Proinflammatory and vasodilator effects of nociceptin/orphanin FQ in the rat mesenteric microcirculation are mediated by histamine

Abstract

Nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand for the N/OFQ peptide receptor (NOP). N/OFQ causes hypotension and vasodilation, and we aimed to determine the role of histamine in inflammatory microvascular responses to N/OFQ. Male Wistar rats (220–300 g, n = 72) were anesthetized with thiopental (30 mg/kg bolus, 40–90 mg·kg−1·h−1 iv), and the mesentery was prepared for fluorescent intravital microscopy using fluorescein isothiocyanate-conjugated BSA (FITC-BSA, 0.25 ml/100 g iv) or 1 μm fluorescently labeled microspheres. N/OFQ (0.6–60 nmol/kg iv) caused hypotension (SAP, baseline: 154 ± 11 mmHg, 15 nmol/kg N/OFQ: 112 ± 10 mmHg, P = 0.009), vasodilation (venules: 23.9 ± 1.2 μm, 26.7 ± 1.2 μm, P = 0.006), macromolecular leak (interstitial gray level FITC-BSA: 103.7 ± 3.4, 123.5 ± 11.8, P = 0.009), and leukocyte adhesion (2.0 ± 0.9, 15.2 ± 0.9/100 μm, P = 0.036). Microsphere velocity also decreased (venules: 1,230 ± 370 μm/s, P = 0.037), but there were no significant changes in blood flow. Flow cytometry measured a concurrent increase in neutrophil expression of cd11b with N/OFQ vs. controls (Geo mean fluorescence: 4.19 ± 0.13 vs. 2.06 ± 0.38, P < 0.05). The NOP antagonist [Nphe1,Arg14,Lys15]N/OFQ-NH2 (UFP-101; 60 and 150 nmol/kg iv), H1 and H2antagonists pyrilamine (mepyramine, 1 mg/kg iv) and ranitidine (1 mg/kg iv), and mast cell stabilizer cromolyn (1 mg·kg−1·min−1) also abolished vasodilation and macromolecular leak to N/OFQ in vivo ( P < 0.05), but did not affect hypotension. Isolated mesenteric arteries (∼200 μm, n = 25) preconstricted with U-46619 were also mounted on a pressure myograph (60 mmHg), and both intraluminally and extraluminally administered N/OFQ (10−5 M) caused dilation, inhibited by pyrilamine in the extraluminal but not the intraluminal (control: −6.9 ± 3.8%; N/OFQ: 32.6 ± 8.4%; pyrilamine: 31.5 ± 6.8%, n = 18, P < 0.05) experiments. We conclude that, in vivo, mesenteric microvascular dilation and macromolecular leak occur via N/OFQ-NOP-mediated release of histamine from mast cells. Therefore, N/OFQ-NOP has an important role in microvascular inflammation, and this may be targeted during disease, particularly as we have proven that UFP-101 is an effective antagonist of microvascular responses in vivo.