Effects of hypoxia and hypercapnia on aerobic metabolic processes in northern elephant seals

An hypoxia-induced metabolic down-regulation has been implicated as an impo rtant protective mechanism against tissue deoxygenation in mammals. Whether the same response to hypoxia occurs in northern elephant seals was studied . The effects of hypercapnia were also examined to determine whether the re duced ventilatory response of seals to CO, is associated with an analogous protective metabolic down-regulation. Thirty three seals (7-300-days-old) w ere studied using open-flow respirometry with simultaneous monitoring of ap nea frequencies and heart rates. Hypoxia (11% O-2) and hypercapnia (7% CO2) caused increases in metabolism of up to 38% with corresponding decreases i n the percent lime spent apneic (%AP) and increases in heart rate. The meta bolic, breathing and heart rate responses to altered inspired gases were in dependent of age. Metabolism was strongly negatively correlated with %AP su ggesting that elevated metabolism during hypoxia and hypercapnia exposure i s attributable to decreases in %AP. In young elephant seals metabolic down- regulation is not an automatic protective response to experimentally-impose d hypoxia or hypercapnia. (C) 1999 Elsevier Science B.V. All rights reserve d.