Figure 1. Neuronal noradrenaline uptake in the heart can be assessed by measuring the transcardiac extraction of plasma tritiated noradrenaline (3H NA) and the overflow of tritiated dihydroxphenylglycol (3H DHPG) into the coronary sinus after reuptake of 3H NA into sympathetic nerves and intraneuronal metabolism by monoamine oxidase (MAO). Additional information is provided by the extraction of plasma tritiated adrenaline in transcardiac passage (adrenaline is also a substrate for the noradrenaline transporter), not shown, and the whole-body clearance of adrenaline and noradrenaline from plasma.