Nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand for the N/OFQ receptor (NOP), whose characteristics in the dog are unknown. We therefore compared [3H]N/OFQ binding in dog and rat brain membranes. Radioligand saturation/competition studies with these membranes and leucyl-[3H]N/OFQ(1– 17)OH or the novel radioligand [3H]N/OFQ(1–13)NH2 were performed to determine receptor density and ligand affinity. The density of classic opioid receptors was determined by using [3H]diprenorphine. Leucyl- [3H]N/OFQ(1–17)OH binding was concentration dependent and saturable in dog (maximum binding capacity [Bmax], 28.7 2.8 fmol/mg of protein; equilibrium dissociation constant as negative log [pKd], 10.27 0.11) and rat (Bmax, 137.0 12.9 fmol/mg of protein; pKd, 10.410.05). In comparison, the Bmax and pKd of [3H]diprenorphine were, respectively, 77.75.3 fmol/mg of protein and 9.74 0.09 in dog and 79.1 18.2 fmol/mg of protein and 9.51 0.04 in rat. In dog, [3H]N/OFQ(1–13)NH2 binding to NOP receptors was also saturable (Bmax, 23.7 2.0 fmol/mg of protein; pKd, 10.16 0.12). In both species, leucyl-[3H]N/ OFQ(1–17)OH was displaced by various NOP ligands. Dynorphin A, N/OFQ(1–5)NH2, and nocistatin were essentially inactive. There was a significant positive correlation (r2 0.95; P 0.0001) between pKi values (an estimate of affinity) obtained in displacement studies in rat and dog. We have demonstrated a low density of NOP receptors, measured with two radioligands, in dog, and these receptors display a high degree of pharmacological similarity with those natively expressed in the rat.
Characterization of nociceptin/orphanin FQ binding sites in dog brain membranes
GUERRINI, Remo;
2003
Abstract
Nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand for the N/OFQ receptor (NOP), whose characteristics in the dog are unknown. We therefore compared [3H]N/OFQ binding in dog and rat brain membranes. Radioligand saturation/competition studies with these membranes and leucyl-[3H]N/OFQ(1– 17)OH or the novel radioligand [3H]N/OFQ(1–13)NH2 were performed to determine receptor density and ligand affinity. The density of classic opioid receptors was determined by using [3H]diprenorphine. Leucyl- [3H]N/OFQ(1–17)OH binding was concentration dependent and saturable in dog (maximum binding capacity [Bmax], 28.7 2.8 fmol/mg of protein; equilibrium dissociation constant as negative log [pKd], 10.27 0.11) and rat (Bmax, 137.0 12.9 fmol/mg of protein; pKd, 10.410.05). In comparison, the Bmax and pKd of [3H]diprenorphine were, respectively, 77.75.3 fmol/mg of protein and 9.74 0.09 in dog and 79.1 18.2 fmol/mg of protein and 9.51 0.04 in rat. In dog, [3H]N/OFQ(1–13)NH2 binding to NOP receptors was also saturable (Bmax, 23.7 2.0 fmol/mg of protein; pKd, 10.16 0.12). In both species, leucyl-[3H]N/ OFQ(1–17)OH was displaced by various NOP ligands. Dynorphin A, N/OFQ(1–5)NH2, and nocistatin were essentially inactive. There was a significant positive correlation (r2 0.95; P 0.0001) between pKi values (an estimate of affinity) obtained in displacement studies in rat and dog. We have demonstrated a low density of NOP receptors, measured with two radioligands, in dog, and these receptors display a high degree of pharmacological similarity with those natively expressed in the rat.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.