Changes in lung tissue nitric oxide synthase (NOS) activity (A) and eNOS protein levels (B) before and 4 h after acute ductal constriction. Top, left: acute ductal constriction decreases total NOS activity in vehicle-treated lambs (n = 5). Values are means ± SE, normalized to preconstriction values, *P < 0.05. Bottom, left: densitometric values for eNOS protein from vehicle-treated lambs (normalized to β-actin; n = 5). Acute ductal constriction does not change eNOS protein levels. Values are means ± SD, normalized to preconstriction values. Top, right: however, total NOS activity does not decrease following acute ductal constriction in PEG-SOD-treated fetal lambs, whereas eNOS protein levels remain unchanged (bottom, right). N = 7 PEG-SOD. Values are means ± SD, normalized to preconstriction values.