Episodic secretion of met-enkephalin immunoreactive material in human plasma and CSF

Plasma and CSF met-enkephalin immunoreactive material (ME-IR) concentrations were measured in 5 subjects at different hours of the day. Within the 24 hrs CSF ME-IR concentrations ranged in the same patient from 20 to 5000 pg/ml. Plasma ME-IR concentrations presented a circadian rhythm with lower values between 4:00 and 8:00 p.m.