Experiments were designed to study functional markers for endothelial constitutive nitric oxide synthase (ecNOS) after transbronchial adenoviral-mediated (AD) transfer to transplanted lungs. Syngenic orthotopic single lung transplantation in rats was performed after airway administration of either AdecNOS or the marker gene AdLacZ to the donor lung (300 ul, 1x109 pfu/ml; n=4 each). Transplanted lungs were harvested at four days and transgene DNA and mRNA were identified by polymerase chain reaction (PCR) and reverse transcriptase PCR (RT-PCR), respectively. Calcium-dependent NOS activity increased in ecNOS compared to LacZ transduced lungs. However, cyclic GMP isolated from lung homogenates was the same in both groups. Positive immunohistochemical staining for ecNOS was observed in pneumocytes only in ecNOS transduced lungs. Preliminary data indicates that oxidized products of nitric oxide (NOx) increased in pulmonary venous blood in ecNOS transduced lungs. These results indicate an effective transduction of pneumocytes with ecNOS that does not alter basal cyclic GMP levels, although NOS protein and nitric oxide does increase.