class="enumerated" style="list-style-type:decimal">Previous studies demonstrated that both ventilatory and phrenic nerve responses to acute hypoxia are greatly attenuated in adult rats (3–5 months old) previously exposed to 1 month of perinatal hyperoxia (60% O2; perinatal treated rats). The present study tested the hypothesis that this functional impairment recovers spontaneously with advancing age in perinatal treated rats.Hypoxia-induced chemoreflexes were examined by measuring integrated phrenic responses to strictly controlled isocapnic hypoxia in urethane-anaesthetized, vagotomized, paralysed and ventilated rats at different ages.At 50 mmHg Pa,O2 (arterial O2 partial pressure), the hypoxia-induced increase in minute phrenic activity was significantly attenuated in both 3- to 5-month-old (166 ± 15% of baseline) and 6-month-old (130 ± 17%) perinatal treated rats, relative to 3- to 6-month-old, untreated control rats (279 ± 28%; both P < 0.05). However, at 40 mmHg Pa,O2, the hypoxic minute phrenic activity response was attenuated only in 3- to 5-month-old (154 ± 33%), but not 6-month-old (232 ± 33%) perinatal treated rats versus control rats (293 ± 30%).The minute phrenic activity response to hypoxia was not significantly different between geriatric perinatal treated rats (14–15 months) and untreated geriatric control rats at either 50 mmHg (treated: 250 ± 20%versus control: 274 ± 23%) or 40 mmHg Pa,O2 (treated: 292 ± 19%versus control: 315 ± 36%).These data suggest that partial spontaneous recovery may occur in 6-month-old perinatal treated rats and that full recovery occurs by 15 months of age.
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