Peptides

Neuropeptides are small proteinaceous cell-cell signaling molecules produced and released by neurons. They differ from peptide hormones in that they are secreted from neurons and act locally on neighbouring neurons, whereas peptide hormones are secreted in to the blood by neuroendocrine cells and act at distant sites. Neuropeptides are the most diverse class of signaling molecules in the brain, and are involved in a broad range of brain functions, including analgesia, reproduction, learning and memory, reward, food intake and more. Characteristics relevant to neuropeptide function are 1) their secretion is through a 'regulated' route, 2) they are not recycled once secreted and 3) they may be modified in the extracellular space by peptidases which can either inactivate their biological activity or conversely, increase target binding affinity.

Neuropeptides often co-exist with other neurotransmitters in defined cell populations, but are contained in separate storage vesicles. Neuropeptides are held within large dense-core vesicles (LDCVs) throughout the cell body, whereas neurotransmitters are contained in small vesicles located at synapses.

In humans there are ~90 genes encoding neuropeptide precursors, which are processed to ~100 bioactive neuropeptides.

Endocrine peptides are the proteinaceous subset of the hormones produced by the glands of the endocrine system. The major endocrine glands include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus, gastrointestinal tract and adrenal glands. Endocrine hormones regulate a vast array of bodily functions including metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood.

The table below provides details of the endocrine glands, the hormones they secrete and some of the principal effects of the hormones. Non-peptide hormones are shown in italics for clarity.