Catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) signal through the α1-adrenergic receptor in the central and peripheral nervous systems. There is no α1C receptor. At one time, there was a subtype known as α1C, but it was found to be identical to the previously discovered α1A receptor subtype.[1] To avoid confusion, naming was continued with the letter D.