Kappa-receptor antagonist reverse 'non-opioid' stress-induced analgesia.

We have evaluated the effects of antagonists to the mu, kappa and opiate receptors on 'opioid' and 'non-opioid mediated' analgesia. Our findings indicate that mu receptors might mediate 'opioid' and kappa receptors 'non-opioid' analgesia. It is suggested that endogenous opiates that act on mu or kappa receptors could be responsible for the different types of stress-induced analgesia.