Abstract
This chapter describes the algesic peptides, opioid peptides, naloxone-sensitive nonopioid peptides, naloxone-insensitive peptides, and peptides with mixed effects. The chapter presents certain criteria that need to be fulfilled to demonstrate the involvement of an endogenous peptide in nociception. Use of both radioimmunoassays (RIA) and immunohistochemical techniques demonstrate that several opioid peptides are localized within the regions of the central nervous system (CNS) that have been implicated in nociception. Measurement of peptide concentrations in tissue or biological fluids may provide valuable information concerning the role of a peptide in nociceptive processes. If various environmental stimuli induce an antinociceptive response, alterations in the concentration of one or another opioid peptide can yield useful information. While several other peptides, including neurotensin, vasopressin, and calcitonin, produce antinociception, there are others that are believed to produce antinociception or enhance nociception, such as bradykinin, substance P, and adrenocorticotrophic hormone (ACTH). Many peptides alter pain perception in laboratory animals and a few—for example, β-endorphin—induce analgesia in humans. This information will undoubtedly lead to a better understanding of chronic pain states and to the development of new analgesics.
