Postnatal development of metabolic rate during normoxia and acute hypoxia in rats: implication for a sensitive period

Previously, we reported that the hypoxic ventilatory response (HVR) in rats was weakest at postnatal day (P) P13, concomitant with neurochemical changes in respiratory nuclei. A major determinant of minute ventilation (Ve) is reportedly the metabolic rate [O2 consumption (Vo2) and CO2 production (Vco2)]. The present study aimed at testing our hypothesis that daily metabolic rates changed in parallel with ventilation during development and that a weak HVR at P13 was attributable mainly to an inadequate metabolic rate in hypoxia. Ventilation and metabolic rates were monitored daily in P0–P21 rats. We found that 1) ventilation and metabolic rates were not always correlated, and Ve/Vo2 and Ve/Vco2 ratios were not constant during development; 2) metabolic rate and Ve/Vo2 and Ve/Vco2 ratios at P0–P1 were significantly different from the remaining first postnatal week in normoxia and hypoxia; 3) at P13, metabolic rates and Ve/Vo2 and Ve/Vco2 ratios abruptly increased in normoxia and were compromis...