The adrenoceptors ADRA2A is expressed in the brain, spleen, kidney, aorta, lung, skeletal muscle, heart and liver. ADRA2A -adrenoceptor knockout mice exhibit disruption of presynaptic inhibition of noradrenaline release at high stimulation frequencies. ADRA2A receptor is the principal autoreceptor in the presynaptic feedback loop regulating noradrenaline release. However, another a2 autoreceptor is also present.