Peripheral and central actions of orphanin FQ (nociceptin) on murine colon.

Orphanin FQ (OFQ), also known as nociceptin, is a recently isolated endogenous peptide with a structure similar to the endogenous opioid peptides. The present study examines the actions of centrally administered OFQ on in vivo murine gastrointestinal and colonic transit as well as the actions of OFQ on the isolated colon. Intracerebroventricular injections of OFQ dose dependently inhibited colonic propulsive activity. OFQ inhibition of colonic propulsion was unaffected by coadministration of the competitive opioid receptor antagonist naltrexone. A subadditive response was observed when approximately equipotent doses of either morphine sulfate or the delta-agonist DPDPE were coadministered with OFQ. No subadditivity was observed with coadministration of the micro-agonist DAMGO, suggesting a functional interaction between OFQ and delta-opioid central pathways regulating colonic transit. High, but not low, doses of OFQ also inhibited the transit of a nonabsorbable charcoal marker through the stomach and/or small intestine. OFQ potently contracted isolated colon preparations; contractile activity was abolished by TTX or chlorpromazine. Our results suggest that OFQ may be an important peptide ligand acting on a novel inhibitory neural pathway that modulates gastrointestinal transit.