Effects of the delta-opioid receptor antagonist naltrindole on antinociceptive responses to selective delta-agonists in post-weanling rats.
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.
Crook
T J
TJ
Receptors and Cellular Regulation Research Group, School of Biological Sciences, University of Surrey, Guildford.
Kitchen
I
I
Hill
R G
RG
D000700:Analgesics / Q000037:antagonists & inhibitors*; D000818:Animals; D020881:Enkephalin, D-Penicillamine (2,5)-; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology; D004745:Enkephalins / Q000037:antagonists & inhibitors; D007211:Indoles / Q000494:pharmacology*; D008297:Male; D009019:Morphinans / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D009271:Naltrexone / Q000031:analogs & derivatives*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009842:Oligopeptides / Q000037:antagonists & inhibitors; D010147:Pain Measurement; D051381:Rats; D017208:Rats, Wistar; D017465:Receptors, Opioid, delta / Q000187:drug effects / Q000502:physiology*
D000700:Analgesics; D004745:Enkephalins; D007211:Indoles; D009019:Morphinans; D009292:Narcotic Antagonists; D009842:Oligopeptides; D017465:Receptors, Opioid, delta; C060208:deltorphin I, Ala(2)-; D009270:Naloxone; D004743:Enkephalin, Leucine; D009271:Naltrexone; C034318:enkephalin, Ser(2), Leu(5), Thr(6)-; D020881:Enkephalin, D-Penicillamine (2,5)-; C040643:N,N-diallyl-tyrosyl-alpha-aminoisobutyric acid-phenylalanyl-leucine; C055382:naltrindole