Opioid Peptide Effects on Leukocyte Migration

Abstract

The recognition that morphine bound stereospecifically to receptors in the brain to exert its effects led to a concerted search for an endogenous ligand for the opiate receptor (Terenius and Wahlstrom, 1975). In 1975, peptides which bound to the opiate receptor were isolated from porcine brain extracts and characterized (Hughes et al., 1975; Hughes et al., 1976). The first opioid peptides characterized were the pentapeptides methionine-and-leucine enkephalin (met- and leu-enkephalin). Simultaneously, a larger (31 amino acid), more active peptide containing the amino acid sequence of met-enkephalin as its first 5 N-terminal amino acids was isolated from porcine and camel pituitary and was named beta-endorphin (a contraction for “endogenous morphine”) (Teschemacher et al., 1975; Li and Chung, 1976). Beta-endorphin and alpha-endorphin (amino acids 1–16 of beta-endorphin), gamma-endorphin (amino acids 1–17 of beta-endorphin), (Ling et al., 1976), as well as other neuropeptides, may arise from a 31 Kd glycoprotein, the proopiomelanocortin molecule (reviewed by Frederickson and Geary, 1982). The discovery that beta-endorphin is released from the pituitary along with the steroidogenic hormone, adrenocorticotropin (ACTH) in response to acute stress suggests that in addition to its numerous actions in the central nervous system, beta-endorphin, like ACTH, also has peripheral hormonal effects (Guillemin et al., 1977; Bossier et al., 1977). The release of both ACTH and beta endorphin may be under the control of the hypothalamic peptide, corticotropin releasing factor (CRF) in some species (Hook et al, 1982 and Knepel et al, 1984).