Neuropeptide Y plasma levels and serum dopamine-beta-hydroxylase activity in MS patients with and without abnormal cardiovascular reflexes

An impairment in the autonomic function has been demonstrated in patients with multiple sclerosis (MS) using electrophysiological, pupillary and biochemical tests. Particularly evident were alterations in the cardiovascular reflexes, cutaneous sympathetic response and lymphomonocyte adrenergic binding. Electrophysiological and biochemical findings in MS patients have only occasionally been compared. Among the peripheral markers of the autonomic system, Neuropeptide Y (NPY) and dopamine-beta-hydroxylase (DBH) have been singled out as reliable indices of sympathetic function. The former is a peptide with a strong vasoconstrictive action, which is released from adrenergic endings together with noradrenaline following sympathetic activation. The latter is the enzyme which catalyses the conversion of dopamine to norepinephrine. It is located both in sympathetic endings and the chromaffin granules of adrenal medulla. To verify a failure in autonomic function in the course of MS, a battery of cardiovascular tests (assessing sympathetic and parasympathetic functions) was performed on 25 MS patients. The results were compared with a group of 20 age- and sex-matched control individuals. The plasma levels of NPY and the serum DBH activity were also determined in both groups. 52% of patients showed an impairment in sympathetic function in one or more tests (sustained handgrip, postural hypotension, cold face test). 48% of the patients had abnormal values in deep breathing test, indicating a failure of the parasympathetic function. 44% of patients showed also a paroxysmal tachycardia after cold face test, indicating an abnormal function of the vagal-cardiac and sympathetic-vascular smooth muscle pathways of the trigeminal nerve.