The Evolutionary Origins of Hormones, Neurotransmitters, and Other Extracellular Chemical Messengers

Abstract

IN the past, each hormonal peptide was traditionally considered a unique product of a single cell type that was localized in distribution to a limited region of the body known as an endocrine gland (Table 1). These boundaries were too limited. For some hormones, the particular type of cells producing them were also found outside those glands. In addition, cancers derived from nonendocrine tissues, as well as diverse neurons, produce hormonal peptides.^{1 2 3} More recently, other cell types (non-neural and nonmalignant) have also been recognized as possible sources of peptide hormones (Table 1).Because the endocrine glands of mammals did not . . .