Ulf von Euler.

During the 1930s, certain investigators alluded to the possibility that norepinephrine might be the neurotransmitter liberated at adrenergic nerve endings. However, it was not until the mid-1940s that Ulf von Euler used various pharmacological and chemical assays to correctly identify the major catecholamine as norepinephrine (noradrenaline) in extracts of adrenergic nerves from different species. When it became necessary to differentiate epinephrine from norepinephrine, von Euler used two bioassays with different sensitivities to the two amines, such as the cat blood pressure and hen rectal caecum.

The discovery of norepinephrine as the neurotransmitter at postganglionic sympathetic nerve endings positioned von Euler at the frontier of research in biogenic amines.