Potentiation of the hypoxic ventilatory response by 1 day of hyperoxia in neonatal rats.

The O(2) sensitivity of the neonatal rat carotid body is increased after 1 day in moderate hyperoxia (60% O(2)) (Donnelly et al., 2009). We investigated whether this enhanced peripheral chemosensitivity increases the hypoxic ventilatory response (HVR) and tested the hypothesis that this plasticity is mediated by the superoxide anion. Neonatal rats (7 d old) were injected with saline or MnTMPyP, a superoxide scavenger, and placed into 60% O(2) for 23-28h. Baseline ventilation was reduced and the acute HVR (12% O(2)) was enhanced in hyperoxia-treated rats relative to age-matched controls; MnTMPyP did not block these effects. An additional group of rats was studied after only 30min in 60% O(2). This shorter exposure had no effect on normoxic ventilation or the HVR. We conclude that 1 d, but not 30min, of 60% O(2) augments the HVR of neonatal rats and that production of the superoxide anion does not contribute to this plasticity.