investigate whether high-frequency periodic fluctuation in the release of plasma immunoreactive (ir)-beta-endorphin occurs in humans. Design, patients and measurements: Blood was collected at 90-s ec intervals for 1 hour from the forearm vein of four healthy women an d subsequently analysed for ir-beta-endorphin by radioimmunoassay. Res ults: In all women circulating beta-endorphin release followed a high- frequency periodic rhythm pattern. The estimated spectral densities wi thin the four subjects varied between 3.6 min to 4.9 min. Conclusions: Our results provide the first in vivo evidence that fluctuations in t he release of beta-endorphin in humans cannot only be characterized by low-frequency pulses, but also by a high frequency periodic rhythm.