In vitro characterization of Ac-RYYRWK-NH(2), Ac-RYYRIK-NH(2) and [Phe1Psi(CH(2)-NH)Gly2] nociceptin(1-13)NH(2) at rat native and recombinant ORL(1) receptors.

ABSTRACT

The pharmacology of ORL(1) compounds, [Phe1Psi(CH(2)-NH)Gly2]nociceptin(1-13)NH(2) (F/GNC13), Ac-RYYRIK-NH(2) and Ac-RYYRWK-NH(2) was evaluated at rat ORL(1) receptors in frontal cortex (CTX), transfected chinese hamster ovary (CHO) cells, vas deferens (VD) and anococcygeus (AC). Ranked affinities for the inhibition of [3H]nociceptin binding to CTX and CHO's were Ac-RYYRWK-NH(2) identical withAc-RYYRIK-NH(2) identical withnociceptin>F/GNC13>Dynorphin A>naloxone. The full agonist, nociceptin stimulated [35S]GTPgammaS binding in CTX (E(max)=174%) and CHO's (E(max)=311%); all other ORL(1) peptides acted as partial agonists with the following rank order for E(max) values Ac-RYYRWK-NH(2) (96% (CTX), 202% (CHO))>F/GNC13 (44% (CTX), 136% (CHO)) identical withAc-RYYRIK-NH(2) (44% (CTX), 115% (CHO)). Schild analysis generated pA(2) values in CTX of 8.59 (F/GNC13) and 9.13 (Ac-RYYRIK-NH(2)). cAMP production in CHO's was inhibited by 77% (nociceptin), 58% (Ac-RYYRWK-NH(2)), 55% (F/GNC13) and 49% (Ac-RYYRIK-NH(2)). Nociceptin inhibited electrically evoked contractions in isolated tissues by 95% (VD) and 98% (AC); partial inhibition was observed with Ac-RYYRWK-NH(2) (72% (VD), 66% (AC)) and Ac-RYYRIK-NH(2) (54% (VD); 37%(AC)). Ineffective in the VD, F/GNC13 caused a small inhibition in the AC that was reversed at higher concentrations. Schild analysis gave pA(2) affinities of 7.32(VD) and 7.34(AC) for F/GNC13 and 8.69(AC) for Ac-RYYRIK-NH(2).