Modulation of hypoxic pulmonary vasoconstriction is time and nitric oxide dependent in a peritonitis model of sepsis

Objective: This study assessed modulation of hypoxic pulmonary vasoconstriction (HPV) in isolated perfused rat lungs during sepsis induced by cecal ligation and perforation (CLP) at different times and its relationship to nitric oxide synthases (NOS). Design and setting: Prospective controlled trial in a university research laboratory. Subjects: 102 male Sprague-Dawley rats. Interventions: Groups 1-3 received sham laparotomy 6 h before lung isolation: group 1, only laparotomy; group 2, concurrently L-N-6-(1-iMi-noethyl)-lysine (L-NIL, 3 mg/kg); group 3, concurrently N-Omega-nitro-L-arginine methylester (L-NAME, 5 mg/kg). Groups 4-6 received CLP 6 h before lung isolation: group 4, only CLP; group 5, concurrently L-NIL; group 6, concurrently L-NAME. The same experiments were carried out with sham and CLP treatment for 24 h (groups 7-12). Exhaled NO from rats' lungs was measured after anesthesia and tracheostomy. After the pulmonary circuit was isolated and perfused, angiotensin II (0.1 mug) was injected into the inflow tract. The lungs were ventilated with the hypoxic mixture (HPV, 3% O-2) for 10 min and then again with the normoxic mixture (21% O-2) for an equal period. Changes in perfusion pressure were measured. Endothelial (eNOS) and inducible NOS (iNOS) expression of the lungs was determined. Measurements and results: Treatment with L-NAME but not L-NIL increased HPV in sham lungs. HPV was unaltered after CLP 6 h and decreased after CLP 24 h compared to sham. In CLP animals eNOS protein expression was reduced whereas iNOS expression was increased compared to sham animals. Exhaled NO, reflecting NOS activity was twice as high in the CLP 24 h group than in the CLP 6 h group. Conclusions: In the CLP sepsis model modulation of HPV was time-dependent. In addition, vasoconstriction to hypoxic stimuli was dependent on NOS activity.