Woods J: Differentiation of kappa opioid agonist-induced antinociception by naltrexone apparent pA, anal- ysis in rhesus monkeys. J Pharmacol Exp Ther

ABSTRACT ); bremazocine, 6.92 (6.73-7.12); enadoline, 6.87 (6.69 -7.05). Pretreatment with clocinnamox, an irreversible mu antagonist, confirmed that mu receptors were not involved in the antinociception produced by the kappa agonists, U69,593, U50,488, bremazocine and enadoline; however, both mu and kappa receptors mediated the antinociceptive effects of ethylketocyclazocine. The apparent NTX pA 2 profile of opioid agonists correlated highly with the radioligand binding studies, which indicates that U69,593 and U50,488 produced antinociception by acting on kappa-1 receptors, whereas bremazocine and enadoline probably acted via non-kappa-1 receptors. This study provides further functional evidence of kappa opioid receptor multiplicity in primates and suggests that NTX may be a useful tool to study this phenomenon in vivo