Chemical Structure and the Definition of Sympathin E

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Abstract
In studying the relation of chemical structure to the action of sympathomimetic amines, a sensitive method was developed for the quantitative detn. of the inhibitory properties. There was utilized the inhibitory effect of sympathomimetic amines on transmission at synapses in sympathetic ganglia. Synaptic transmission was kept at a control level by applying electrical stimuli of constant intensity to the preganglionic nerves and recorded by registering the postsynaptic action potentials from the postganglionic nerves by high-gain amplifiers. A drug injd. intraven. shows its inhibitory effect by a reduction in the height of the postsynaptic potentials. It was thus shown that when adrenaline and nor-adrenaline were intravenously injected in a cat anesthetized with nembutal and the superior cervical ganglion studied, nor-adrenaline had a considerable inhibitory effect. Since these synapses are adrenergic, this disqualifies nor-adrenaline from being sympathin E unless the definition of E as a purely excitatory substance without inhibitory action is negated. Neither nor-adrenaline nor any of the sympathomimetic amines in a series of 21 compds. studied can be sympathin E. An alternative is to regard sympathin E as a substance that is only predominantly rather than purely excitatory.

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