The apparent in vivo dissociation constant (1<A) and relative efficacy values for alfentanil, Etonitazene, morphine, and nalbuphine were determined by comparing the effects of these agonists in the presence of buprenorphine with the results of these agonists alone in the rhesus monkey tail-withdrawal procedure. Initial time course studies of buprenorphine alone indicated that 3.2 and 10 mg/kg produced increases in tail-with-drawal latencies when studied with 48#{176}Cwater for 48 hr.

Still, No increases in tail-withdrawal latency were found with either dose studied with 55#{176}Cwater. Buprenorphine produced dose-de-pendent shifts to the right for the antinociceptive effects of alfentanil, Etonitazene, morphine, and nalbuphine 72 hr after administration. It decreased the maximal impact of morphine in 48#{176} C water and those of alfentanil and Etonitazene in 55#{176}C water. Buprenorphine administration decreased the receptor.