METHYSERGIDE INHIBITS OR BLOCKS THE EFFECTS OF SEROTONIN, A SUBSTANCE WHICH MAY BE INVOLVED IN THE MECHANISM OF VASCULAR HEADACHES, ACTING DIRECTLY OR INDIRECTLY TO LOWER PAIN THRESHOLD AS AN INTRINSIC "MOTOR HORMONE" OF THE G.I. TRACT, AND AS A "HORMONE" INVOLVED IN CONNECTIVE TISSUE REPARATIVE PROCESSES.