Neuroendocrine insights from the laboratory to the clinic

The interaction between adrenergic nerves and enterochromaffin (EC) cells was studied in health and disease using animal models and patients with the midgut carcinoid syndrome.

The methods included morphological techniques (fluorescence microscopy/cytofluorimetry, electronmicroscopy), experimental models (in vivo/in vitro nerve stimulation, pharmacological analyses, axonal transport, tumor transplantation, tumor cell cultures) and clinical tests (pentagastrin provocation, octreotide scintigraphy).

From vagal nerve stimulation studies it was clear that activation of adrenergic fibers could release serotonin (5-HT) from EC cells, which led to the mapping of a vagal adrenergic pathway. Ultrastructurally a direct innervation of EC cells was demonstrated. It was confirmed in vitro that adrenoceptors controlled the release of 5-HT; it was maintained in neoplasia as studied in the tumor models. The tumor cells shared several functional and morphological characteristics with adrenergic neurons and exerted trophic actions on neurons grown in co-culture.

Pentagastrin provocation of 5-HT release in carcinoid patients may be mediated via release of catecholamines from the adrenals in turn activating adrenoceptors on tumor cells. Pretreatment with a somatostatin analog can reduce these reactions and thus minimize the risk for carcinoid crisis during surgery.