Increase in plasma methionine-enkephalin levels during the pain attack in episodic cluster headache.

Since high levels of endogenous opioids (endorphins, enkephalins) were found in brain areas classically related to nociception, their peripheral levels in humans were studied in different pain syndromes yielding contradictory results. This study was undertaken to assess changes in plasma methionine-enkephalin (met-enkephalin) levels in patients with episodic cluster headache associated with the pain period. Twenty-nine patients, 24 in the cluster period (6 of them during an attack) and 3 in the remission period were studied. Two other patients were subjected to a longitudinal follow-up. Plasma met-enkephalin levels were determined by radioimmunoassay (RIA) with specific antibody. Plasma peptide concentration (pmol/ml) was higher (p less than 0.001) in patients during the pain attack (3.97 +/- 1.18) than in controls (0.25 +/- 0.03). When measured 4 and 48 h after the pain attack lower levels were found (0.46 +/- 0.06) which decreased to control values after 24 h. These results may suggest involvement of peripheral enkephalins in pain modulation in patients with episodic cluster headache.