Substance P mechanism in cluster headache: evaluation in plasma and cerebrospinal fluid.

Substance P (SP), present in sensory afferent neurons, seems to process nociceptive information in the trigeminal system. SP, released from peripheral trigeminal endings, causes typical cluster headache (CH) signs, e.g. vasodilatation, conjunctival and nasal edema and miosis. Opiates and somatostatin (SRIF), both active in relieving CH attack, inhibit SP release from the central and peripheral trigeminal system. In the present study, plasma and cerebrospinal fluid (CSF), SP-like immunoreactivity (SPLI) and enkephalinase activity (EKA), and plasma SRIF-like immunoreactivity (SRIFLI) have been evaluated during spontaneous and histamine induced attacks in the cluster phase. During the histamine provoked attacks, CSF SPLI and plasma SRIFLI and EKA were unchanged, while plasma SPLI decreased significantly. During spontaneously occurring attacks, plasma SRIFLI was found to be unmodified and a significant lowering of SPLI was detected when compared with controls. Moreover, both during and between attacks in the cluster phase, plasma EKA was increased in comparison with the values in controls. It remains to be seen whether variations of plasma SPLI and EKA levels play a role in the CH mechanism.