Serum prolactin levels in active multiple sclerosis and during cyclosporin treatment

Prolactin is essential for immune function. Excess prolactin augments some immune reactions, whereas low serum levels of prolactin inhibit immune function and prevent experimental allergic encephalomyelitis, an animal model of multiple sclerosis (MS). Activated lymphocytes, characteristics of MS, release prolactin. In this study, serum prolactin levels were normal in 35 patients with chronic progressive MS and 19 patients with acute exacerbations. These results suggest it is unlikely that prolactin contributes to the enhanced immune reactivity characteristic of MS. Acute cyclosporin A (CsA) administration increases circulating prolactin levels in animals and might paradoxically augment some immune reactions. We find that chronic CsA therapy for MS does not cause elevations in serum prolactin and should not reverse any therapeutic effect of CsA. Disturbances of prolactin regulation are not characteristic of MS.