Characterization of nociceptin receptors in the periphery: in vitro and in vivo studies

Abstract

Nociceptin (NC), a series of NC fragments, naloxone as well as the pseudopeptide [Phe1psi(CH2-NH)Gly2]NC(1-13)NH2 ([F/G]NC(1-13)NH2) were used to characterize NC receptors in peripheral isolated organs and in vivo. Experiments on isolated organs were performed in the mouse (mVD) and rat (rVD) vas deferens (noradrenergic nerve terminals), in the guinea pig ileum (gpI; cholinergic nerves) and in the renal pelvis (gpRP; sensory nerves), and, in vivo, by measuring the blood pressure (BP) and heart rate (HR) in anaesthetised rats. NC, NCNH2 and NC(1-13)NH2 acted as full agonists with similar affinities, while shorter fragments (e.g. NC(1-12)NH2, NC(1-9)NH2, NC(1-5)NH2) were much weaker or inactive. The inhibitory effects of NC were not modified by naloxone. [F/G]NC(1-13)NH2 acted as an antagonist with similar pA2-values (6.75 mVD, 6.83 rVD, 7.26 gpI) in the three species. In addition, it blocked NC actions in the rat in vivo. Linear Schild plots with slopes near to unity indicated that [F/G]NC(1-13)NH2 is a competitive antagonist, specific for NC receptors both in vitro (since it was inactive on opioid receptors) and in vivo (since it was inactive against carbachol). [F/G]NC(1-13)NH2 showed a residual agonistic activity in vitro (alpha = 0.2-0.3 in the rVD and gpI) and especially in vivo (alpha = 0.4 BP, 0.2 HR). These pharmacological data indicate that NC and related peptides exert their inhibitory effects in peripheral organs of various species by activating the same receptor type. Moreover, [F/G]NC(1-13)NH2 appears to be a useful tool for receptor characterization and classification.

Functional Selectivity of Nociceptin/Orphanin FQ Peptide Receptor Partial Agonists on Cardiovascular and Renal Function

“…However, there is now considerable evidence that each of these ligands can behave as pure antagonists Bigoni et al, 1999;Madeddu et al, 1999, Berger et al, 2000Malinowska et al, 2000b), partial agonists (Dooley et al, 1997;Bigoni et al, 1999;Berger et al, 2000;, or full agonists (Butour et al, 1998;Berger et al, 2000;Malinowska et al, 2000a;Olszewski et al, 2000) across different in vitro and in vivo systems (for review, see Calo' et al, 2000). The results of the present studies extend these observations and clearly demonstrate that these same NOP receptor ligands can display mixed pharmacological behavior from full/partial agonist to antagonist activity within a given biological system, in this case involving processes regulating cardiovascular and renal function in vivo.…”

“…These observations are of interest considering that N/OFQ (30 or 100 nmol/kg) characteristically produces an immediate and marked bradycardia and hypotension after i.v. bolus injection in conscious or anesthetized rats Bigoni et al, 1999;Madeddu et al, 1999;Kapusta, 2000;Malinowska et al, 2000aMalinowska et al, , 2002. However, as partial agonists, it might be expected that these ligands are required to bind to and activate more receptors to elicit an equal response.…”

“…In comparison with these centrally evoked responses, i.v. bolus N/OFQ also produces a dose-dependent hypotension that occurs with bradycardia and not a baroreflex-evoked tachycardia Bigoni et al, 1999;Madeddu et al, 1999;Kapusta, 2000;Malinowska et al, 2000aMalinowska et al, , 2002. However, these cardiovascular depressor responses are immediate in onset and of brief duration (3-10 min).…”

In vitro and in vivo studies on UFP-112, a novel potent and long lasting agonist selective for the nociceptin/orphanin FQ receptor

“…Vas deferens taken from Swiss or CD1/C57BL6/J-129 NOP +/+ and NOP −/− mice were prepared as previously described [4]. Tissues were continuously stimulated through two platinum ring electrodes with supramaximal voltage rectangular pulses of 1 msec duration and 0.05 Hz frequency.…”

Pharmacodynamic Characterization of ZP120 (Ac-RYYRWKKKKKKK-NH2), a Novel, Functionally Selective Nociceptin/Orphanin FQ Peptide Receptor Partial Agonist with Sodium-Potassium-Sparing Aquaretic Activity

“…Thus, N/OFQ relaxes vascular smooth muscle (Gumusel et al, 1997;Armstead, 1999;Champion et al, 1999) and when administered as an intravenous (i.v.) bolus to anesthetized (Champion and Kadowitz, 1997;Bigoni et al, 1999) or conscious (Giuliani et al, 1997;Madeddu et al, 1999;Kapusta, 2000) rats or mice, this peptide produces dose-dependent hypotensive and bradycardic responses. In addition, we have demonstrated that the continuous i.v.…”