Kappa opioids in rhesus monkeys. II. Analysis of the antagonistic actions of quadazocine and beta-funaltrexamine.

In rhesus monkeys, kappa opioid agonists have been shown to increase urinary output, increase tail-withdrawal latencies from warm water and produce distinct discriminative stimulus effects. In order to explore further the relation between these effects and activity at the kappa opioid receptor type, the antagonist activity of quadazocine against several kappa opioid agonists was examined with the tail-withdrawal and drug-discrimination procedures. Quadazocine dose dependently antagonized the increases in tail-withdrawal latency produced by the kappa agonists bremazocine, ethylketazocine and U-50, 488, as well as the discriminative stimulus effects of these drugs. The dose-ratio analysis of Schild revealed apparent pA2 values for quadazocine in combination with bremazocine, ethylketazocine and U-50, 488 of 6.1, 6.4 and 6.4, respectively, with the tail-withdrawal procedure and 6.3, 6.4 and 6.1, respectively, with the drug-discrimination procedure. Quadazocine also antagonized the effects of a mu agonist (morphine) in the tail-withdrawal procedure, and the apparent pA2 value for these data was 8.2. The activity of the mu-selective alkylating agent, beta-funaltrexamine (beta-FNA), was examined alone and in combination with the kappa agonist ethylketazocine in the urinary-output, tail-withdrawal and drug-discrimination procedures. At about 30 to 60 min postinjection, beta-FNA alone produced ethylketazocine-appropriate responding under the drug-discrimination procedure and increased urine output but did not increase tail-withdrawal latencies. At 24 to 48 hr postinjection, beta-FNA did not antagonize effects of ethylketazocine in any of the three procedures.(ABSTRACT TRUNCATED AT 250 WORDS)