SPINAL KAPPA(1) AND KAPPA(2) OPIOID BINDING-SITES IN RATS, GUINEA-PIGS, MONKEYS AND HUMANS

SEVERAL lines of work demonstrate that there are two subtypes of kappa opioid receptors. Intrathecally administered agonists for the kappa(1 ) subtype are not effective in treating pain, whereas agonists for the kappa(2) receptor are anti-hyperalgesic and anti-allodynic. The quest ion addressed here was whether the ratio of spinal kappa(1) to kappa(2 ) receptors was conserved across species. Thus, binding experiments we re performed on spinal cord membranes from rats, guinea pigs, monkeys and humans. We found that kappa(2) receptors were approximately ten ti mes more abundant than kappa(1) receptors in all species tested. This suggests that the anti-hyperalgesic and anti-allodynic properties of k appa(2) agonists may also be conserved. Therefore, selective K-2 agoni sts may be effective in treating chronic pain in humans. NeuroReport p ort 9:2523-2525 (C) 1998 Rapid Science Ltd.