The Role of Adrenaline in Neurally Mediated Syncope

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yncope is a common problem associated with a poor quality of life. A majority of patients suffer from neurally mediated syncope (NMS), which is poorly understood in its pathophysiology. We evaluated cardiovascular autonomic functions as well as genetic polymorphisms of the α2B adrenoceptors (α2B-AR) predisposed to NMS patients (n=8, age 39±11 year, BMI 24±4 kg/m2) and healthy subjects (n=10, age 30±7 year, BMI 25±3 kg/m2). The standard autonomic function test (AFT) and head-up tilt (HUT) test were performed on each subject. Plasma catecholamines (CATs), renin, and aldosterone were measured after 30 minutes supine and at the end of the HUT. Twenty-four-hour urine collections were used to measure sodium and CATs excretion. A polymorphism of glutamic acid (Glu) repeats (Glu 12 or Glu 9, amino acids residues 301-303) present in the α2B AR was identified. We had three Glu 12/12, twelve Glu 12/9, and two Glu 9/9 subjects among the NMS patients and healthy controls; all of the NMS patients showed Glu 12/9. Syncopal subjects had Glu12/12 or Glu12/9 whereas subjects who had Glu9/9 did not have orthostatic symptom (OS). Therefore, we will investigate the possibility of this polymorphism as a marker of human vasomotor responses during orthostatic stress using subjects with and without NMS