Role of free radicals in vascular dysfunction induced by high tidal volume ventilation.
OBJECTIVE
To demonstrate that increased formation of reactive oxygen (ROS) and nitrogen species (RNS) is involved in VILI-induced vascular dysfunction.


METHODS
Male Sprague-Dawley anesthetized rats were ventilated for 60 min using low V(T) ventilation [V(T) 9 ml/kg, positive end-expiratory pressure (PEEP) 5 cmH(2)O, n = 18], and high V(T) ventilation (V(T) 35 ml/kg, zero PEEP, n = 18). Arterial pressure and respiratory system mechanics were monitored. Blood samples for the determination of arterial blood gases and lactate concentration were drawn. Vascular rings from the thoracic aortae were mounted in organ baths for isometric tension recording. We studied endothelium-dependent relaxation in norepinephrine-precontracted rings (acetylcholine, 10 nM-10 microM) and contraction induced by norepinephrine (1 nM-10 microM) in resting vessels. Vascular rings were preincubated for 30 min with Zn-Mn-SOD (100 u/ml) or tempol (10(-4) M) (extracellular and intracellular superoxide scavengers, respectively) or MnTMPyP (10(-5) M) (a superoxide and peroxynitrite scavenger). The presence of superoxide and nitrotyrosine in aortic rings was evaluated by immunofluorescence.


RESULTS
High V(T) ventilation induced hypotension, systemic acidosis, hypoxemia and hyperlactatemia, as well as impairment in acetylcholine and norepinephrine-induced responses in vitro. Responses to acetylcholine were improved by tempol (P = 0.004) and completely corrected (P < 0.001) by MnTMPyP. Responses to norepinephrine were also improved by treatment with tempol (P < 0.001) and MnTMPyP (P < 0.001). However, Zn-Mn-SOD did not improve acetylcholine- or norepinephrine-induced responses. Immunostaining for both superoxide and nitrotyrosine was increased in aortic rings from the high V(T) group.


CONCLUSIONS
Our data support a role for intracellular ROS and peroxynitrite in the high V(T) ventilation-induced vascular dysfunction.
Centro de Investigación en Red de Enfermedades Respiratorias (CibeRes), Hospital Universitario de Getafe, Universidad Europea de Madrid, Carretera de Toledo, km 12.500, Getafe, 28905 Madrid, Spain.
Leticia
L
Martínez-Caro
José A
JA
Lorente
Judith
J
Marín-Corral
Carolina
C
Sánchez-Rodríguez
Alberto
A
Sánchez-Ferrer
Nicolás
N
Nin
Antonio
A
Ferruelo
Marta
M
de Paula
Pilar
P
Fernández-Segoviano
Esther
E
Barreiro
Andrés
A
Esteban
D000109:Acetylcholine / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D001794:Blood Pressure / Q000502:physiology; D016166:Free Radical Scavengers / Q000378:metabolism* / Q000494:pharmacology; D055370:Lung Injury / Q000503:physiopathology; D008297:Male; D009638:Norepinephrine / Q000008:administration & dosage / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D026361:Reactive Nitrogen Species; D017382:Reactive Oxygen Species; D012121:Respiration, Artificial / Q000009:adverse effects*; D013990:Tidal Volume / Q000502:physiology*; D014662:Vasoconstrictor Agents / Q000008:administration & dosage / Q000494:pharmacology; D014665:Vasodilator Agents / Q000008:administration & dosage / Q000494:pharmacology
D016166:Free Radical Scavengers; D026361:Reactive Nitrogen Species; D017382:Reactive Oxygen Species; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D000109:Acetylcholine; D009638:Norepinephrine