The role of mu- and delta- opioid receptors on the intestinal propulsion in rats.
The agonist effects on intestinal transit of relatively selective mu- and delta- ligands, administered intraperitoneally, and their antagonism by the preferentially mu- and delta- antagonists naloxone and ICI 174,864 were studied in rats 5 min after a charcoal meal. The dose-response curves of the preferential mu- ligands morphine and [D-Ala2, MePhe4, Gly-ol5] enkephalin (DAGO) were shifted by naloxone at low doses but not by ICI 174,864. The preferential delta-peptide [D-Pen2, D-Pen5] enkephalin (DPDPE) had no significant agonist activity. [D-Ala2, D-Leu5] enkephalin (DADLE) induced dose-related effects that were weakly antagonized by ICI 174,864 and partly by low-dose naloxone. Thus the inhibition of intestinal transit induced by opioids may depend mainly on the interaction of the agonists at the mu-receptors, while the delta- receptors may play only a secondary role. DADLE agonist effects probably depend on interaction at mu-, delta- and at non-opioid receptors.
Sbacchi
M
M
Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy.
La Regina
A
A
Petrillo
P
P
Tavani
A
A
D000818:Animals; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D004743:Enkephalin, Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D004745:Enkephalins / Q000494:pharmacology*; D005772:Gastrointestinal Transit / Q000187:drug effects*; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu
D004745:Enkephalins; D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D009270:Naloxone; D004743:Enkephalin, Leucine; D020881:Enkephalin, D-Penicillamine (2,5)-; C040643:N,N-diallyl-tyrosyl-alpha-aminoisobutyric acid-phenylalanyl-leucine