Hypophagia-induced hypometabolism during experimental anaemia in rats

Several investigators have reported a drop in oxygen (O-2) consumption (Vo(2)) and body temperature in laboratory animals during normobaric or hypobaric hypoxia. Hypophagia, with normal efficiency of protein utilisation for growth, was also observed. It has recently also been observed that hypometabolism is present during anaemic hypoxia. The present study was designed to test the experimental hypothesis that anaemic hypoxia induces hypometabolism secondary to hypophagia. Episodes of anaemia were created in adult male rats by either blood withdrawal through cardiac puncture (haemorrhagic anaemia) or phenylhydrazine administration (haemolytic anaemia). Haematrocrit, Vo(2), and food consumption, as indirect estimations of the level of anaemia, energy production, and appetite, respectively, were serially measured in all animals during 7 days (acute experiments) or 17 days (chronic experiments). Positive correlations were found between the three parameters during development of and recovery from anaemia during each anaemic episode. When the amount of food offered to non-anaemic rats was equalised to that freely eaten by anaemic rats, Vo(2) dropped in the former to almost the level found in the latter. Body composition changed during chronic anaemia because of a decrease in the lipid fraction of the body. The results confirmed the working hypothesis that hypometabolism, which has been considered as an immediate, emergency-type response to both hypoxic and anaemic hypoxia, can be considered as a response secondary to hypophagia because of depressed appetite. How appetite is adapted to the mechanisms which control O-2 convection and O-2 availability is not known at present.