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

Proinflammatory and vasodilator effects of nociceptin/orphanin FQ in the rat mesenteric microcirculation are mediated by histamine Am J Physiol Heart Circ Physiol 293: H2977-H2985, 2007. First published August 31, 2007; doi:10.1152/ajpheart.00448.2007. - 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 isothiocyanateconjugated BSA (FITC-BSA, 0.25 ml/100 g iv) or 1 mu m 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 mu m, 26.7 +/- 1.2 mu m, 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 mu m, P = 0.036). Microsphere velocity also decreased ( venules: 1,230 Z +/- 370 mu m/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 [Nphe(1), Arg(14), Lys(15)]N/OFQ-NH2 (UFP-101; 60 and 150 nmol/kg iv), H-1 and H-2 antagonists 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 (similar to 200 mu m, 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.