Superoxide and endothelium‐dependent constriction to flow in porcine small pulmonary arteries

Abstract

1 The aim of this study was to determine the response of porcine small pulmonary arteries to intralumenal ow and to identify the cellular mechanisms and potential mediators involved in the response. 2 Porcine small pulmonary arteries were isolated from a branch of the main intrapulmonary artery of the lower lung lobe and studied in a perfusion myograph system that allowed independent control of transmural pressure and intralumenal¯ow. At a transmural pressure of 20 mmHg, the baseline internal diameter (BID) of the arteries was 251.2+16.1 mm (n=16). 3 Under quiescent conditions or during constriction with U46619 to *60% of BID, intralumenal¯ow caused reversible constriction in arteries with endothelium (in the presence of U46619,¯ow decreased diameter from 60.0+2.5% to 49.5+3.0% BID at 10 ml min 71 , n=16, P50.05) but no change in diameter of arteries without endothelium. 4 In the presence of superoxide dismutase (SOD, 150 u ml 71 ), the response to¯ow was converted from constriction to vasodilatation (in presence of U46619 and SOD,¯ow increased diameter from 54.2+3.4% to 76.7+4.5% BID at 10 ml min 71 , n=10, P50.05). Inhibition of NO synthase with L-NAME (3610 75 M) abolished the¯ow-induced vasodilatation occurring in the presence of SOD and thē ow-induced constriction occurring in the absence of SOD. In arteries with endothelium, L-NAME (3610 75 M) caused signi®cant vasoconstriction, whereas SOD did not alter vasomotor tone. 5 Acetylcholine (10 78 to 10 76 M) caused endothelium-dependent relaxation of small pulmonary arteries that was not signi®cantly a ected by SOD (150 u ml 71 ) but was inhibited by L-NAME (3610 75 M).6 These results suggest that in small, porcine, isolated pulmonary arteries, intralumenal¯ow increases the production of NO but this is obscured by the generation of superoxide which causes vasoconstriction.

Role of Superoxide Anion on Basal and Stimulated Nitric Oxide Activity in Neonatal Piglet Pulmonary Vessels

“…In the present study, the ability of Cu/Zn SOD to promote endothelium-dependent relaxation of piglet pulmonary vessels was shared by the simple metal salts CuSO 4 and MnCl 2 . MacKenzie et al (13) described similar effects of CuSO 4 and MnCl 2 in rat aorta, but the sensitivity of that preparation to the metal salt-induced relaxation was significantly higher than that presently observed in piglet pulmonary vessels. The free metal ions released from CuSO 4 and MnCl 2 at the high concentrations that are needed to induce vascular effects limit their potential use as SOD mimetics (13).…”

“…L-NAME, U46619, SOD (Cu/Zn superoxide dismutase from bovine erythrocytes), PEG-SOD (from bovine erythrocytes), catalase (from bovine liver), xanthine, xanthine oxidase, NBT, DETCA, tiron, tempol, PTIYO, CuSO 4 , and MnCl 2 were obtained from Sigma Chemical Co. (St. Louis, MO, U.S.A.), ACh chloride from Janssen Chimica (Beersen, Belgium), MnTMPyP from Alexis Corporation Ltd (Nottingham, U.K.), and DHE (5 mM solution in DMSO) from Molecular Probes Europe (Leiden, The Netherlands). All the drugs were dissolved initially in distilled deionized water and further dilutions were made in Krebs-Ringer bicarbonate buffer.…”

“…This effect of DETCA on ACh-induced relaxation was not affected by exogenous Cu/Zn SOD supplementation, but was reversed by PEG-SOD. Finally, we have tested several putative SOD mimetics and observed that the ability of Cu/Zn SOD to promote endothelium-dependent relaxation is shared by CuSO 4 and MnCl 2 , but not by tiron, tempol, or PTIYO. The low molecular weight manganese-porphyrin-based SOD mimetic, MnTMPyP, produced an augmentation of vascular tone that was abolished by NO ⅐ synthase inhibition, suggesting that its actions are more consistent with destruction rather than potentiation of basal NO ⅐ activity.…”

“…The pulmonary vessels are continually exposed to free radicals and reactive oxygen species originating from inspired air or inflammatory cells, and pulmonary vascular tone is dramatically altered by reactive oxygen species such as O 2 ⅐Ϫ (3,4). At birth, the newborn encounters a much more oxygen-enriched world than the relatively hypoxic fetus.…”

“…We also examined the ability of several putative SOD mimetics to induce changes in pulmonary vascular contractility. The SOD mimetics examined were the simple metal salts CuSO 4 and MnCl 2 , the spin trap agents tiron (4,5-dihydroxy-1,3-benzene disulfonic acid), tempol (4-hydroxy 2,2,6,6-tetramethylpiridine-1-oxyl), and PTIYO (4-phenyl-2,2,5,5-tetramethyl imidazolin-1-yloxy-5-oxide), and the metal-based compound MnTMPyP (Mn [III] tetrakis [1-methyl-4-pyridyl] porphyrin). Some of these compounds have been shown to share the ability of SOD to promote endothelium-dependent relaxation (13).…”