Evidence from a variety of experimental models has suggested the existence of mu1, mu2 and delta binding sites for morphine and the enkephalins in the central nervous system. Additional biochemical experiments now support this concept of a common high affinity site for opiates and opioid peptides. Mu sites have now been implicated in a number of pharmacological actions, including supraspinal analgesia, prolactin release, and catalepsy, but not in others (spinal analgesia, respiratory depression, and the guinea pig ileum). The hypothesis of mu1 sites was supported by the unique opioid meptazinol, which selectively bound to mu1 sites. As expected from its mu1 binding selectivity, its analgesic actions in the mouse, localized supraspinally, were antagonized by the selective mu1 antagonist naloxonazine and it had no respiratory depressant actions. Other binding studies suggested the presence of discrete SKF10, 047-selective (KD approximately 5 nM) binding sites in rat brain which differed from both kappa sites and the previously reported PCP-binding sigma sites. Additional binding and autoradiograpical studies have also implied the presence of β-endorphin, or epsilon, sites in the CNS.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Pharmacology, Toxicology and Pharmaceutics(all)