Effects of the delta-opioid receptor antagonist naltrindole on antinociceptive responses to selective delta-agonists in post-weanling rats

Br J Pharmacol. 1992 Oct;107(2):573-6. doi: 10.1111/j.1476-5381.1992.tb12785.x.


1. Antagonism, by the selective delta-opioid receptor antagonist naltrindole, of the antinociceptive effects of [D-Pen2, D-Pen5] enkephalin (DPDPE), [D-Ser2, Leu5, Thr6] enkephalin (DSLET) and D-Ala2 deltorphin I (DELT I) has been studied in 25 day old rats. 2. Antinociception was measured by the 50 degrees C tail immersion test following i.p. administration of agonists and/or antagonists. 3. Dose-related antinociception was observed with DPDPE, DSLET and DELT I and ED75 doses were computed (0.66 mg kg-1, 0.65 mg kg-1, 0.032 mg kg-1 respectively) and used for antagonism studies. 4. Naltrindole (0.01 mg kg-1) significantly attenuated the antinociceptive effects of DPDPE and DSLET with 0.1 mg kg-1 producing complete reversal of the effects of the ED75 dose. In contrast, naltrindole at 0.01 and 0.1 mg kg-1 did not alter antinociceptive responses to DELT I. Naltrindole at 1 mg kg-1 significantly attenuated DELT I antinociception. 5. Naloxone (1 mg kg-1) produced equivalent degrees of antagonism of the antinociceptive effects of DPDPE, DSLET and DELT I. ICI 174,864 (1 mg kg-1) also antagonized antinociception with a differential degree of attenuation (DSLET > DPDPE > DELT I). 6. Naltrindole (1 mg kg-1) had no effect on the antinociception induced by the selective mu-agonist alfentanil (60 micrograms kg-1). Naltrindole, naloxone or ICI 174,864 had no effect on nociceptive latencies. 7. The differential antagonism by naltrindole of the effects of three selective delta-agonists suggests delta-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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analgesics / antagonists & inhibitors*
  • Animals
  • Enkephalin, D-Penicillamine (2,5)-
  • Enkephalin, Leucine / analogs & derivatives
  • Enkephalin, Leucine / antagonists & inhibitors
  • Enkephalin, Leucine / pharmacology
  • Enkephalins / antagonists & inhibitors
  • Indoles / pharmacology*
  • Male
  • Morphinans / pharmacology*
  • Naloxone / pharmacology*
  • Naltrexone / analogs & derivatives*
  • Narcotic Antagonists / pharmacology*
  • Oligopeptides / antagonists & inhibitors
  • Pain Measurement
  • Rats
  • Rats, Wistar
  • Receptors, Opioid, delta / drug effects
  • Receptors, Opioid, delta / physiology*


  • Analgesics
  • Enkephalins
  • Indoles
  • Morphinans
  • Narcotic Antagonists
  • Oligopeptides
  • Receptors, Opioid, delta
  • deltorphin I, Ala(2)-
  • Naloxone
  • Enkephalin, Leucine
  • Naltrexone
  • enkephalin, Ser(2), Leu(5), Thr(6)-
  • Enkephalin, D-Penicillamine (2,5)-
  • N,N-diallyl-tyrosyl-alpha-aminoisobutyric acid-phenylalanyl-leucine
  • naltrindole