Altered thermal and metabolic control in newborn rats at high altitude

Abstract

In acute hypoxia, newborn reduce oxygen consumption (VO2) and rectal temperature (Tr), but it remains unclear if these responses are maintained in chronic hypoxia. We used rats living at high altitude (3600 m, La Paz Bolivia) at postnatal days 7–8 (P7, n=5, body weight 13±1 g) and 15–16 (P15, n=6, 21±1 g). Tr and VO2 were measured in 21%O2 (room air), 35%O2 (sea level PO2), and 10%O2 (hypoxia), during 20 minutes each. Ambient temperature (Ta) was 34°C at P7 and 30°C at P15. Tr‐Ta was used as an index of thermoregulatory control. At P7, Tr‐Ta was −0.1±0.2°C, suggesting that thermoregulatory control is not established. In 35%O2, Tr was 34.8±0.2°C, and 32.0±0.6°C in 10%O2. At P15, Tr‐Ta was 5.2±0.2°C in room air, Tr did not increased in 35%O2, and was 31.8±0.4°C in 10%O2. VO2 was high (P7=8.6±0.8; P15=9.4±0.4 ml/min/100g) compared to sea level rats (5 ml/min/100g in 20g P10 rats). In P7 and P15 rats, VO2 increased in 35%O2 and dropped in 10%O2. Our results suggest that chronic hypoxia delays the establishment of thermoregulation and increases metabolic rate in newborn rats. The drop of Tr and VO2 in 10%O2 were however well maintained. Founded by NSERC