Sympathetic Receptor Action

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Abstract
Exptl. results descr. suggest that the nature of the sympathetic receptor determines whether or not sympathomimetic drugs cause excitation or inhibition. The molecular configuration optimal for each type of action differs. With epinephrine-like compounds the m-hydroxyl group is most important for stimulation of the excitatory (Ac) receptor; the alcoholic hydroxyl on the side chain for the inhibitory (Ar) receptor. The pressor potency of m-hydroxyphenethylamine is comparatively low. The addition of each group which characterizes the epinephrine molecule results in an increase in potency. The pressor action of l-phenyl-2-aminoethanol is comparatively low. The subsequent addition of each of the epinephrine groups other than the m-hydroxyl leads to a reduction in pressor potency. The replacement of the N-methyl by larger alkyl groups gives rise to depressor compounds. The sympathetic receptors of the myocardium appear to be undifferentiated (Acr) mediating only excitation in opposition to the inhibitory actions of the parasympathetic mechanism. Receptor patterns of the bronchioles, uterus and small intestine are descr. Those for the bronchioles are predominantly inhibitory (Ar) whereas in most spp. both inhibitory and excitatory receptors (Ac) are found in the uterus and intestine.