Differential effects of inhaled nitric oxide and hyperoxia on pulmonary dysfunction in newborn guinea pigs

This study tested the hypothesis that inhaled nitric oxide (NO) and combine d NO and hyperoxia will result in less pulmonary dysfunction and delay onse t of respiratory signs compared with hyperoxia-exposed newborn guinea pigs (GPs). GPs were exposed to room air (n = 14), 95% O-2 (n = 36), 20 parts pe r million (ppm) NO (n = 14), or combined 20 ppm NO and 95% O-2 (NO/O-2, n = 13) for up to 5 days. Data evaluated included latency interval for onset o f respiratory distress, pressure volume curves, lung histology, and broncho alveolar lavage (BAL) polymorphonuclear cells (PMNs), proteolytic activity, and total protein. NO-exposed GPs did not develop respiratory distress and had no evidence of pulmonary dysfunction. O-2-exposed GPs developed respir atory distress after 1-5 days (median 4.0) vs. 3-5 days (median 5.0) for NO /O-2 exposure (P < 0.05). BAL from O-2-exposed GPs showed increased PMNs co mpared with NO/O-2-exposed GPs. O-2- and NO/O-2-exposed GPs had comparable reduced lung volumes, lung histology, and increased BAL proteinase activity and total protein. In summary 1) O-2 exposure resulted in multiple measure s of pulmonary dysfunction in newborn GPs, 2) 5-day exposure to NO produced no noticeable respiratory effects and pulmonary dysfunction, and 3) short- term exposure (<less than or equal to>5 days) to NO/O-2 delayed onset of re spiratory distress and neither exacerbated nor attenuated pulmonary dysfunc tion compared with O-2 exposure alone.