Endogenous opioids and their receptors in stress-induced analgesia.

Stress can induce a naloxone reversible and a naloxone non reversible analgesia according to its parameters. We showed that naloxone non reversible analgesia can be reversed by antagonists of the kappa opiate receptor and that naloxone reversible analgesia can be related to mu receptors and beta-endorphin, while the kappa receptor mediated analgesia can be related to dynorphin. We have also shown that the characteristics of the receptors might change in consequence to stress and that the analgesic responses might be modulated by benzodiazepine agonists and antagonists.