Sympathetic innervation of the liver in man and dog: an immunohistochemical study.

The sympathetic innervation of human and dog livers was examined by immunohistochemical localization of neuron-specific enolase to visualize the total complement of hepatic nerves and the localization of two enzymes involved in catecholamine synthesis, tyrosine hydroxylase and dihydroxyphenylalanine decarboxylase, to visualize sympathetic nerves. Similar results were obtained for both man and dog. About 60% of the non-myelinated axons supplying the hepatic parenchyma, and virtually all those supplying the vasculature, appeared to be sympathetic. The pattern of dihydroxyphenylalanine decarboxylase immunoreactivity was compatible with innervation of the intrahepatic hepatic arteries and portal veins by dopaminergic as well as by noradrenergic sympathetic nerves. By contrast, there was no evidence for a dopaminergic component in the parenchymal sympathetic innervation.