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

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 x kg(-1) x 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 microm 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 microm, 26.7 +/- 1.2 microm, 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 microm, P = 0.036). Microsphere velocity also decreased (venules: 1,230 +/- 370 microm/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-NH(2) (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 x kg(-1) x min(-1)) also abolished vasodilation and macromolecular leak to N/OFQ in vivo (P < 0.05), but did not affect hypotension. Isolated mesenteric arteries (approximately 200 microm, 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.

Intravenous anesthesia inhibits leukocyte-endothelial interactions and expression of CD11b after hemorrhage.

UNLABELLED: Hemorrhage increases adhesion of leukocytes to the venular endothelium, mediated by increased expression of the Mac-1 integrin complex (CD18/CD11b) present on leukocytes. Anesthetic agents may possess anti-inflammatory properties. Hence, this study determined the effects of i.v. anesthesia on leukocyte adhesion after hemorrhage in relation to expression of CD11b. METHODS: Male Wistar rats were (n = 57) anesthetized i.v. with propofol (Diprivan) and fentanyl, ketamine, or thiopental. During anesthesia, 10% of total blood volume was removed and intravital microscopy used to observe the rat mesentery and measure leukocyte (neutrophils) rolling and adhesion in postcapillary venules (15 - 25 microm). Flow cytometry was also used to determine CD11b expression on neutrophils from blood removed at the end of these experiments (n = 25) or blood incubated with anesthetic agents and activated with platelet activating factor ex vivo (0.1 micromol/L) (n = 24). RESULTS: Hemorrhage increased leukocyte adhesion (stationary count per 150 microm) in rats anesthetized with thiopental (baseline, 3.4 +/- 1.2; hemorrhage, 6.7 +/- 2.0; P < 0.05) but not in those receiving either ketamine (baseline, 3.6 +/- 1.3; hemorrhage, 3.3 +/- 1.3) or propofol/fentanyl (baseline, 6.2 +/- 2.0; hemorrhage, 5.8 +/- 0.8). Neutrophils collected from thiopental-treated rats had elevated CD11b expression with thiopental (mean fluorescence baseline, 67.5 +/- 1.3; hemorrhage, 83.6 +/- 5.3; P < 0.05) but not with propofol/fentanyl (mean fluorescence baseline, 69.1 +/- 1.3; hemorrhage, 65.9 +/- 1.6), and ketamine-treated rats (mean fluorescence baseline, 74.3 +/- 2.1; hemorrhage, 74.8 +/- 1.1). Ketamine also inhibited upregulation of CD11b with platelet activating factor ex vivo. CONCLUSIONS: After hemorrhage, leukocyte adhesion and CD11b expression increased during thiopental anesthesia, but propofol/fentanyl and ketamine protected against hemorrhage-induced leukocyte adhesion. The anti-inflammatory effect of ketamine was mediated by direct inhibition of CD11b expression on leukocytes.