Gender considerations in ventilatory and metabolic development in rats: Special emphasis on the critical period

•Hypoxic response was weakest during the critical period in both male and female rats.•Age effect was highly significant in both genders in all parameters and ages tested.•Gender was never significant as a main effect analyzed statistically from P0 to P21.•Both genders exhibited comparable developmental trends in normoxia and hypoxia.•The critical period exists in both genders in rats.

In rats, a critical period exists around postnatal day (P) 12–13, when an imbalance between heightened inhibition and suppressed excitation led to a weakened ventilatory and metabolic response to acute hypoxia. An open question was whether the two genders follow the same or different developmental trends throughout the first 3 postnatal weeks and whether the critical period exists in one or both genders. The present large-scale, in-depth ventilatory and metabolic study was undertaken to address this question. Our data indicated that: (1) the ventilatory and metabolic rates in both normoxia and acute hypoxia were comparable between the two genders from P0 to P21; thus, gender was never significant as a main effect; and (2) the age effect was highly significant in all parameters studies for both genders, and both genders exhibited a significantly weakened response to acute hypoxia during the critical period. Thus, the two genders have comparable developmental trends, and the critical period exists in both genders in rats.