Biphasic regulation of the acute µ-withdrawal and CCk-8 contracture responses by the ORL-1 system in guinea pig ileum

Pietro Marini, Luca Romanelli, Daniela Valeri, Maria Grazia Cascio, Paolo Tucci, Pacifico Valeri, Maura Palmery

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4 Citations (Scopus)


The cloning of the opioid-receptor-like receptor (ORL-1) and the identification of the orphaninFQ/nociceptin (OFQ/N) as its endogenous agonist has revealed a new G-protein-coupled receptor signalling system. The structural and functional homology of ORL-1 to the opioid receptor systems has posed a number of challenges in the understanding the often competing physiological responses elicited by these G-protein-coupled receptors.

We had previously shown that in guinea pig ileum (GPI), the acute μ-withdrawal response is under the inhibitory control of several systems. Specifically, we found that the exposure to a μ-opioid receptor agonist activates indirectly the κ-opioid, the A1-adenosine and the cannabinoid CB1 systems, that in turn inhibit the withdrawal response. The indirect activation of these systems is prevented by the peptide cholecystokinin-8 (CCk-8).

In the present study, we have investigated whether the ORL-1 system is also involved in the regulation of the acute μ-withdrawal response.

Interestingly, we found that in GPI preparation, the ORL-1 system is not indirectly activated by the μ-opioid receptor stimulation, but instead the system is able by itself to directly regulate the acute μ-withdrawal response.

Moreover, we have demonstrated that the ORL-1 system behaves both as anti-opioid or opioid-like system based on the level of activation. The same behaviour has also been observed in presence of CCk-8. Furthermore, in GPI, the existence of an endogenous tone of the ORL-1 system has been demonstrated. We concluded that the ORL-1 system acts as a neuromodulatory system, whose action is strictly related to the modulation of excitatory neurotrasmitters released in GPI enteric nervous system.
Original languageEnglish
Pages (from-to)100-110
Number of pages11
JournalPharmacological Research
Issue number1
Publication statusPublished - Jan 2012


  • acute µ-withdrawal
  • cholecystokinin-8 (CCk-8)
  • opioid-receptor like receptor (ORL-1)
  • orphaninFQ/nociceptin (OFQ/N)
  • UFP-101
  • guinea pig ileum (GPI)


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