1 Antagonism, by the selective b-opioid receptor antagonist naltrindole, of the antinociceptive effects of enkephalin (DPDPE), Leu5, Thr6] 4 Naltrindole (0.01 mg kg-') significantly attenuated the antinociceptive effects of DPDPE and DSLET with 0.1 mg kg-' producing complete reversal of the effects of the ED75 dose. In contrast, naltrindole at 0.01 and 0.1 mg kg-did not alter antinociceptive responses to DELT I. Naltrindole at mg kg' significantly attenuated DELT I antinociception. 5 Naloxone (1 mg kg-') produced equivalent degrees of antagonism of the antinociceptive effects of DPDPE, DSLET and DELT I. ICI 174,864 (1 mg kg-') also antagonized antinociception with a differential degree of attenuation (DSLET> DPDPE> DELT I). 6 Naltrindole (1 mg kg-') had no effect on the antinociception induced by the selective n-agonist alfentanil (60 pg kg-'). Naltrindole, naloxone or ICI 174,864 had no effect on nociceptive latencies. 7 The differential antagonism by naltrindole of the effects of three selective 6-agonists suggests 6-receptor heterogeneity. Further, the lower sensitivity of response to DELT I suggests that this agent may exert its antinociceptive effects at a different 6 receptor subtype from DPDPE or DSLET.

No abstract

No abstract

No abstract

No abstract