Activity of the uptake-1 norepinephrine transporter as measured by I-123 MIBG in heart failure patients with a loss-of-function polymorphism of the presynaptic α2C–adrenergic receptor

Abstract Background Patients with a deletion of 4 consecutive amino acids in the gene encoding for the α 2C –adrenergic receptor (α 2C Del322-325) have an increased prevalence of clinical heart failure, worse clinical status, and a lower left ventricular ejection fraction compared with patients without this deletion. We postulated that patients with the α 2C Del322-325 polymorphism would have a compensatory increase in norepinephrine uptake-1 transporter activity as measured by iodine 123 metaiodobenzylguanidine (MIBG). Methods and results Thirty-nine patients with heart failure related to idiopathic dilated cardiomyopathy were studied. Demographic characteristics, left ventricular ejection fraction, maximum oxygen consumption, exercise duration, and plasma norepinephrine levels did not differ between patients with the α 2C receptor polymorphism (n = 9) and those without it (n = 30). Patients with the α 2C Del322-325 polymorphism had significantly greater heart-to-mediastinum ratios of I-123 MIBG at 4 hours after tracer injection (1.60 ± 0.19 vs 1.41 ± 0.19, P = .0117) and greater background-corrected heart counts per pixel at 4 hours compared with patients without the polymorphism. Conclusions Patients with genetic impairment of the α 2C –adrenergic receptor have augmented activity of the norepinephrine uptake-1 transporter as measured by I-123 MIBG. Further studies are needed to clarify the mechanism by which uptake-1 transporter activity is increased in this setting.