In a recent study, we found that sodium nitroprusside (SNP) attenuated hypoxic vasoconstriction more in 2 day (d) than 1 month (m) old lamb lungs (J Appl Physiol 79: 824, 1995), suggesting that pulmonary vascular responsiveness to endothelium-derived nitric oxide decreases with age. However, SNP may have different effects than nitric oxide (NO) on vascular smooth muscle. Therefore, in this study we compared pulmonary artery dose-responses to inhaled NO (2.5 - 100 ppm) in indomethacin-treated 1d and 1m lamb lungs ventilated with 4% O2 (hypox). All lungs were perfused with autologous blood at a constant flow of 100 ml/kg.min. Data are expressed as mean pulmonary artery pressure(Ppa in mmHg) ± SEM. Groups were compared by ANOVA (* different at p< 0.05). Inhaled NO caused a significantly greater decrease in hypox Ppa in 1d compared to 1m lungs. Maximal dilation occurred at 100 ppm NO at both ages. 5 ppm NO caused a 49±8.2% decrease in Ppa relative to maximal dilation in 1d lungs, but only a 25.1±13% decrease in 1m lungs. Over 10 ppm NO were required to cause a 50% decrease in Ppa in 1m lungs. Thus, 1d lungs appeared more responsive and sensitive to NO. Whether this was due to higher baseline Ppa in 1d lungs or to age-dependent differences in metabolism of cGMP(or other steps in signal transduction) remains to be determined. Support: American Heart Assoc, MD Affiliate, Inc. Table
