title: Postnatal development of metabolic rate during normoxia and acute hypoxia in rats: implication for a sensitive period.
abstract: 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 [O(2) consumption (Vo(2)) and CO(2) production (Vco(2))]. 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/Vo(2) and Ve/Vco(2) ratios were not constant during development; 2) metabolic rate and Ve/Vo(2) and Ve/Vco(2) ratios at P0-P1 were significantly different from the remaining first postnatal week in normoxia and hypoxia; 3) at P13, metabolic rates and Ve/Vo(2) and Ve/Vco(2) ratios abruptly increased in normoxia and were compromised in acute hypoxia, unlike more stable trends during the remaining second and third postnatal weeks; and 4) the respiratory quotient (Vco(2)/Vo(2)) was quite stable in normoxia and fluctuated slightly in hypoxia from P0 to P21. Thus our data revealed heretofore unsuspected metabolic adjustments at P0-P1 and P13. At P0-P1, ventilation and metabolic rates were uncorrelated, whereas at P13, they were closely correlated under normoxia and hypoxia. The findings further strengthened the existence of a critical period of respiratory development around P13, when multiple physiological and neurochemical adjustments occur simultaneously.
authors.affiliation: Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226, USA.
authors.forename: Qiuli
authors.initials: Q
authors.lastname: Liu
authors.forename: Charles
authors.initials: C
authors.lastname: Fehring
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Lowry
authors.forename: Margaret T T
authors.initials: MT
authors.lastname: Wong-Riley
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D002245:Carbon Dioxide / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D000860:Hypoxia / Q000378:metabolism*; D008660:Metabolism / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D010993:Plethysmography, Whole Body; D051381:Rats; D017207:Rats, Sprague-Dawley; D015656:Respiratory Mechanics / Q000502:physiology
chemical_list: D002245:Carbon Dioxide