THE FASTING RESPIRATORY METABOLISM OF THE WHITE RAT FOR 36 HOURS FOLLOWING CONTROLLED FEEDING

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Abstract
The fasting respiratory metabolism of the albino rat (avg. age 11 mos.; wt., 340 g.) is described hr-by-hr. for the first 36 hrs. following controlled feeding. Metabolic rate, as calculated from O2 consumption and R.Q. and using Diack'' s formula for estimation of body surface, dropped from an immediate post-ingestion maximum of 954 cal./m2/ 24 hrs. steadily and uniformly to 78% of this value at the 20th fasting hr. During the next 8 hrs. the rate was elevated in semblance of a specific dynamic reaction to fat, with maximum of 84% at the 22nd hr. and return to 76.6% by the 28th hr. Thereafter, until 36 hrs., the trend was horizontal with oscillation about the value 78%, previously reached at the 20th hr. R.Q. dropped from an immediate post-ingestion maximum of 0.97 to approx. 0.79 at the 9th hr. Thereafter, until the 19th hr. it indicated the combustion of the usual post-absorptive mixture of foodstuffs and merely oscillated about this as an avg. value. Beginning with the 20th hr. decline was resumed to reach 0.70 at the 28th hr., but was interrupted by a temporary rise between the 22nd and 26th hr., to a maximum of 0.774 at the 24th hr. From the 28th-36th hr. there was oscillation about an avg. fat value of 0.71. These results indicate the 24-hr. fasting rat is a peculiarly unfortunate choice for a metabolic standard, since this point is apparently midway in the transition from the metabolism of mixed foodstuffs to one exclusively of fat; consequently the slightest inaccuracy in estimation of fasting time at this particular interval will eventuate in results of relatively wide diversity.