Effects of L-NG-Nitroarginine (L-NNA) and N-([3-(Aminomethyl) phenyl] methyl) ethanimidamide dihydrochloride (1400 W) on pulmonary vascular tone during normoxic ventilation. Normoxic ΔPAP values in the absence of L-NNA and 1400 W are identical to those depicted in Figure 1. A. L-NNA-treated normoxic normocapnia (n = 5), B. L-NNA-treated normoxic hypercapnic acidosis (n = 5), C. L-NNA-treated normoxic hypercapnia without acidosis (n = 4), D. 1400 W-treated normoxic normocapnia (n = 6), E. 1400 W-treated normoxic hypercapnic acidosis (n = 4), F. 1400 W-treated normoxic hypercapnia without acidosis (n = 6) compared to ΔPAP from lungs in the absence of L-NNA or 1400 W during 190 min of normoxic ventilation. ΔPAP: change of PAP referenced to the value at time set at zero. Data are mean ± SEM. *, significant difference (P < 0.05) between treated and untreated groups.