Details

Autor(en) / Beteiligte

• Martins Laurindo, Francisco Rafael
• de Almeida Pedro, Marcelo
• Barbeiro, Hermes Vieira
• Pileggi, Fuilvio
• Catelli Carvalho, Maria Helena
• Augusto, Ohara
• da Luz, Protásio Lemos

Titel

Vascular Free Radical Release: Ex Vivo and In Vivo Evidence for a Flow-Dependent Endothelial Mechanism

Ist Teil von

• Circulation research, 1994-04, Vol.74 (4), p.700-709

Ort / Verlag

Hagerstown, MD: American Heart Association, Inc

Erscheinungsjahr

1994

Quelle

MEDLINE

Beschreibungen/Notizen

• Mechanisms underlying production of vascular free radicals are unclear. We hypothesized that changes in blood flow might serve as a physiological stimulus for endothelial free radical release. Intact isolated aortas from 45 rabbits were perfused with the spin trap α-phenyl-N-tert-butylnitrone (PBN, 20 mmol/L) and formed radical adducts detected by electron paramagnetic resonance spectroscopy (EPR). Sequential perfusion at 2, 7.5, and 12 mL/min changed cumulative vascular PBN radical adduct yields, respectively, from 3.2±0.9 to 4.1±0.7 (P<.05) and 7.0±1.5 (P<.005) pmol/mg with endothelium and from 3.6±1.6 to 3.8±1.4 and 2.2±0.8 pmol/mg without endothelium (P=NS). In endothe-lialized aortas, superoxide dismutase (SOD) completely blocked flow-induced free radical production, whereas inactivated SOD, indomethacin, and the nitric oxide synthetase antagonist nitro-L-arginine methyl ester (L-NAME) had no effect; relaxations to acetylcholine remained unchanged with higher flows. To assess the role of flow on in vivo radical production, femoral arterial plasma levels of the ascorbyl radical, a stable ascorbate oxidation product, were measured by direct EPR in 56 other rabbits. Ascorbyl levels were assessed at baseline (30.2±0.7 nmol/L) and at peak-induced iliac flow changes. Flow increases from 25% to 100% due to saline injections through an extracorporeal aortic loop induced significant dose-dependent increases in ascorbyl levels (n=5). In addition, after papaverine bolus injections, flow increased by 114±8% versus baseline, and ascorbyl levels increased by 5.4±0.7 nmol/L (n=31, P<.001); similar results occurred with adenosine, isoproterenol, or hyperemia after 30-second occlusions (P<.05, n=4 or 5 in each group). Active SOD completely blocked papaverine-induced ascorbyl radical increase, despite preserved flow response (Aascorbyl=0.02±1.6 nmol/L, P=NS); inactivated SOD, catalase, indomethacin, and L-NAME had no effect. Blood flow decreases of 65% to 100% due to phenylephrine or 60-second balloon occlusions were accompanied by an average decrease of 4.4 nmol/L (P<.05) in ascorbyl levels. No change in ascorbyl signal was observed when rabbit blood alone was submitted to in vitro flow increases through a tubing circuit. Thus, increases in blood flow trigger vascular free radical generation; such a response seems to involve endothelium-derived superoxide radicals unrelated to cyclooxygenase or nitric oxide synthetase activities. This mechanism may contribute to explain vascular free radical generation in physiological or pathological circumstances.