title: Circadian variations of human flexion reflex.
abstract: We investigated 8 healthy male volunteers, evaluating RII and RIII thresholds every 6 h starting from noon, for a 24-h period. Both reflex responses exhibited a circadian rhythmicity: the lowest values were found in the early morning (9.1 +/- 3.0 and 13.1 +/- 4.4 mA, respectively), while the highest values were observed at midnight (13.1 +/- 3.5 and 18.5 +/- 5.3 mA). Also mean cosinor analysis indicated the existence of a significant rhythm with acrophase at 20:12 for RII and 22:29 for RIII. In 4 subjects, beta-endorphin plasma (beta-EP) level was tested during the day. No correlation was observed between circadian changes of beta-EP and RIII threshold. Other factors are likely to be involved in the circadian variation of nociceptive flexion reflex in man.
mesh_terms: D000328:Adult; D002940:Circadian Rhythm; D004723:Endorphins / Q000097:blood; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D009132:Muscles / Q000294:innervation; D009619:Nociceptors / Q000503:physiopathology; D010146:Pain / Q000503:physiopathology*; D011930:Reaction Time / Q000502:physiology; D012018:Reflex / Q000502:physiology*; D012684:Sensory Thresholds; D013497:Sural Nerve / Q000503:physiopathology; D014110:Touch / Q000502:physiology; D001615:beta-Endorphin
chemical_list: D004723:Endorphins; D001615:beta-Endorphin