The dispersed neuroendocrine cells: the structure, function, regulation and effects of xenobiotics on this system

Cells which express morphological and functional markers originally described in neurons and neural crest-derived endocrine cells are now known to originate from both ectodermal and endodermal progenitors. These cells are organized to secrete peptides, amines, and other regulatory products in response to neurogenic or chemical stimulation. Individual products may function in endocrine, paracrine, neurotransmitter, or neuromodulatory roles. Multiple products are often produced by individual cells and stored in the same secretory granules. The hormonal profiles of particular types of neuroendocrine cells can, to varying degrees, be changed by environmental signals during development or in adult life. These changes are caused both by transcriptional and post-transcriptional mechanisms. Hormonal profiles are also altered during the development and progression of neoplasia. Signals which stimulate hormone secretion produce a number of ancillary effects, including activation and induction of enzymes which replenish hormone stores, activation of cellular oncogenes, and stimulation of cell proliferation. The effects of environmental signals on neuroendocrine cells are mediated by intracellular transduction pathways which involve cyclic AMP, phosphatidylinositol, calcium, and receptor protein kinase activity. These effects can be potentiated, inhibited, or qualitatively altered by exogenous agents.