Opioid receptor affinities of kappa agonists, agonist/antagonists and antagonists in vitro and in vivo.

The CNS opioid receptors consist of a major triad: mu, delta and kappa. The kappa agonists presently available act as kappa agonists, delta antagonists and mu2 isoreceptor antagonists. Pure opiate antagonists possess a broad spectrum of activity at all 3 opioid receptor populations. The Ag/Ant analgesics also possess a broad spectrum of receptor affinities which awaits the definition of complex species differences in their actions. The design of more specific opioid agonists and antagonists will lead to a greater understanding of the many possible roles opioids serve within the CNS.