Abstract.
As part of a structure–activity study focused on the Phe4 residue of nociceptin (NC) (1-13)NH2, we identified two highly potent and selective agonists for the OP4 receptor, [(pF)Phe4]NC(1-13)NH2 and [(pNO2)Phe4]NC(1-13)NH2, whose in vitro pharmacological profiles have been described in the companion paper. In the present study, we investigated the actions of [(pF)Phe4]NC(1-13)NH2 and compared it with those of NC(1-13)NH2 in a battery of vivo assays.
In the locomotor activity test in mice, 1 nmol NC(1-13)NH2 given intracerebroventricularly (i.c.v.) caused a significant decrease (about 70% inhibition) in activity for the first 15 min following injection; [(pF)Phe4]NC(1-13)NH2, at the same dose, exerted a similar inhibitory effect that continued until the end of the observation period (30 min). This effect was prevented by the selective OP4 receptor antagonist [Nphe1]NC(1-13)NH2 (10 nmol, i.c.v.). In the tail-withdrawal assay in mice, [(pF)Phe4]NC(1-13)NH2 mimicked the effects of NC(1-13)NH2 producing pronociceptive and antimorphine effects following i.c.v. administration. In both experimental paradigms, the actions of [(pF)Phe4]NC(1-13)NH2 were longer lasting (>60 min) compared to those of NC(1-13)NH2 (ca. 30 min). In unanaesthetised normotensive mice, bolus intravenous (i.v.) injection of 100 nmol/kg of [(pF)Phe4]NC(1-13)NH2 decreased mean blood pressure and heart rate; these effects were longer lasting than those elicited by the same dose of NC(1-13)NH2. I.c.v. administration of [(pF)Phe4]NC(1-13)NH2 dose-dependently stimulated feeding in rats, and was about tenfold more potent than NC(1-13)NH2.
Collectively, the present data demonstrate that, in a variety of in vivo assays, NC(1-13)NH2 and [(pF)Phe4]NC(1-13)NH2 mimicked the actions of NC. [(pF)Phe4]NC(1-13)NH2 was more potent and its in vivo effects were longer lasting than those of NC(1-13)NH2 and NC.
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Rizzi, A., Salis, M., Ciccocioppo, R. et al. Pharmacological characterisation of [(pX)Phe4]nociceptin(1-13)NH2 analogues. Naunyn-Schmiedeberg's Arch Pharmacol 365, 450–456 (2002). https://doi.org/10.1007/s00210-002-0549-7
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DOI: https://doi.org/10.1007/s00210-002-0549-7