Consumption of O2 and early detection of fa/fa genotype in rats.

Oxygen consumption was determined in 10--12-wk-old fa/fa and non-fa/fa rats at ambient temperatures of 10 degrees--40 degrees C. The fa/fa rats exhibited a lower oxygen consumption than non-fa/fa rats from 10 degrees--30 degrees C, but not at 35 degrees C and 40 degrees C. A lower oxygen consumption was also observed among fa/fa rats as early as 18 days of age, prior to the phenotypic expression of apparent obesity. Fourteen hundred microliter O2 consumed/hr/g body weight at STP was used as a value, below which future obese rats could be identified among 18-day-old pups from fa/+ X fa/+ crosses. Only a 10% error was found in the use of this value for the early identification of the fa/fa genotype.