Pharmacology of psychotropic analgesic nitrous oxide as a multipotent opioid agonist.

We show that psychotropic analgesic nitrous oxide is a partial opioid agonist since it fulfills all the following criteria to be classified as an opioid: 1) its effects are antagonised by various opioid antagonists including stereospecific naloxone antagonism; 2) it is cross tolerant with morphine; 3) its effects are potentiated by enkephalinase inhibition; 4) it provokes the release of endogenous opioids; 5) it interferes at low concentrations with specific opioid ligand binding at radio-receptor assay. Like the prototype opioid morphine it acts directly and indirectly at opioid receptors. PAN, although considered an exogenous inorganic molecule was also the first gas to be shown to have a direct role in influencing neurotransmission. We also describe some of the relationships that exist between nitrous oxide and its close relative, the endogenous gas nitric oxide. We describe the use of PAN as a safe, effective tool for investigating and treating the endogenous opioid system in man.