Circulating beta-endorphin levels at various stages of life: possible connections with migraine pathogenesis.

Recently, the existence of a circulating peptide, beta-endorphin (B-EP) with potent analgesic properties has been revealed. Our group has evaluated B-EP plasma levels in several physiological and pathological models. The life span pattern of this newly identified hormone was characterized by a progressive increase during prepuberal development, by stable levels in adults with typical circadian and monthly variations, and by a decrease in aging subjects. Cerebrospinal fluid B-EP contents inversely showed a declining linear trend throughout life, which suggests an independent source of B-EP in this compartment. The concomitant changes in the reproductive system suggested the possible influence of gonads on B-EP plasma levels, as confirmed by decreasing B-EP levels in gonadectomized humans and rats. Headache, which is likely to occur concomitantly with hormonal milieu variations, appeared to be associated with a deficiency in the B-EP system, centrally and peripherally, the lowest values being found in the protracted forms of headache.