VOL. 4 (1950) BIOCHIMICA ET BIOPHYSICA ACTA 249 



BODY SIZE AND TISSUE RESPIRATION 



by 



H. A. KREBS 



Medical Research Council Unit for Research in Cell Metabolism, Department of Biochemistry, 



University of Sheffield (England) 



It has long been known that in homoiothermic animals the basal metabolic rate, 

 per unit of body weight, decreases with the size of the animal, and the question has 

 often been discussed whether the respiration of individual tissues of animals of different 

 size shows the same differences as the intact organisms. Terroine and Roches and 

 Grafe, Reinwein, and Singer^ measured the respiration of various tissues in vitro and 

 came to the conclusion that homologous tissues of different animals respire in vitro at 

 about the same rate, irrespective of the size of the animal. They ascribed the differences 

 found in the intact animal to the regulatory influences of the nervous system and of 

 hormones. Kleiber^' * on the other hand, reported that the rate of respiration of liver 

 slices of rats, rabbits, sheep, horses and cows, per unit of weight, decreased with 

 increasing size of the animal. The decrease observed was of the same order as the 

 decrease of the basal metabolism of the living animal. 



This lack of agreement is not due to discrepancies in experimental observations but 

 arises from difficulties of procedure and interpretation. Whilst the measurement of the 

 basal metabolic rate is a standardized technique, no accepted standards exist for the 

 measurement of the oxygen uptake of isolated tissues in vitro. It has often been demon- 

 strated that the oxygen uptake of tissues in vitro is not a constant value. Specimens of 

 the same tissue can show wide and reproducible variations, depending on the conditions 

 under which the measurements are made. Among the factors responsible for these 

 variations two are of special importance: the composition of the medium in which the 

 tissue is suspended and the physical treatment of the material. As the part played by 

 these factors was not fully appreciated in previous investigations it was thought that 

 new measurements of the rate of respiration of isolated tissues under standard conditions 

 are needed. As a preliminary it was necessary to define standard conditions which 

 would resemble as closely as possible the state of the tissues in the intact, possibly 

 resting, animal, and which would yield a "standard rate" of tissue respiration. 



A. GENERAL CONSIDERATIONS CONCERNING THE MEASUREMENT OF THE 

 "standard rate" OF TISSUE RESPIRATION 



I. Treatment of tissue 



In order to measure the rates of metabolic processes in isolated tissues it is, as a 

 rule, unavoidable to subject the tissues to procedures like shcing, mincing or homo- 

 genizing, so that the cells can be satisfactorily supplied with oxygen and substrates. 



References p. 267— 26g. 



