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. 2013 Aug 15;188(2):200-7.
doi: 10.1016/j.resp.2013.06.013. Epub 2013 Jun 21.

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

Qiuli Liu  1 , Margaret T T Wong-Riley
Affiliations

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

Qiuli Liu et al. Respir Physiol Neurobiol. .

Abstract

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.

Keywords: Carbon dioxide production; Gender difference; Hypoxia; Oxygen consumption; Respiration.

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Figures

Fig. 1
Fig. 1. Minute ventilation (V̇E) in normoxia and hypoxia (10% O2 for 7 min)
A. Normalized (to 100 g body weight) V̇E in normoxia from P0 to P21. Both genders had significant rises at P2 and P13 and a significant fall at P16. B. Normalized V̇E in hypoxia from P0 to P21. Both genders showed a significant rise at P2. C. V̇E in hypoxia (V̇E (H)) versus V̇E in normoxia (V̇E (N)) from P0 to P21. A significant fall in the ratio was found at P13 in both genders. No gender difference was found at any age. Values expressed here and in subsequent figures represent the mean of raw data ± standard errors of the means (SEM), whereas values in normoxia were expressed as 1 when compared with those in hypoxia. Statistical significance was based on mixed model analysis with false discovery rate (FDR). *, P < 0.05; significance for both genders between one age group and its immediately adjacent younger age group. M, male rats, F, female rats.
Fig. 2
Fig. 2. Postnatal developmental trend of oxygen consumption (V̇O2) and carbon dioxide production (V̇CO2) in normoxia and hypoxia
A. Normalized V̇O2 in normoxia from P0 to P21. Both genders exhibited a significant day-to-day rise at P2. B. Normalized V̇O2 in hypoxia from P0 to P21. Both genders showed a significant rise at P2 and a significant fall at P13. C. V̇O2 in hypoxia (V̇O2 (H)) versus that in normoxia (V̇O2 (N)) from P0 to P21. Both genders exhibited a significant fall at P13. D. Normalized V̇CO2 in normoxia from P0 to P21. Both genders exhibited significant day-to-day rises at P1 and P2. E. Normalized V̇CO2 in hypoxia from P0 to P21. Both genders showed significant rises at P1 and P2. F. V̇CO2 in hypoxia (V̇CO2 (H)) versus that in normoxia (V̇CO2 (N)). Both genders exhibited significant falls at P2 and P13 as well as a significant rise at P9. *, P < 0.05; significance for both genders between one age group and its immediately adjacent younger age group.
Fig. 3
Fig. 3. Postnatal changes in V̇E/V̇O2 and V̇E/V̇CO2 ratios in normoxia and hypoxia
A. V̇E/V̇O2 ratios in normoxia (V̇E(N)/V̇O2(N)) from P0 to P21. No significant gender difference was found at any age. B. V̇E/V̇O2 in hypoxia (V̇E (H)/V̇O2 (H)) from P0 to P21. A significant age-by-gender interaction was found at P1, when the male value was much higher than that of the female. C. V̇E/V̇O2 in hypoxia versus that in normoxia from P0 to P21. The ratio was lowest at P0 and P13. No significant gender difference was found at any age. D. V̇E/V̇CO2 ratios in normoxia (V̇E (N)/V̇CO2 (N)) from P0 to P21. No significant gender difference was found at any age. E. V̇E/V̇CO2 in hypoxia (V̇E (H)/V̇CO2 (H)) from P0 to P21. A significant age-by-gender interaction was found at P2, with the male value higher than that of the female. F. V̇E/V̇CO2 in hypoxia versus that in normoxia from P0 to P21. The ratio was lowest at P0 and P13 in both genders. #, P < 0.05; significance in FDR analysis of age-by-gender interactions.
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